JP4715302B2 - Control device for electric power steering device - Google Patents

Description

  The present invention relates to a steering assist control mechanism having an electric motor that applies a steering assist force to a steering system, a steering torque detector that detects a steering torque transmitted to the steering system, and a drive current of the electric motor. A steering assist command value is calculated based on the motor current detection circuit, the steering torque detected by the steering torque detection unit, and the drive current detection value detected by the motor current detection circuit, and the steering assist command value is calculated based on the steering assist command value. The present invention relates to a control device for an electric power steering apparatus including a drive control unit that drives and controls an electric motor.

As a control device for a conventional electric power steering device, for example, a control unit estimates a motor winding temperature and performs the motor temperature protection operation based on the estimated temperature value (for example, a patent) Reference 1).
Japanese Patent Application Laid-Open No. 10-10093 (first page, FIG. 8, FIG. 9)

However, in the conventional example described in Patent Document 1, the motor temperature estimated value t is expressed by the following equation (1), and the motor terminal voltage V is divided by the motor current i. Calculation is made based on the resistance between terminals (winding resistance) R and the resistance between motor terminals R _{20 at} 20 ° C.
t = (R−R ₂₀ ) / α + 20 (1)
Here, α is a temperature coefficient of the motor winding.

For this reason, when a component of the current detection circuit provided in the control unit that recognizes the motor current fails, the motor current i cannot be detected, and normal temperature estimation cannot be performed. There is a problem, and this influence may adversely affect the control unit and the motor.
Therefore, the present invention has been made paying attention to the unsolved problems of the above-described conventional example, and it is possible to reliably detect an abnormality in the motor current detection circuit and accurately estimate the temperature of the electric motor. An object of the present invention is to provide a control device for a steering device.

In order to achieve the above object, a control device for an electric power steering apparatus according to claim 1 is provided with a steering assist control mechanism including an electric motor that applies a steering assist force to a steering system of a vehicle, and is transmitted to the steering system. a steering torque detector for detecting a steering torque, a motor current detection circuit for detecting a driving current of said electric motor, calculates the steering assist command value based on the steering torque detected by the steering torque detecting unit, the A control device for an electric power steering apparatus, comprising: a steering assist command value; and a drive control unit that drives and controls the electric motor based on a drive current detection value detected by the motor current detection circuit. an abnormality detection unit for detecting an abnormality, when detecting the abnormality of the motor current detection circuit in the abnormal detection circuit, of the motor based on the steering assist command value motor A motor current estimation unit that calculates a current estimation value, and an abnormality control unit that controls the drive of the motor while suppressing the steering assist command value based on the motor current estimation value estimated by the motor current estimation unit and protecting against overheating. And the drive control unit is configured to drive-control the electric motor by a pulse width modulation signal having a duty ratio based on the steering assist command value and the drive current detection value, and the abnormality detection unit detects the steering torque detection An abnormality of the motor current detection circuit is detected on the basis of the steering torque detected by the unit and the duty ratio of the pulse width modulation signal .

According to a second aspect of the present invention, there is provided the control device for an electric power steering apparatus according to the first aspect, wherein the abnormality detection unit is configured such that the steering torque is equal to or lower than a low torque set value and the duty of the pulse width modulation signal. When the ratio is greater than or equal to a set value, the motor current detection circuit is determined to be abnormal.

Further, a control device for an electric power steering apparatus according to a third aspect of the present invention is the invention according to the first or second aspect , further comprising a vehicle speed detection unit that detects a vehicle speed of the vehicle, wherein the drive control unit is configured to detect the steering torque detection value. The steering assist command value is calculated with reference to a control map for calculating the steering assist command value based on the vehicle speed and the vehicle speed .

Furthermore, the control device for an electric power steering apparatus according to claim 4, in any one invention of claims 1 to 3, wherein the abnormality control unit, the motor current estimated value estimated by the motor current estimating unit, Calculating a resistance between terminals of the electric motor based on the duty ratio and battery voltage, estimating a motor temperature based on the calculated resistance between terminals, calculating a command value limit value based on the estimated motor temperature; The steering assist command value is limited based on the calculated command value limit value .

Still further, according to a fifth aspect of the present invention, in the control device for an electric power steering apparatus according to any one of the first to third aspects, the drive control unit corrects steering by multiplying a steering assist command value by a control gain. Calculated as an auxiliary command value, and configured to drive and control the electric motor based on the corrected steering auxiliary command value, and the abnormality control unit includes a motor current estimated value estimated by the motor current estimating unit, the duty ratio, and A terminal-to-terminal resistance of the electric motor is calculated based on a battery voltage, a motor temperature is estimated based on the calculated terminal-to-terminal resistance, and the control gain is configured to decrease based on the calculated motor temperature . It is characterized by that.

According to the present invention, when an abnormality of the motor current detection circuit is detected by the abnormality detection unit, the abnormality control unit suppresses the steering assist command value based on the motor current estimation value estimated by the motor current estimation unit, thereby heating protection. Since the motor is driven and controlled, the temperature of the motor can be accurately estimated even if an abnormality occurs in the motor current detection circuit.
Further, by detecting an abnormality in the motor current detection circuit based on the steering torque detected by the steering torque detection unit and the duty ratio of the pulse width modulation signal output from the drive control unit, the motor current enters a hunting state. effect that is able to accurately detect Ru obtained.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram showing an embodiment of the present invention. In the figure, 1 is a steering wheel, and a steering force applied to the steering wheel 1 from a driver is an input shaft 2a and an output shaft. And 2b to the steering shaft 2. The steering shaft 2 has one end of the input shaft 2a connected to the steering wheel 1 and the other end connected to one end of the output shaft 2b via a steering torque sensor 3 as steering torque detecting means.

The steering force transmitted to the output shaft 2 b is transmitted to the lower shaft 5 via the universal joint 4 and further transmitted to the pinion shaft 7 via the universal joint 6. The steering force transmitted to the pinion shaft 7 is transmitted to the tie rod 9 via the steering gear 8 and steers steered wheels (not shown). Here, the steering gear 8 is configured in a rack and pinion type having a pinion 8a connected to the pinion shaft 7 and a rack 8b meshing with the pinion 8a, and the rotational motion transmitted to the pinion 8a is linearly moved by the rack 8b. It has been converted to movement.
A steering assist mechanism 10 for transmitting a steering assist force to the output shaft 2b is connected to the output shaft 2b of the steering shaft 2. The steering assist mechanism 10 includes a reduction gear 11 coupled to the output shaft 2b and an electric motor 12 as an electric motor that generates a steering assist force coupled to the reduction gear 10.

The steering torque sensor 3 detects the steering torque applied to the steering wheel 1 and transmitted to the input shaft 2a. For example, the steering torque sensor 3 is a torsion bar (not shown) in which the steering torque is interposed between the input shaft 2a and the output shaft 2b. It is configured to convert to a torsional angular displacement and detect the torsional angular displacement with a potentiometer. As shown in FIG. 2, when the input steering torque is zero, the torque sensor 3 has an offset torque T ₀ that is a predetermined neutral voltage. When the steering torque is increased from the torque T _{0 and} turned to the left from the zero state, a steering torque detection value T that decreases from the offset torque T ₀ in accordance with the increase of the steering torque is output.

The detected steering torque value T output from the torque sensor 3 is input to the controller 14. In addition to the steering torque detection value T, the controller 14 also receives a vehicle speed detection value V detected by the vehicle speed sensor 15 and a drive current detection value _IMD flowing in the electric motor 12, and the input steering torque detection value T and vehicle speed are inputted. A steering assist command value I _M ^* generated by the electric motor 12 to generate a steering assist force corresponding to the detected value V is calculated, and the electric motor 12 is subjected to the calculated steering assist command value I _M ^* and the motor current detection value I _MD. The drive current to be supplied is feedback controlled.

As shown in FIG. 3, the controller 14 controls the drive current supplied to the electric motor 12 based on the microcomputer 16 that executes control processing of the electric motor 12 and the motor drive current I _M output from the microcomputer 16. the motor driving circuit 18, a motor current detecting circuit 19 for detecting a driving current flowing through the electric motor 12, the motor angular velocity ω based from the motor current and the motor drive circuit 18 to the drive voltage V _M supplied to the electric motor 12 A motor angular velocity estimation circuit 20 for estimation.

  Here, as shown in FIG. 4, the motor drive circuit 18 includes an H bridge circuit composed of FET 1 to FET 4, and field effect transistors (FETs) FET 1 to FET 4 based on the current control value E output from the microcomputer 16. It comprises an FET gate drive circuit 181 for driving the gate. The FET1 and FET2 are turned on / off by a PWM (pulse width modulation) signal having a duty ratio D1 determined based on the current control value E, and the magnitude of the current Ir that actually flows through the motor 12 is controlled. FET3 and FET4 are driven by a PWM signal having a duty ratio D2 defined by a predetermined linear function equation (D2 = a · D1 + b with a and b as constants) in a region where the duty ratio D1 is small, and a region where the duty ratio D1 is large. Then, it is turned ON / OFF according to the rotation direction of the motor determined by the sign of the PWM signal. For example, when the FET 3 is in a conductive state, the current flows through the FET 1, the electric motor 12, the FET 3, and the resistor R 1, and a positive current flows through the electric motor 12. Further, when the FET 4 is in a conductive state, the current flows through the FET 2, the electric motor 12, the FET 4, and the resistor R 2, and a negative current flows through the electric motor 12. Therefore, the current control value E output from the microcomputer 16 is also a PWM output.

Further, the motor current detection circuit 19 detects the magnitude of the positive current based on the voltage drop across the resistor R1 connected between the FET 3 and the ground, and also connects the resistor connected between the FET 4 and the ground. Based on the voltage drop across R2, the magnitude of the current in the negative direction is detected.
The electric motor 12 has one input side connected to a power source Vig via a resistor R3 and a diode DO, and the other input side grounded via a resistor R4. The resistors R3 and R4 are set to a very large value compared to the inter-terminal resistor Rm of the electric motor 12, and the motor terminal voltage Vm is obtained from the connection point between the input side terminal of the electric motor 12 and the diode DO.
Further, the microcomputer 16 includes a torque detection value T detected by the torque sensor 3, a motor current detection value I _MD detected by the motor current detection circuit 19, a motor terminal voltage Vm, and a motor angular velocity ω estimated by the motor angular velocity estimation circuit 20. Are converted into digital values by the A / D converters 21, 22, 23, and 24, respectively.

The microcomputer 16 includes an input interface circuit 31 to which a torque detection value T, a vehicle speed detection value V, a motor current detection value I _MD and a motor angular velocity ω are input, a steering torque detection value T, a motor current detection value I _MD and a motor. Steering assist control processing for driving the electric motor 12 based on the angular velocity ω to generate a steering assist force according to the steering torque, abnormality detection processing for detecting an abnormality in the motor current detection circuit 19, and estimating the motor temperature A central processing unit (CPU) 32 that executes a motor protection process that protects the motor 12 from overcurrent, a ROM (read only memory) 33 that stores a steering assist control processing program executed by the central processing unit 32, and the steering torque detection value T, the motor current detection value I _MD and the motor angular speed ω or the like of the detection data, the steering assist is executed by the central processing unit 32 Has a RAM (random access memory) 34 for storing data and processing results required by your treatment process, and an output interface circuit 35 to an alarm device 26 is connected to emit a motor drive circuit 18 and an alarm.

As shown in FIG. 5, the steering assist control process executed by the central processing unit 32 first reads the steering torque detection value T detected by the steering torque sensor 3 in step S1, and then proceeds to step S2. Then, the actual steering torque Ts (= T−T ₀ ) is calculated by subtracting the offset torque T ₀ from the detected steering torque T. Next, the process proceeds to step S3, where the vehicle speed detection value V detected by the vehicle speed sensor 15 is read, and then the process proceeds to step S4, where the steering assist command value calculation shown in FIG. With reference to the map, a steering assist command value I _M ^* which is a motor current command value is calculated.

Here, as shown in FIG. 6, the steering assist command value calculation map has the steering torque detection value T on the horizontal axis, the steering assist command value I _M ^* on the vertical axis, and the vehicle speed detection value V as a parameter. A straight line portion L1 which is configured by a characteristic diagram and extends with a relatively gentle gradient regardless of the vehicle speed detection value V until the steering torque Ts increases in the positive direction from “0” and reaches the first set value Ts1. When the steering torque Ts increases from the first set value Ts1, the straight portions L2 and L3 that extend with a relatively gentle gradient and the steering torque detection value Ts are the first in the state where the vehicle speed detection value V is relatively fast. Straight line portions L4 and L5 that are parallel to the horizontal axis in the vicinity of the second set value Ts2 that is greater than the set value Ts1 of 1, and in a state where the vehicle speed detection value V is slow, the straight line portions L6 and L7 having a relatively large gradient, Gradient is greater than these straight line portions L6 and L7 Four characteristic lines composed of straight portions L8 and L9, a straight portion L10 having a larger gradient than the straight portion L8, and straight portions L11 and L12 extending in parallel with the horizontal axis from the ends of the straight portions L9 and L10 Similarly, when the steering torque Ts increases in the negative direction, four characteristic lines to be pointed with the above and the origin are formed.

Then, the processing proceeds to step S5, it is determined whether or not the steering assist command value I _M ^* calculated in step S4 exceeds the command value limit value I _LIM to be set by a motor protection processing to be described later, I _M ^* If> I _LIM , the process _proceeds to step S6, the steering assist command value I _M ^* is limited to the command value limit value I _LIM , and then the process _proceeds to step S7. If I _M ^* ≦ I _LIM , the process directly proceeds to step S7. Migrate to

In step S7, reads the motor acceleration omega estimated by the motor angular velocity estimation circuit 20, and then proceeds to step S8, is multiplied by the inertia gain K _i to the motor angular velocity omega, the steering torque Ts of the torque to the motor inertia acceleration The inertia compensation value I _i (= K _i · ω) for inertia compensation control for obtaining a steering feeling without inertia is calculated, and the friction coefficient gain is added to the absolute value of the steering assist command value I _M ^* By multiplying K _f , a friction compensation value I _f (= K _f · I _M ^* ) for friction compensation control is calculated in order to eliminate the influence of the friction of the power transmission unit and the electric motor on the steering force. Here, the sign of the friction compensation value _If is determined on the basis of the sign of the steering torque Ts and the steering direction signal for determining whether the steering is increased / returned based on the steering torque Ts.

Then, the processing proceeds to step S9, to ensure stability of the steering torque Ts in differential operation processing to assist characteristic dead band, and calculates the center response improving command value I _r to compensate the static friction, the process proceeds to step S10 The calculated inertia compensation value I _i , friction compensation value _If and center response improvement command value I _r are added to the steering assist command value I _M ^* to obtain the steering assist compensation value I _M ^* ′ (= I _M ^* + I _i + I _f + I _r ) is calculated, and then the process proceeds to step S11 where the steering assist compensation value I _M ^* ′ is differentiated to calculate a differential value Id for feedforward control.

Next, the process proceeds to step S12, the motor current detection value _IMD is read, then the process proceeds to step S13, the motor current detection value _IMD is subtracted to calculate the current deviation ΔI, and then the process proceeds to step S14. Then, a proportional calculation process is performed on the current deviation ΔI to calculate a proportional value ΔIp for proportional compensation control, and then the process proceeds to step S15 where an integral calculation process is performed on the current deviation ΔI to calculate an integral value ΔIi for integral compensation control. .

Next, the process proceeds to step S16, and the motor drive current I _M (= Id + ΔIp + ΔIi) is calculated by adding the differential value Id, the proportional value ΔIp, and the integral value ΔIi, and then the process proceeds to step S17 and is calculated in step S16. The current control value E formed by converting the motor drive current I _M converted into a pulse width modulation (PWM) signal is output to the motor drive circuit 18 and the process returns to step S1.

Further, in the abnormality detection process for detecting an abnormality of the motor current detection circuit 19 executed by the central processing unit 32, first, as shown in FIG. 7, the steering torque detection value T detected by the steering torque sensor 3 is obtained in step S21. Then, the process proceeds to step S22 to calculate the actual steering torque Ts (= T−T ₀ ) by subtracting the offset torque T ₀ from the detected steering torque value T, and then proceeds to step S23 to drive the motor. After reading the duty ratio D of the pulse width modulation (PWM) signal output to the circuit 18, the process proceeds to step S24.

  In this step S24, it is determined whether or not the absolute value | Ts | of the steering torque Ts is equal to or lower than a preset low torque set value TL. If | Ts |> TL, it is not necessary to diagnose the motor current. The process proceeds to step S25, the abnormality determination flag AF is reset to “0”, and the abnormality determination process is terminated. When | Ts | ≦ TL, it is necessary to diagnose the motor current. Determination is made and the process proceeds to step S26.

In this step S26, it is determined whether or not the duty ratio D of the pulse width modulation signal is equal to or greater than a set value Ds close to 100%, for example. If D <Ds, it is determined that the motor current detection circuit 19 is normal. Then, the process proceeds to step S25, and when D ≧ Ds, it is determined that the motor current detection circuit 19 is abnormal, and the process proceeds to step S27.
In this step S27, the abnormality detection process is terminated after the abnormality determination flag AF is set to “1”.

Further, as shown in FIG. 8, the motor protection process executed by the central processing unit 32 is executed as a timer interrupt process for every predetermined time for a predetermined main program. First, in step S31, an abnormality determination flag is set by an abnormality detection process. It is determined whether or not AF is reset to “0”, and when the motor current detection circuit 19 is normal and the abnormality determination flag AF is reset to “0”, the process proceeds to step S32, and the motor current detection circuit reads a motor current detection value I _MD detected in 19, then proceeds to step S33, reads the duty ratio D of the battery voltage Vb and the pulse width modulated signal, then the process proceeds to step S34, the following equation (2) After calculating the inter-terminal resistance (winding resistance) R of the electric motor 12, the process proceeds to step S39.
_{R = D · Vb / I MD} ............ (2)

On the other hand, when the motor current detection circuit 19 is abnormal and the abnormality determination flag AF is set to “1”, the determination result of step S31 is shifted to step S35 and calculated by the steering assist control process described above. The auxiliary steering command value I _M ^* is read, and then the process proceeds to step S36, the read steering auxiliary command value I _M ^* is set as the motor current estimated value I _MP , and then the process proceeds to step S37, where the battery voltage Vb and The duty ratio D of the pulse width modulation signal is read, and then the process proceeds to step S38, the calculation of the following equation (3) is performed to calculate the inter-terminal resistance (winding resistance) R, and then the process proceeds to step S39.
R = D ・ Vb / I _MP (3)

In step S39, the motor temperature t is estimated by performing the following equation (4) based on the inter-terminal resistance R calculated in step S34 or step S38.
t = (R−R ₂₀ ) / α + 20 (4)
Here, R ₂₀ is a resistance value between motor terminals at 20 ° C., and α is a temperature coefficient of the motor winding.
Next, the process proceeds to step S40, where it is determined whether or not the estimated motor temperature t calculated in step S39 is equal to or greater than a first preset value ts1, and if t <ts1, the motor temperature is low. After determining that the command value limit value I _LIM is set to the maximum value I _MAX , the timer interrupt process is terminated and the process returns to the predetermined main program.

When the determination result in step S40 is t ≧ ts1, it is determined that the motor temperature is high, the process proceeds to step S42, and the estimated motor temperature value t is higher than the preset first set value ts1. It is determined whether or not it is the second set value ts2 or more that can be determined as an overheat state. If t <ts2, the process proceeds to step S43 to protect the electric motor 12 with the command value limit value I _LIM and the minimum required value. after setting the current value I _H for generating a steering assist force limit to end the timer interrupt processing returns to the predetermined main program.

Further, when the determination result of step S42 is t ≧ ts2, it is determined that the electric motor 12 is in an overheated state, the command value limit value I _LIM is set to “0”, and the timer interrupt process is terminated. Then, the program returns to the predetermined main program.
5, 7, and 8, the drive control unit is configured by the process of FIG. 5 and the steering assist mechanism 10, and the process of FIG. 7 corresponds to the abnormality detection unit, and steps S <b> 5 and S <b> 6 of FIG. 5 are performed. The process of FIG. 8 and the process of FIG. 8 correspond to the abnormality control unit.

Next, the operation of the above embodiment will be described.
Now, in order to start using the vehicle, by turning on the key switch, the controller 14 is powered on, and the central processing unit 32 of the microcomputer 16 performs the processing of FIGS. Execution starts.
At this time, when it is determined in the abnormality detection process of FIG. 7 that the motor current detection circuit 19 is normal and the abnormality determination flag AF is reset to “0”, the motor protection process of FIG. S32~S33 proceeds to step S34 via calculates the motor terminal resistor R by performing the calculation of the equation (1) based on the motor current detection value I _MD output from the motor current detection circuit 19, calculates Based on the motor terminal resistance R, the calculation of the equation (3) is performed to calculate the estimated motor temperature t.
Then, when the calculated motor temperature estimated value t is less than the first set value ts1, it is determined that the temperature of the electric motor 12 is low and is in a normal state, the process proceeds to step S41, and the command current limit value I _LIM is obtained. A maximum current value I _MAX is set.

Therefore, when the steering assist control process of FIG. 5 is executed, the steering assist command value I _M ^* calculated in step S4 can be output up to the maximum current value I _MAX , and normal steering assist control becomes possible. .
Therefore, the steering torque Ts is calculated by subtracting the offset torque T ₀ from the steering torque detection value T detected by the steering torque sensor 3 in the steering assist control process of FIG. 5 (step S 2), and then the vehicle speed sensor 14 detects the vehicle speed. The value V is read (step S3), and the steering assist command value I _M ^* is calculated with reference to the steering assist command value calculation map shown in FIG. 6 based on the steering torque Ts and the vehicle speed detection value V (step S4).

On the other hand, the motor angular velocity ω estimated by the motor angular velocity estimation circuit 20 is read (step S7), the inertia compensation value I _i for inertia compensation control is calculated based on the motor angular velocity ω, and the friction compensation value for friction compensation control is calculated. calculating the I _f (step S8), and further the steering torque Ts differential operation to calculate a center response improving command value I _r (step S9), and these inertia compensation value I _i, friction compensation value I _f and the center response The steering assist compensation value I _M ^* ′ is calculated by adding the performance improvement compensation value I _r to the steering assist command value I _M ^* (step S10).

The steering assist compensation value I _M ^* ′ is differentiated to calculate a differential value Id for differential compensation control in feedforward control (step S11), and then the motor current detection value _IMD is subtracted to obtain a current deviation. ΔI is calculated (step S12), the calculated current deviation ΔI is proportionally calculated to calculate a proportional value ΔIp for proportional compensation control, and the integral calculation processing is performed to calculate an integral value ΔIi for integral compensation control ( Then, the motor drive current I _M is calculated by adding the differential value Id, the proportional value ΔIp and the integral value ΔIi (step S15).

Then, a current control value E obtained by converting the calculated motor drive current I _M into a pulse width modulation signal is output to the motor drive circuit 18, whereby a drive current is supplied from the motor drive circuit 18 to the electric motor 12. A steering assist force corresponding to the steering torque applied to the steering wheel 1 is generated by the motor 12 and transmitted to the output shaft 2 b via the reduction gear 11.
At this time, in a so-called stationary state in which the steering wheel 1 is steered while the vehicle is stopped, a large steering angle with a small steering torque Ts is obtained due to the large gradient of the characteristic line of the steering assist command value calculation map shown in FIG. Since the auxiliary command value I _M ^* is calculated, a large steering assist force can be generated by the electric motor 12 to perform light steering.

On the other hand, when the vehicle starts and exceeds the predetermined vehicle speed, the gradient of the characteristic line of the steering assist command value calculation map shown in FIG. 6 is reduced, so that a small steering assist command value I _M ^* is calculated even with a large steering torque Ts. Therefore, the steering assist force generated by the electric motor 12 is reduced, and the steering of the steering wheel 1 can be suppressed from becoming too light and optimal steering can be performed.

If an abnormality occurs in the motor current detection circuit 19 at the time t1 in FIG. 9 from the normal state of the motor current detection circuit 19, the steering torque increases as shown in FIG. 9A until the time t1. 9B, the duty ratio D of the pulse width modulation signal becomes a large value as shown in FIG. 9B, and the motor current I _M also changes according to the duty ratio D as shown in FIG. 9C. , an abnormality of the earth絡等the motor current detecting circuit 19 is generated at time t1, the motor current detection value I _MD with respect to the steering assist command value I _M ^* calculated by the steering assist control process to be a "0" As a result, the motor drive current I _M becomes a large value, and accordingly, the duty ratio D becomes close to 100%, and this state is maintained. Therefore, since an excessive steering assist force is generated by the electric motor 12, the steering torque decreases as shown in FIG. 9A, but the motor current has a large positive and negative value as shown in FIG. 9C. The hunting state repeats alternately.

In this state, when the absolute value | Ts | of the steering torque Ts drops below the predetermined value TL in the abnormality detection process of FIG. 7, the duty ratio D becomes equal to or higher than the set value Ds. It is determined that there is an abnormality, and the abnormality determination flag AF is set to “1”.
When the abnormality determination flag AF is set to “1” in this way, the steering assist command value I _M ^* is replaced with the motor current in place of the motor current detection value I _M of the motor current detection circuit 19 in the motor protection process of FIG. The estimated value I _MP is set, and the motor terminal resistance R is calculated by calculating the equation (2) based on the motor current estimated value I _MP , the battery voltage Vb, and the duty ratio. The motor temperature estimated value t is calculated by performing the calculation of the equation (3) based on the resistance R.

When the estimated motor temperature value t is less than the first set value ts1, it is determined that the motor temperature is low, the command value limit value I _LIM is set to the maximum current value I _MAX , and steering is performed as usual. Auxiliary force can be generated, but when the estimated motor temperature t is equal to or greater than the first set value ts1, the command value limit value I _LIM is a small value that is a current value I _H that generates the minimum necessary steering assist force. As a result, the steering assist command value I _M ^* is limited to the command value limit value I _LIM in step S6 in the steering assist control process of FIG. The steering assist force is generated. For this reason, even if an abnormality occurs in the motor current detection circuit 19, the minimum necessary steering assist force is generated without overheating the electric motor 12, so that the vehicle can be reliably driven to a repair place such as a repair shop. it can.

However, when the estimated motor temperature t becomes equal to or higher than the second set value ts2, it is determined that the motor is in an overheated state, and the command value limit value I _LIM is set to “0”. I _M ^* becomes “0”, the duty ratio D becomes “0”%, the drive of the electric motor 12 is stopped, and the steering assist force becomes “0”.
In the above embodiment, the case where the command value limit value I _LIM is set based on the estimated motor temperature t has been described. However, the present invention is not limited to this, and the control gain Gi is set to the steering assist command value I _M ^*. was calculated by multiplying the value as a correction steering assist command value I _MA, performs current feedback control (step S7 and subsequent steps in FIG. 5) based on the corrected steering assist command value I _MA, electric current control gain Gi When the motor 12 is not in an overheated state, the control gain Gi is set to 100%, and when the electric motor 12 is in an overheated state, the maximum value at that time is set to the command value limit value I _LIM or a value near it. You may make it do. In this case, since the entire motor current is limited, overheating of the electric motor 12 can be significantly suppressed.

In the above embodiment, the case where the motor driving current I _M is calculated by software processing executed by the central processing unit 32 has been described. However, the present invention is not limited to this, and the steering assist command value calculator, center response, The motor drive current I _M may be calculated by hardware combining a performance improvement circuit, an inertia compensator, a friction compensator, a differential compensator, a subtractor, a proportional calculator, an integral calculator, an adder, and the like. Similarly, the abnormality detection process of FIG. 7 and the motor protection process of FIG. 8 can also be configured by hardware.

It is a schematic structure figure showing one embodiment of the present invention. FIG. 6 is a characteristic diagram of a torque detection signal detected by a steering torque sensor. FIG. 2 is a block diagram illustrating a specific configuration of the controller in FIG. 1. It is a block diagram which shows an example of a motor drive circuit. It is a flowchart which shows an example of the steering assistance control processing procedure performed with the central processing unit of a microcomputer. It is a characteristic diagram which shows a steering assistance command value calculation map. It is a flowchart which shows an example of the abnormality detection process procedure performed with the central processing unit of a microcomputer. It is a flowchart which shows an example of the motor protection processing procedure performed with the central processing unit of a microcomputer. It is a time chart with which it uses for description of operation | movement of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Steering wheel, 2 ... Steering shaft, 3 ... Steering torque sensor, 8 ... Steering gear, 12 ... Electric motor, 14 ... Controller, 15 ... Vehicle speed sensor, 16 ... Microcomputer, 18 ... Motor drive circuit, 19 ... Motor current Detecting circuit, 31 ... input interface circuit, 32 ... central processing unit, 33 ... ROM, 34 ... RAM, 35 ... output interface circuit

Claims (5)

A steering assist control mechanism including an electric motor that applies a steering assist force to a steering system of a vehicle, a steering torque detector that detects a steering torque transmitted to the steering system, and a motor that detects a drive current of the electric motor a current detection circuit, the steering calculates the steering assist command value based on the steering torque detected by the torque detection unit, the steering assist command value and the motor based on the drive current detection value detected by the motor current detecting circuit A control device for an electric power steering device comprising a drive control unit for driving and controlling
An abnormality detection unit that detects an abnormality of the motor current detection circuit, and calculates an estimated motor current value of the electric motor based on the steering assist command value when the abnormality detection circuit detects an abnormality of the motor current detection circuit. A motor current estimation unit, and an abnormality control unit that controls the drive of the motor while suppressing overheating based on the motor current estimation value estimated by the motor current estimation unit and overheating protection ,
The drive control unit is configured to drive and control the electric motor by a pulse width modulation signal having a duty ratio based on the steering assist command value and the drive current detection value, and the abnormality detection unit is the steering torque detection unit. A control device for an electric power steering device, wherein an abnormality of the motor current detection circuit is detected based on the detected steering torque and the duty ratio of the pulse width modulation signal . The abnormality detecting unit, the steering torque is equal to or less than the low torque setting, and when the duty ratio of the pulse width modulation signal is equal to or higher than a set value, said motor current detection circuit is abnormal The control apparatus for an electric power steering apparatus according to claim 1, wherein the control apparatus is an electric power steering apparatus. A vehicle speed detection unit that detects a vehicle speed of the vehicle, wherein the drive control unit refers to a control map that calculates a steering assist command value based on the steering torque detection value and the vehicle speed; It is comprised so that it may calculate , The control apparatus of the electric power steering apparatus of Claim 1 or 2 characterized by the above-mentioned. The abnormality control unit calculates an inter-terminal resistance of the electric motor based on the estimated motor current value estimated by the motor current estimation unit, the duty ratio, and the battery voltage, and motor temperature based on the calculated inter-terminal resistance. The command value limit value is calculated based on the estimated motor temperature, and the steering assist command value is limited based on the calculated command value limit value. 4. The control device for an electric power steering device according to any one of items 1 to 3. The drive control unit is configured to calculate a value obtained by multiplying a steering assist command value by a control gain as a corrected steering assist command value, and to drive and control the electric motor based on the corrected steering assist command value. The unit calculates the inter-terminal resistance of the electric motor based on the estimated motor current value estimated by the motor current estimation unit, the duty ratio, and the battery voltage, and estimates the motor temperature based on the calculated inter-terminal resistance. 4. The control device for an electric power steering apparatus according to claim 1, wherein the control gain is set to decrease based on the calculated motor temperature . 5.

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