JP5082666B2 - Motor control device, transmission ratio variable device, and vehicle steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a motor control apparatus capable of stably performing motor control while detecting overcurrent with high precision. <P>SOLUTION: As a threshold value of a power source current IO as a base of overcurrent detection, a second threshold value Ith2 having a lower value than a first threshold value corresponding to a generated overcurrent value to stop the motor control is set. When the power current IO to be detected is the second threshold value Ith2 or more, control is performed to lower a voltage to be applied to the motor. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to a motor control device, a transmission ratio variable device, and a vehicle steering device.

Conventionally, many motor control apparatuses have a function of detecting an excessive current supply to a motor to be driven, that is, an occurrence of an overcurrent. For example, the motor control device described in Patent Document 1 detects a power supply current supplied from a DC power supply to a drive circuit, detects a motor current supplied from the drive circuit to the motor, and corrects the current using the drive current. The occurrence of the overcurrent is detected on the basis of the comparison between the power supply current and the threshold value. And when generation | occurrence | production of the said overcurrent is detected, it has the structure which stops supply of the drive electric power with respect to a motor rapidly, and aims at fail safe.
JP 2003-219675 A JP 2007-106227 A

  In the motor control device of the above conventional example, the power supply current is corrected by using a separately detected motor current value in order to improve the detection accuracy of the power supply current that is the basis of overcurrent detection. Originally, the overcurrent detection is intended primarily for early detection of the main factor of the overcurrent occurrence, that is, the short-circuit fault occurring in each switching element constituting the drive circuit. Therefore, as long as the detection accuracy of the power supply current is ensured, usually such detection of the motor current is not necessarily indispensable.

  However, when used in an environment where the power supply voltage and the ambient temperature of the motor are not always constant, the overcurrent of the overcurrent is not affected by the change in the power supply voltage and the motor resistance, even though the short-circuit failure described above has not occurred. A power supply current having a value corresponding to occurrence, that is, a value at which motor control should be stopped may be detected. Therefore, in an application with a high probability of being used in such an environment, it is desirable to have a configuration that includes a function of detecting a motor current and a function of determining a short-circuit fault based on the motor current.

  However, for example, many motor control devices that generate and output motor control signals by executing position control, such as the control means of the driving force transmission device described in Patent Document 2 (see FIGS. 4 and 5). Does not have a configuration for detecting such a motor current. For this reason, in the motor control device having such a configuration, the threshold used for overcurrent detection is set higher than the original optimum value in order to avoid the system stop caused by the detection of the overcurrent that occurs exceptionally. The actual situation is that it must be set, and this has limited the accuracy of overcurrent detection.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a motor control device capable of stably executing motor control while performing highly accurate overcurrent detection, and An object of the present invention is to provide a transmission ratio variable device and a vehicle steering device.

In order to solve the above-mentioned problems, the invention according to claim 1 is provided with a drive circuit that is provided in the middle of a power supply path between a motor and a DC power supply and generates drive power to be supplied to the motor, and a motor Control means for controlling the operation of the drive circuit through output of a control signal; and current detection means for detecting a power supply current supplied to the drive circuit, wherein the control means has a predetermined power supply current detected A motor control device that controls to stop the supply of drive power to the motor when the threshold is equal to or greater than a threshold, the control means is configured to stop the supply of the drive power from the detected power source current; if the second threshold or more which is set to a value lower than the first threshold is configured to control so as to reduce the voltage applied to the motor, wherein the drive circuit, the motor control signal and The voltage applied to the motor is reduced through control of the duty ratio, and the control means includes the duty ratio. An upper limit value is set for the ratio, and the duty ratio control for reducing the applied voltage to the motor is performed by changing the upper limit value, and a lower limit is set for the change of the upper limit value, and the control means Is to change the upper limit value so that the upper limit value drops to a value corresponding to the lower limit, and whether or not the period of changing the upper limit value should stop the supply of the drive power The gist is that it is set to be shorter than the period of overcurrent determination for determining .

  That is, as long as no short-circuit failure occurs in the drive circuit (each switching element constituting the drive circuit), the value of the power supply current can be lowered by reducing the voltage applied to the motor. Therefore, as described above, when the value of the power supply current is lower than the first threshold value corresponding to the occurrence of the overcurrent, the reduction is attempted to cause a change in the power supply voltage or the temperature of the motor (surrounding). Exceptional overcurrent can be suppressed. As a result, the first threshold value at which the motor control is to be stopped is optimized, that is, a value that does not take into account the occurrence of the above-mentioned exceptional overcurrent, while improving the accuracy of overcurrent detection and stably driving the motor. The control can be executed.

According to the above configuration, the overcurrent suppression control as described above can be easily added without affecting the normal control system.
Further, by reducing the duty ratio until the detected power source current becomes lower than the second threshold value, the voltage applied to the motor may be lowered more than necessary. In particular, when used as a control means of the transmission ratio variable device, if the duty ratio is “0%”, that is, the applied voltage is “0”, the second steering angle based on the motor drive is set. There is a possibility that the vehicle cannot be maintained, that is, a so-called steering-free state is brought about. However, according to the above configuration, the duty ratio is not less than the lower limit. As a result, it is possible to stably continue the motor control while avoiding an excessive decrease in the applied voltage as described above.
According to a second aspect of the present invention, the control means generates the motor control signal every predetermined cycle, and the change of the upper limit value is performed stepwise for each cycle. The gist.

According to the above configuration, it is possible to suppress the occurrence of steep torque fluctuations by making the current change gentle .

According to a third aspect of the present invention, the control means changes the upper limit value stepwise so that the upper limit value decreases to a value corresponding to the lower limit at a timing corresponding to a next overcurrent determination cycle. The gist of this is to calculate the gradual change amount.
According to the above configuration, the power supply current (motor current) can be changed more smoothly, and the torque fluctuation can be made more gentle.

The gist of the invention described in claim 4 is that the control means calculates a value estimated to generate a power supply current corresponding to the second threshold value as a lower limit in the change of the upper limit value.

According to the above configuration, even when overcurrent suppression control is executed, it is possible to apply the maximum voltage to the motor within a range that does not exceed the reference first threshold value.
The invention according to claim 5 includes temperature detection means for detecting the temperature of the motor and voltage detection means for detecting a power supply voltage of the DC power supply, and the control means is based on the detected temperature. The gist is to estimate the resistance of the motor and calculate the lower limit in the change of the upper limit value based on the resistance and the power supply voltage.

According to the above configuration, it is possible to more accurately determine a value that is estimated to generate a power supply current corresponding to the second threshold value .

The invention described in 請 Motomeko 6, the power supply current to be the detection is lower than the second threshold, increasing the upper limit value, and the gist.

  According to the above configuration, smooth and quick return to normal control is ensured when the possibility of occurrence of overcurrent is reduced. Furthermore, the maximum voltage can be applied to the motor even when overcurrent suppression control is executed.

The gist of the seventh aspect of the invention is that it is a transmission ratio variable device that controls the motor of the drive source by the motor control device according to any one of the first to sixth aspects.
The gist of an eighth aspect of the invention is a vehicle steering apparatus provided with the transmission ratio variable device according to the seventh aspect.

  According to each of the above configurations, it is possible to provide a transmission ratio variable device and a vehicle steering device capable of stably performing motor control while performing highly accurate overcurrent detection.

  According to the present invention, a motor control device capable of stably performing motor control while performing highly accurate overcurrent detection, a transmission ratio variable device including the motor control device, and a vehicle steering device are provided. Can do.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, an embodiment of the invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram of a vehicle steering apparatus 1. As shown in the figure, the steering shaft 3 to which the steering wheel 2 is fixed is connected to a rack 5 via a rack and pinion mechanism 4, and the rotation of the steering shaft 3 accompanying the steering operation is performed by the rack and pinion mechanism 4. Is converted into a reciprocating linear motion of the rack 5. Then, the steering angle of the steered wheels 6, that is, the steered angle is varied by the reciprocating linear motion of the rack 5, so that the vehicle traveling direction is changed. The vehicle steering apparatus 1 according to the present embodiment is a so-called rack assist type electric power steering apparatus (EPS), and generates an assist torque generated by a motor 7 as a drive source via a ball screw mechanism (not shown). By transmitting to the rack 5, an assist force is applied to the steering system.

  Further, the vehicle steering apparatus 1 of the present embodiment is provided in the middle of the steering transmission system between the steering 2 and the steered wheels 6, and the steering angle (steering angle) of the steering 2 and the steered angle (turning wheel) of the steered wheels 6. The transmission ratio variable device 8 that varies the transmission ratio (gear ratio) between the steering angle and the IFSECU 9 that controls the operation of the transmission ratio variable device 8 is provided.

  More specifically, the steering shaft 3 includes a first shaft 10 to which the steering 2 is connected and a second shaft 11 to be connected to the rack and pinion mechanism 4, and the transmission ratio variable device 8 includes the first shaft 10 and the first shaft 10. A differential mechanism 12 for connecting the two shafts 11 and a motor 13 for driving the differential mechanism 12 are provided. The transmission ratio variable device 8 adds the rotation driven by the motor to the rotation of the first shaft 10 accompanying the steering operation and transmits it to the second shaft 11, thereby inputting the steering shaft to the rack and pinion mechanism 4. 3 is increased (or decelerated), thereby changing the transmission ratio between the steering angle and the turning angle.

  In the present embodiment, a brushless motor is employed as the motor 13 that is a drive source of the transmission ratio variable device 8, and the motor 13 is supplied with driving power of three phases (U, V, W) from the IFSECU 9. To rotate. And IFSECU9 as a motor control apparatus controls the action | operation of the transmission ratio variable apparatus 8 by controlling rotation of the motor 13 through supply of this drive electric power.

  Specifically, the steering sensor 14 and the vehicle speed sensor 15 are connected to the IFSECU 9, and the IFSECU 9 detects the steering angle θs and the steering speed ωs detected by the steering sensor 14 and the vehicle speed detected by the vehicle speed sensor 15. Based on V, an optimal transmission ratio is determined. And it is the structure which controls the action | operation of the transmission ratio variable apparatus 8 so that it may become the determined transmission ratio (transmission ratio variable control).

Next, the electrical configuration of the vehicle steering apparatus of the present embodiment will be described.
As shown in FIG. 2, the IFSECU 9 is provided in the middle of a power supply path Lp between a motor 13 that is a drive source of the transmission ratio variable device 8 and an in-vehicle power source (battery) 16 that is a DC power source. It comprises a drive circuit 20 that generates drive power to be supplied, and a microcomputer 21 that serves as control means for controlling the operation of the drive circuit 20 through the output of a motor control signal.

  That is, the steering angle θs and the steering speed ωs detected by the steering sensor 14 and the vehicle speed sensor 15 (see FIG. 1) and the vehicle speed V are input to the microcomputer 21, and the microcomputer 21 inputs the steering angle θs and the vehicle speed V. The optimum transmission ratio is determined according to. The microcomputer 21 outputs a motor control signal for supplying driving power to the motor 13 in order to rotate the motor 13 based on the determined control target, and the drive circuit 20 is based on the motor control signal. Thus, three-phase drive power is supplied to the motor 13.

  In the present embodiment, the drive circuit 20 employs a known PWM inverter formed by connecting a plurality of switching elements that are turned on / off based on an input motor control signal. Then, the combination of the switching elements to be turned on / off, that is, the energization pattern is sequentially switched, whereby the DC voltage of the in-vehicle power supply 16 is converted into three-phase driving power and supplied to the motor 13. .

  More specifically, the microcomputer 21 of this embodiment includes a gear ratio variable control calculation unit 23 and a differential steer control calculation unit 24 as control component calculation means for calculating each control component for executing the transmission ratio variable control. ing. In the present embodiment, the steering angle θs and the vehicle speed V are input to the gear ratio variable control calculation unit 23, and the gear ratio variable control calculation unit 23 transmits the transmission ratio based on these state quantities. A gear ratio variable command angle θgr * which is a basic control component of variable control is calculated. Further, the steering speed ωs and the vehicle speed V are input to the differential steer control calculation unit 24, and the differential steer control calculation unit 24 determines the gear ratio variable command angle based on these state quantities. The differential steering command angle θls * is calculated as a correction component of θgr *. These gear ratio variable command angle θgr * and differential steer command angle θls * are input to the adder 25. Then, by superimposing in the adder 25, an ACT command angle θta * which is a target control amount of the transmission ratio variable control is generated.

  The ACT command angle θta * generated as described above is input to the motor control signal generation unit 26. The microcomputer 21 is configured to output the motor control signal generated by the motor control signal generator 26 to the drive circuit 20.

  More specifically, the ACT command angle θta * as the target control amount input to the motor control signal generator 26 is combined with the ACT angle θta as the actual control amount of the transmission ratio variable control calculated in the ACT angle calculator 27. Are input to the subtractor 28.

  In the present embodiment, the ACT command angle θta * and the ACT angle θta are values indicating the rotation angle of the steering shaft 3 (second shaft 11) added by the operation of the transmission ratio variable device 8 (so-called “so-called”). The ACT angle calculation unit 27 calculates the ACT angle θta based on the motor rotation angle θm detected by the rotation angle sensor 29.

  The subtractor 28 calculates the deviation Δθta based on the inputted ACT command angle θta * and ACT angle θta, and outputs it to the F / B control calculation unit 30. The F / B control calculation unit 30 executes a feedback control calculation based on the deviation Δθta, so that a voltage command that is a control target value of the applied voltage to the motor 13 that is a drive source of the transmission ratio variable device 8 is obtained. The value V * is calculated.

  That is, the microcomputer 21 of the present embodiment generates and outputs a motor control signal by executing position control so that the ACT command angle θta * that is the target control amount follows the ACT angle θta that is the actual control amount. . Specifically, a motor control signal is generated to execute so-called rectangular wave energization that switches the energization pattern in accordance with the motor rotation angle θm. The voltage command value V * is a value corresponding to the applied voltage for the energized phase.

  The voltage command value V * calculated by the F / B control calculation unit 30 is input to the duty ratio calculation unit 31, and the duty ratio calculation unit 31 determines a duty ratio (on-duty ratio) corresponding to the voltage command value V *. ) D is calculated. In this embodiment, the duty ratio D is input to the duty ratio limiting unit 32, and the duty ratio limiting unit 32 limits the value of the input duty ratio D within a predetermined range. A restriction process (guard process) is executed. That is, in the present embodiment, an upper limit value is set for the duty ratio D.

  The duty ratio D ′ after the restriction process is performed in the duty ratio limiting unit 32 is input to the PWM output unit 33, and the PWM output unit 33 generates a pulse signal having the input duty ratio D ′. As a result, a motor control signal capable of generating a motor applied voltage corresponding to the voltage command value V * is generated. As described above, the motor control signal has an energization pattern corresponding to the motor rotation angle θm detected by the rotation angle sensor 29. Then, the microcomputer 21 outputs the motor control signal thus generated to the drive circuit 20.

  Further, the microcomputer 21 of the present embodiment has a function of detecting an excessive current supply to the motor 13 as described above, that is, an occurrence of an overcurrent. Specifically, the microcomputer 21 of the present embodiment is provided with an overcurrent detection unit 34 that detects the occurrence of the overcurrent. The overcurrent detection unit 34 receives a power supply current I0 detected by a current sensor 35 as a current detection unit provided in a power supply path Lp between the in-vehicle power supply 16 and the drive circuit 20. The overcurrent detection unit 34 detects the occurrence of the overcurrent based on a comparison between the detected power supply current I0 and a predetermined threshold value Ith1. Then, the microcomputer 21 of the present embodiment promptly fails-safe by controlling the supply of drive power to the motor 13 to stop when the overcurrent detection unit 34 detects the occurrence of overcurrent. It is the structure which aims at.

  That is, as shown in the flowchart of FIG. 3, the microcomputer 21 determines whether or not the detected power supply current I0 is equal to or greater than a predetermined threshold value Ith1 (step 101), and if it is equal to or greater than the threshold value Ith1 (step 101). : YES), the supply of the driving force to the motor 13 is stopped, that is, the motor control is stopped (step 102). When the power supply current I0 is smaller than the predetermined threshold value Ith1 (step 101: NO), the motor control is continued (step 103).

(Overcurrent suppression control)
Next, an aspect of overcurrent suppression control in the present embodiment will be described.
As described above, when used in an environment where the power supply voltage and the temperature around the motor are not constant, a short circuit failure has not occurred in each switching element constituting the drive circuit due to a change in the power supply voltage and the motor resistance. Nevertheless, a power supply current corresponding to an overcurrent at which the motor control should be stopped may be detected. The IFSECU 9 of the present embodiment generates and outputs a motor control signal by performing position control so that the ACT angle θta, which is the actual control amount, follows the ACT command angle θta *, which is the target control amount. Therefore, there is no configuration for detecting the current supplied from the drive circuit 20 to the motor 13, that is, the motor current. Therefore, the determination result of the overcurrent detection based on the power supply current cannot be evaluated based on the motor current, and the overcurrent detection is performed in order to avoid the system stop due to the detection of the overcurrent that occurs exceptionally. The actual situation is that the threshold Ith1 to be used must be set higher than the original optimum value, which has been an impediment to improving the overcurrent detection accuracy.

  In consideration of this point, in the present embodiment, as the threshold value regarding the power supply current I0 that is the basis of the overcurrent detection, a value lower than the first threshold value Ith1 is set together with the first threshold value Ith1 to stop the motor control. A second threshold value Ith2 is set. Then, the microcomputer 21 of the present embodiment controls the applied voltage to the motor 13 to be reduced when the detected power supply current I0 becomes equal to or greater than the second threshold value Ith2.

  That is, in the present embodiment, when the detected power supply current I0 increases to a value close to the first threshold value Ith1 at which the motor control is to be stopped, at an early stage before exceeding the first threshold value Ith1, The motor applied voltage is reduced to suppress the increase in the power supply current I0. As a result, the generation of the power supply current I0 that is equal to or higher than the first threshold value Ith1 at which the motor control should be stopped, that is, the generation of overcurrent is suppressed.

  More specifically, in the present embodiment, the reduction of the motor applied voltage for suppressing the overcurrent is performed by controlling the duty ratio of the pulse signal input as the motor control signal to the drive circuit 20 (each switching element constituting the drive circuit 20). Done.

  As shown in FIG. 2, the microcomputer 21 (the motor control signal generation unit 26 thereof) of the present embodiment is provided with a duty limit value calculation unit 36, and a limit process (guard) performed by the duty ratio limiter 32. The process is performed with the duty limit value Dlim calculated by the duty limit value calculator 36 as an upper limit. That is, the duty ratio of the motor output signal output from the microcomputer 21 is equal to or less than the duty limit value Dlim.

  In the present embodiment, the power source current I 0 detected by the current sensor 35 is input to the duty limit value calculation unit 36, and the duty limit value calculation unit 36 receives the power source input thereto. It is determined whether or not the current I0 is equal to or greater than the second threshold value Ith2. When it is determined that the power supply current I0 is equal to or greater than the second threshold value Ith2 (I0 ≧ Ith2), the duty limit value Dlim output to the duty ratio limiter 32 is gradually changed to a lower value. (Slow down).

  Specifically, the calculation cycle of the duty limit value Dlim in the duty limit value calculation unit 36 of the present embodiment is shorter than the cycle of overcurrent determination in the overcurrent detection unit 34, and the duty limit value Dlim Is gradually reduced by subtracting a predetermined constant (gradual change amount α) for each period. Then, by performing a limit process (guard process) based on the duty limit value Dlim changed to a lower value, the duty ratio of the motor control signal, that is, the voltage applied to the motor 13 is gradually reduced. Yes.

  The duty limit value calculation unit 36 of the present embodiment gradually increases the output duty limit value Dlim when the detected power source current I0 becomes lower than the second threshold value Ith2 (I0 <Ith2). Change to a large value (gradual increase). The duty limit value Dlim is gradually increased by adding a predetermined constant (gradual change amount β) to the duty limit value Dlim for each calculation cycle. As a result, a smooth and quick return to normal control is ensured when the possibility of occurrence of overcurrent is reduced.

In the present embodiment, a lower limit is set for the change (gradual decrease) of the duty limit value Dlim by the duty limit value calculator 36.
Specifically, the duty limit value calculation unit 36 of the present embodiment corresponds to the second threshold value Ith2 as a lower limit value in the change (gradual decrease) of the duty limit value Dlim, that is, the gradually decreasing lower limit value Dlim_Lo. A value estimated to generate the power supply current I0 is calculated. In the change (gradual decrease) of the duty limit value Dlim, when the value of the duty limit value Dlim becomes equal to or less than the gradual decrease lower limit value Dlim_Lo, the value of the duty limit value Dlim is changed to the gradual decrease lower limit value Dlim_Lo. To do.

  Specifically, the duty limit value calculation unit 36 of the present embodiment includes the power supply voltage V0 detected by the voltage sensor 37 and the temperature of the motor 13 (ambient) detected by the temperature sensor 38 (see FIG. 1). Tmp is inputted, and the duty limit value calculation unit 36 estimates the resistance value R of the motor 13 based on the power supply voltage V0 and the temperature Tmp. That is, in this embodiment, the voltage sensor 37 constitutes a voltage detection means, and the temperature sensor 38 constitutes a temperature detection means. Then, the duty limit value calculation unit 36 is based on the estimated resistance value R and the power supply voltage V0, and the gradual decrease lower limit value having a value estimated to generate the power supply current I0 corresponding to the second threshold value Ith2. Calculate Dlim_Lo.

  In the present embodiment, the resistance value R is estimated by a known calculation method that takes into account the tolerance and temperature characteristics. The gradual decrease lower limit value Dlim_Lo is calculated by using the following equation (1).

Dlim_Lo = √ (Ith2 × R / V0) (1)
That is, by gradually decreasing the duty limit value Dlim until the detected power source current I0 becomes lower than the second threshold value Ith2, in some cases, the duty limit value Dlim, that is, the duty ratio D ′ after the limit process is set. It may decrease more than necessary. If the duty ratio D ′ becomes “0%”, the steering angle based on the motor drive, that is, the ACT angle θta cannot be maintained, that is, a so-called steering-free state may occur.

  However, as described above, such a situation can be avoided by setting a lower limit for the gradual decrease of the duty limit value Dlim. Then, as the gradual decrease lower limit value Dlim_Lo, a value estimated to generate the power supply current I0 corresponding to the second threshold value Ith2 is calculated, thereby reducing the motor applied voltage to suppress the occurrence of overcurrent. Even in such a case, the maximum voltage can be applied to the motor 13 within a range that does not exceed the first threshold value Ith1 as a reference.

Next, a procedure for changing (gradual decrease and gradual increase) of the duty limit value Dlim performed by the duty limit value calculation unit 36 will be described.
As shown in the flowchart of FIG. 4, when the duty limit value calculation unit 36 acquires each state quantity (step 201), it first estimates the resistance value R of the motor 13 (step 202), and then continues to the estimated resistance. Based on the value R and the power supply voltage V0, a lower limit value for the gradual decrease of the duty limit value Dlim, that is, a gradual decrease lower limit value Dlim_Lo is calculated (step 203).

  Next, the duty limit value calculation unit 36 determines whether or not the detected power supply current I0 is equal to or greater than the second threshold value Ith2 (step 204). When it is determined that the power supply current I0 is equal to or greater than the second threshold value Ith2 (I0 ≧ Ith2, step 204: YES), the duty limit value Dlim is subtracted from the duty limit value Dlim to thereby reduce the duty limit. The duty limit value gradual reduction operation for gradually changing the value Dlim to a low value, that is, gradual reduction is executed (Dlim = Dlim−α, step 205).

  Next, the duty limit value calculation unit 36 determines whether or not the duty limit value Dlim after the gradual decrease calculation is equal to or less than the gradual decrease lower limit value Dlim_Lo (step 206). In (Dlim ≦ Dlim_Lo, step 206: YES), the value of the duty limit value Dlim is set as the gradual decrease lower limit value Dlim_Lo (Dlim = Dlim_Lo, step 207). When the duty limit value Dlim is larger than the gradual decrease lower limit value Dlim_Lo (Dlim> Dlim_Lo, step 206: NO), the process of step 207 is not executed. Then, the duty limit value calculation unit 36 outputs the duty limit value Dlim calculated by the execution of steps 205 to 207 to the duty ratio limit unit 32 (step 208).

  On the other hand, when it is determined in step 204 that the power supply current I0 is smaller than the second threshold value Ith2 (I0 <Ith2, step 204: NO), a predetermined gradual change amount β is added to the duty limit value Dlim, The duty limit value Dlim is gradually changed to a higher value, that is, a duty limit value gradual increase calculation for gradually increasing is executed (Dlim = Dlim + β, step 209).

  Next, the duty limit value calculation unit 36 determines whether or not the duty limit value Dlim after the gradual increase calculation is greater than or equal to the gradual increase upper limit value Dlim_Hi (step 210), and is greater than or equal to the gradual increase upper limit value Dlim_Hi. In (Dlim ≧ Dlim_Hi, step 210: YES), the value of the duty limit value Dlim is set to the gradually increasing upper limit value Dlim_Hi (Dlim = Dlim_Hi, step 211). In this embodiment, the gradual increase upper limit value Dlim_Hi is a preset constant. Further, when the duty limit value Dlim is smaller than the gradual increase upper limit value Dlim_Hi (Dlim <Dlim_Hi, step 210: NO), the process of step 211 is not executed. Then, the duty limit value calculation unit 36 outputs the duty limit value Dlim calculated by the execution of steps 209 to 211 to the duty ratio limit unit 32 (step 208).

  As described above, the duty limit value calculation unit 36 according to the present embodiment executes the duty limit value Dlim changing process shown in steps 201 to 211 at predetermined intervals. Thus, the maximum voltage is applied to the motor 13 while suppressing the power supply current I0 to the extent that the first threshold value Ith1 corresponding to the occurrence of overcurrent is not exceeded.

  That is, as shown in FIG. 5, when the power supply current I0 exceeds the second threshold value Ith2, the duty ratio D rises and falls according to the change of the duty limit value Dlim, so that the power supply current I0 becomes an overcurrent. It moves up and down in a range not exceeding the first threshold value Ith1 corresponding to the occurrence. As a result, as shown in FIG. 6, even when the power supply voltage V0 exceeds a specified value (in this case, 12V), the maximum current can be supplied while suppressing the occurrence of overcurrent. It has become. The situation where the power supply voltage V0 exceeds the specified value includes, for example, the case of cranking at engine start.

As described above, according to the present embodiment, the following operations and effects can be obtained.
(1) A second threshold value Ith2 having a value lower than the first threshold value Ith1 corresponding to the occurrence of an overcurrent at which the motor control is to be stopped is set as a threshold value related to the power supply current I0 serving as a basis for overcurrent detection. . When the detected power supply current I0 becomes equal to or greater than the second threshold value Ith2, control is performed to reduce the voltage applied to the motor 13.

  That is, as long as no short circuit failure has occurred in each switching element constituting the drive circuit 20, the value of the power supply current I0 can be reduced by reducing the voltage applied to the motor 13. Therefore, as described above, when the power supply current I0 is lower than the first threshold value Ith1 corresponding to the occurrence of overcurrent, the power supply voltage V0 and the temperature Tmp of the motor 13 (around) are reduced by reducing the power supply current I0. Exceptional overcurrent caused by the change of can be suppressed. As a result, the value of the first threshold value Ith1 at which the motor control should be stopped is optimized, that is, a value that does not take into account the occurrence of the exceptional overcurrent, while improving the accuracy of the overcurrent detection and stably. Motor control can be executed.

  (2) The microcomputer 21 includes a duty ratio limiter 32 that limits the value of the duty ratio D within a predetermined range, and a duty limit value calculator 36 that calculates the duty limit value Dlim that is the upper limit. The voltage applied to the motor 13 is reduced by changing the duty limit value Dlim by the duty limit value calculator 36.

According to the said structure, the said overcurrent suppression can be added easily, without affecting the control system at the time of normal.
(3) The duty limit value calculation unit 36 calculates the duty limit value Dlim every predetermined period. Then, the duty limit value Dlim is reduced stepwise by subtracting a predetermined constant (gradual change amount α) for each cycle.

  According to the above configuration, it is possible to suppress the occurrence of steep torque fluctuations by making the current change gentle. As a result, good steering feeling can be ensured even when overcurrent suppression control is executed.

(4) A lower limit is set for the change (gradual decrease) of the duty limit value Dlim by the duty limit value calculation unit 36.
That is, by gradually decreasing the duty limit value Dlim until the detected power source current I0 becomes lower than the second threshold value Ith2, in some cases, the duty limit value Dlim, that is, the duty ratio D ′ after the limit process is set. It may decrease more than necessary. If the duty ratio D ′ becomes “0%”, the steering angle based on the motor drive, that is, the ACT angle θta cannot be maintained, that is, a so-called steering-free state may occur.

  However, according to the above configuration, the duty ratio D ′ after the limiting process does not become less than the gradual decrease lower limit value Dlim_Lo. As a result, it is possible to stably continue the motor control while avoiding an excessive decrease in the applied voltage as described above.

(5) The duty limit value calculation unit 36 calculates a value estimated to generate the power supply current I0 corresponding to the second threshold value Ith2 as the gradual decrease lower limit value Dlim_Lo.
According to the above configuration, even when overcurrent suppression control is executed, the maximum voltage can be applied to the motor 13 within a range that does not exceed the reference first threshold value Ith1.

  (6) The duty limit value calculation unit 36 estimates the resistance value R of the motor 13 based on the power supply voltage V0 and the temperature Tmp of the motor 13 (around). Then, the duty limit value calculation unit 36 calculates the gradual decrease lower limit value Dlim_Lo based on the estimated resistance value R and the power supply voltage V0.

According to the above configuration, it is possible to more accurately determine a value estimated to generate the power supply current I0 corresponding to the second threshold value Ith2.
In addition, you may change this embodiment as follows.

In the present embodiment, the voltage applied to the motor 13 is reduced by changing the duty limit value Dlim by the duty limit value calculator 36. However, the present invention is not limited to this, and the duty ratio calculation in the duty ratio calculation unit 31 may be changed, or may be performed by other configurations such as limiting the voltage command value V *.
In the present embodiment, the duty limit value Dlim is reduced stepwise by subtracting a predetermined constant (gradual change amount α) every period, that is, gradually reduced. However, the present invention is not limited to this, and it may be configured to reduce at a time.

In the present embodiment, the gradual decrease lower limit value Dlim_Lo is obtained by calculation, but a predetermined value may be set in advance as the gradual decrease lower limit value Dlim_Lo.
In the present embodiment, the gradual change amount α when the duty limit value Dlim is reduced is a predetermined constant. However, the present invention is not limited to this, and the gradual change amount α may be obtained by calculation. For example, when the calculation cycle of the duty limit value Dlim is shorter than the overcurrent determination cycle, as shown in FIG. 7, when the power supply current I0 exceeds the second threshold Ith2 (time t1), the next overcurrent determination cycle It is preferable to calculate the gradual change amount α so that the duty limit value Dlim decreases from the current value D1 to the gradual decrease lower limit value Dlim_Lo at the timing corresponding to (time t2). With such a configuration, the power supply current I0 (motor current) can be changed more smoothly, and the torque fluctuation can be made more gentle. As a result, it is possible to secure a better steering feeling during execution of the overcurrent suppression control. Such a calculation technique may be applied to the gradual change amount β when the duty limit value Dlim is increased.

  In the present embodiment, the present invention is embodied in the control means of the transmission ratio variable device 8 provided in the vehicle steering device, that is, the IFSECU 9. However, the present invention is not limited to this, and the present invention may be embodied in a motor control device used for applications other than the control means of the transmission ratio variable device.

The schematic block diagram of the steering apparatus for vehicles. The control block diagram of the steering device for vehicles. The flowchart which shows the process sequence of the fail safe control at the time of overcurrent detection. The flowchart which shows the process sequence of Duty limit value change. The wave form diagram which shows transition of each current and Duty ratio at the time of overcurrent suppression control. Explanatory drawing which shows the effect of overcurrent suppression. Explanatory drawing which shows an example of the gradual change amount calculation at the time of reduction of Duty limit value.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Vehicle steering device, 8 ... Transmission ratio variable device, 9 ... IFSECU, 13 ... Motor, 16 ... In-vehicle power supply, 20 ... Drive circuit, 21 ... Microcomputer, 32 ... Duty ratio limiting part, 34 ... Overcurrent detection part, 35 ... Current sensor, 36 ... Duty limit value calculation unit, 37 ... Voltage sensor, 38 ... Temperature sensor, Lp ... Power supply path, I0 ... Power supply current, Ith1, Ith2 ... Threshold, D, D '... Duty ratio, Dlim ... Duty limit value, Dlim_Lo, gradually decreasing lower limit value, α, β, gradually varying amount, V0, power supply voltage, Tmp, temperature, R, resistance value.

Claims (8)

A drive circuit that is provided in the middle of a power supply path between the motor and a DC power supply to generate drive power to be supplied to the motor, a control unit that controls the operation of the drive circuit through output of a motor control signal, and Current detection means for detecting a power supply current supplied to the drive circuit, and the control means stops the supply of drive power to the motor when the detected power supply current is greater than or equal to a predetermined threshold value. A motor control device for controlling
When the detected power supply current is equal to or higher than a second threshold set to a value lower than the first threshold at which the supply of the driving power is to be stopped, the control means sets the applied voltage to the motor. Configured to control to reduce ,
The drive circuit is configured by a switching element that is turned on / off based on a duty ratio of a pulse signal input as the motor control signal, and the voltage applied to the motor is reduced through the control of the duty ratio. And
The control means sets an upper limit value for the duty ratio, and the duty ratio control for reducing the voltage applied to the motor is performed by changing the upper limit value,
A lower limit is set for the change of the upper limit value, and the control means changes the upper limit value so that the upper limit value decreases to a value corresponding to the lower limit,
The cycle for changing the upper limit value is set shorter than an overcurrent determination cycle for determining whether or not to stop the supply of drive power . The motor control device according to claim 1 ,
The said control means produces | generates the said motor control signal for every predetermined period, The change of the said upper limit is performed in steps for every said period, The motor control apparatus characterized by the above-mentioned. The motor control device according to claim 2 ,
Before SL control means at a timing corresponding to the next overcurrent determination period, so that the upper limit is reduced to a value corresponding to the lower limit, calculating a gradual change when to change the upper limit value in stages To do,
A motor control device. In the motor control device according to any one of claims 1 to 3 ,
The said control means calculates the value estimated that the power supply electric current equivalent to a said 2nd threshold value generate | occur | produces as a minimum in the change of the said upper limit value, The motor control apparatus characterized by the above-mentioned. The motor control device according to claim 4 ,
Temperature detecting means for detecting the temperature of the motor;
Voltage detecting means for detecting a power supply voltage of the DC power supply,
The control means estimates the resistance of the motor based on the detected temperature, and calculates a lower limit in changing the upper limit value based on the resistance and the power supply voltage;
A motor control device. The motor control device according to any one of claims 1 to 5,
The motor control device, wherein the upper limit value is increased when the detected power supply current is lower than a second threshold value. The transmission ratio variable apparatus which controls the motor of a drive source with the motor control apparatus as described in any one of Claims 1-6 . A vehicle steering apparatus comprising the transmission ratio variable device according to claim 7 .

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