JP2008278584A - Motor controller, and motor control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a motor controller which properly controls the drive of a motor according to the heat generation state of a device, performs control for getting the effect of suppressing a temperature rise when the temperature of each part of the device goes up accompanying the drive control of the motor and a margin is lost to its tolerable temperature, and performs control for getting the effect of reducing the noise caused by the distortion of a motor current or its switching action when there is a margin to its tolerable temperature. <P>SOLUTION: The controller includes a switching circuit 4 which is interposed in a line which supplies a motor 50 with a drive current, a predriver 3 which drives the switching circuit 4, a control means 20 which controls the drive of the motor 50 by driving the predriver 3, an operation speed switching means 11 which switches the operation speed at switching changeover of the switching circuit 4, and a switching control means 20 which switches the setting of the operation speed switching means 11, based on the heating state. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to a motor control device and a motor control method, and more specifically, when a drive control of a motor is performed, a dead time is provided in a drive signal of a switching unit interposed in a line that supplies a drive current to the motor. The present invention relates to a motor control device that performs control and a motor control method.

FIG. 1 is a diagram showing a schematic configuration of an in-vehicle electric power steering control device in which a conventional motor control device is adopted.
An electric power steering control device (hereinafter referred to as an EPS control device) 1 gives a steering assist force by driving a motor 50 connected to a steering mechanism (not shown) of a vehicle in accordance with the driving state of the vehicle. Which controls the microcomputer 2 and
A pre-driver 3, a switching circuit 4, a current detection circuit 5, and a temperature sensor 6 are included.

Further, various sensors (not shown) for obtaining information on various parts of the vehicle necessary for steering assist control, such as a torque sensor 7 for detecting the steering state of the steering wheel, are connected to the microcomputer 2, and various sensors such as the torque sensor 7 are provided. A signal detected by the sensor is input to the microcomputer 2. Further, the current value of the motor 50 detected by the current detection circuit 5 is input to the microcomputer 2, and the signal detected by the temperature sensor 6 installed at a predetermined location in the apparatus is also input to the microcomputer 2. Yes.

The switching circuit 4 includes an N-channel MOSFET (hereinafter referred to as MO) that is a switching element.
S) 1) It is composed of an H bridge circuit including a pair of upper and lower arm elements composed of MOS2 and a pair of upper and lower arm elements composed of MOS3 and MOS4, and a connection point between MOS1 and MOS2 and between MOS3 and MOS4 Are connected to the terminals of the motor 50, and M
Depending on the switching state of OS1 to MOS4, the battery B serving as a DC power source is connected to the motor 5
A current is supplied to zero.

Further, gate resistors R1 to R4 set to predetermined values are interposed between the gate terminals of the MOS1 to MOS4 and the pre-driver 3. Also, MOS2 and MOS4 and ground GN
Between D, a current detection resistor R11 is interposed. Each MOS1-MOS4
A feedback diode (not shown) is connected in parallel.

Further, the pre-driver 3 is connected to the MOS based on the control signal (PWM signal) from the microcomputer 2.
1 to 4 includes a pulse modulation circuit that generates and outputs a switching signal that can turn on and off the MOS 4. The switching signal output from the pre-driver 3 to the MOS 1 to MOS 4 suppresses a through current. A dead time of a predetermined period is provided.
A motor drive circuit is configured including the pre-driver 3 and the switching circuit 4.

The operation of the motor drive circuit of the EPS control apparatus 1 configured as described above will be described based on the timing chart shown in FIG. Although the control for MOS1 and MOS2 will be described here, the same control is performed for MOS3 and MOS4.

2A shows the waveform of the drive signal output from the pre-driver 3 to the MOS 1, and FIG.
The waveform of the drain current of the MOS 1, (c) is the waveform of the drive signal output from the pre-driver 3 to the MOS 2, (d) is the waveform of the drain current of the MOS 2, and (e) is the battery B to M
The waveform of the through current flowing through OS1 and MOS2 is shown.

In the pre-driver 3, based on the control signal from the microcomputer 2, the MOS1 and the MOS2 are not turned on at the same timing, that is, alternately turned on and off repeatedly.
A drive signal (switching signal) with a set duty ratio is generated and output.

However, when the drive signal output from the pre-driver 3 is switched on / off, M
OS1 and MOS2 do not instantly switch between the on state and the off state, and the gate resistance R
Set values of 1 to R4 and electrical characteristics of MOS1 and MOS2 (parasitic capacitance existing between terminals, etc.)
As a result, the rise and fall of the drain currents of the MOS1 and MOS2 are delayed, so-called turn-on time and turn-off time are required.

For this reason, a drive signal for turning on (or turning off) the MOS 1 from the pre-driver 3 and the MOS
When the drive signal for turning off (or turning on) 2 is output at the same time, the period in which the rise (or fall) of the drain current of MOS1 overlaps with the fall (or rise) of the drain current of MOS2 becomes longer. In the meantime, the MOS1 and the MOS2 are simultaneously turned on and a through current flows.

Therefore, the pre-driver 3 is designed so that the period during which the MOS1 and the MOS2 are simultaneously turned on is shortened by the delay of the rise and fall of the drain currents of the MOS1 and MOS2.
Does not output an H level drive signal for turning on MOS1 (or MOS2) immediately after outputting an L level drive signal for turning off MOS2 (or MOS1), but has a period of dead time DT between them. H1 that turns on MOS1 (or MOS2)
By outputting a level driving signal, a configuration is adopted in which the period during which the MOS1 and the MOS2 are simultaneously turned on is shortened and the through current is suppressed.

However, the drain current rise and fall speed of MOS1 to MOS4,
That is, if the period of the dead time DT is sufficiently large with respect to the switching operation speed,
The switching circuit 4 can be driven so that no through current flows. However, if the period of the dead time DT is increased, the motor voltage and current are increased and torque ripple is increased, and the motor 50 is driven. The adverse effect on the control will increase.

Therefore, conventionally, considering the balance between the two, penetration through design calculation and actual machine check so that individual product specifications (for example, allowable temperature (heat-resistant temperature) of each part of the device, steering feeling, etc.) can be satisfied. A value that is considered appropriate is obtained from the result of current waveform observation and the like, and the value is written in the software in advance as a fixed value used for control. In practice, however, as shown in FIG. Even if a value obtained from a result of design calculation or actual machine confirmation in advance is provided as the dead time DT, a through current flows to some extent when the MOS1 and MOS2 are switched on and off.

Therefore, if the state in which a large through current flows intermittently continues, the temperature of the component exceeds the allowable temperature, the component may be damaged, or the deterioration may be accelerated.To cope with such a temperature increase, The conventional EPS control apparatus 1 is equipped with an overheat protection function. That is,
The microcomputer 2 detects the temperature in the apparatus through the temperature sensor 6 and performs control to limit the current supplied to the motor 50 before the detected temperature reaches a predetermined allowable temperature.

In addition, in the following Patent Document 1, as a configuration in which a gate signal adjustment circuit including a diode, a resistor, and a capacitor is interposed between a booster circuit constituting a motor drive circuit and a control terminal of a switching element, By setting the values of the resistor and the capacitor to appropriate values, the power loss of the switching element is reduced, the switching element is protected, and the EMI
A technique for reducing noise is disclosed.

However, when the overheat protection function (driving current limitation) described above is activated, the steering assist amount by the motor 50 is greatly limited, so that the necessary steering assist amount cannot be given, and the driver's There was a problem that the steering feeling deteriorated.

In addition, it may be possible to adopt parts with excellent heat resistance to cope with temperature rise, but this causes another problem that the parts cost is high, so that it is not necessary to use expensive parts. Therefore, a countermeasure capable of enhancing the effect of suppressing the temperature rise of the apparatus has been demanded.

In the technique disclosed in Patent Document 1 described above, the values of the resistors and capacitors constituting the gate signal adjustment circuit can be set to appropriate values in advance, but the set values (fixed) are fixed. Therefore, during the motor drive control, the operation speed of the switching element cannot be switched to an appropriate speed according to the heat generation state of each part of the apparatus.
Japanese Patent Laid-Open No. 2003-189592

Means for solving the problems and their effects

The present invention has been made in view of the above problems, and when the temperature of each part of the device rises along with the drive control of the motor and there is no room for the allowable temperature (heat-resistant temperature), each part of the device The control to obtain the effect of suppressing the temperature rise is performed while the allowable temperature (heat-resistant temperature)
If there is a margin for this, control can be performed to reduce the noise caused by motor current distortion and switching operation, and appropriate motor drive control is performed according to the heat generation state of each part of the device An object of the present invention is to provide a motor control device and a motor control method that can be used.

In order to achieve the above object, a motor control device (1) according to the present invention comprises a switching means interposed in a line for supplying a driving current to the motor, a driving means for driving the switching means, and the driving Motor control means for controlling the drive of the motor by driving the means, operating speed switching means for switching the operating speed at the time of switching switching of the switching means, and switching of the setting of the operating speed switching means based on the heat generation state And a switching control means.

According to the motor control device (1), the setting of the operation speed switching means for switching the operation speed at the time of switching switching of the switching means is switched by the switching control means based on the heat generation state. The drive control of the motor can be performed by switching to the switching operation speed corresponding to the situation in correspondence with the heat generation state (temperature change).

Therefore, for example, when the temperature of the switching means has no room for its allowable temperature, at the time of switching switching of each switching means forming the upper and lower arms,
By switching so as to increase the switching operation speed so as not to be turned on at the same time, it is possible to prevent a through current from flowing through the switching means, and to suppress the heat generation of the switching means and prevent a temperature rise. be able to. Therefore, it is not necessary to use costly parts with a high allowable temperature (high heat resistance), and thus the cost of the apparatus can be suppressed.

Further, when the temperature of the switching means has a margin with respect to the allowable temperature, the switching operation speed is switched so as not to be turned off at the time of switching switching of the switching means forming the upper and lower arms. As a result, undesirable effects on motor control such as motor voltage and current distortion can be reduced, and the motor can be rotated more smoothly. Further, noise due to the switching operation can be reduced.

In addition, the motor control method (1) according to the present invention includes a step of acquiring temperature information and an operation speed for switching the operation speed at the time of switching switching of the switching means interposed in the line for supplying the drive current to the motor. A step of switching the setting of the switching means based on the acquired temperature information, and a step of performing control to drive the switching means in the switched setting state of the operating speed switching means. .

According to the motor control method (1), the setting of the operation speed switching means for switching the switching operation speed of the switching means is switched based on the temperature information.
The motor can be controlled by switching to the switching operation speed corresponding to the actual temperature change.

Therefore, when the temperature of the switching means becomes less than the allowable temperature, by performing switching to increase the switching operation speed, it is possible to prevent a through current from flowing through the switching means, Heat generation of the switching means can be suppressed and temperature rise can be prevented. In addition, when the temperature of the switching means has a margin with respect to the allowable temperature, switching which reduces the switching operation speed reduces undesirable influences on motor control such as motor voltage and current distortion. Therefore, the rotational drive of the motor can be made smoother. Further, noise due to the switching operation can be reduced.

Embodiments of a motor control device and a motor control method according to the present invention will be described below with reference to the drawings.
FIG. 3 is a diagram illustrating a schematic configuration of an in-vehicle electric power steering control device in which the motor control device (and the motor control method) according to the embodiment (1) is employed. However, components having the same functions as those of the EPS control device 1 shown in FIG.

The EPS control device 10 for controlling the electric power steering device includes a CPU 21, a RAM
22, a microcomputer 20 including a ROM 23 and an EEPROM 24, a pre-driver 3, a switching circuit 4, a current detection circuit 5, a temperature sensor 6, and an operating speed switching means 1.
1. The switching circuit 4 is connected to a motor (DC brush motor) 50 provided in a vehicle steering mechanism (not shown), and includes a pre-driver 3, a switching circuit 4, and an operation speed switching means 11. A drive circuit is configured.

In addition, various sensors (not shown) for obtaining information on various parts of the vehicle necessary for steering assist control, such as a torque sensor 7 for detecting the steering state of the steering wheel, are connected to the microcomputer 20. A signal detected by the sensor is input to the microcomputer 20. Further, the current value of the motor 50 detected by the current detection circuit 5 is input to the microcomputer 20, and the signal detected by the temperature sensor 6 such as a thermistor installed at a predetermined location in the apparatus is also input to the microcomputer 20. It has become.

The switching circuit 4 includes an N-channel MOSFET (hereinafter referred to as MO) that is a switching element.
S) 1) It is composed of an H bridge circuit including a pair of upper and lower arm elements composed of MOS2 and a pair of upper and lower arm elements composed of MOS3 and MOS4, and a connection point between MOS1 and MOS2 and between MOS3 and MOS4 Are connected to the terminals of the motor 50, and M
Depending on the switching state of OS1 to MOS4, the battery B serving as a DC power source is connected to the motor 5
A current is supplied to zero.

Further, variable resistance means 11a to 11d are interposed between the gate terminals G (control terminals) of the MOS1 to MOS4 and the pre-driver 3, and the operation speed switching means 11 is changed by the variable resistance means 11a to 11d. It is configured. The variable resistance means 11a to 11d are MOS1 to MO.
A digital potentiometer having a function as a variable resistor is employed here, and the digital signal output from the microcomputer 20 (resistance value switching signal) is configured so that the value of the gate resistance of S4 can be switched. Based on the above, the setting of the resistance value can be switched to an arbitrary value within a predetermined variable range.

Further, a resistor R11 for current detection is interposed between the MOS2 and MOS4 and the ground GND. A feedback diode (not shown) is connected to each of the MOS1 to MOS4 in parallel.

Further, the pre-driver 3 is connected to the MOS based on the control signal (PWM signal) from the microcomputer 2.
1 to 4 includes a pulse modulation circuit that generates and outputs a switching signal capable of turning on and off the MOS 4. The switching signal output from the pre-driver 3 to each of the MOS 1 to MOS 4 includes a through current. A dead time of a predetermined period is provided for suppression.

In the EPS control device 10 according to the embodiment (1), the pre-driver 3 and the MOS1 to MOS
The variable resistance means 11a to 11d as the operation speed switching means 11 between each of the four gate terminals G.
Is configured so that during EPS control, the resistance values set in the variable resistance means 11a to 11d are appropriately switched based on the heat generation state of the device, and the switching operation speed of the MOS1 to MOS4 can be adjusted. There is a feature in that.

More specifically, when the temperature of each part of the apparatus is no longer sufficient with respect to a predetermined allowable temperature (heat-resistant temperature), the resistances set in the variable resistance means 11a to 11d are controlled in order to suppress further temperature rise. The value is switched to a small value, the switching operation speed of MOS1 to MOS4 is increased, and drive control is performed so that no through current flows through each pair of upper and lower arm elements during switching.

In addition, when the temperature of each part of the apparatus has a margin with respect to a predetermined allowable temperature, EPS control can be performed in a state where noise due to motor voltage and current distortion, and further, switching operation of MOS1 to MOS4 is reduced. Drive control is performed so that the resistance values of the variable resistance means 11a to 11d are switched to a large value, the switching operation speed of the MOS1 to MOS4 is slowed, and there is no period in which the upper and lower arm element pairs are both turned off during switching. Is done.

Further, in the EPS control device 10 according to the embodiment (1), the EPS control device 10 is in an inspection process before factory shipment of the EPS control device 10, or during inspection energization of the EPS control device 10 in a vehicle assembly process or an inspection process after the process. Then, a program for storing the relationship between the resistance value of the variable resistance means 11a to 11d and the temperature rise stored in the ROM 23 is executed, and the relationship between the resistance value of the variable resistance means 11a to 11d and the temperature rise is stored in the EEPROM 24. It is configured to be used for actual EPS control after being mounted on the vehicle.

FIG. 4 shows a map information storage processing operation (processing operation for storing the relationship between the resistance value of the variable resistance means 11a to 11d and the temperature rise) performed by the microcomputer 20 in the EPS control apparatus 10 according to the embodiment (1). It is a flowchart. This processing operation is performed by the EPS control device 10.
EPS in the inspection process before factory shipment or the vehicle assembly process and the inspection process after the process
Although described as being executed when the control device 10 is energized for inspection, it may be configured to be executed when energizing after the engine is started.

When inspection energization to the EPS control device 10 is started in the predetermined process, first, the storage execution flag F indicating that the relationship between the resistance value of the variable resistance means and the temperature rise is already stored is 1.
(Step S1), and if the storage execution flag F is 1, that is, if it is determined that the storage has been completed, the process ends, while the storage execution flag F is not 1, that is, not stored If it is determined, the process proceeds to step S2.

In step S2, the setting information of the resistance values of the variable resistance means 11a to 11d for obtaining the relationship with the temperature rise is read, and the resistance value having the smallest value is first selected from the setting information.
The process of setting the resistance values 1a to 11d is performed, and then control for driving each pair of upper and lower arm elements (MOS1 and MOS2, and MOS3 and MOS4) of the switching circuit 4 so that no current flows through the motor 50 is started. Then (step S3), a process of measuring a temperature rise when the drive control is executed for a predetermined time is performed (step S4).

In step S3, MOS1 and MOS3 output from the pre-driver 3
On the other hand, the ON / OFF duty ratio is set to 50%, while the drive signal for MO
The drive signals for S2 and MOS4 are set so as to be switched on and off at a timing at which a predetermined dead time DT is provided for switching on and off of the drive signals for MOS1 and MOS3. That is, drive control is performed so that the MOS1 and the MOS3 are turned on (or off) at the same time, and the MOS2 and the MOS4 are turned off (or turned on) at the same time.

Subsequently, it is determined whether or not a predetermined time has elapsed (step S5). If it is determined that the predetermined time has elapsed, the temperature that has risen within the predetermined time is calculated (step S6), and the set resistance value and the increase are determined. A process for storing the temperature in association with the temperature in the EEPROM 24 is performed (step S7).

In the next step S8, it is determined whether there is a resistance value to be set next. If it is determined that there is a resistance value to be set next, a resistance value having the next smallest value is selected from the setting information. Mean 11
A process of setting resistance values a to 11d is performed (step S9), and then the process returns to step S3 to repeat the process. On the other hand, if it is determined in step S8 that there is no resistance value to be set next,
The storage execution flag F is set to 1 (step S10), and then the process ends.

FIG. 5 shows an example of map information stored in the EEPROM 24 and showing the relationship between the set resistance values of the variable resistance means 11a to 11d and the rising temperature.
Four values (Rmin within the variable range (Rmin to Rmax) of the variable resistance means 11a to 11d
<Ra <Rb <Rc <Rd <Rmax) is set, and the rising temperature at each set resistance value is ΔTa <ΔTb <ΔTc <ΔTd, that is, the rising temperature increases as the resistance value increases. (Prone to generate heat easily due to through current).

Next, the resistance value setting processing operation of the variable resistance means 11a to 11d performed by the microcomputer 20 in the EPS control apparatus 10 according to the embodiment (1) will be described based on the flowchart shown in FIG. This processing operation is executed after the vehicle engine is started.

After the engine is started, first, a process of setting the resistance values of the variable resistance means 11a to 11d to a preset default value is performed (step S11), and then normal EPS control is started (step S12). . The default value of the resistance set in step S11 is associated with a slightly larger value within the variable range or the temperature detected by the temperature sensor 6, for example, because the temperature rise is small after the engine is started. Value is set.

Thereafter, the steering torque command value T * calculated based on the signal acquired from the torque sensor 7
It is determined whether or not (target value of steering assist torque) is equal to or greater than a predetermined value T ′ (step S13).
If it is determined that the steering torque command value T * is equal to or greater than the predetermined value T ′, that is, the driving situation requires steering assist, each part of the device, for example, MOS1 to MOS4, for example, based on the signal acquired from the temperature sensor 6. Temperature (estimated temperature) Ts is calculated (step S14).

Next, whether the difference between the allowable temperature (ie, heat-resistant set temperature) Tmax of MOS1 to MOS4 and the calculated estimated temperature Ts is equal to or greater than a predetermined value ΔT, that is, whether there is a margin with respect to the allowable temperature of MOS1 to MOS4 (Step S15), and the difference between the allowable temperature Tmax of the MOS1 to MOS4 and the estimated temperature Ts is less than a predetermined value ΔT, that is, MOS1 to MOS.
If it is determined that there is no allowance for the allowable temperature 4, processing for switching the resistance values set in the variable resistance means 11 a to 11 d to a small value is performed so that the operating speed of the MOS <b> 1 to MOS <b> 4 is increased (step S <b> 16). Then, the process returns to step S13 to repeat the process.

That is, in step S16, the allowable temperature Tmax and the estimated temperature Tmax of MOS1 to MOS4.
The relationship between the set resistance value stored in the EEPROM 24 and the temperature rise (
5), a setting resistance value corresponding to the temperature difference is obtained from the relationship map, and the resistance values set in the variable resistance means 11a to 11d are switched to the setting resistance value obtained from the temperature difference. I do. Thereafter, EPS control is performed with the switched resistance value.

In this case, there is no allowance for the allowable temperature, that is, the temperature difference between the allowable temperature of the MOS1 to MOS4 and the estimated temperature is small, so that a temperature increase beyond the temperature difference does not occur (in other words, Then, a resistance value (that is, a smaller resistance value) for setting the temperature so as not to exceed the allowable temperature is set. The operation of each part of the motor drive circuit when a small resistance value is set in a situation where there is no allowance for the allowable temperature will be described later.

On the other hand, in step S15, the allowable temperature Tmax and the estimated temperature Ts of the MOS1 to MOS4.
Is determined to be greater than or equal to a predetermined value ΔT, a process of switching the resistance values set in the variable resistance means 11a to 11d to a large value is performed so as to slow down the switching operation speed of the MOS1 to MOS4 (step S17). Then, the process returns to step S13 to repeat the process.

That is, in step S17, the allowable temperature Tmax of MOS1 to MOS4 and the estimated temperature T
The relationship between the set resistance value stored in the EEPROM 24 and the temperature rise (
5), a resistance value corresponding to the temperature difference is obtained from the relationship map, and the resistance value set in the variable resistance means 11a to 11d is switched to the resistance value obtained from the temperature difference. . Thereafter, EPS control is performed with the switched resistance value.

In this case, there is a margin with respect to the allowable temperature, that is, the temperature difference between the allowable temperature Tmax of the MOS1 to MOS4 and the estimated temperature Ts is large. A larger resistance value can be set. The operation of each part of the motor drive circuit when a large resistance value is set in a situation where there is a margin with respect to the allowable temperature will be described later.

On the other hand, if it is determined in step S13 that the steering torque command value T * is not equal to or greater than the predetermined value T ′, that is, if the driving situation does not require steering assist, step S13 is performed.
Proceeding to 17, a process of switching the resistance values set in the variable resistance means 11a to 11d is performed so as to slow down the switching operation speed of the MOS1 to MOS4, and then the process returns to step S13 to repeat the process.

Next, the operation of each part of the motor drive circuit in the EPS control apparatus 10 according to the embodiment (1) will be described based on the waveform diagrams shown in FIGS. Here, MOS1, M
The control for the upper and lower arm element pairs composed of OS2 will be described.
The same control is performed for the upper and lower arm element pairs consisting of

FIG. 7 shows the operation after the resistance value set in the variable resistance means 11a to 11d is switched to a small value (a smaller value within the variable range) in step S16 of FIG.
(A) is the waveform of the drive signal output from the pre-driver 3 to the MOS 1, (b) is the waveform of the drive signal output from the pre-driver 3 to the MOS 2, and (c) to (g) are in order of the MOS 1
Each waveform of the gate voltage and drain current, each waveform of the gate voltage and drain current of MOS2,
The waveform of the through current flowing through MOS1 and MOS2 is shown.

First, when an H level signal is output from the pre-driver 3 to the MOS 1 at time t1, the gate voltage Vg begins to be applied to the gate terminal of the MOS 1 through the variable resistance means 11a, and the variable resistance means 11a The gate voltage Vg of the MOS 1 starts to rise during the period α by the action of the set small value resistor and the parasitic capacitance between the gate and the source inherent in the MOS 1. When the gate voltage Vg of the MOS 1 exceeds the switching threshold voltage Vth of the MOS 1 in the middle of the period α, the drain current Id of the MOS 1 starts to flow, and the MO
Conduction is started between the drain and source of S1 with on-resistance.

When the drain current Id starts to flow through the MOS1, the resistance of a small value set by the variable resistance means 11a and the combined capacitance between the gate and the source and the drain and the gate inherent in the MOS1 during the next period β, The gate voltage Vg rises more gently.

Then, during the next period γ, the gate voltage Vg increases while increasing the slope, and the rising of the gate voltage Vg is completed after the period γ has elapsed. Note that a period Ton from when the threshold voltage Vth is exceeded until the period β elapses corresponds to a turn-on time, and the MOS1 is turned on after the period Ton.

After that, when an L level signal is output from the pre-driver 3 to the MOS 1 at time t2, the charge stored in the MOS 1 is discharged and flows into the variable resistance means 11a as a current. Then, during the period δ, the gate voltage Vg decreases while increasing the negative slope.

During the next period ε, the charge stored in the gate-source parasitic capacitance and the drain-gate parasitic capacitance inherent in the MOS1 begins to be discharged, the decreasing tendency becomes moderate, and the turn-off starts. When the drain current Id begins to decrease and the discharge of the parasitic capacitance is completed, the drain-source connection of the MOS 1 is cut off, and during the next period ζ, the gate voltage Vg further decreases, and the threshold voltage of the MOS 1 When Vth falls below, turn-off ends and MOS
1 completes the transition to the off state. Note that the period Toff from the start of the period ε to the time when it falls below the threshold voltage Vth corresponds to the turn-off time, and the MOS1 is turned off after the lapse of the period Toff.

Then, after time t2 when the pre-driver 3 outputs the L level signal for the MOS1, the pre-driver 3 outputs an H level signal to the MOS 2 at the time t3 when the dead time DT has elapsed. Then, the gate voltage Vg starts to be applied to the gate terminal of the MOS2 through the variable resistance means 11b. Hereinafter, the gate voltage Vg and the drain current Id of the MOS2 are substantially the same pattern as the gate voltage Vg and the drain current Id of the MOS1. It changes with.

In this case, since the resistance values of the variable resistance means 11a and 11b are set to a smaller value within the variable range, the switching operation speeds of the MOS1 and MOS2, that is, the rising and falling speeds of the respective drain currents are set. MOS can be speeded up when switching switching
Since there is no period during which both 1 and MOS2 are in the ON state, it is possible to prevent the occurrence of a through current and to suppress the temperature rise caused by the heat generation of MOS1 and MOS2.

FIG. 8A shows the waveform of the drive signal output from the pre-driver 3 to the MOS 1, and FIG.
The waveforms (c) to (g) of the drive signal output from the pre-driver 3 to the MOS 2 are obtained when the resistance values of the variable resistance means 11a and 11b are set to a large value within the variable range. M
The waveforms of the OS1 gate voltage and drain current, the MOS2 gate voltage and drain current, and the through current flowing through the MOS1 and MOS2 are shown.

Hereinafter, differences from FIG. 7 will be described. 8 (c)-(g) and FIGS. 7 (c)-(g)
As is clear from the comparison with FIGS. 8C and 8E, the lengths of the periods α ′, β ′, and γ ′ indicating the rise of the gate voltage Vg and the periods δ ′ indicating the fall of the gate voltage Vg shown in FIGS. The lengths of ε ′ and ζ ′ are respectively longer than the periods α, β, and γ indicating the rising edge of the gate voltage Vg and the periods δ, ε, and ζ indicating the falling edge shown in FIGS. It is getting longer.

Accordingly, the timing at which the drain current Id shown in FIGS. 8D and 8F begins to flow is delayed from the timing shown in FIGS. 7D and 7F, and the turn-on time Ton and the turn-off time Toff. The switching operation speed of MOS1 and MOS2
That is, the rising and falling speeds of each drain current are more gradual.

As a result, during the dead time DT from when the pre-driver 3 outputs the MOS 1 (or MOS 2) L-level signal to when the pre-driver 3 outputs the MOS 2 (or MOS 1) H-level signal next time, The transition to the off state of the MOS1 (or MOS2) is not completed, and the transition to the off state is completed after the H level signal of the MOS2 (or MOS1) is output from the pre-driver 3.

Accordingly, a period in which the MOS1 and the MOS2 are simultaneously turned on occurs and a through current flows. In this case, since there is a margin with respect to the allowable temperature of the MOS, the temperature rise is not a problem. On the contrary, since there is no period in which both MOS1 and MOS2 are off during switching, it is possible to reduce motor current distortion and radiation noise, and to perform steering assist control with good steering feeling. Is possible.

According to the EPS control apparatus 10 according to the embodiment (1), the resistance values set in the variable resistance means 11a to 11d constituting the operation speed switching means 11 are switched in multiple stages based on the heat generation state of the apparatus. Therefore, the drive control of the motor 50 can be performed by switching to the switching operation speed corresponding to the actual heat generation state (temperature change).

Therefore, when the temperature of the MOS1 to MOS4 has no room for the allowable temperature, at the time of switching switching between the upper and lower arm element pairs,
By reducing the value of the resistance set in the variable resistance means 11a to 11d, it is possible to prevent a through current from flowing through the MOS1 to MOS4 when switching is performed.
The temperature rise can be prevented by suppressing the heat generation of the OS4. Therefore, it is not necessary to use costly parts with a high allowable temperature (high heat resistance), and thus the cost of the apparatus can be suppressed.

Further, when the temperatures of the MOS1 to MOS4 have a margin with respect to the allowable temperature, the variable resistance means 11a is set so that both the upper and lower arm element pairs are not turned off at the time of switching switching.
By increasing the resistance value set to ˜11d, it is possible to reduce undesirable effects on the control of the motor 50 such as motor voltage and current distortion, and to make the rotation driving of the motor 50 smoother. be able to. Further, noise due to the switching operation can be reduced.

In the embodiment (1), the variable resistance means 11 constituting the operation speed switching means 11 is used.
Although the case where a digital potentiometer is applied as a to 11d has been described, in the EPS control apparatus 10A according to another embodiment, the operation speed switching means 11A is connected to each gate of the MOS1 to MOS4 as shown in FIG. Resistors R1 to R4 and analog switches 12a to 12
12d and resistors R21 to R24 are connected in parallel, and these analog switches 12a to 12d are switched on / off based on a control signal from the microcomputer 20A, whereby the predriver 3 and the MOS1 to MOS4 The resistance value set between each of the gate terminals can be switched. Such a configuration can be applied to a case where a sufficient current cannot flow because the allowable current of the variable resistor is small.

Further, in the EPS control apparatus 10B according to another embodiment, as shown in FIG. 10, the operation speed switching means 11B is connected between the pre-driver 3 and the gate terminals of the MOS1 to MOS4. The MOS 14 and gate resistors R1 to R4 can be connected in series.

That is, the pre-driver 3 is connected to each drain terminal D of the MOSs 11 to 14 and M
The source terminals S of the OS11 to MOS14 are connected to the gate resistors R1 to R4, and the MOS11
Each gate terminal G of the MOS 14 is connected to the microcomputer 20B via the gate resistors R21 to R24, and the voltage signal converted from the microcomputer 20B by the DA converter (DAC) 25 is output as MO.
Applied to each gate terminal G of S11 to MOS14, and MOS11 to MOS in accordance with the voltage signal
By adjusting the drain current Id of 14, the amount of current flowing to the gate terminals G of the MOS1 to MOS4 can be adjusted, and the switching operation speed of the MOS1 to MOS4 can be switched.

FIG. 11 is a diagram illustrating a schematic configuration of an in-vehicle electric power steering control device in which the motor control device according to the embodiment (2) is employed. However, the EPS control device 1 shown in FIG.
Constituent parts having the same function as 0 are given the same reference numerals and their description is omitted.

In the EPS control apparatus 10 according to the embodiment (1), as the operation speed switching means 11, the variable resistance means 11a to 11 are provided between the pre-driver 3 and the gate terminals of the MOS1 to MOS4.
In the EPS control device 10C according to the embodiment (2), an analog switch is provided between the gate terminals G and the source terminals S of the MOS1 to MOS4 as the operation speed switching means 11C. 13a to 13d and capacitors C1 to C4 are interposed,
The main difference is that fixed-value gate resistors R1 to R4 are interposed between the pre-driver 3 and the gate terminals of the MOS1 to MOS4.

As described above, in the EPS control apparatus 10C, variable capacitance means configured to include the analog switches 13a to 13d and the capacitors C1 to C4 are interposed between the gate terminals and the source terminals of the MOS1 to MOS4. During the EPS control, the analog switch 13a
By switching the on / off states of ˜13d, the combined capacitance between the gate terminals and the source terminals of the MOS1 to MOS4 is appropriately switched based on the heat generation state of the device.
It is characterized in that the switching operation speed of the MOS 4 can be adjusted.

More specifically, when the temperature of each part of the apparatus becomes less than a predetermined allowable temperature (heat-resistant temperature), the analog switches 13a to 13d constituting the variable capacitance means are used to suppress further temperature rise. Is switched off, and the capacitance between each gate terminal and the source terminal of the MOS1 to MOS4 is limited to the inherent parasitic capacitance, and the combined capacitance is reduced.
Driving control is performed so as to increase the switching operation speed of OS1 to MOS4 and prevent a through current from flowing through the pair of upper and lower arm elements during switching.

Further, when the temperature of each part of the apparatus has a margin with respect to a predetermined allowable temperature, EPS control can be performed in a state in which motor voltage and current distortion and noise due to switching operation of MOS1 to MOS4 are reduced. Thus, the analog switch 13a constituting the variable capacitance means
To 13d are turned on, the combined capacitance between the gate terminals and the source terminals of the MOS1 to MOS4 is increased, the switching operation speed of the MOS1 to MOS4 is slowed, and the upper and lower arm element pairs are connected together at the time of switching. Drive control is performed so that there is no period in which it is turned off.

FIG. 12 is a flowchart showing the capacity setting processing operation of the variable capacity means performed by the microcomputer 20C in the EPS control apparatus 10C according to the embodiment (2). This processing operation is executed after the vehicle engine is started.

After the engine is started, the analog switches 13a to 13d are first turned on. That is, the gate-source capacitance is determined by the gate-source parasitic capacitance inherent in each of the MOS1 to MOS4 and the capacitance of the capacitors C1 to C4. (Step S21)
Subsequently, normal EPS control is started (step S22).

Thereafter, the steering torque command value T * calculated based on the signal acquired from the torque sensor 7
Is determined to be equal to or greater than a predetermined value T ′ (step S23), and it is determined that the steering torque command value T * is equal to or greater than the predetermined value T ′, that is, a driving situation requiring steering assist. Based on the signal acquired from the temperature sensor 6, the temperature (estimated temperature) Ts of each part of the device, for example, the MOSs 1 to 4, is calculated (step S24).

Next, whether the difference between the allowable temperature (ie, the heat-resistant set temperature) Tmax of the MOS1 to 4 and the calculated estimated temperature Ts is equal to or greater than the predetermined value ΔT, that is, there is a margin with respect to the allowable temperature of the MOS1 to MOS4. (Step S25), the allowable temperature T1 of MOS1 to MOS4
If it is determined that the difference between max and the estimated temperature Ts is less than the predetermined value ΔT, that is, there is no allowance for the allowable temperature, the analog switches 13a to 13d are turned off, that is, the switching operation of the MOS1 to MOS4 In order to increase the speed, the capacitance between the gate and the source is made only the parasitic capacitance of the MOS to reduce the capacitance (step S26),
Then, it returns to step S23 and repeats a process.

On the other hand, in step S25, the allowable temperature Tmax and the estimated temperature Ts of the MOS1 to MOS4.
Is determined to be greater than or equal to the predetermined value ΔT, the process of continuing the ON state of the analog switches 13a to 13d is performed, that is, the capacity between the gate and the source is increased so as to reduce the operating speed of the MOS1 to MOS4. The process which continues the state which performed is performed (step S27), and it returns to step S23 and repeats a process after that.

On the other hand, if it is determined in step S23 that the steering torque command value T * is not equal to or greater than the predetermined value T ′, that is, the driving situation does not require steering assist, the process proceeds to step S27, and the operating speed of the MOS1 to MOS4 is set. In order to loosen, the process which continues the ON state of analog switch 13a-13d is performed, and it returns to step S23 and repeats a process after that.

Thus, when there is no allowance for the allowable temperature, that is, when the temperature difference between the allowable temperature of MOS1 to MOS4 and the estimated temperature is small, the analog switches 13a to 13d are turned off, and the motor drive circuit at this time is configured. The operation of each part is performed in a pattern substantially the same as the operation of each part shown in FIG. 7, and the switching operation speed of MOS1, MOS2, that is, the rise and fall speeds of each drain current is increased, and the switching of MOS1 Is prevented from occurring during the period in which both of the MOS1 and the MOS2 are turned on, thereby preventing the occurrence of a through current.
The temperature rise accompanying the heat generation of the MOS 2 is suppressed.

Further, when there is a margin with respect to the allowable temperature, that is, when the difference between the allowable temperature of MOS1 to MOS4 and the estimated temperature is large, the analog switches 13a to 13d are turned on, and the components of the motor drive circuit at this time The operation is performed in a pattern substantially the same as the operation of each part shown in FIG. 8, and the switching operation speed of MOS1, MOS2, that is, the rise and fall speeds of each drain current is slowed down. Thus, the steering assist control with good steering feeling is performed by reducing the distortion of the motor current and the radiation noise so as not to cause a period in which both of them are off.

According to the EPS control device 10A according to the above embodiment (2), the operation speed switching means 11C.
Since the on / off of the analog switches 13a to 13d constituting the variable capacity means is switched based on the heat generation state of the device, it corresponds to the actual heat generation state (temperature change),
The drive control of the motor 50 can be performed by switching to the switching operation speed according to the situation.

Therefore, when the temperature of the MOS1 to MOS4 has no room for the allowable temperature, the analog switches 13a to 13d are turned off to reduce the capacitance.
The switching operation speed of the upper and lower arm element pairs can be increased so that the upper and lower arm element pairs are not simultaneously turned on at the time of switching, that is, no through current flows through the MOS1 to MOS4. It is possible to prevent the temperature from rising. Therefore, it is not necessary to use costly parts with a high allowable temperature (high heat resistance), and thus the cost of the apparatus can be suppressed.

Further, when the temperatures of the MOS1 to MOS4 have a margin with respect to the allowable temperature, the analog switches 13a to 13d are turned on to increase the capacity, thereby slowing the switching operation speed of the upper and lower arm element pairs and switching. Both can be prevented from being turned off at the time of switching, unfavorable influence on the control of the motor 50 such as motor voltage and current distortion can be reduced, and the rotational drive of the motor 50 can be made smoother. be able to. Further, noise due to the switching operation can be reduced.

In the EPS control device 10C according to the above embodiment (2), as the variable capacity means,
The analog switch 13 is connected between the gate terminals and the source terminals of the MOS1 to MOS4, respectively.
Although a case where a to 13d and capacitors C1 to C4 are interposed has been described, in the EPS control device 10D according to another embodiment, as illustrated in FIG.
The analog switches 14a to 14d and the capacitors C11 to C14 are respectively interposed between the gate terminals and the drain terminals of the first and second terminals, and the capacitance between the gate and the drain is turned on / off of the analog switches 14a to 14d. It can also be set as the structure increased / decreased based on switching control.

Furthermore, in another embodiment EPS control apparatus 10E, as shown in FIG.
Analog switches 15 are connected between the drain terminals and the source terminals of S1 to MOS4, respectively.
It is also possible to adopt a configuration in which a to 15d and capacitors C21 to C24 are interposed, and the capacitance between the drain and the source is increased or decreased based on on / off switching control of the analog switches 15a to 15d.

Furthermore, the above-mentioned analog switch is provided at any two or more positions between each gate terminal and source terminal of MOS1 to MOS4, between each gate terminal and drain terminal, or between each drain terminal and source terminal. A configuration in which a capacitor is interposed may be employed.

In the above embodiment, the case where one analog switch and one capacitor are interposed in parallel between the terminals of the MOS1 to MOS4 has been described. However, the analog switch and the capacitor are connected between the terminals of the MOS1 to MOS4. A capacitor may be connected in parallel to switch the capacitance between the terminals of the MOS1 to MOS4 in multiple stages.

FIG. 15 is a diagram illustrating a schematic configuration of an in-vehicle electric power steering control device in which the motor control device according to the embodiment (3) is employed. However, the EPS control device 1 shown in FIG.
Constituent parts having the same function as 0 are given the same reference numerals and their description is omitted.

In the EPS control apparatus 10 according to the embodiment (1), the variable resistance means 11 is provided as the operation speed switching means 11 between the pre-driver 3 and the gate terminals of the MOS1 to MOS4.
a to 11d are interposed, but in the EPS control device 10F according to the embodiment (3), the operation speed switching unit 11F is variable between the pre-driver 3 and each gate terminal of the MOS1 to MOS4. Resistance means 11a to 11d are interposed, and MOS1 to MOS4
The main difference is that analog switches 13a to 13d and capacitors C1 to C4 are interposed between the gate terminals and the source terminals of the above.

That is, the operation speed switching means 1 in the EPS control apparatus 10F according to the embodiment (3).
1F is a combination of the operation speed switching means 11 in the embodiment (1) and the operation speed switching means 11C in the embodiment (2).

Next, the resistance value / capacitance setting processing operation performed by the microcomputer 20F in the EPS control apparatus 10F according to the embodiment (3) will be described based on the flowchart shown in FIG. This processing operation is executed after the vehicle engine is started.

After the engine is started, first, a process of setting the resistance values of the variable resistance means 11a to 11d to a preset default value and a process of turning on the analog switches 13a to 13d are performed (step S31). Then, normal EPS control is started (step S32).

Thereafter, the steering torque command value T * calculated based on the signal acquired from the torque sensor 7
It is determined whether (target value of steering assist torque) is equal to or greater than a predetermined value T ′ (step S33).
If it is determined that the steering torque command value T * is equal to or greater than the predetermined value T ′, that is, the driving situation requires steering assist, each part of the device, for example, MOS1 to MOS4, for example, based on the signal acquired from the temperature sensor 6. Temperature (estimated temperature) Ts is calculated (step S34).

Next, whether the difference between the allowable temperature (ie, heat-resistant set temperature) Tmax of MOS1 to MOS4 and the calculated estimated temperature Ts is equal to or greater than a predetermined value ΔT, that is, whether there is a margin with respect to the allowable temperature of MOS1 to MOS4 (Step S35), and the difference between the allowable temperature Tmax of the MOS1 to MOS4 and the estimated temperature Ts is less than a predetermined value ΔT, that is, MOS1 to MOS.
If it is determined that there is no room for the allowable temperature of 4, the process of switching the resistance values set in the variable resistance means 11a to 11d to a small value and / or analog so that the operating speed of the MOS1 to MOS4 increases. Processing for turning off the switches 13a to 13d is performed (step S36).
Then, the process returns to step S33 to repeat the process.

That is, in step S36, the allowable temperature Tmax and the estimated temperature Tmax of the MOS1 to MOS4.
The temperature difference from s is applied to the relationship map between the set resistance value and the rising temperature stored in the EEPROM in the microcomputer 20F, and the set resistance value corresponding to the temperature difference is obtained from the relationship map.
A process of switching the resistance value set in the variable resistance means 11a to 11d to a set resistance value obtained from the temperature difference and / or a process of turning off the analog switches 13a to 13d to reduce the capacitance between the gate and the source I do. Thereafter, EPS control is performed with the switched resistance value.

In this case, there is no allowance for the allowable temperature, that is, the temperature difference between the allowable temperature of the MOS1 to MOS4 and the estimated temperature is small, so that a temperature increase beyond the temperature difference does not occur (in other words, Then, a resistance value (that is, a smaller resistance value) for setting the temperature so as not to exceed the allowable temperature is set. FIG. 7 shows the operation of each part of the motor drive circuit when a small resistance value is set in a situation where there is no allowance for the allowable temperature and / or when the analog switches 13a to 13d are turned off. Since it is substantially the same as the operation shown, the description is omitted here.

On the other hand, in step S35, the allowable temperature Tmax and the estimated temperature Ts of the MOS1 to MOS4.
And the analog switches 13a to 13a to switch the resistance values set in the variable resistance means 11a to 11d to a large value so as to slow down the switching operation speed of the MOS1 to MOS4. The process of continuing the ON state of 13d is performed (step S37), and then the process returns to step S33 to repeat the process.

That is, in step S37, allowable temperature Tmax and estimated temperature Tmax of MOS1 to MOS4.
The temperature difference from s is applied to a relationship map between the set resistance value and the rising temperature stored in the EEPROM in the microcomputer 20F, and a resistance value corresponding to the temperature difference is obtained from the relationship map, and the variable resistance means 11a to 11a- A process of switching the resistance value set to 11d to the resistance value obtained from the temperature difference and a process of continuing the ON state of the analog switches 13a to 13d are performed. Thereafter, EPS control is performed with the switched resistance value.

In this case, there is a margin with respect to the allowable temperature, that is, the temperature difference between the allowable temperature Tmax of the MOS1 to MOS4 and the estimated temperature Ts is large. A larger resistance value can be set. The operation of each part of the motor drive circuit when a large resistance value is set in a situation where there is a margin with respect to the allowable temperature and the analog switches 13a to 13d are in the on state is shown in FIG. The description thereof is omitted here.

On the other hand, if it is determined in step S33 that the steering torque command value T * is not equal to or greater than the predetermined value T ′, that is, if the driving situation does not require steering assist, step S33 is performed.
37, the process of switching the resistance values set in the variable resistance means 11a to 11d and the analog switches 13a to 13d so as to slow down the switching operation speed of the MOS1 to MOS4.
The process of continuing the ON state is performed, and then the process returns to step S33 to repeat the process.

According to the EPS control device 10F according to the above embodiment (3), the operation speed switching means 11F.
Since the resistance values set in the variable resistance means 11a to 11d constituting the switch and the on / off of the analog switches 13a to 13d constituting the variable capacitance means are switched based on the heat generation state of the device, the actual temperature change The switching operation speed according to the situation can be adjusted more finely.

In the above embodiment, a case where a motor with a DC brush is applied to the motor 50 has been described. However, the present invention can also be applied to a motor having another configuration such as a three-phase brushless motor. When a phase brushless motor is applied, a DC voltage supplied from a corresponding motor drive circuit, for example, battery B, is converted into a three-phase AC voltage by pulse width modulation (PWM) control and supplied to the motor. It is only necessary to use a configured circuit, and a switching circuit having a three-phase bridge circuit configuration including a pair of upper and lower arm elements corresponding to each of the U-phase, V-phase, and W-phase may be used. Good.

In the above embodiment, the temperature is detected on the basis of a signal acquired from the temperature sensor 6 provided in the apparatus. However, the current value flowing in the motor 50 or the switching circuit 31 is calculated by calculation. A configuration for obtaining the temperature can also be adopted.

The motor control device according to the present invention can be applied not only to the above-described electric power steering control device but also to other motor control devices that drive a motor by driving a switching circuit having a pair of upper and lower arm elements. it can.

It is the figure which showed schematic structure of the conventional electric power steering control apparatus. It is a wave form diagram for demonstrating operation | movement of the motor drive circuit in the conventional electric power steering control apparatus. It is the figure which showed schematic structure of the electric power steering control apparatus which concerns on Embodiment (1) of this invention. It is the flowchart which showed the map information storage processing operation which the microcomputer in the electric power steering control device which relates to execution form (1). It is a figure for demonstrating the map information stored in EEPROM of the microcomputer in the electric power steering control apparatus which concerns on embodiment (1). It is the flowchart which showed the resistance value switching process operation | movement which the microcomputer in the electric power steering control apparatus which concerns on embodiment (1) performs. (A)-(g) is a wave form diagram for demonstrating operation | movement of the motor drive circuit in the electric power steering control apparatus which concerns on embodiment (1). (A)-(g) is a wave form diagram for demonstrating operation | movement of the motor drive circuit in the electric power steering control apparatus which concerns on embodiment (1). It is a schematic block diagram of the electric power steering control apparatus which concerns on another embodiment. It is a schematic block diagram of the electric power steering control apparatus which concerns on another embodiment. It is the figure which showed schematic structure of the electric power steering control apparatus which concerns on embodiment (2). It is the flowchart which showed the capacity | capacitance switching process operation which the microcomputer in the electric power steering control apparatus which concerns on embodiment (2) performs. It is a schematic block diagram of the electric power steering control apparatus which concerns on another embodiment. It is a schematic block diagram of the electric power steering control apparatus which concerns on another embodiment. It is the figure which showed schematic structure of the electric power steering control apparatus which concerns on embodiment (3). It is the flowchart which showed the capacity | capacitance switching process operation which the microcomputer in the electric power steering control apparatus which concerns on embodiment (3) performs.

Explanation of symbols

3 Pre-driver 4 Switching circuit 6 Temperature sensor 10, 10A to 10F Electric power steering control device 11, 11A to 11F Operating speed switching means 20, 20A to 20F Microcomputer 50 Motor

Claims (5)

Switching means interposed in a line for supplying drive current to the motor;
Drive means for driving the switching means;
Motor control means for controlling the drive of the motor by driving the drive means;
An operation speed switching means for switching the operation speed at the time of switching of the switching means;
A motor control device comprising switching control means for switching the setting of the operation speed switching means based on a heat generation state. The operating speed switching means includes variable resistance means capable of switching a resistance value connected to a control terminal of the switching means,
2. The motor control device according to claim 1, wherein the switching control unit includes a resistance switching control unit that switches setting of a resistance value of the variable resistance unit based on a heat generation state. The operating speed switching means includes variable capacity means capable of switching the inter-terminal capacity of the switching means,
3. The motor control device according to claim 1, wherein the switching control unit includes a capacity switching control unit that switches a setting of a capacity of the variable capacity unit based on a heat generation state. According to the driving situation of the vehicle, it is adopted in an electric power steering control device that performs control to assist steering by driving a motor provided in a steering mechanism,
A determination means for determining whether or not the driving situation requires steering assist;
The motor control device according to any one of claims 1 to 3, wherein the switching control unit switches the setting of the operation speed switching unit in consideration of a determination result by the determination unit. . Obtaining temperature information; and
Switching the setting of the operation speed switching means for switching the operation speed at the time of switching switching of the switching means interposed in the line for supplying the drive current to the motor based on the acquired temperature information;
And a step of performing control to drive the switching means in the switched setting state of the operation speed switching means.

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