JPH1120718A - Electric-type power steering control device and its motor current controlling method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize size reduction of a heat sink and of switching elements, by estimating temperature of a junction based on heat generation of the junction and on heat emission of the heat sink and by making smaller an error in the estimated temperature. SOLUTION: A CPU part 20a computes a current value for controlling output torque of a steering motor 5, and outputs, to a switching element 16, a command for controlling a voltage impressed on the steering motor 5 so that this current value can be attained. The switching element 16 controls the impressed voltage by switching it so as to become a fixed voltage value. As a junction 17 of the element 16 generates heat and its temperature rises by repetition of switching, the heat is emitted via a heat sink 15. A control device 20 estimates the temperature of the junction 17 as junction temperature, and causes a maximum value of current flowing in the switching element 16 to fall below a fixed value when this temperature reaches the fixed value. A temperature error in the switching element thereby becomes smaller.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric power steering control device for protecting a switching element for controlling an output torque of a steering motor for steering by a current from thermal destruction, and a motor current control method thereof.

[0002]

2. Description of the Related Art In recent years, a power steering device for a vehicle has been reduced in size and weight, and has advantages such as:
Electric ones are being used. Such an electric power steering device is provided with a steering motor, and the steering motor controls the output torque by controlling the current to steer the tire. Usually, the control of the current is often performed by a semiconductor switching element provided in a power circuit of the control device by switching an applied voltage and performing pulse width modulation. This switching causes the switching element to generate a large amount of heat, but the semiconductor switching element has a characteristic of being weak against heat. For this reason, the control device is provided with a heat radiation member called a heat sink, and the switching element is mounted on the heat sink. However, when the amount of heat generated by the switching element becomes larger than the amount of heat radiation of the heat sink and the temperature of the switching element rises and exceeds the allowable temperature in use, the switching element is thermally destroyed.

Therefore, for example, Japanese Patent Application Laid-Open No. 06-144279
Japanese Patent Application Laid-Open Publication No. H11-163,055 discloses a technique of an electric power steering apparatus for preventing the thermal destruction. According to the disclosed technology, as shown in FIG. 7, when the motor temperature rises and an abnormal lower limit is detected by the temperature sensor, the control device outputs the current command value of the steering assist motor flowing through the switching element to the maximum output. To 70%. And when this motor temperature falls and reaches the return upper limit,
The control device returns the current command value to the maximum output value again. When this operation is repeated for the third time, the current command value is reduced to 40% of the maximum output and maintained for T1 time. After the T1 time has elapsed, the temporarily reduced current command value is reduced to 80% of the maximum output. % And maintained for T2 hours. When the time T2 elapses, the current command value is returned to the initial maximum output value. As described above, in the related art, the temperature of the switching element is estimated based on the motor temperature of the steering assist motor, and the number of times of occurrence of abnormality in the motor temperature is determined so that the temperature of the switching element becomes equal to or lower than a predetermined temperature. The current command value of the steering assist motor is controlled by the detection. By suppressing the temperature rise due to the heat generated by the switching element, the switching element is protected from thermal destruction.

[0004]

However, in such a conventional technique, the temperature of the switching element is estimated based on the detected motor temperature to judge whether the temperature is abnormal or not. The operating environments of the switching elements and the motors mounted on the vehicle greatly differ, for example, in the ambient temperature and the state of ventilation. For this reason, when estimating the temperature of the switching element from the motor temperature, the temperature of the switching element includes a large estimation error. Therefore, when designing a heat sink that dissipates the heat of the switching element and this switching element, a safety margin can be expected in consideration of the estimation error of the temperature.Therefore, a large-sized heat sink or switching element must be used. I can't. As a result, there is a problem in that the control device becomes large and therefore expensive, and the control device is liable to be restricted by the mounting position on the vehicle body.

The present invention has been made in view of the above-mentioned problems, and an electric power steering control capable of reducing the size of a heat sink and a switching element by improving the accuracy of the estimated temperature of the switching element. It is an object of the present invention to provide a device and a motor current control method thereof.

[0006]

Means for Solving the Problems, Functions and Effects In order to achieve the above object, the invention according to claim 1 comprises a torque detecting sensor 4 for detecting a steering torque of a steering wheel (1) during steering of a vehicle, A steering motor 5 that outputs a predetermined torque by the controlled current to steer the tire 11, and a motor instruction current that calculates an instruction current of the steering motor 5 based on the steering torque detected by the torque detection sensor 4. The calculating means 26 receives the command current calculated by the motor command current calculating means 26 as a current command.
Drive power control means 28 for controlling the steering motor 5 by the switching element 16 for switching by applying pulse width modulation to the voltage applied to the motor, and motor current detection means 21 for detecting the current of the steering motor 5 In the steering control device, a heat sink 15 on which the switching element 16 is mounted, and the heat sink 15 and the switching element 1
6, an ambient temperature detection sensor 22 for detecting an ambient temperature, based on the ambient temperature detected by the ambient temperature detection sensor 22 and the current of the steering motor 5 detected by the motor current detection means 21. A junction temperature calculating means 23 for calculating a junction temperature of the switching element 16, a motor maximum current setting means 25 for setting a maximum current of the steering motor 5 based on the junction temperature calculated by the junction temperature calculating means 23. By comparing the maximum current set by the motor maximum current setting means 25 with the command current calculated by the motor command current calculation means 26, the smaller current value is given to the motor drive control means 28 as a current command. Output motor current comparison setting means 27
And a configuration of an electric power steering control device including:

According to the first aspect of the present invention, the junction temperature of the switching element 16 is estimated by the junction temperature calculation means 23 from the heat generation amount of the junction 17, the heat release amount of the heat sink 15, and the ambient temperature of the heat sink 15. be able to. That is, the amount of heat generated at the junction 17 can be determined based on the current value of the steering motor 5 detected by the motor current detection unit 21 and the previously determined on-resistance value of the switching element 16. On the other hand, the temperature difference between the previously calculated junction temperature of the junction temperature calculated every time period of the predetermined cycle and the peripheral temperature of the heat sink 15 detected by the ambient temperature detection sensor 22 and the heat sink heat determined in advance The heat radiation amount of the junction 17 can be obtained based on the resistance. The difference between the heat generation amount and the heat release amount of the junction 17 obtained in this way is integrated over time to obtain an integral value, and the integrated value and the heat capacity obtained as the characteristic value of the junction 17 are used to calculate the integral value.
The rising temperature or the falling temperature of the junction 17 can be obtained. Then, the temperature of the junction 17 can be estimated from the rising temperature or the falling temperature and the surrounding temperature when the integrated value is obtained. Then, when the estimated temperature reaches a predetermined upper limit, the motor maximum current setting means 25 sets the maximum current to be lower than a predetermined initial value based on the estimated temperature to be a predetermined limited current value. When the estimated temperature reaches a predetermined lower limit,
Reset the maximum current to a predetermined initial value. Further, the motor command current calculating means 26 calculates a command current value for controlling the steering motor 5 based on the steering torque detected by the torque detection sensor 4. And
The motor current comparison and setting means 27 compares the calculated indicated current value with the maximum current value set by the motor maximum current setting means 25, and controls the steering motor 3 with the smaller current value. Drive control means 2
8 is output. Therefore, conventionally, the heat radiation amount is calculated by assuming the estimated error of the junction temperature as a safety margin, and a large heat sink 15 that satisfies the heat radiation amount or a switching element 16 having a larger allowable value of the junction temperature is selected. However, in the present invention, since the junction temperature is estimated based on the heat generated by the junction 17 and the heat radiation of the heat sink 15, an error in the estimated temperature can be reduced. Therefore,
Conventionally, a heat radiation amount is calculated by assuming an estimated error of the junction temperature as a safety margin, and a large heat sink 15 that satisfies the heat radiation amount is selected, or a switching element 16 having a larger allowable value of the junction temperature is selected. However, in the present invention, since the junction temperature is estimated based on the heat generated by the junction 17 and the heat radiation of the heat sink 15, the error in the estimated temperature can be reduced, and the amount of heat radiation expected as a safety margin is reduced. Can be. Therefore, the heat sink 15 and the switching element 16 can be reduced in size. As a result,
Since the control device 20 can be manufactured at a low cost and in a small size, there is obtained an advantage that the control device 20 is less likely to be restricted when mounted on a vehicle.

[0008] The invention described in claim 2 is the first invention.
In the electric power steering control device described above, a junction temperature storage means 24 for storing the junction temperature calculated by the junction temperature calculation means 23 is provided, and the junction temperature calculation means 23 keeps the junction even after the control device is turned off. Calculate the temperature and calculate the junction temperature and heat sink 15
The electric power steering control device stores the junction temperature in the junction temperature storage means 24 until the difference from the ambient temperature becomes equal to or less than a predetermined value or until a predetermined time elapses after the power is turned off. I have.

According to the second aspect of the present invention, the junction temperature storage means stores the junction temperature calculated by the junction temperature calculation means even after the power supply of the control device is cut off, with the junction temperature and the peripheral temperature of the heat sink. Is stored until the difference becomes equal to or less than a predetermined value, or until a predetermined time elapses after the power is turned off. Therefore, in addition to the effect of the first aspect, when the power is turned on again when the junction temperature is high immediately after the power is turned off, the junction temperature is estimated using the stored junction temperature as an initial value. , The junction temperature can be estimated with high accuracy.

According to the third aspect of the present invention, a command current for controlling the output torque of the steering motor 5 by detecting the steering torque of the steering wheel 1 is calculated and applied by the switching element 16 so as to be the command current. In a motor current control method for an electric power steering that controls a steering motor 5 by pulse width modulation of a voltage, a current of the steering motor 5 and the switching element 1 are controlled.
The junction temperature of the switching element 16 is estimated based on the ambient temperature of the switching element 6 and the maximum current of the steering motor 5 is limited so that the junction temperature becomes equal to or lower than a predetermined value. The motor current control method of the electric power steering is such that the junction temperature is continuously estimated and the maximum current of the steering motor 5 is limited by estimating the junction temperature using the estimated junction temperature as an initial value when the current is supplied.

According to the third aspect of the present invention, the command current of the steering motor 5 obtained from the steering torque is compared with the maximum current of the steering motor 5 such that the junction temperature becomes equal to or lower than a predetermined value. Since the current value is used as the instruction current of the steering motor 5, the switching element 16 can be protected from thermal destruction, and the junction temperature can be controlled by the control current of the steering motor 5 which causes heat generation and the switch heat sink 15 which causes heat radiation. , The estimation accuracy is improved. In addition, the junction temperature is estimated even after the power is turned off, and until the difference from the ambient temperature becomes a predetermined value or less, or
It is stored until a predetermined time has elapsed. Therefore, even when the power is turned on immediately after the power is turned off, the junction temperature is estimated using the stored junction temperature as an initial value, so that the estimation can be performed with high accuracy. Therefore,
Conventionally, a heat radiation amount is calculated by assuming an estimated error of the junction temperature as a safety margin, and a large heat sink 15 that satisfies the heat radiation amount is selected, or a switching element 16 having a larger allowable value of the junction temperature is selected. However, in the present invention, since the junction temperature is estimated based on the heat generated by the junction 17 and the heat radiation of the heat sink 15, the error in the estimated temperature can be reduced, and the amount of heat radiation expected as a safety margin is reduced. Can be. Therefore, the heat sink 15 and the switching element 16 can be reduced in size. As a result,
Since the control device 20 can be manufactured at a low cost and in a small size, there is obtained an advantage that the control device 20 is less likely to be restricted when mounted on a vehicle.

[0012]

Embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 schematically shows a steering device equipped with an electric power steering control device according to the present invention. The handle 1 is rotatably mounted on a vehicle body (not shown).
It is connected to the upper end of the steering input shaft 3. The lower end of the steering input shaft 3 is connected to the upper end of the turning torque output shaft 7 via a torque detection sensor 4 substantially coaxially. A gear box 8 is attached to the lower end of the turning torque output shaft 7, and the gear box 8 is connected to a steering member 9. The gear box 8 includes a pinion, a rack, and the like.
The rotation of the pinion connected to the steering wheel gives a predetermined stroke to the steering member 9 via the rack in a substantially horizontal plane in the left-right direction of the vehicle. A tire 11 is mounted on the steering member 9 so as to be rotatable in a traveling direction, and the tire 11 is swingable within a predetermined angle range in a traveling plane. The tire 11 is steered following the movement of the steering member 9.

On the other hand, a gear train 6 for reducing rotation by a combination of a plurality of gears is provided at a predetermined position between both ends of the turning torque output shaft 7. The final gear on the output side of the gear train 6 is fixed to a turning torque output shaft 7 penetrating the center portion, and the input gear on the input side of the gear train 6 is fixed to the output shaft of the steering motor 5. Have been. The gear train 6 transmits the output torque of the steering motor 5 to the turning torque output shaft 7. Further, a control device 20 is connected to the torque detection sensor 4 and the steering motor 5 so that electric signals can be transmitted and received. The control device 20 includes a CPU such as a computer,
It is composed of a so-called power circuit for controlling current. The control device 20 is connected to a battery 12 that stores electric energy for driving the steering motor 5.

In such a steering device, when the steering wheel 1 is turned during steering, the rotation of the steering wheel 1 is transmitted to the steering input shaft 3. When the steering input shaft 3 rotates, a twist corresponding to the rotation angle of the steering wheel 1 is generated between the steering input shaft 3 inserted into the torque detection sensor 4 and the turning torque output shaft 7. Torque detection sensor 4
Converts the magnitude of this twist into an electrical signal and transmits it to the control device 20. The control device 20 controls the output torque of the steering motor 5 based on the electric signal based on the electric signal so that the twist between the steering input shaft 3 and the turning torque output shaft 7 becomes zero. The steering motor 5 transmits the output torque to the gear train 6 to rotate the turning torque output shaft 7, and the rotation of the turning torque output shaft 7 is transmitted to the tire 11 via the gear box 8 and the steering member 9. To rotate the tire 11. At this time, the control device 2
0 controls the output torque by controlling the current of the steering motor 5 based on the torsion fed back by the torque detection sensor 4. This allows
The handle 1 can be operated with a predetermined steering force according to the rotation angle.

Next, FIG. 2 shows a control device 2 according to the present invention.
FIG. 2 shows a block diagram of a hardware configuration of No. 0. The control device 20 is roughly divided into a CPU section 20a for inputting, calculating, storing, or outputting a control value for controlling the steering motor 5, and a motor drive control for controlling a current of the steering motor 5 based on the control value. And the unit 20b. The motor drive control unit 20b includes a heat sink 15, a switching element 16 mounted on the heat sink 15, and an ambient temperature detection sensor 22.
It is composed of The heat sink 15 is formed to have good thermal conductivity like aluminum material and the like, and to have fins so as to be excellent in heat dissipation. The switching element 16 mounted on the heat sink 15 is made of a semiconductor such as a power transistor, and has a junction 17 inside. Also, this switching element 1
6 are used, for example, four switching elements 1
6 are formed. And
The ambient temperature detection sensor 22 attached to the heat sink 15 is provided at a position at a predetermined distance from the switching element 16 and detects the temperature around the heat sink 15 as the ambient temperature.

On the other hand, the CPU section 20a comprises a general-purpose computer or the like. The CPU 20a calculates a current value for controlling the output torque of the steering motor 5, and sets the steering motor 5 so that the current value is obtained.
A command to control the voltage applied to the switching element 16 by pulse width modulation is output to the switching element 16. Switching element 1
The reference numeral 6 controls the voltage applied to the steering motor 5 based on the command so as to switch to a predetermined current value. By repeating this switching, the junction 17 of the switching element 16 generates heat and the temperature rises, so that the heat generated to prevent this temperature rise is radiated through the heat sink 15. The control device 20 according to the present invention estimates the temperature of the junction 17 as the junction temperature, and when this temperature reaches a predetermined value, the switching element 1
6 is reduced so that the junction temperature becomes equal to or lower than a predetermined value.

FIG. 3 shows the control device 2 of FIG. 2 according to the present invention.
0 is a functional block diagram showing the details of 0. The motor current detecting means 21 detects a motor current value controlling the steering motor 5. The ambient temperature detection sensor 22 is connected to the heat sink 1 that controls the motor current.
The ambient temperature around 5 is detected. Then, the junction temperature calculating means 23 estimates the junction temperature of the switching element 16 based on the motor current value and the surrounding temperature. This junction temperature can be estimated from the heat generation amount of the junction 17, the heat release amount of the heat sink 15, and the ambient temperature of the heat sink 15.

That is, for example, the expression "Tj = (1 /
K ₃ ) ∫ ^j _j−1 (K ₂ I ² R− (1 / K ₁ ) (T _j−1 −
Ts)) dt + Ts ”. Here, Tj is the heat capacity of the junction temperature, K ₃ is the junction 17, K ₂ is the thermal conversion factor of the power, I is the control current of the switching element 16 (= the current of the steering motor 5), R is the ON resistance of the switching element 16 , K ₁ is the thermal resistance of the heat sink 15, T _j-1 is the junction temperature were determined in the previous calculation, and Ts represents the ambient temperature of the heat sink 15. As a boundary condition, when t = 0, T _j-1 = Ts. According to this equation, the steering motor 5 detected by the motor current detecting means 21
Current I and the switching element 16 determined in advance.
Of the junction 17 of the switching element 16 can be determined based on the on-resistance R of the switching element 16 (= K ₂ I ² R). On the other hand, the temperature difference (T _j-1) between the junction temperature T _j-1 calculated last time of the junction temperature calculated every time of the predetermined cycle and the peripheral temperature Ts of the heat sink 15 detected by the ambient temperature detection sensor 22. −
Ts), and based on the thermal resistance K ₁ of the heat sink which has been determined in advance, the heat radiation amount Q2 of the junction 17 (=
(1 / K ₁ ) (T _j−1 −Ts)) can be obtained.

The junction 17 thus determined
(Q1-Q2) (= (K ₂ I ²⁾
R− (1 / K ₁ ) (T _j−1 −Ts))) is integrated over a minute predetermined time t = (j−1) to j to obtain an integrated value, and this integrated value and the heat capacity of the junction 17 are obtained. based on the K _3,
The rise temperature or fall temperature ΔTj of the junction 17 within a predetermined time is calculated by the equation “ΔTj = (1 / K ₃ ) ∫
^j _j-1 (K ₂ I ² R- (1 / K ₁ ) (T _j-1 −Ts))
dt ”. Then, the surrounding temperature Ts at the time when the integrated value is obtained is added to the rising temperature or the falling temperature ΔTj, and the junction temperature Tj (=
ΔTj + Ts) can be estimated. Since the heat generated at the junction 17 does not occur when no current flows, it is determined by integrating the time during which the switching element 16 is energized. The initial value of the junction temperature at the time of starting the calculation at the time of steering is determined by the heat sink 1
5 can be considered to be approximately equal to the ambient temperature. Then, after the start of the steering, the junction temperature is calculated at every minute time of a predetermined small cycle.

On the other hand, the junction temperature storage means 24
Indicates the junction temperature calculated by the junction temperature calculating means 23 at all times. And
The junction temperature storage means 24 stores the junction temperature until the power supply of the control device 20 is cut off and the difference between the junction temperature and the ambient temperature becomes equal to or less than a predetermined value or until a predetermined time elapses. When the power of the control device 20 is turned on again, the junction temperature calculating means 23 calculates the junction temperature using the junction temperature stored in the junction temperature storage means 24 as an initial value. The motor maximum current setting means 25 has a predetermined initial value as the maximum current for controlling the steering motor 5. When the junction temperature calculated by the junction temperature calculation means 23 reaches a predetermined upper limit, the motor maximum current setting means 25 sets the maximum current of the steering motor 5 based on the magnitude of the estimated temperature and the temperature gradient. It is set so as to decrease to a predetermined limit current value. This upper limit of the junction temperature is a set value for current control, and is lower than the upper limit allowable temperature that the junction 17 can withstand by a predetermined value.

A method for setting the limiting current value is as follows.
For example, when the junction temperature rises above the upper limit by a predetermined ratio, the maximum current is lowered by that ratio from the initial value, and when the junction temperature further rises by a predetermined ratio, the maximum current is further lowered by that ratio from the initial value. To do. This is repeated to fix the limit current value set when the temperature rise is completed as the maximum current, and control the steering motor 5 thereafter. Further, when the junction temperature reaches the upper limit value, the maximum current may be reduced from the initial value by a predetermined ratio at a time to be the limited current value.
Further, when the junction temperature reaches the upper limit value, the maximum current is reduced by a predetermined ratio from the initial value and maintained for a predetermined time, and thereafter, the limit current value is set so as to gradually reduce the maximum current in the same manner. You may. In addition to these,
Using the above formula for calculating the junction temperature,
A current value such that the heat release amount becomes larger than the heat generation amount by a predetermined amount may be obtained, and a limit current value with this current value as the maximum current may be set. Note that the algorithm for setting such a limited current value is not limited in the present invention. Then, when the estimated temperature reaches a lower limit set for controlling a predetermined current, the limit current is canceled and the maximum current is reset to a predetermined initial value. The set maximum current value is output to the motor current comparison and setting means 27.

The motor command current calculating means 26 controls the steering motor 5 to output a predetermined torque based on the torque value detected by the torque detection sensor 4 so that the steering motor 5 outputs a predetermined torque. Is calculated. Then, the calculated instruction current value is output to the motor current comparison and setting means 27. Next, the motor current comparison and setting means 27 compares the command current value with the maximum current value set by the motor maximum current setting means 25, and uses the smaller current value as a current command as a motor drive control means 28. Output to By this current command, the steering motor 5 is controlled to be equal to or less than the set maximum current value. The motor drive control means 28 controls the steering motor 5 based on the current command.

Next, the control operation of the control device 20 will be described.
This will be described with reference to the flowcharts of FIGS. FIG. 4 shows a flowchart in the case of normal continuous steering. First, in step S1, the motor command current calculating means 26 calculates a command current value for controlling the output torque of the steering motor 5 based on the steering torque of the steering wheel 1 detected by the torque detection sensor 4. In step S2, the motor current comparison and setting unit 27 compares the indicated current value with the maximum current value set by the motor maximum current setting unit 25, and if the indicated current value is equal to or smaller than the maximum current value. Step S3 is executed, and if the indicated current value is larger than the maximum current value, step S4 is executed. In step S3, the motor current comparison and setting unit 27 controls the steering motor 5 by outputting the command current value to the motor drive control unit 28. In step S4, the motor current comparison and setting means 27 controls the steering motor 5 by outputting the maximum current value set by the motor maximum current setting means 25 to the motor drive control means. Subsequent to step S3, step S5 is executed.

In step S5, the motor current detecting means 21 detects the current value driving the steering motor 5, and the ambient temperature detecting sensor 22 detects the ambient temperature of the heat sink 15. In step S6, the junction temperature calculating means 23 determines the junction 17 based on the detected current value and the ambient temperature.
Calculate the junction temperature of As described above, the junction temperature is determined by calculating the heat generation amount due to the motor drive current and the heat release amount due to the difference between the calculated nearest junction temperature and the peripheral temperature. It is obtained by adding the ambient temperature used at this time. The junction temperature is calculated every time of a predetermined cycle.
It is assumed that the initial value of the junction temperature at the start of the calculation is equal to the temperature around the heat sink 15 because no heat is generated.

In step S7, the motor maximum current setting means 25 determines whether the junction temperature has reached a predetermined upper limit temperature, and if so, executes the next step S8. Step S9 is executed. In step S8, the motor maximum current setting means 2
5 is set so as to reduce the maximum current from the initial maximum current value to a predetermined limit current value based on the junction temperature. The setting of the limiting current value is performed by the method described above. Subsequent to step S8, step S8 is performed based on the set current limit value.
The processing is executed from 1.

In step S9, it is determined by the motor current comparison and setting means 27 whether or not the motor is being controlled by the control current value. If the motor is being controlled, step S10 is executed. If not, the process proceeds to step S1. Return. In step S10, the motor drive control unit 28 drives the steering motor 5 with the control current value, so that the junction temperature decreases to reach the lower limit temperature. And
In step S11, the motor maximum current setting means 25 cancels the control current value and resets the maximum current to a predetermined initial value. When the above processing is completed, step S1 and subsequent steps are executed again.

FIG. 5 shows a flowchart in the case where the power supply to the control device 20 is once cut off and then the steering is started again. First, in step S21, the control device 20
Is shut off. In the next step S22, the junction temperature calculating means 23
The calculation of the junction temperature is continuously performed in the same manner as before the power supply to the power supply is cut off.
In, the junction temperature storage means 24 always stores the calculated junction temperature. At this time, the timing at which the junction temperature is calculated and stored is a predetermined cycle time or a temperature interval, but is not particularly limited. Then, step S2
In 4, the junction temperature calculating means 23 determines whether or not the power is turned on. If the power is turned on, the next step S25 is executed. If not, the step S26 is executed.
Execute In step S25, the junction temperature calculation means 23 reads the junction temperature stored in the junction temperature storage means 24 in step S23 as initial value data, and thereafter, the operation shown in FIG.
The processing is executed from step S6 based on the flowchart shown in FIG.

In step S26, the junction temperature calculating means 23 calculates the difference between the junction temperature and the ambient temperature. In the next step S27, if the difference is larger than a predetermined value, the process returns to step S22, where the difference is smaller than the predetermined value. If so, step S28 is executed. In step S28, the junction temperature calculation means 23 ends the calculation of the junction temperature, erases the junction temperature data stored in the junction temperature storage means 24, and ends the processing. In this way, the calculation is terminated when the junction temperature becomes substantially equal to the ambient temperature, and when the power is turned on again, the first step S1 and subsequent steps of the processing flow shown in FIG. 4 are executed. In step S26, if the difference between the junction temperature and the ambient temperature is within a predetermined value, the calculation of the junction temperature has been completed. However, the calculation may be terminated after a predetermined time has elapsed since the power was turned off.

The graph of FIG. 6 shows an example of a time transition of the maximum current setting of the steering motor 5 controlled by the control device 20 as described above. In this graph, the vertical axis shows four characteristics of the ambient temperature Ts, the motor current C, the junction temperature Tj, and the set value Cs of the maximum current, and the horizontal axis shows the steering characteristic common to the respective characteristics of the vertical axis. The time t has elapsed. This ambient temperature T
s changes little due to the heat radiation effect of the heat sink 15, but rises when the motor current C is applied due to the heat generated by the motor current C. Further, the motor current C generates a predetermined current value based on the steering torque,
Is controlled. The junction temperature Tj calculated from the motor current C and the ambient temperature Ts is
The temperature rises with the passage of time t due to heat generated by the motor current C during energization.

Under such an operating environment, the control device 20
Controls the set value Cs of the maximum current as follows. That is, when the junction temperature Tj increases with the lapse of the time t at the time of steering and reaches the upper limit temperature Tu, the set value Cs of the maximum current is changed from the initial value Cm of the set value Cs of the maximum current by the method described above. The current limit value Cf is set to a small value. The setting of the limiting current value Cf is performed by the above-described method. For example, the limiting current value Cf shown in this graph has a gradually gentle gradient from the upper limit temperature Tu of the junction 17 at which the maximum current starts to decrease. A function of time. When a command current value larger than the limit current value Cf is calculated, the limit current value Cf is output to control the steering motor 3, so that the junction temperature Tj falls with time. And the junction temperature T
When j reaches the lower limit temperature Td, the set value Cs of the maximum current is reset to the initial value Cm because the limit current value Cf is canceled. In this way, the control of the set value Cs of the maximum current is repeated between the upper limit temperature Tu and the lower limit temperature Td, and the junction temperature Tj is maintained at or below the allowable upper limit temperature.

As described above, the switching element 16
The junction temperature can be accurately estimated in order to protect the device from thermal destruction. Therefore, in the related art, the heat radiation amount is calculated in consideration of the estimated error of the temperature as a safety margin, and a large heat sink 15 that satisfies the heat radiation amount or a switching element 16 having a larger allowable value of the junction temperature are selected. However, in the present invention, since the junction temperature is estimated based on the heat generated by the junction and the heat radiation of the heat sink 15, the error in the estimated temperature can be reduced, and the amount of heat radiation expected as a safety margin is reduced. Can be. Therefore, the heat sink 15 and the switching element 16 can be reduced in size. As a result, the control device 20 can be manufactured at a low cost and in a small size, so that an advantage is obtained in that the control device 20 is less likely to be restricted when mounted on a vehicle.

[Brief description of the drawings]

FIG. 1 is a schematic view of a steering device according to the present invention.

FIG. 2 is a block diagram of a hardware configuration of a control device according to the present invention.

FIG. 3 is a functional block diagram of the control device of the present invention.

FIG. 4 is a flowchart illustrating a control operation of the control device of the present invention.

FIG. 5 is a flowchart illustrating another control operation of the control device according to the present invention.

FIG. 6 is a graph showing a control operation of the control device of the present invention.

FIG. 7 is a diagram showing a current command value of a control device according to the related art.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... steering wheel, 3 ... steering input shaft, 4 ... torque detection sensor, 5 ... steering motor, 6 ... gear train, 7 ... turning torque output shaft, 8 ... gear box, 9 ... steering member, 11 ...
Tires, 12 ... batteries, 15 ... heat sinks, 16 ...
Switching element, 17 junction, 20 control device, 20a CPU unit, 20b motor drive control unit,
Reference numeral 21: motor current detection means, 22: ambient temperature detection sensor, 23: junction temperature calculation means, 24: junction temperature storage means, 25: motor maximum current setting means, 26: motor instruction current calculation means, 27: motor current comparison setting Means, 28 ... motor drive control means.

Claims (3)

[Claims] 1. A torque detection sensor (4) for detecting a steering torque of a steering wheel (1) during steering of a vehicle, and a steering motor (5) for outputting a predetermined torque by a controlled current to steer a tire (11). A motor command current calculating means (26) for calculating a command current for the steering motor (5) based on the steering torque detected by the torque detection sensor (4); and a motor command current calculating means (26). A motor that receives the command current calculated by the above as a current command, and controls the steering motor (5) by a switching element (16) that switches the voltage applied to the steering motor (5) by pulse width modulation based on the current command. An electric power steering control device comprising: a drive control means (28); and a motor current detection means (21) for detecting a current of the steering motor (5). Heat sink (1
5) and the heat sink (15) and the switching element
An ambient temperature detection sensor (22) provided in the vicinity of (16) and detecting an ambient temperature, and an ambient temperature detected by the ambient temperature detection sensor (22) and detected by the motor current detection means (21). A junction temperature calculating means (23) for calculating a junction temperature of the switching element (16) based on a current of the steering motor (5), and a junction temperature calculated by the junction temperature calculating means (23). Steering motor
Motor maximum current setting means for setting the maximum current of (5) (25)
And comparing the maximum current set by the motor maximum current setting means (25) with the command current calculated by the motor command current calculation means (26), and using the smaller current value as a current command, An electric power steering control device, comprising: a motor current comparison setting means (27) for outputting to a drive control means (28). 2. The electric power steering control device according to claim 1, wherein said junction temperature calculating means is provided.
A junction temperature storage means (24) for storing the junction temperature calculated by (23) is provided, and the junction temperature calculation means (23) calculates the junction temperature even after the power supply of the control device is cut off. The junction temperature is stored in the junction temperature storage means (24) until the difference from the ambient temperature of the heat sink 15 becomes a predetermined value or less, or until a predetermined time elapses after the power is turned off. Electric power steering control device. 3. A steering element for detecting a steering torque of a steering wheel, calculating an instruction current for controlling an output torque of a steering motor, and a switching element for obtaining the instruction current.
(16) A motor current control method for an electric power steering that controls a steering motor (5) by pulse width modulation of an applied voltage according to (16), wherein a current of the steering motor (5), an ambient temperature of the switching element (16) and Switching element based on (16)
Estimate the junction temperature of the steering motor, limit the maximum current of the steering motor (5) so that this junction temperature is equal to or lower than a predetermined value, and continue to estimate the junction temperature even when the power is turned off. A motor current control method for an electric power steering, wherein the junction temperature is estimated using the estimated junction temperature as an initial value to limit the maximum current of the steering motor (5).