JP5605714B2 - Motor drive device and electric power steering device using the same - Google Patents

Description

  The present invention relates to a motor driving device that drives a motor, and an electric power steering device using the same.

  Conventionally, an electric power steering device including a motor and a motor driving device is known. The motor generates auxiliary torque that assists the driver's steering operation. The motor drive device has a protection function that controls multiple elements that switch energization to the motor, and the maximum value of current that can be energized (hereinafter referred to as “current limit value”) so that the temperature of the element does not exceed the heat resistance temperature. I have. Patent Document 1 describes an electric power steering device that calculates the current limit value of each element from the estimated temperature of the element and uses the smallest current limit value as an actual command current value to suppress overheating of the switching element. ing.

Japanese Patent No. 3601967

  However, in the electric power steering apparatus described in Patent Document 1, it is necessary to create a current limit value map indicating the relationship between the current value and the element temperature for all of the plurality of elements mounted on the motor drive device. Therefore, in the manufacturing stage of the electric power steering device, the number of steps for creating the current limit value map increases. In actual use, the element characteristics change depending on the temperature of the element. Therefore, when the element characteristics change, the current limit value map cannot prevent the element from being overheated, or the current limit may be excessive. .

  An object of the present invention is to provide a motor drive device that can reduce the number of steps for creating a current limit value map at the time of manufacture and can change the current limit value at the time of actual use.

According to the first aspect of the present invention, a motor drive device for driving a motor includes a drive circuit, elements constituting the drive circuit, temperature detection means, temperature change rate calculation means, temperature arrival time calculation means, and current arrival time calculation means. And current limit value changing means. The temperature detecting means detects the temperature of the element and outputs a signal corresponding to the temperature of the element. The temperature change rate calculating means calculates the temperature change rate of the element based on the detected temperature of the element. The temperature arrival time calculating means reaches the temperature necessary for the element temperature to change from the current temperature to the target temperature based on the current temperature of the element, the target temperature, and the temperature change rate calculated by the temperature change rate calculating means. Time is calculated every predetermined time . The current arrival time calculation means calculates the current limit value from the current current limit value based on the current current limit value currently set for the element, the target current limit value set for the element, and a predetermined current limit value change rate. The current arrival time required to change to the target current limit value is calculated every predetermined time . Current limit changing means, by comparing the temperature reaching time calculated in the temperature reaching time calculation means, a current arrival time calculated by the current arrival time calculating means, changes the current limit value of the element. The motor drive device of the present invention is characterized in that the current limit value changing means changes the current limit value every predetermined time.

The motor driving apparatus according to claim 1 calculates the following two times when changing the current limit value of the element.
One is the temperature arrival time, which is the time required for the temperature of the element to change from the current temperature to the target temperature according to the temperature change rate. The temperature change rate of the element is obtained by dividing the amount of change from the past temperature of the element to the current temperature by the corresponding time. The temperature change rate of the element is calculated every predetermined time by the temperature change rate calculating means based on the temperature of the element detected by the temperature detecting means. In addition, the target temperature is set to a temperature lower than the heat-resistant temperature at which a malfunction occurs in the element. The other is the current arrival time, which is the time required for the current limit value of the element to change from the currently set current limit value to the target current limit value according to a predetermined current limit value change rate. . The predetermined current limit value change rate is obtained by dividing the amount of change of the current limit value set in the element by time.

  The element is set with a current limit value to prevent overheating due to energization. In the initial operation state of the motor driving device, the temperature of the element is low, so that the current limit value of the element becomes the maximum value in the element. However, when the motor drive device operates continuously, the temperature of the element rises due to continuous energization, and is close to the heat resistant temperature. At this time, the current limit value changing means compares the temperature arrival time calculated by the temperature arrival time calculation means with the current arrival time calculated by the current arrival time calculation means, so that the temperature of the element is equal to or higher than the heat resistance temperature. Change the current limit value so that it does not occur. That is, in the motor drive device, the current limit value is set based on the element temperature detected by the temperature detecting means, and the current limit value can be set in accordance with the actual element state. Thereby, the temperature of an element can be kept below heat-resistant temperature.

The motor drive device according to claim 1 sets a current limit value corresponding to the situation by setting a current limit value change rate, a target current limit value, and a target temperature of the element. Therefore, the creation of the current limit value map can be omitted in the manufacturing stage of the motor drive device, and the number of steps in the manufacturing stage can be reduced.
In addition, the temperature state of the element and the electrical characteristics of the element change with time due to a continuously flowing current. Therefore, in the motor drive device according to the first aspect, the current limit value is set and changed every predetermined time from the temperature of the element detected by the temperature detecting means. As a result, a current limit value can be set in accordance with the actual state of the element.

According to the second aspect of the present invention, when the temperature arrival time is equal to or shorter than the current arrival time, the current limit value changing means decreases the current limit value of the element. According to the third aspect of the present invention, when the temperature arrival time is equal to or shorter than the current arrival time, the current limit value changing means decreases the current limit value of the element according to the current limit value change rate.
In the motor drive device, when it is determined that the temperature arrival time is equal to or less than the current arrival time, it is predicted that the temperature of the element exceeds the target temperature unless the current limit value is changed. Therefore, in the motor drive device according to the second aspect, when the temperature arrival time is equal to or shorter than the current arrival time, the current limit value changing unit changes the current limit value of the element to be small. As a result, the value of current that can be passed through the element decreases. Therefore, the temperature reached by the element is lowered, and the temperature of the element can be kept below the heat resistant temperature. Further, the current limit value changing means changes the current limit value so as to become smaller according to a predetermined current limit value change rate. That is, the current limit value of the element becomes smaller at a predetermined current limit value change rate. By setting the predetermined current limit value change rate small, a steep current fluctuation due to a large change in the current limit value is suppressed. As a result, it is possible to prevent a sudden change in the assist torque that assists the driver's steering operation.

According to the fourth aspect of the present invention, when the temperature arrival time is longer than the current arrival time and the temperature change rate is 0 or less, the current limit value changing means increases the current limit value. According to the fifth aspect of the present invention, the current limit value changing means increases the current limit value according to the current limit value change rate.
When it is determined that the temperature arrival time is greater than the current arrival time, the temperature of the element does not exceed the target temperature even if the current limit value is not decreased with respect to the element at the time of the determination. Further, when the temperature change rate of the element is 0 or less, the element temperature changes from the high temperature side to the low temperature side. Therefore, the temperature of the element does not exceed the target temperature to reach the heat resistant temperature. Therefore, in the motor drive device according to the fourth aspect, the current limit value changing means changes the current limit value of the element so as to increase. As a result, a large amount of current can flow through the element. Further, the current limit value changing means changes the current limit value so as to increase according to a predetermined current limit value change rate. That is, the current limit value of the element increases at a predetermined current limit value change rate. By setting the predetermined current limit value change rate small, a steep current fluctuation due to a large change in the current limit value is suppressed. As a result, it is possible to prevent a sudden change in the assist torque that assists the driver's steering operation.

According to the sixth aspect of the present invention, when the temperature arrival time is longer than the current arrival time and the temperature change rate is greater than 0, the current limit value changing means does not change the current limit value.
When it is determined that the temperature arrival time is greater than the current arrival time, the temperature of the element does not exceed the target temperature even if the current limit value is not decreased with respect to the element at the time of the determination. However, since the temperature change rate of the element is larger than 0, the temperature of the element changes from the low temperature side to the high temperature side. Therefore, the current limit value changing means does not change the current limit value so that the element can be maintained as it is.

According to the invention described in claim 8 , a plurality of target temperatures are set. According to the eighth aspect of the invention, the current limit value change rate is set larger as the target temperature is higher.
The motor drive device according to claim 8 sets a plurality of target temperatures. In the motor drive device, the minimum target temperature among the plurality of set target temperatures is compared with the current temperature of the element. At this time, when the current temperature of the element is higher than the minimum target temperature, the temperature arrival time is calculated based on a target temperature that is next to the lowest target temperature among a plurality of set target temperatures. In this way, the motor drive device sets the temperature arrival time in stages from a low target temperature to a high target temperature close to the heat resistant temperature with respect to the heat resistant temperature of the element.

When calculating the temperature arrival time for a target temperature close to the heat resistant temperature of the element, the current temperature of the element is close to the heat resistant temperature of the element. Therefore, in order not to exceed the heat resistance temperature of the element, it is necessary to reduce the current value flowing through the element by quickly reducing the current limit value of the element. Therefore, in the motor drive device according to the ninth aspect , the current limit value change rate is set to a larger value as the target temperature becomes higher. Thereby, when the current temperature of the element is close to the heat-resistant temperature, the current limit value of the element can be quickly reduced. Therefore, the temperature at which the element reaches can be lowered, and the temperature of the element can be kept below the heat resistant temperature.

According to the tenth aspect of the present invention, the motor driving device calculates the temperature arrival time using the annealing temperature as the element temperature.
By using the annealing temperature as the element temperature, even if a sudden value is detected in the element temperature, the influence on the calculated temperature arrival time is reduced. As a result, a current limit value that is not affected by unexpected disturbance can be set.

  According to an eleventh aspect of the present invention, an electric power steering device is driven by the motor driving device according to any one of the first to tenth aspects, and an assist that assists a driver's steering operation. A motor for generating torque and power transmission means for transmitting the driving rotational force of the motor to the steering shaft are provided.

It is a lineblock diagram showing the whole electric power steering system composition provided with the motor drive unit in a 1st embodiment of the present invention. It is a schematic diagram which shows the electrical structure of the motor drive device in 1st Embodiment of this invention. It is a flowchart explaining the action | operation of the motor drive device in 1st Embodiment of this invention. It is a graph which shows the relationship between the temperature of the switching element of the motor drive device in 1st Embodiment of this invention, the electric current limiting value set to a switching element, and time. It is a flowchart explaining the action | operation of the motor drive device in 2nd Embodiment of this invention.

Hereinafter, a plurality of embodiments of the present invention will be described with reference to the drawings.
(First embodiment)
A motor driving apparatus according to a first embodiment of the present invention will be described with reference to FIGS.
As shown in FIG. 1, an electronic control device (hereinafter referred to as “ECU”) 10 as a “motor drive device” 10 is, for example, an electric power steering device 12 (hereinafter referred to as “EPS”) for assisting the steering operation of the vehicle. ) Applies.

  FIG. 1 shows the overall configuration of the steering system 1. The steering shaft 2 connected to the handle 4 is provided with a torque sensor 5 for detecting steering torque. A pinion gear 3 is provided at the tip of the steering shaft 2, and the pinion gear 3 meshes with the rack shaft 6. A pair of wheels 7 are rotatably connected to both ends of the rack shaft 6 via tie rods or the like. The rotational motion of the steering shaft 2 is converted into linear motion of the rack shaft 6 by the pinion gear 3, and the pair of wheels 7 are steered at an angle corresponding to the linear motion displacement of the rack shaft 6.

  The steering system 1 includes a motor 9 that generates a steering assist torque, an ECU 10 that controls driving of the motor 9, and a reduction gear 8 as a “power transmission unit” that decelerates forward and reverse rotations of the motor 9 and transmits it to the steering shaft 2. Is provided. The electric power steering device 12 generates a steering assist torque for assisting the steering of the handle 4 and transmits the steering assist torque to the steering shaft 2.

  The ECU 10 includes a power unit 50 and a control unit 60. FIG. 2 shows a circuit configuration of the ECU 10. The ECU 10 controls the drive of the motor 9 so as to generate a steering assist torque for assisting the steering of the handle 4 according to the rotation angle of the handle 4.

  The power unit 50 of the ECU 10 includes a first capacitor 51, a choke coil 52, a power module 53 as the inverter circuit 1, a second capacitor 55, a power module 54 as the inverter circuit 2, and the like.

  Power is supplied to the power unit 50 from a power source 20 provided outside the ECU 10. The first capacitor 51 and the choke coil 52 constitute a filter circuit, and reduce noise transmitted from the other device sharing the power source 20 to the ECU 10 and reducing noise transmitted from the ECU 10 to another device sharing the power source 20. . The choke coil 52 is connected in series between the power supply 20 and the power module 53 and the power module 54 to attenuate voltage fluctuations. The first capacitor 51 and the choke coil 52 correspond to “elements” recited in the claims.

The power module 53 is a semiconductor module integrally formed by covering the switching elements 501, 502, 503, 504, 505, 506, the power relays 507, 508, the shunt resistor 509, etc. with a sealing body such as resin. .
In the present embodiment, the switching elements 01, 502, 503, 504, 505, and 506 are MOSFETs (metal-oxide-semiconductor field-effect transistors) that are a kind of field effect transistors. The switching elements 501, 502, 503, 504, 505, and 506 are ON / OFF controlled between the source and the drain by the gate voltage. The switching elements 01, 502, 503, 504, 505, and 506 correspond to “elements” recited in the claims.

  The switching elements 501, 502, and 503 have drains connected to the power supply 20 side and sources connected to drains of switching elements 504, 505, and 506 corresponding to the switching elements 501, 502, and 503, respectively. The sources of the switching elements 504, 505, and 506 are connected to the ground side. Connection points of the switching elements 501, 502, and 503 and the corresponding switching elements 504, 505, and 506 are electrically connected to the motor 9 via individual relays 510.

  Similarly to the switching elements 501, 502, 503, 504, 505, and 506, the power relays 507 and 508 are configured by MOSFETs. The power supply relays 507 and 508 are provided between the switching elements 501, 502, 503, 504, 505, and 506 and the choke coil 52. The current flowing to the motor 9 side can be cut off.

The shunt resistor 509 is electrically connected between the switching elements 504, 505, and 506 and the ground. By detecting the voltage or current applied to the shunt resistor 509, the current flowing through the motor 9 can be detected.
Since the power module 54 as the inverter circuit 2 has the same configuration as the power module 53 as the inverter circuit 1 described above, the description thereof is omitted.

  The second capacitor 55 is connected to the wiring on the power source 20 side of the switching elements 501, 502, and 503 and the ground. That is, the second capacitor 55 is connected in parallel with the switching elements 501, 502, 503, 504, 505, and 506. The second capacitor 55 accumulates electric charges to assist power supply to the switching elements 501, 502, 503, 504, 505, and 506, and absorbs a ripple current generated by switching the current. The second capacitor 55 corresponds to an “element” recited in the claims.

The control unit 60 includes a custom IC 61, a rotation angle sensor 62, a control IC 63, a temperature sensor 70, and the like.
The custom IC 61 is a semiconductor integrated circuit including a regulator 64, a rotation angle sensor signal amplification unit 65, a detection voltage amplification unit 66, and the like.

  The regulator 64 is a stabilization circuit that stabilizes the power from the power supply 20. The regulator 64 stabilizes the power supplied to each unit. For example, the microcomputer 67 described later operates at a stable predetermined voltage (for example, 5 V) by the regulator 64.

A signal from the rotation angle sensor 62 is input to the rotation angle sensor signal amplification unit 65. The rotation angle sensor 62 is provided in the motor 9, detects a change in the surrounding magnetic field, and transmits the detected value to the rotation angle sensor signal amplification unit 65 as a signal related to the rotation angle of the motor 9. The rotation angle sensor signal amplification unit 65 amplifies the signal related to the rotation angle of the motor 9 transmitted from the rotation angle sensor 62 and outputs the amplified signal to the microcomputer 67 described later.
The detection voltage amplification unit 66 detects the voltage across the shunt resistor 509, amplifies the detected value, and outputs the amplified detection value to the microcomputer 67 described later.

The control IC 63 is a semiconductor integrated circuit including a microcomputer 67, pre-drivers 68 and 69, and the like.
The microcomputer 67 is a small computer having a CPU as arithmetic means and ROM and RAM as storage means. The microcomputer 67 executes various processes by the CPU according to various programs stored in the ROM. The microcomputer 67 corresponds to “temperature change rate calculation means”, “temperature arrival time calculation means”, “current arrival time calculation means”, and “current limit value changing means” described in the claims.

  The microcomputer 67 includes a signal from the rotation angle sensor signal amplifying unit 65 relating to the rotation angle of the motor 9, a voltage across the shunt resistor 509 from the detection voltage amplifying unit 66, a steering torque signal from the torque sensor 5 via the second connector 43, A signal related to the temperature in the ECU 10 is input from the temperature sensor 70 as “temperature detection means”, and vehicle speed information is input from the CAN. When these signals are input, the microcomputer 67 controls the power module 53 via the pre-driver 68 based on the rotation angle of the motor 9. A control flow of the power module 53 by the microcomputer 67 will be described later.

  Further, the microcomputer 67 controls the power module 53 so that the current supplied to the motor 9 approaches a sine wave based on the voltage across the shunt resistor 509 input from the detection voltage amplifier 66. The microcomputer 67 controls the power module 54 with the pre-driver 69 in the same manner as the power module 53 is controlled with the pre-driver 68.

  The microcomputer 67 is connected via the pre-driver 68 and the pre-driver 69 so as to assist the steering 4 in accordance with the vehicle speed based on the vehicle speed information from the rotation angle sensor 62, the torque sensor 5, the shunt resistor 509, and the CAN. A pulse signal generated by PWM control is generated. This pulse signal is output to two systems of inverter circuits composed of the power module 53 and the power module 54, and the switching elements 501, 502, 503, 504, 505, and 506 of the power module 53 and the power module 54 are switched on and off. Control the behavior. As a result, sinusoidal currents having different phases flow through the motor 9 to generate a rotating magnetic field. Upon receiving this rotating magnetic field, the motor 9 generates a rotating force, and the steering by the driver's steering 4 is assisted.

(Function)
Next, the operation of the ECU 10 will be described.
The pulse signal generated by the microcomputer 67 of the control unit 60 is output from the microcomputer 67 to the power modules 53 and 54 via the pre-drivers 68 and 69. At this time, the microcomputer 67 does not exceed the heat resistance temperature of the switching elements 501, 502, 503, 504, 505, 506, the first capacitor 51, the second capacitor 55, and the choke coil 52 constituting the power modules 53, 54. The maximum value of current flowing through each element (hereinafter referred to as “current limit value”) is set.

  Here, as an example, a flow for setting the current limit values of the switching elements 501, 502, and 503 constituting the power module 53 will be described below. The ECU 10 performs the same processing on the switching elements 504, 505, 506, the first capacitor 51, the second capacitor 55, and the choke coil 52.

  In the first step (hereinafter, “step” is omitted, and simply indicated by the symbol S) 101, the element temperature T1 at the time t1 at which the current limiting starts and the element temperature T0 at the time t0 one second before the time t1 The temperature difference ΔT is calculated. A signal corresponding to the temperature Te in the ECU 10 detected by the temperature sensor 70 is input to the microcomputer 67. The microcomputer 67 has a correlation map between the temperature Te and the switching element temperatures 501, 502, and 503 in advance, and calculates the element temperature T of the switching elements 501, 502, and 503 from the temperature Te. In S101, a temperature difference ΔT that is a difference between the element temperature T1 at time t1 and the element temperature T0 at time t0 is calculated. In the first embodiment, the microcomputer 67 calculates the element temperature T of the switching elements 501, 502, and 503 every second. Therefore, the temperature change rate ΔT1 which is the time change rate of the element temperature T is the same as the temperature difference ΔT.

  Next, in S102, it is determined whether or not the element temperature T1 at time t1 is lower than the first target temperature T01. The first target temperature T01 is a target temperature arbitrarily set for the switching elements 501, 502, and 503. The first target temperature T01 is a temperature lower than the heat resistance temperature of the switching elements 501, 502, and 503. When it is determined that the element temperature T1 is lower than the first target temperature T01, the process proceeds to S103. When it determines with element temperature T1 being 1st target temperature T01 or more, it transfers to S108.

  Next, in S103, the microcomputer 67 calculates the temperature arrival time P1 and the current arrival time P2. The temperature arrival time P1 is a time required for the element temperature T to change from the element temperature T1 at the time t1 to the first target temperature T01. The temperature arrival time P1 is the time required to reach the first target temperature T01 when the element temperature T changes from the element temperature T1 at the time t1 at the change rate of the temperature change rate ΔT1 as shown in FIG. It is. As shown in FIG. 4, the slope of the straight line connecting the element temperature T1 at time t1 and the element temperature T0 at time t0 is the temperature change rate ΔT1. That is, the temperature change rate ΔT1 is a ratio of the temperature increase c to the predetermined time d. (See FIG. 4) Time t2 is the time at which the straight line of the gradient of the temperature change rate ΔT1 crosses the first target temperature T01 through the point of the element temperature T1 at time t1. The temperature arrival time P1 is a time between time t2 and time t1.

  On the other hand, the current arrival time P2 is a time required for the current limit value E to change from the current limit value E1 at the time t1 set in the switching elements 501, 502, and 503 to the first target current limit value E01. is there. The current arrival time P2 reaches the first target current limit value E01 when the current value changes with the change rate of the first current limit value change rate ΔE1 set in advance from the current limit value E1 at the time t1. It takes time to complete. The first current limit value change rate ΔE1 is a ratio of a decrease a of the current limit value to a predetermined time b. (See FIG. 4) The first current limit value change rate ΔE1 is arbitrarily set for each group unit in which the current limit value is set. For example, in this example, the switching elements 501, 502, and 503 are set as one group unit. The first current limit value change rate ΔE1 is smaller than the reference current limit value change rate set in advance as the same value for all the same switching elements. The reference current limit value change rate can be, for example, a current limit value change rate at which the assist torque for assisting the driver's steering operation due to current fluctuation does not change abruptly. A time at which the straight line of the slope of the first current limit value change rate ΔE1 passes through the point of the current limit value E1 at time t1 is defined as time t3. The current arrival time P2 is a time between time t3 and time t1.

  Next, in S104, the magnitude of the temperature arrival time P1 and the current arrival time P2 is determined. When the temperature arrival time P1 is less than or equal to the current arrival time P2, the process proceeds to S105. If the temperature arrival time P1 is greater than the current arrival time P2, the process proceeds to S106. For example, in the case of FIG. 4, the process proceeds to S105.

  Next, in S105, the current limit values of the switching elements 501, 502, and 503 are changed. Specifically, the current limit value E4 at the time t4 one second after the time t1 is set to be smaller than the current limit value E1 by the first current limit value change rate ΔE1. Therefore, the current limit value E at the time t4 of the switching elements 501, 502, and 503 is the current limit value E1−ΔE1. That is, the current limit value E of the switching elements 501, 502, and 503 is changed as indicated by a thick broken line. As a result, the element temperature T of the switching elements 501, 502, and 503 also decreases as shown by the thick broken lines in FIG.

  On the other hand, if it is determined in S104 that the temperature arrival time P1 is greater than the current arrival time P2, it is determined in S106 whether the temperature difference ΔT is greater than zero. That is, it is determined whether the element temperature T of the switching elements 501, 502, and 503 is rising or falling. When it is determined that the temperature difference ΔT is larger than 0, the current limit value E of the switching elements 501, 502, and 503 is not changed, and this flow is finished. When it is determined that the temperature difference ΔT is 0 or less, that is, when it is determined that the element temperature T is decreasing, the process proceeds to S107.

  Next, in S107, the current limit values of the switching elements 501, 502, and 503 are changed. Specifically, the current limit value E4 at the time t4 one second after the time t1 is set to be larger than the current limit value E1 by the first current limit value change rate ΔE1. The current limit value E at the time t4 of the switching elements 501, 502, and 503 is the current limit value E1 + ΔE1.

  If it is determined in S102 that the element temperature T1 is equal to or higher than the first target temperature T01, the microcomputer 67 calculates a temperature arrival time P3 and a current arrival time P4. The temperature arrival time P3 is a time required for the element temperature T to change from the element temperature T1 at the time t1 to the second target temperature T02. The temperature arrival time P3 is a time required to reach the second target temperature T02 when the element temperature T changes from the element temperature T1 at the time t1 at the change rate of the temperature change rate ΔT1 described above. At this time, the second target temperature T02 is set higher than the first target temperature T01. Therefore, the temperature arrival time P3 is longer than the current arrival time P1. On the other hand, the current arrival time P4 is a time required for the limit current value E to change from the current limit value E1 at the time t1 set to the switching elements 501, 502, and 503 to the second target current limit value E02. is there. The current arrival time P4 reaches the second target current limit value E02 when the current value changes with the change rate of the second current limit value change rate ΔE2 set in advance from the current limit value E1 at the time t1. It is time until. At this time, the second current limit value change rate ΔE2 is set higher than the first current limit value change rate ΔE1. Therefore, the current arrival time P4 is shorter than the current arrival time P3.

  Next, in S109, the magnitude of the temperature arrival time P3 and the current arrival time P4 is determined. When the temperature arrival time P3 is equal to or shorter than the current arrival time P4, the process proceeds to S110. When the temperature arrival time P3 is larger than the current arrival time P4, the process proceeds to S111.

  Next, in S110, the current limit values of the switching elements 501, 502, and 503 are changed. Specifically, the current limit value E4 at the time t4 one second after the time t1 is set to be smaller than the current limit value E1 by the second current limit value change rate ΔE2. Therefore, the current limit value E at the time t4 of the switching elements 501, 502, and 503 is the current limit value E1−ΔE2.

  On the other hand, if it is determined in S109 that the temperature arrival time P3 is greater than the current arrival time P4, it is determined in S111 whether the temperature difference ΔT is greater than zero. That is, it is determined whether the element temperature T of the switching elements 501, 502, and 503 is rising or falling. When it is determined that the temperature difference ΔT is larger than 0, the current limit value E of the switching elements 501, 502, and 503 is not changed, and this flow is finished. When it is determined that the temperature difference ΔT is 0 or less, that is, when it is determined that the element temperature T is decreasing, the process proceeds to S112.

  Next, in S112, the current limit values of the switching elements 501, 502, and 503 are changed. Specifically, the current limit value E4 at the time t4 one second after the time t1 of the switching elements 501, 502, and 503 is set larger than the current limit value E1 by the second current limit value change rate ΔE2. Accordingly, the current limit value E of the switching elements 501, 502, and 503 at time t4 is the current limit value E1 + ΔE2.

  The microcomputer 67 of the control unit 60 determines the current limit value E of the switching elements 501, 502, and 503 every second along the flow described above. The microcomputer 67 controls the power unit 50 so that a current equal to or less than the determined current limit value E flows through the switching elements 501, 502, and 503. The controlled power unit 50 supplies the motor 9 with a current equal to or less than the current limit value E. The motor 9 outputs a driving force to the steering shaft 2 via the reduction gear 8 and assists the steering by the driver's handle 4.

(effect)
(A) The ECU 10 that controls the driving of the motor 9 changes the current limit value that is the maximum value of the current flowing through the switching elements 501, 502, and 503. When the ECU 10 changes the current limit value, the temperature change rate ΔT1 which is the change rate of the element temperature T1, the first target temperature T01, and the temperature from the time t0 to the time t1 of the switching elements 501, 502, and 503. Based on the above, the temperature arrival time P1 is calculated. On the other hand, the ECU 10 sets the current limit value E1, the first target current limit value E01, and the first current limit value change rate set in the switching elements 501, 502, and 503 at the time t1 of the switching elements 501, 502, and 503. Based on ΔE1, the current arrival time P2 is calculated. The ECU 10 compares the temperature arrival time P1 and the current arrival time P2, and when the temperature arrival time P1 is equal to or less than the current arrival time P2, the current limit value E is changed so as to decrease according to the first current limit value change rate ΔE1. To do. When the temperature arrival time P1 is equal to or shorter than the current arrival time P2, the element temperature T of the switching elements 501, 502, and 503 may exceed the heat resistance temperature unless the current limit value E is changed. Therefore, the ECU 10 determines whether or not the current limit value E needs to be changed based on the element temperature T detected by the temperature sensor 70, and if the current limit value E needs to be changed, the ECU 10 increases or decreases the current limit value. Such a determination is made. As a result, the switching elements 501, 502, and 503 are set with current limit values in accordance with actual use conditions. It is possible to prevent the temperature of the switching elements 501, 502, and 503 from becoming higher than the heat resistant temperature, and to prevent the switching elements 501, 502, and 503 from being damaged.

  (B) Conventionally, at the manufacturing stage of the motor drive device, a current limit value map is created for one element in order to prevent destruction of the element due to energization. Therefore, it is necessary to create a current limit value map for all of the plurality of elements used in the motor drive device, which increases the number of steps in the manufacturing stage. However, the ECU 10 of the first embodiment changes the current limit value E in consideration of the actual usage state of the switching elements 501, 502, and 503. Thereby, it is not necessary to create a current limit value map at the manufacturing stage, and man-hours can be reduced.

  (C) When the ECU 10 changes the current limit value E of the switching elements 501, 502, and 503, it changes according to the first current limit value change rate ΔE1 or the second current limit value change rate ΔE2 set in advance. . The first current limit value change rate ΔE1 and the second current limit value change rate ΔE2 are set to values smaller than the reference current limit value change rate. Thereby, the value of the current flowing through the switching elements 501, 502, and 503 does not fluctuate rapidly. Therefore, it is possible to prevent the occurrence of a cause that hinders the drivability of the vehicle, such as a sudden change in the steering assist torque due to a change in the current limit value in the motor drive device.

  (D) On the other hand, when the element temperature T of the switching elements 501, 502, and 503 is small, that is, when the element temperature T1 at the time t1 is smaller than the element temperature t0 at the time t0, the ECU 10 of the first embodiment The current limit value E is increased to increase the current value that can be energized. As a result, a large amount of current can flow through the switching elements 501, 502, and 503.

  (E) The ECU 10 of the first embodiment sets two target temperatures. When the element temperature T of the switching elements 501, 502, and 503 is higher than the relatively low first target temperature T01, the ECU 10 calculates the temperature arrival time P3 for the relatively high second target temperature T02. At this time, the ECU 10 calculates the current arrival time P4 for the second current limit value change rate ΔE2 having a change rate larger than the first current limit value change rate ΔE1. When the element temperature T of the switching elements 501, 502, and 503 is higher than the relatively low first target temperature T01, the element temperature T of the switching elements 501, 502, and 503 is close to the heat resistance temperature of the switching elements 501, 502, and 503 Therefore, it is necessary to prevent the element temperature T from exceeding the heat resistance temperature by quickly reducing the current limit value. The ECU 10 sets a relatively large second current limit value change rate ΔE2 with respect to the relatively high second target temperature T02, and changes the current limit value E of the switching elements 501, 502, and 503. Thereby, the temperature of the switching elements 501, 502, and 503 can be kept below the heat resistant temperature.

(Second Embodiment)
Next, a second embodiment of the present invention will be described with reference to FIG. The second embodiment differs from the first embodiment in the element temperature used when changing the current limit value. In addition, the same code | symbol is attached | subjected to the site | part substantially the same as 1st Embodiment, and description is abbreviate | omitted.

  In the second embodiment, when the current limit value E of the switching elements 501, 502, and 503 is changed, the annealing element temperature is used as the element temperature. Specifically, the annealing element temperature T6 at the time t6 when the current limit is started is calculated by averaging the data of the ten element temperatures T going back from the time t6. Further, the annealing temperature T5 at time t5, which is one second before time t6, is calculated by averaging the data of 10 element temperatures going back from time t0.

FIG. 5 shows a flow for determining the current limit value E of the switching elements 501, 502, and 503 when the annealing element temperature is used as the element temperature.
In the second embodiment, the annealing temperature difference ΔT of the switching elements 501, 502, and 503 is calculated in S201. In S202, it is determined whether or not the annealing element temperature T6 at time t6 is lower than the first target temperature T01. In S203, a temperature arrival time P1 required for the element temperature T to change from the annealing element temperature T6 at the time t6 to the first target temperature T01 is calculated. In S208, the temperature arrival time P3 required for the element temperature T to change from the annealing element temperature T6 at the time t6 to the second target temperature T02 is calculated. In S206 and S211, it is determined whether the annealing temperature difference ΔT is greater than zero.

  In the second embodiment, as the element temperatures of the switching elements 501, 502, and 503, an annealing temperature that averages the element temperatures within a predetermined time is used. By using the annealing temperature, the current limit value E of the switching elements 501, 502, and 503 can be changed without being affected by a sudden value detected in the element temperature. Thereby, in addition to the effects (A) to (E) of the first embodiment, the current limit value E that is not affected by the disturbance can be set.

(Other embodiments)
(A) In the above-described embodiment, the current limit value is determined for the switching element of the inverter circuit 1. However, the target for providing the current limit value is not limited to this. In the power section, a current limit value may be provided for the switching element, the first capacitor, the second capacitor, and the choke coil of the inverter circuit 2.

  (A) In the above-described embodiment, the temperature of the switching element is estimated from the temperature in the ECU detected by the temperature sensor. However, the method for detecting the temperature of the switching element is not limited to this. A temperature sensor may be directly attached to the switching element to detect the temperature of the switching element. Thereby, the exact temperature of a switching element can be known. Therefore, the current limit value set in the switching element can be set to a value more appropriate to the actual state.

  (C) In the above-described embodiment, the target temperature of the switching element is two. However, the target temperature of the switching element is not limited to this. One may be sufficient and three or more may be sufficient. When the target temperature of the switching element is set to three or more, it is possible to prevent a temperature rise to near the heat-resistant temperature of the switching element.

  (D) In the above-described embodiment, the change width of the current limit value of the switching element is determined according to the current limit value change rate. However, the change width of the current limit value of the switching element is not limited to this. The change range of the current limit value near the heat-resistant temperature of the switching element may be larger than the rate of change of the current limit value. Thereby, the temperature rise to near the heat-resistant temperature of a switching element can be prevented. Further, the change width of the current limit value near the heat-resistant temperature of the switching element may be smaller than the current limit value change rate. Thereby, the fluctuation range of the assist torque for the steering wheel operation due to the change of the current limit value can be reduced.

  (E) In the above-described embodiment, the first current limit value change rate and the second current limit value change rate are set to values smaller than the reference current limit value change rate. However, the magnitude relationship among the first current limit value change rate, the second current limit value change rate, and the reference current limit value change rate is not limited to this. The reference current limit value change rate may be larger than the first current limit value change rate and smaller than the second current limit value change rate, and the reference current limit value change rate may be the same as the first current limit value change rate. It may be. Further, the reference current limit value change rate may be the same as the second current limit value change rate.

  (F) In the above-described embodiment, the sampling interval of the temperature sensor is 1 second. However, the sampling interval of the temperature sensor is not limited to this. For example, the interval may be 5 seconds, or may be 0.5 seconds.

  (G) In the above-described embodiment, the current limit value of the switching element is provided using the temperature and the current limit value at a time one second before the time when the current limit is started. However, the time before the time when the current limit is started is not limited to this. It may be 5 seconds ago or 0.5 seconds ago.

  (H) In the second embodiment described above, the annealing element temperature is an average value of 10 data traced back from the time. However, the method for calculating the annealing element temperature is not limited to this. It may be a numerical value obtained by filtering the 10 data.

  (K) In the second embodiment described above, the annealing element temperature is an average value of 10 data traced back from the time. However, the number of data necessary for calculating the annealing element temperature is not limited to this. 2-9 may be sufficient and 11 or more may be sufficient.

  As mentioned above, this invention is not limited to such embodiment, It can implement with a various form in the range which does not deviate from the summary.

2 ... Steering shaft,
4 ... handle,
8 ... Reduction gear (power transmission means),
9: Motor,
10: ECU (motor drive device),
50 ... Power section (drive circuit),
501, 502, 503, 504, 505, 506... Switching element (element),
51... First capacitor (element),
52 ・ ・ ・ Choke coil (element),
55 ・ ・ ・ Second capacitor (element),
67... Microcomputer (temperature change rate calculation means, temperature arrival time calculation means, current arrival time calculation means, current limit value changing means),
70 ・ ・ ・ Temperature sensor (temperature detection means),
E, E1, E4 ... current limit values,
P1, P3 ... temperature arrival time,
P2, P4 ... current arrival time,
T01 ... 1st target temperature (target temperature),
T02 ... second target temperature (target temperature),
ΔE: Current limit value change rate,
ΔE1 ... First current limit value change rate (current limit value change rate),
ΔE2 ... second current limit value change rate (current limit value change rate),
ΔT ... temperature difference, annealing temperature difference,
ΔT1: Temperature change rate.

Claims (11)

A motor drive device comprising a drive circuit for driving a motor,
Elements constituting the drive circuit;
Temperature detecting means for detecting the temperature of the element and outputting a signal corresponding to the temperature of the element;
A temperature change rate calculating unit that receives a signal output from the temperature detecting unit and calculates a temperature change rate of the element based on the temperature of the element;
Based on the current temperature of the element, the target temperature of the element, and the rate of temperature change, a temperature arrival time required for the temperature of the element to change from the current temperature to the target temperature is calculated every predetermined time. Temperature arrival time calculation means,
Based on the current current limit value currently set for the element, the target current limit value set for the element, and a predetermined current limit value change rate, the current limit value is changed from the current current limit value to the target current limit. Current arrival time calculating means for calculating the current arrival time required to change to a value every predetermined time ;
Current limit value changing means capable of changing the current limit value of the element by comparing the temperature arrival time and the current arrival time;
Equipped with a,
The motor drive device characterized in that the current limit value changing means changes the current limit value every predetermined time .   2. The motor drive device according to claim 1, wherein when the temperature arrival time is equal to or shorter than the current arrival time, the current limit value changing unit decreases the current limit value.   The motor drive device according to claim 2, wherein the current limit value changing unit decreases the current limit value in accordance with the current limit value change rate.   The current limit value changing means increases the current limit value when the temperature arrival time is longer than the current arrival time and the temperature change rate is 0 or less. The motor drive device as described in any one.   The motor drive device according to claim 4, wherein the current limit value changing unit increases the current limit value in accordance with the current limit value change rate.   6. The current limit value changing unit does not change the current limit value when the temperature arrival time is longer than the current arrival time and the temperature change rate is greater than zero. The motor driving device according to claim 1.   The motor drive device according to any one of claims 2 to 6, wherein the current limit value change rate is set to a value smaller than a reference current limit value change rate. The target temperature is the motor driving apparatus according to any one of 7 from claim 1, characterized in that a plurality set. The motor driving apparatus according to claim 8 , wherein the current limit value change rate is set larger as the target temperature is higher. The motor driving device according to claim 1, wherein the temperature of the element is an annealing temperature. The motor drive device according to any one of claims 1 to 10,
Said driven by a motor driving device, said motor for generating an assist torque for assisting the steering operation of the driver,
Power transmission means for transmitting the driving rotational force of the motor to a steering shaft;
Electric power steering device with

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