JP2011088517A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering control device carrying out trouble shooting such as suppressing motor current before starting the steering maneuver, to prevent the variation of steering assist force during a steering maneuver. <P>SOLUTION: The electric power steering device includes: steering torque detecting means 3; an electric motor 12 generating the steering assist force; steering assist control means 16 outputting a command value to the electric motor; and motor driving means 18 controlling the drive of the electric motor based on the command value. This device also includes: temperature detecting means 13 detecting the temperature of the motor driving means 18; failure detecting means detecting the failure of the temperature detecting means; and failure control means carrying out a predetermined trouble shooting when the result detected by the failure detecting means appears to be that the temperature detecting means is abnormal. The failure detecting means forcibly drives the motor driving means in a predetermined drive pattern in a state where the drive control of the electric motor by the motor driving means is stop, to detect the temperature variation of the temperature detecting means 13. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an electric power steering apparatus that generates a steering assist force with an electric motor for a steering system based on a steering torque transmitted to the steering system.

  In this type of electric power steering control device, for example, the temperature of the portion that generates heat is estimated based on the current value of the current that flows to the electric motor, and the estimated temperature is calculated from a temperature at a predetermined time point to a first predetermined temperature (8 When the temperature condition is satisfied, the detected temperature by the substrate temperature sensor does not change from the detected temperature at the predetermined time by more than the second predetermined temperature (2.5 ° C.). There is known an electric power steering device for a vehicle in which it is determined that a substrate temperature sensor is abnormal when a condition indicating the above is satisfied (see, for example, Patent Document 1).

Japanese Patent No. 3409756

  However, in the conventional example described in Patent Document 1, the temperature within the temperature range that can be detected by the substrate temperature sensor is shown, but it is certain that an abnormal state that remains at a constant temperature has occurred. However, when temperature determination is performed, the temperature of the portion that generates heat is estimated based on the current value of the current that flows to the electric motor, and this estimated temperature is calculated from the temperature at a predetermined time. Since the temperature determination start condition is that the temperature has changed by more than the first predetermined temperature (8 ° C.), the temperature determination of the substrate temperature sensor cannot be performed unless the vehicle steering assist control is being performed. When the sensor is abnormal, the motor current supplied to the electric motor is immediately limited, and the steering assist force for the steering system is reduced. As a result, the steering becomes heavy and the driver feels uncomfortable. There is an unsolved problem in that.

  Therefore, the present invention has been made paying attention to the unsolved problems of the above-described conventional example, and when the vehicle is not in a steering state, an abnormality determination of the temperature detection means is performed, so that the motor current before the steering is started. It is an object of the present invention to provide an electric power steering control device that performs an abnormal process such as suppression of the steering to prevent a change in steering assist force during steering.

  In order to achieve the above object, an electric power steering apparatus according to an embodiment includes a steering torque detecting means for detecting a steering torque transmitted to a steering system, and an electric motor for generating a steering assist force for the steering system. Steering assist control means for outputting a command value for the electric motor based on the steering torque; and motor drive means for driving and controlling the electric motor based on the command value output from the steering assist control means. An electric power steering apparatus comprising: a temperature detecting means for detecting the temperature of the motor driving means; an abnormality detecting means for detecting an abnormality of the temperature detecting means; and a detection result of the abnormality detecting means is an abnormality of the temperature detecting means. An abnormality control means for performing a predetermined abnormality process at the time of In to that state, it is characterized by being configured to forcibly driven to the motor driving means in a predetermined drive pattern for detecting the temperature change of the temperature detecting means.

An electric power steering control device according to another aspect is characterized in that the predetermined drive pattern is set to a drive pattern in which the change amplitude of the duty ratio of the motor current gradually increases.
Furthermore, in the electric power steering apparatus according to another aspect, the abnormality detection unit is configured to change the motor drive unit to a predetermined drive pattern when a temperature detected by the temperature detection unit is lower than an overheat protection start temperature of the motor drive unit. It is characterized by forcibly driving.
Still further, an electric power steering apparatus according to another aspect includes motor temperature estimation means for estimating the temperature of the electric motor, and the abnormality detection means has a motor temperature estimated value estimated by the motor temperature estimation means as a motor. When the temperature is lower than the overheat protection start temperature, the motor drive means is forcibly driven with a predetermined drive pattern.

  According to the present invention, when the vehicle is stopped and the motor drive means is in a stopped state, the abnormality detection means forcibly drives the motor drive means with a predetermined drive pattern to change the temperature of the temperature detection means. Since the abnormality of the temperature detecting means is determined by detecting the abnormality, the abnormality of the temperature detecting means can be determined in a state where the steering system of the vehicle is not being steered, and the abnormality of the temperature detecting means is detected. It is possible to perform a motor current limiting process before the driver starts steering, to prevent a change in the steering assist force during steering when an abnormality is detected, and to give the driver a sense of incongruity. It can be surely prevented.

It is a schematic structure figure showing a 1st embodiment of the present invention. FIG. 2 is a block diagram illustrating a specific configuration of the controller in FIG. 1. It is a flowchart which shows an example of the steering assistance control processing procedure performed with a controller. It is a characteristic diagram which shows a steering auxiliary current command value calculation map. It is a flowchart which shows an example of the abnormality detection process procedure performed with a controller. It is a flowchart which shows an example of the temperature detection circuit abnormality detection process sequence in FIG. It is a characteristic figure which shows the duty ratio of the motor drive current at the time of forced drive. It is a characteristic diagram which shows the characteristic for abnormality determination of a temperature sensor.

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 which 1 is a steering wheel. A steering force applied to the steering wheel 1 from a driver is transmitted to a steering shaft 2 having an input shaft 2a and an output shaft 2b. 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 a steering torque detector.

  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 mechanism 8 to steer a steered wheel (not shown). Here, the steering gear mechanism 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 transmitted by the rack 8b. It has been converted to straight 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 connected to the output shaft 2 b and an electric motor 12 as an electric motor that generates a steering assist force connected to the reduction gear 11.
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, detect this torsional angular displacement with a non-contact magnetic sensor, and output a steering torque detection value T.

The steering torque detection value T output from the steering torque sensor 3 is input to the controller 14 to which power is supplied from the battery B via the ignition switch IG. To the ignition switch IG, a switching element SW controlled by a microcomputer 16 (to be described later) that constitutes a self-holding circuit SH is connected in parallel with the ignition switch IG.
In addition to the torque detection value T, the vehicle speed detection value V detected by the vehicle speed sensor 15, the motor terminal voltage Vm of the electric motor 12, and the motor current detection value Im flowing in the electric motor 12 are also input to the controller 14. A steering assist torque command value Iref for generating a steering assist force according to the torque detection value T and the vehicle speed detection value V by the electric motor 12 is calculated, and the electric motor is calculated based on the calculated steering assist command value Iref and the motor current detection value Imd. The drive current supplied to the motor 12 is subjected to feedback control processing, and various compensation processes are performed based on the motor terminal voltage Vm and the motor current detection value Imd to calculate the voltage command value Vref for driving the electric motor 12. The voltage command value is subjected to pulse width modulation processing to form a gate drive signal Sg which is a pulse width modulated signal, and this gate drive signal To form a motor drive current based on g.

As shown in FIG. 2, the controller 14 controls the electric motor 12 based on a microcomputer 16 as steering assist control means for executing control processing of the electric motor 12 and a gate drive signal Sg output from the microcomputer 16. A motor drive circuit 18 as motor drive means for controlling the motor drive current Im to be supplied, a motor current detection circuit 19 for detecting the motor drive current Imd flowing through the electric motor 12, and the motor drive circuit 18 supply the electric motor 12 with the motor drive current Im. A motor angular speed estimation circuit 20 that receives the motor terminal voltage Vm and the motor current Im and estimates the motor angular speed ω based on these is provided.
The microcomputer 16 receives the torque detection value T detected by the steering torque sensor 3, the motor current detection value Imd detected by the motor current detection circuit 19, and the motor angular velocity ω estimated by the motor angular velocity estimation circuit 20, respectively. It is converted into a digital value by the converters 21, 22 and 23 and inputted.

  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 Imd, and a motor angular speed ω are input, a torque detection value T, a vehicle speed detection value V, and a motor current detection value Imd. And a central processing unit 32 that performs a steering assist control process for generating a steering assist force in accordance with the steering torque by controlling the driving of the electric motor 12 based on the motor angular velocity ω, and a steering assist control that is executed by the central processing unit 32. ROM (read only memory) 33 for storing a processing program and the like, electrically erasable EEPROM 34 as a nonvolatile storage unit for storing abnormality information such as a temperature sensor abnormality flag, torque detection value T, motor current detection value Detection data such as Imd and motor angular velocity ω, etc., in the process of steering assist control processing executed by the central processing unit 32 Has a RAM (random access memory) 35 for storing data and processing results to a main, an output interface circuit 36 to the motor drive circuit 18 is connected. Here, the motor drive circuit 18 has an H bridge circuit composed of switching elements such as four field effect transistors that supply a motor current to the electric motor 12, and each switching element constituting the H bridge circuit is a circuit. A temperature sensor 13 composed of a thermistor, for example, is disposed in the vicinity of the switching element of the circuit board. A temperature detection value Ts detected by the temperature sensor 13 is input to the input interface circuit 31.

Then, the central processing unit 32 executes a steering assist control process shown in FIG.
In this steering assist control process, first, in step S1, it is determined whether or not the temperature sensor abnormality flag FTA stored in the EEPROM 34 is set to "1", and if this is reset to "0", the step is performed. The process proceeds to S2 and a correction coefficient K described later is set to “1”, and then the process proceeds to Step S4.

If the determination result in step S1 indicates that the temperature sensor abnormality flag FTA is set to “1”, the process proceeds to step S3, and a correction coefficient K described later is set to, for example, “0.5”. The process proceeds to S4.
In step S4, various sensors such as a steering torque detection value T detected by the steering torque sensor 3, a vehicle speed detection value V detected by the vehicle speed sensor 15, and a motor current Imd (Iu, Iv, Iw) detected by the motor current detection circuit 19 are used. Then, the process proceeds to step S5, and the steering assist current command value Iref is calculated with reference to the steering assist current command value calculation map shown in FIG. 5 based on the steering torque T and the vehicle speed detection value V. .

Here, as shown in FIG. 4, the steering assist current command value calculation map has a steering torque detection value T on the horizontal axis, a steering assist current command value Iref on the vertical axis, and a parabola with the vehicle speed Vs as a parameter. The current command value Iref is maintained at “0” and the steering torque T is set to the set value when the steering torque T is from “0” to the set value Ts1 in the vicinity thereof. When Ts1 is exceeded, initially, the steering assist current command value Iref increases relatively slowly as the steering torque T increases, but when the steering torque T further increases, the steering assist current command value Iref increases sharply. The characteristic curve is set so that the slope becomes smaller as the vehicle speed increases.

  Next, the process proceeds to step S6, where the calculated steering assist current command value Iref is multiplied by the correction coefficient K to calculate the corrected steering assist current command value Iaref (= K · Iref), and then the process proceeds to step S7 to calculate. The motor current detection value Imd is subtracted from the corrected steering assist current command value Iaref to calculate the current deviation ΔI, and then the process proceeds to step S8 to perform PI (proportional / integral) control calculation on the calculated current deviation ΔI. Thus, the voltage command value Vref is calculated.

Next, the process proceeds to step S9, where pulse width modulation processing is performed based on the calculated voltage command value Vref, and each switching of the H bridge circuit of the motor drive circuit 18 expressed by a duty ratio corresponding to the voltage command value Vref. A gate drive signal for the element is formed, and then the process proceeds to step S10, where the formed gate drive signal is output to the inverter of the motor drive circuit 18, and then the process returns to step S1.
In the process of FIG. 3, the processes of steps S1 to S3 correspond to the abnormality control means.

Further, the central processing unit 32 executes an abnormality diagnosis process shown in FIG.
This abnormality diagnosis process is started when the ignition switch IG is turned on and power is supplied from the battery B to the controller 14. First, in step S 11, the self-holding switching element SW is turned on. The control signal CS is output at a high level, and then the process proceeds to step S12, the temperature sensor abnormality flag FTA stored in the EEPROM 34 is read, and whether or not the temperature sensor abnormality flag FTA is set to “1”. Determine.

As a result of the determination, when the temperature sensor abnormality flag FTA is set to “1”, the process proceeds to step S13, for example, the warning lamp 40 provided on the instrument panel is turned on, and then the process proceeds to step S14. When the sensor abnormality flag FTA is reset to “0”, the process directly proceeds to step S14.
In step S14, initial diagnosis processing is executed to perform initial diagnosis of various devices including the temperature sensor 13. When this initial diagnosis is completed, the process proceeds to step S15, and constant diagnosis of predetermined devices including the temperature sensor 13 is performed. Then, the process proceeds to step S16, where it is determined whether or not the ignition switch IG is turned off. When the ignition switch IG is kept on, the process returns to step S15, where the ignition switch IG is turned on. When it is turned off, the process proceeds to step S17.

In this step S17, it is determined whether or not the vehicle is stopped and in a non-steering state where the vehicle speed detection value V is 0 [km / h] and the steering torque detection value T is O [Nm], and V> 0. Alternatively, when | T |> 0, the system waits until the vehicle stops and becomes non-steered, and when the vehicle stops and becomes non-steered, the process proceeds to step S18.
In this step S18, the temperature sensor abnormality detection process for detecting the abnormality of the temperature sensor 13 shown in FIG. 6 is executed. When this temperature sensor abnormality detection process is completed, the process proceeds to step S19, and the self-holding switching element SW is set. After the low level control signal CS to be turned off is output, the abnormality diagnosis process is terminated.
Here, in the temperature sensor abnormality detection process in step S18, as shown in FIG. 6, first, in step S21, the temperature detection value Ts detected by the temperature sensor 13 is read, and the initial temperature Ts0 is stored in a predetermined storage area of the RAM 35. Remember.

Next, the process proceeds to step S22, where the motor terminal voltage Vm and the motor drive current Im are read, and the motor terminal resistance R (= Vm / Im) is calculated based on these.
Next, the process proceeds to step S23, where the calculation of the following equation (1) is performed based on the calculated motor terminal resistance R to calculate the estimated motor temperature Tm.
Tm = (R−R20) / α + 20 (° C.) (1)
Here, R20 is the resistance between the motor terminals at 20 ° C., and α is the temperature coefficient of the motor winding.

  Next, the process proceeds to step S24, where it is determined whether or not the initial temperature Ts0 detected by the temperature sensor 13 is lower than the overheat protection start temperature Tos of the semiconductor switching element mounted on the circuit board of the motor drive circuit 18, and Ts0. When ≧ Tos, it is determined that there is a possibility that the semiconductor switching element and the circuit components mounted on the circuit board may be burned when the energization process is performed on the electric motor 12, and the process proceeds to step S25. After the temperature sensor abnormality flag FTA is reset to “0”, the temperature sensor abnormality detection process is terminated, and the process proceeds to step S19 in FIG.

  If the determination result in step S24 is Ts0 <Tos, it is determined that the temperature of the motor drive circuit 18 is normal, and the process proceeds to step S26. The estimated motor temperature Tm calculated in step S23 is the motor temperature estimated value Tm. It is determined whether or not the overheat protection start temperature Tom is equal to or higher than Tm. If Tm ≧ Tom, the electric motor 12 is in an overheated state, and when the electric motor 12 is energized, the excitation coil of the electric motor 12 It is determined that there is a possibility of burning, and the process proceeds to step S25 as it is.

Furthermore, when the determination result in step S26 is Tm <Tom, it is determined that the electric motor 12 is normal, and the process proceeds to step S27, where a predetermined forced driving pattern set in advance is set in the electric motor 12. The duty ratio is output to the motor drive circuit 18.
Here, as shown in FIG. 7, the forced drive pattern is such that the duty ratio is alternately changed in the direction of increasing the duty ratio and decreasing the duty ratio from the stopped state of the electric motor 12 whose duty ratio is 50%. It is set so that the amplitude sandwiching the median value 50% of the duty ratio gradually increases.

  By outputting the duty ratio of such a forced drive pattern to the motor drive circuit 18, a motor drive current Ima that alternately switches between positive and negative is supplied to the electric motor 12. The electric motor 12 is energized by supplying the electric motor 12 with the motor drive current Ima that alternately switches between positive and negative in this way, but the positive and negative are alternately switched. The output shaft maintains a state where the rotation is stopped.

Next, the process proceeds to step S28, and the temperature detection value Ts detected by the temperature sensor 13 at the end of forced driving of the electric motor 12 is read as the driving end temperature Ts1, and then the process proceeds to step S29 to read the current The temperature change amount ΔT (= Ts1−Ts0) is calculated by subtracting the initial temperature Ts0 from the temperature detection value Ts1.
Next, the process proceeds to step S30, where it is determined whether or not the temperature sensor 13 for which the temperature change amount ΔT is set in advance is within the range of the upper limit value TH and the lower limit value TL of the normal temperature change range. When ΔT> TL, it is determined that the temperature sensor 13 is normal and the process proceeds to step S25. When ΔT ≧ TH or ΔT ≦ TL, it is determined that the temperature sensor 13 is abnormal and the process proceeds to step S31. Transition.

In step S31, the temperature sensor abnormality flag FTA stored in the EEPROM 34 is set to "1" indicating that the temperature sensor 13 is abnormal, and then the temperature sensor abnormality detection process is terminated, and the step S19 in FIG. Migrate to
The processing in FIGS. 5 and 6 corresponds to the abnormality detection means, and the processing in steps S12 and S13 in FIG. 5 corresponds to the abnormality control means.

Next, the operation of the above embodiment will be described.
Now, the temperature sensor 13 is normal, the temperature sensor abnormality flag FTA stored in the EEPROM 34 is reset to “0”, the vehicle is stopped, the ignition switch IG is off, and the self-holding switching element It is assumed that the SW is in an off state and the controller 14 is not powered from the battery B.

In this state, when the ignition switch IG is turned on, the power of the battery B is supplied to the controller 14 through the ignition switch IG, and the microcomputer 16, the motor drive circuit 18, the motor current detection circuit 19, and the motor in the controller 14 are supplied. The angular velocity estimation circuit 20 and the like are activated.
At this time, when the steering wheel 1 is not being steered, the steering torque T detected by the steering torque sensor 3 is substantially “0”.
Further, in the steering assist control process shown in FIG. 3 executed by the central processing unit 32 in the microcomputer 16 of the controller 14, the temperature sensor abnormality flag FAT is reset to “0”, so that the correction coefficient K is set to the normal control state. Is set to "1" representing (step S2).

  The steering assist command value Iref calculated based on the steering torque T and the vehicle speed detection value V with reference to the steering assist current command value calculation map shown in FIG. 4 is also “0”. On the other hand, since the electric motor 12 has also stopped rotating and the motor drive current Im is also “0”, the current deviation ΔI is also “0”, and the voltage command value Vref obtained by performing PI control processing on the current deviation ΔI is also “0”. ", A gate drive signal having a duty ratio of" 0 "is formed and output to the motor drive circuit 18. For this reason, the motor drive current Im is not output from the motor drive circuit 18, and the electric motor 12 maintains a stop state.

  When the driver stops the steering wheel 1 to the right, for example, when the vehicle is stopped, the steering torque detection value T detected by the steering torque sensor 3 increases in the positive direction. Accordingly, the steering assist current command value Iref increases in the positive direction and the correction coefficient K is “1”. Therefore, the correction current command value Iaref is the same value as the steering assist current command value Iref.

On the other hand, since the electric motor 12 continues the stopped state, the motor current detection value Im is "0", the voltage command value Vref of the correction current command value Iaref is greater is the PI control process is immediately value calculated The voltage command value Vref is subjected to pulse width modulation to form a gate drive signal having a duty ratio between 50% and 100%, which is output to the motor drive circuit 18.

  Therefore, the motor drive circuit 18 determines the rotation direction depending on whether the duty ratio is 50% or more, and scales the duty ratio to drive the switching element of the H bridge circuit with a duty ratio of 0 to 100%. As a result, a motor drive current Im is formed, and this motor drive current Im is output to the electric motor 12. For this reason, the electric motor 12 is rotationally driven with respect to the steering shaft 2 so as to be in the same direction as the steering direction to generate a steering assist force. The generated steering assist force is transmitted to the output shaft 2 b of the steering shaft 2 through the reduction gear 11. Thereby, the steering wheel 1 can be steered with a light steering force.

  Thereafter, when the vehicle is started while continuing the steering state of the steering wheel 1, steering is performed based on the steering torque detection value T detected by the steering torque sensor 3 at that time and the vehicle speed detection value V detected by the vehicle speed sensor 15. An auxiliary current command value Iref is calculated. Even if the steering assist current command value Iref is the same steering torque detection value T, the steering assist current command value Iref becomes a small value as the vehicle speed detection value V increases. For this reason, the steering assist force generated by the electric motor 12 also decreases as the vehicle speed detection value V increases, and optimal steering control according to the traveling state can be performed.

On the other hand, in the abnormality diagnosis process of FIG. 5, when the controller 14 is powered on, in step S11, a high-level control signal CS for controlling the self-holding switching element SW to be turned on is output. The self-holding switching element SW is turned on, and a self-holding circuit parallel to the ignition switch IG is formed.
After that, an initial diagnosis process is performed to perform abnormality diagnosis of various sensors and circuit configurations. When this initial diagnosis process is completed, a continuous diagnosis process is performed while the ignition switch IG is kept on, and various sensors and circuits are Diagnose configuration abnormalities.

  In this continuous diagnosis process, when one diagnosis is completed, the process proceeds from step S15 to step S16 to determine whether or not the ignition switch IG has been determined to be off from the on state, and the ignition switch IG continues to be on. When the ignition switch IG is turned off, the process moves from step S16 to step S17. In this step S17, it is determined whether the vehicle speed detection value V is “0” and the steering torque T is “0” or whether the vehicle is stopped and in a non-steering state, and the vehicle speed detection value V is V> 0. If the steering torque | T |> 0 or V> 0 and | T |> 0, it is determined that the steering state or the state where the steering possibility is high, and the process returns to step S16.

On the other hand, if the determination result of step S17 is that the vehicle speed detection value V is V = 0 and the steering torque T is T = 0, the vehicle is in the stop state and the non-steering state. The temperature sensor abnormality detection process shown in FIG.
In this temperature sensor abnormality detection process, first, the temperature detection value Ts detected by the temperature sensor 13 is read as the initial temperature Ts0, and then the motor terminal resistance R is calculated based on the motor terminal voltage Vm and the motor drive current Im ( Step S22) Next, based on the calculated resistance R between the motor terminals, the calculation of the equation (1) is performed to calculate the estimated motor temperature Tm.

  Then, it is determined whether or not the initial temperature Ts0 exceeds the circuit board overheat protection start temperature Tos (step S24). When Ts0 ≧ Tos, the motor drive circuit 18 detects when the electric motor is driven for abnormality detection. It is determined that the switching element mounted on the circuit board may be burned out, and the process proceeds to step S25 to continue the state in which the temperature sensor abnormality flag FTA is reset to “0”.

  When the initial temperature Ts0 is lower than the circuit board overheat protection start temperature Tos, it is determined that the circuit board temperature of the motor drive circuit 18 is normal, and then the motor temperature estimated value Tm is lower than the motor overheat protection start temperature Tom. If Tm ≧ Tom, the temperature of the electric motor 12 is too high, and the excitation coil may burn out when the electric motor 12 is driven to detect an abnormality in the temperature sensor 13. The process proceeds to step S25, and the temperature sensor abnormality flag FTA is reset to “0”.

  Further, when the estimated motor temperature Tm is less than the motor overheat protection start temperature Tom, it is determined that the electric motor 12 can be driven, and the process proceeds to step S27, where the duty ratio of the electric motor 12 is set with the drive pattern shown in FIG. Output to the motor drive circuit 18. In this state, the motor drive current Im that is alternately switched between positive and negative is supplied from the motor drive circuit 18 to the electric motor 12. For this reason, although the electric motor 12 itself is not rotationally driven, the motor drive circuit 18 forms a motor current Im to be supplied to the exciting coil of the electric motor 12, so that the switching elements constituting the H-bridge circuit are The circuit board temperature rises due to heat generation. Therefore, when the temperature sensor 13 is normal, the temperature detection value Ts changes within the range of the characteristic curves L1 and L2 indicating the upper limit temperature TH and the lower limit temperature TL indicated by broken lines in FIG. Therefore, the temperature change amount ΔT with respect to the driving end temperature Ts1 at the time when the temperature detection value Ts gradually increases from the initial temperature Ts0 and the forced driving of the electric motor 12 is finished is within the range of the upper limit TH and the lower limit TL. When there is a certain time, it is determined that the temperature sensor 13 is normal, the process proceeds to step S25, and the temperature sensor abnormality flag FTA is reset to “0”.

However, although the temperature detection value Ts detected by the temperature sensor 13 increases from the initial temperature Ts0, as shown by the characteristic curve L3 in FIG. 8, when the driving end temperature Ts1 is lower than the normal range, or in FIG. As indicated by the characteristic line L4, when the temperature detection value Ts detected by the temperature sensor 13 does not increase from the initial temperature Ts0, or as indicated by the characteristic line L5 in FIG. 8, the temperature detection value Ts detected by the temperature sensor 13 is When the temperature rapidly rises from the initial temperature Ts0 and the temperature change is larger than that in the normal state, it is determined that the temperature sensor 13 is abnormal, the process proceeds from step S30 to step S31, and the temperature sensor abnormality flag FTA is set to “1”. Then, the process proceeds to step S19 in FIG. 5, and the low-level control signal CS for turning off the self-holding switching element SW is supplied to the self-holding switching element. And outputs it to the SW. For this reason, by releasing the self-holding state, the electric power input from the battery B to the controller 14 is cut off, and the steering assist control process and the abnormality diagnosis process are ended.
Thus, even when the power from the battery B to the controller 14 is cut off, the temperature sensor abnormality flag FTA stored in the EEPROM 34 is maintained without disappearing.

  For this reason, when the ignition switch IG is turned on next time, in the steering assist control process of FIG. 3, the temperature sensor abnormality flag FTA is set to “1”, so that the process proceeds from step S1 to step S3. Thus, the correction coefficient K is set to “0.5”. For this reason, the correction current command value Iaref calculated in step S6 is half the steering assist current command value Iref calculated with reference to the steering assist current command value calculation map. The motor driving current Im supplied to the motor is also halved, and the steering assist control is continued while suppressing the overheating of the switching elements constituting the H bridge circuit of the motor driving circuit 18 and suppressing the overheating of the electric motor 12. be able to. At the same time, in the abnormality diagnosis process, the process proceeds from step S12 to step S13, and the warning lamp 40 is turned on, so that the abnormality of the temperature sensor 13 can be notified to the driver.

  As described above, according to the embodiment, after the ignition switch IG is turned off, the temperature sensor abnormality detection process is executed to detect the abnormality of the temperature sensor 13, and when the abnormality of the temperature sensor 13 is detected. Then, the temperature sensor abnormality flag FTA is set to “1”, and the steering assist control in which the motor drive current Im is suppressed at the start of the steering assist control when the ignition switch IG is turned on next is started. When the steering wheel 1 is being steered, the steering assist force suddenly changes as in the case where the correction coefficient K is changed during the steering assist control, such as when an abnormality of the temperature sensor 13 is detected. Can be reliably prevented.

In the above embodiment, the case where the motor temperature estimated value Tm is calculated by calculating the motor terminal resistance R to calculate the motor temperature estimated value Tm has been described. However, the present invention is not limited to this. A temperature sensor may be provided directly on the electric motor 12 to detect the motor temperature.
In the above-described embodiment, the case where the temperature sensor abnormality detection process is executed when the ignition switch IG is reversed from the on state to the off state has been described. However, the present invention is not limited to this. The temperature sensor abnormality detection process may be executed when the state is reversed from the off state to the on state.

Furthermore, in the above-described embodiment, the case where the forced drive pattern is set so that the amplitude of the duty ratio gradually increases has been described. However, the present invention is not limited to this, and the duty ratio is output with a constant amplitude. In short, any forced drive pattern can be applied as long as the temperature of the switching elements constituting the H-bridge circuit of the motor drive circuit 18 can be increased without rotating the electric motor 12.
In the above embodiment, the case where the correction coefficient K is set to “0.5” when abnormality of the temperature sensor 13 is detected has been described. However, the present invention is not limited to this, and the value of the correction coefficient K is the temperature sensor. It is sufficient to set the temperature rise of the motor drive circuit 18 to a value that can be kept below the circuit board protection start temperature even at the time of 13 abnormality.

  Furthermore, in the said embodiment, although the case where the DC motor with a brush was applied as the electric motor 12 was demonstrated, it is not limited to this, A three-phase brushless motor can also be applied, In this case, A three-phase inverter circuit is applied in place of the H-bridge circuit for the motor drive circuit 18, and the dq axis current command value is calculated based on the steering assist current command value Iref in the steering assist control process of FIG. The dq-axis current command value is converted into two-phase / 3-phase to calculate a three-phase current command value, and a current deviation between the calculated three-phase current command value and the three-phase drive current detection value of the electric motor 12 is calculated. Then, the calculated current deviation is subjected to PI control calculation processing to calculate a three-phase voltage command value, and this three-phase voltage command value is subjected to pulse width modulation and supplied to the inverter circuit constituting the motor drive circuit 18. Yo . In addition, what is necessary is just to apply the multiphase inverter circuit according to this, when applying the polyphase brushless motor more than four phases as the electric motor 12. FIG.

In the above embodiment, the case where the self-holding switching element is applied as the self-holding circuit has been described. However, the present invention is not limited to this, and a self-holding relay circuit can be applied. As long as the computer 16 can be turned on and off, a self-holding circuit having an arbitrary configuration can be applied.
In the above embodiment, the column assist type electric power steering apparatus in which the steering assist mechanism 10 is disposed on the output shaft 2b of the steering shaft 2 has been described. However, the present invention is not limited to this, and the steering gear mechanism 8 The present invention can also be applied to a pinion assist type electric power steering device or a rack assist type electric power steering device in which a steering assist mechanism is mounted on a pinion shaft or a rack shaft.

  DESCRIPTION OF SYMBOLS 1 ... Steering wheel, 2 ... Steering shaft, 3 ... Steering torque sensor, 8 ... Steering gear mechanism, 12 ... Electric motor, 14 ... Controller, 15 ... Vehicle speed sensor, 16 ... Microcomputer, 18 ... Motor drive circuit, 19 ... Motor current detection circuit, 20 ... Motor angular velocity estimation circuit, 31 ... Input interface circuit, 32 ... Central processing unit, 33 ... ROM, 34 ... EEPROM, 35 ... RAM, 36 ... Output interface circuit, SW ... Self-holding switching element

Claims (4)

Steering torque detecting means for detecting a steering torque transmitted to the steering system, an electric motor for generating a steering assist force for the steering system, and a steering assist for outputting a command value for the electric motor based on the steering torque An electric power steering apparatus comprising: a control unit; and a motor driving unit that controls driving of the electric motor based on a command value output from the steering assist control unit,
A temperature detecting means for detecting the temperature of the motor driving means; an abnormality detecting means for detecting an abnormality of the temperature detecting means; and a predetermined abnormality process when the detection result of the abnormality detecting means is an abnormality of the temperature detecting means. An abnormality control means to perform,
The abnormality detection means detects a temperature change of the temperature detection means by forcibly driving the motor drive means with a predetermined drive pattern in a state where the drive control of the electric motor by the motor drive means is stopped. An electric power steering apparatus characterized by being configured as described above.   The electric power steering apparatus according to claim 1, wherein the predetermined drive pattern is set to a drive pattern in which a change amplitude of a duty ratio of a motor current is gradually increased.   The abnormality detecting means forcibly drives the motor driving means with a predetermined driving pattern when a temperature detected by the temperature detecting means is lower than an overheat protection start temperature of the motor driving means. The electric power steering apparatus according to 1 or 2.   Motor temperature estimation means for estimating the temperature of the electric motor, and the abnormality detection means, when the estimated motor temperature estimated by the motor temperature estimation means is less than the motor overheat protection start temperature, The electric power steering apparatus according to claim 1, wherein the electric power steering apparatus is forcibly driven in a predetermined drive pattern.

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