JP2008118729A - Motor power steering system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a motor power steering system which can distribute the quantity of an applied current into two or more phases without applying a large current to a specified element, especially, a single phase. <P>SOLUTION: A steering system is equipped with a three-phase brushless motor 12 which gives steering supplementary power for mitigating the steering burden of an operator, and it controls the drive of the above motor 12, referring to the rotating angle θ of the motor so as to generate steering supplementary power geared to at least steering torque T. At this time, it switches the phase to which a large current is applied, by rotating the motor 12 a little by offsetting the rotating angle θ of the motor used for control of steering supplementary power, when it detects the motor 12 being in a stop state and that in a high load state, whereby it distributes the load from the motor 12 to a motor driving circuit. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electric power steering apparatus that applies a steering assist force to a steering system.

Conventionally, by estimating the temperature of the electric motor based on the value of the current flowing in the coil of the electric motor in different calculation modes in the rotating state and the stopped state of the electric motor, the motor temperature is independent of the rotating state of the electric motor. There is known a motor temperature estimation device that accurately estimates the above (see, for example, Patent Document 1).
Also, as a conventional electric power steering device, the three-phase current when the steering angle reaches the maximum steering angle is monitored, and if any of the three-phase currents reaches 90% or more of the maximum current value, the PWM duty It is known that heat generation of the drive element is reduced by reducing the ratio (for example, Patent Document 2).
JP 2003-284375 A JP 2005-289296 A

However, in the motor temperature estimation device described in Patent Document 1, overheating protection can be performed by estimating the temperature of an element that generates heat depending on whether or not the motor is rotating, but prevents overheating of the element itself. It is not possible.
In the electric power steering device described in Patent Document 2, excessive energization to one phase that occurs in steering at the maximum steering angle is reduced by reducing the PWM duty ratio. Although the abnormal overheating of a specific element can be prevented, the effect of dispersing the heat generation part is small.

  Therefore, an object of the present invention is to provide an electric power steering device that can disperse the amount of energization current into two or more phases without energizing a specific element, particularly a single phase, with a large current.

  In order to solve the above problems, an electric power steering apparatus according to claim 1 is an electric motor that applies a steering assist force to reduce a steering burden on a driver to a steering system, and a motor that detects a rotation angle of the electric motor. A steering assist command value is calculated based on at least the steering torque detected by the steering torque detecting means, a steering torque detecting means for detecting a steering torque transmitted to the steering system, and the calculated steering assist command. An electric power steering device comprising: motor control means for performing drive control of the electric motor based on the value and the motor rotation angle detected by the motor rotation angle detection means, wherein the electric motor is in a stopped state A motor stop state detection means for detecting that the load is present and a load distribution state from the electric motor to the electric motor drive circuit Load distribution state detection means, wherein the motor control means detects that the electric motor is stopped by the motor stop state detection means, and the load distribution state detection means detects the electric motor from the electric motor. Load distribution processing means for distributing the load from the electric motor to the electric motor drive circuit when it is detected that the load distribution state is a high load state between the drive circuit and the drive circuit. Yes.

According to a second aspect of the present invention, there is provided the electric power steering apparatus according to the first aspect, wherein the load distribution processing unit sets a predetermined offset value with respect to the motor rotation angle detected by the motor rotation angle detection unit. In addition, the motor drive control is configured to be added.
The electric power steering apparatus according to a third aspect is the invention according to the first aspect, wherein the load distribution processing means adds a predetermined offset value to the steering torque detected by the steering torque detecting means. The motor drive control is performed.

According to a fourth aspect of the present invention, there is provided the electric power steering apparatus according to the second or third aspect, wherein the load distribution processing unit has a maximum offset value according to the load distribution state detected by the load distribution state detection unit. It is characterized by setting.
Furthermore, the electric power steering apparatus according to claim 5 is characterized in that, in the invention according to claim 4, the maximum offset value is set according to the number of phases of the electric motor.

According to a sixth aspect of the present invention, in the electric power steering apparatus according to the fourth or fifth aspect of the invention, the load distribution processing unit includes a gradual change unit that gradually changes the offset addition value to the maximum offset value. It is characterized by that.
Furthermore, the electric power steering device according to claim 7 is the invention according to claim 6, wherein the gradual change means adds a small offset value when the rate of change of the motor rotation angle is not more than a predetermined value. The offset addition value is gradually increased, and when the change rate of the motor rotation angle is larger than a predetermined value, the minute offset value is decreased or made zero.

  Furthermore, the electric power steering device according to claim 8 is the load according to any one of claims 1 to 7, wherein the load distribution processing by the load distribution processing means is canceled when a predetermined condition is satisfied. It is characterized by comprising distributed processing cancellation means.

  An electric power steering device according to a ninth aspect is the invention according to any one of the second to eighth aspects, wherein the electric motor has reached a steering limit and has been stopped, or the load Load distribution processing prohibiting means for prohibiting load distribution processing by the load distribution processing means when the position of the electric motor after adding the maximum offset value determined by the distribution processing means is expected to reach a steering limit. It is characterized by.

  Furthermore, the electric power steering apparatus according to claim 10 is the invention according to any one of claims 2 to 8, wherein the load distribution processing means determines that the electric motor has reached a steering limit and has stopped. If the position of the electric motor after adding the maximum offset value determined by the load distribution processing means is expected to reach the steering limit, the offset value added in the load distribution process is opposite to the steering limit. It is characterized by setting the direction.

  According to the electric power steering device of the present invention, when it is determined that the electric motor is in a stopped state and a high load state, the phase in which a large current is passed can be switched by slightly rotating the electric motor. In particular, it is possible to prevent local overheating between the elements of the motor drive circuit from the single-phase coil without deteriorating the steering feeling, especially by preventing a large current from being continuously applied to the single phase. And the effect of dispersing the heat generating portion can be obtained.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is an overall configuration diagram showing an embodiment of an electric power steering apparatus according to the present invention.
In the figure, reference numeral 1 denotes a steering wheel, and 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 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 connected to the output shaft 2b, and a three-phase brushless motor 12 as an electric motor that is connected to the reduction gear 11 and generates a steering assist force for the steering system. Yes.
The torque sensor 3 detects a steering torque applied to the steering wheel 1 and transmitted to the input shaft 2a, and a torsional angle displacement of a torsion bar (not shown) in which the steering torque is interposed between the input shaft 2a and the output shaft 2b. The torsional angular displacement is detected by, for example, a potentiometer.

  Further, as shown in FIG. 2, the three-phase brushless motor 12 has a U-phase coil Lu, a V-phase coil Lv, and a W-phase coil Lw connected at one end to form a star connection, and the coils Lu, Lv, and Lw The other end is connected to the steering assist control device 20, and motor drive currents Iu, Iv, and Iw are individually supplied. In addition, the three-phase brushless motor 12 includes a rotor position detection circuit 13 as a motor rotation angle detection unit that includes a resolver, an encoder, and the like that detect the rotation position of the rotor.

  As shown in FIG. 2, the steering assist control device 20 receives the steering torque T detected by the torque sensor 3 and the vehicle speed detection value Vs detected by the vehicle speed sensor 21 and is detected by the rotor position detection circuit 13. Is output from the motor current detection circuit 22 that detects the motor drive currents Iu, Iv, and Iw supplied to the phase coils Lu, Lv, and Lw of the three-phase brushless motor 12. The phase current detection values Iud, Ivd and Iwd are input.

  The steering assist control device 20 calculates a steering assist target current value based on the steering torque T, the vehicle speed detection value Vs, and the motor rotation angle θ, and outputs motor voltage command values Vu, Vv, and Vw, for example. The control arithmetic device 23 configured, a motor drive circuit 24 configured by a field effect transistor (FET) that drives the three-phase brushless motor 12, and phase voltage command values Vu, Vv, and Vw output from the control arithmetic device 23. And an FET gate drive circuit 25 for controlling the gate current of the field effect transistor of the motor drive circuit 24. This steering assist control device 20 corresponds to a motor control means.

As shown in FIG. 3, the control arithmetic unit 23 determines the current command values of the vector control d and q components using the excellent characteristics of vector control, and then sends the current command values to the respective excitation coils Lu to Lw. A vector control phase command value calculation circuit 30 that converts and outputs the corresponding phase current command values Iu ^* , Iv ^*, and Iw ^* , and each phase current command value Iu that is output from the vector control device command value calculation circuit 30 ^A current control circuit 40 that performs current feedback processing using ^* , Iv ^* and Iw ^* and motor phase current detection values Iud, Ivd, and Iwd detected by the motor current detection circuit 22 is provided.

As shown in FIG. 3, the vector phase command value calculation circuit 30 receives the steering torque T detected by the torque sensor 3 and the vehicle speed Vs detected by the vehicle speed sensor 21, and based on these, the steering assist current command value I _M ^{* Based} on the steering assist current command value calculation unit 31 for calculating ^* , the actual motor rotation angle θ detected by the rotor position detection circuit 13, and the motor phase current detection values Iud, Ivd and Iwd detected by the motor current detection circuit 22. The motor angle output unit 32 for outputting the motor rotation angle θm used for the control, and the motor rotation angle θm output by the motor angle output unit 32 is converted into the electrical angle θe and output, and the electrical angle θe is differentiated. an electric angle conversion unit 33 for outputting an electrical angular velocity .omega.e, the d-axis command current calculating portion 34 for calculating a d-axis command current Id ^* based on the steering assist current command value I _M ^* and the electrical angular velocity .omega.e, electrostatic A d-q axis voltage calculation unit 35 that calculates the d-axis voltage ed (θ) and the q-axis voltage eq (θ) based on the angle θe, and the d-axis voltage ed (θ), the q-axis voltage eq (θ), and d A q-axis command current calculation unit 36 that calculates a q-axis command current Iq ^* based on the axis command current Id ^* and the steering auxiliary current command value I _M ^* , and a d-axis command output from the d-axis command current calculation unit 34 A two-phase / three-phase conversion unit 37 that converts the current Id ^* and the q-axis command current Iq ^* output from the q-axis command current calculation unit 36 into three-phase current command values Iu ^* , Iv ^*, and Iw ^*. ing.

Further, the current control circuit 40 is a motor that flows in the phase coils Lu, Lv, Lw detected by the current detection circuit 22 from the current command values Iu ^* , Iv ^* , Iw ^* supplied from the vector control phase command value calculation unit 30. Subtractors 41u, 41v, and 41w for subtracting phase current detection values Iud, Ivd, and Iwd to obtain phase current errors ΔIu, ΔIv, and ΔIw, and proportional-integral control for the obtained phase current errors ΔIu, ΔIv, and ΔIw To calculate the command voltages Vu, Vv, Vw, and pulse width modulation (corresponding to the field effect transistors Qua to Qwb of the motor drive circuit 24 based on the calculated command voltages Vu, Vv, Vw ( PWM) 43 that forms signals PWMua to PWMwb.

Then, the pulse width modulation signals PWMua to PWMwb output from the PWM control unit 43 are supplied to the FET gate drive circuit 25.
In this manner, steering assist force control is performed to drive and control the motor with reference to the motor rotation angle θm in order to generate the steering assist force according to the steering torque T and the vehicle speed detection value Vs. The motor rotation angle θm is output from the motor angle output unit 32. In the present embodiment, the motor angle output unit 32 is used by the rotor position detection circuit 13 in the normal state where the three-phase brushless motor 12 is not stopped. The detected actual motor rotation angle θ is directly output as the motor rotation angle θm, and the motor is driven and controlled based on the output.

On the other hand, in the high load state where the three-phase brushless motor 12 is stopped and a large current is applied, the motor angle output unit 32 adds a predetermined offset value to the normal angle (motor actual rotation angle θ). The motor rotation angle θm is output, and the motor is driven and controlled based on this.
FIG. 4 is a block diagram illustrating a detailed configuration of the motor angle output unit 32. Here, the switches A and B are in a state indicated by a solid line when the high load state detection signal F is not input from the phase current monitoring unit 52 described later, and the high load state detection signal is output from the phase current monitoring unit 52. When F is input, the state is switched to a state indicated by a broken line.

  The motor stop determination unit 51 determines whether or not the three-phase brushless motor 12 is stopped based on the actual motor rotation angle θ, and outputs a motor stop state flag MS. Here, when the rate of change of the actual motor rotation angle θ is equal to or less than a predetermined value for a predetermined time, it is determined that the motor is stopped and the motor stop state flag MS is set to “1”. Set to, and output this. In other cases, the motor stop state flag MS is reset to “0” and output.

  In the phase current monitoring unit 52, based on the motor stop state flag MS output from the motor stop determination unit 51 and the motor phase current detection values Iud, Ivd and Iwd detected by the motor current detection circuit 22, the three-phase brushless It is determined whether or not the motor 12 is in a stopped state and a high load state. When it is determined that the motor 12 is in a stopped state and a high load state, a high load state detection signal F is output.

  The phase current monitoring unit 52 executes integration processing, which will be described later, based on the detected current value of each phase and outputs an integrated value of the phase current, and outputs from the integration processing units 52a to 52c. And a high load state determination unit 52d that determines whether the three-phase brushless motor 12 is in a stopped state and a high load state by executing a load state determination process, which will be described later, based on the integrated value. .

FIG. 5 is a flowchart showing the integration process procedure executed by each of the integration processors 52a to 52c.
This integration process is performed every predetermined time (for example, 1 msec). First, in step S1, an offset addition flag OFS set by an offset addition processing unit 53 described later is being offset added. It is determined whether or not it is set to “1”, and when OFS = 1, the process proceeds to step S2 to reset the integrated value I _add of the phase current, and then the integration process is terminated.

On the other hand, when it is determined in step S1 that the offset addition flag OFS has been reset to “0” meaning that the offset addition is not being performed, the process proceeds to step S3.
In step S3, it is determined whether or not the motor stop state flag MS output from the motor stop determination unit 51 is set to “1” which means that the motor is stopped. The process proceeds to step S4, and when MS = 0, the process proceeds to step S2.

In step S4, the deviation between the phase current detected in the previous sampling process (previous current detection value) and the phase current detected in the current sampling process (current current detection value), that is, the current change rate ΔI is calculated. The process proceeds to S5.
In step S5, the current detected value is stored in the memory and the process proceeds to step S6. Whether the current change rate ΔI calculated in step S4 is equal to or less than a predetermined change rate threshold value ΔI _TH (for example, ± 1A). Determine. When the current change rate ΔI is equal to or less than the change rate threshold value ΔI _TH , the process proceeds to step S7, and when the current change rate ΔI is greater than the change rate threshold value ΔI _{TH, the} process proceeds to step S2.

Here, the change rate threshold value ΔI _TH is determined by the detection accuracy of the current detection value. When the current change rate ΔI remains at a change rate equal to or less than the change rate threshold value ΔI _TH , a high load current is applied to the specific phase. Set to a value that can be judged to be.
In step S7, it is determined whether or not the absolute value | I | of the current detection value this time is equal to or greater than a predetermined current threshold I _TH . When | I | ≧ _ITH , the process proceeds to step S8. When | I | < _ITH , the process proceeds to step S2.

Here, the current threshold value I _TH is set to an upper limit value (for example, 10 A) of current at which each part (or component) between the motor and the drive circuit is difficult to generate heat even when continuous energization is performed.
In step S8, the phase current detection values are integrated and the integrated value _Iadd is output, and then the integration process is terminated. That is, in this step S8, the total of the phase current after the motor is stopped is calculated.

Here, the absolute value of the present current detection value is | I |, but has been described for the case of integration when it is more than the current threshold I _TH, dare without so integrating the detected current value exceeds the current threshold I _TH, this The current detection value I may be integrated as it is.
FIG. 6 is a flowchart showing a load state determination processing procedure executed by the high load state determination unit 52d.

  This load state determination process is performed every predetermined time (for example, 1 msec). First, in step S11, an offset addition flag OFS set by an offset addition processing unit 53 described later is offset addition. It is determined whether it is set to “1” meaning that it is in the middle, and when OFS = 1, the load state determination process is terminated as it is.

On the other hand, when it is determined in step S11 that the offset addition flag OFS has been reset to “0” meaning that the offset addition is not being performed, the process proceeds to step S12.
In step S12, sort processing is performed on the integrated values Iu _add , Iv _add and Iw _{add of} the phase currents calculated by the integrating processors 52a to 52c, respectively, and the maximum integrated value is selected, and the process proceeds to step S13.

In step S13, it is determined whether or not the maximum integrated value selected in step S12 is equal to or greater than a predetermined high load determination threshold value. When the maximum integrated value ≧ the high load determination threshold value, the three-phase brushless motor 12 is stopped. If the maximum integrated value <the high load determination threshold value, the load state determination process is terminated as it is.
Here, the high load determination threshold value is set to an integrated current amount at which each portion (or component) between the motor and the drive circuit is likely to generate heat when continuously energized.

In step S14, the high load state detection signal F is output, the process proceeds to step S15, the maximum offset value of the motor rotation angle is determined, and the load state determination process is terminated.
Here, the maximum offset value is set in accordance with a high load state (amount of integrated values) of the motor and the number of phases of the motor. In the case of a three-phase motor as in the present embodiment, an electrical angle of 60 deg is set as a minimum, and an integer multiple of 60 deg is set to a maximum offset so as to ensure phase commutation as the load is higher (the integrated value is larger). Set as a value. At this time, it is advisable to prevent energization of the specific phase again by energization control to the motor by the angle after application of the maximum offset value.

In the offset addition processing unit 53 of FIG. 4, when the high load state determination unit 52d determines that the motor is in a stopped state and a high load state, a motor rotation angle θm obtained by adding an offset value to the motor actual rotation angle θ. Is output.
FIG. 7 is a flowchart showing an offset addition processing procedure executed by the offset addition processing unit 53.

  This offset addition process is performed every predetermined time (for example, 1 msec). First, in step S21, it is determined whether or not the high load state detection signal F is output from the high load state determination unit 52d. Determine. When the high load state detection signal F is output, it is determined that the motor is stopped and is in a high load state, and the process proceeds to step S22. When it is not output, the offset addition process is terminated.

In step S22, it is determined whether or not the offset addition flag OFS is set to “1” which means that offset addition is being performed. If OFS = 0, it is determined that the offset addition is not being performed and step S23 is performed. Migrate to
In step S23, the theta current motor rotation angle stored in the memory as the motor rotation angle (initial angle) theta ₀ at offset addition process starts, the process proceeds to step S24.

In step S24, it calculates the target motor rotational angle θt obtained by adding the maximum offset value set in the high-load state determining unit 52d in the initial angle theta _0. This target motor rotation angle θt corresponds to the final target angle of the motor rotation angle θm in the offset addition process.
Next, in step S25, an offset addition process is performed on the current motor rotation angle θ. Specifically, the current motor rotation angle θ is offset by a minute angle Δθ _OFS , which is output as the motor rotation angle θm, and the process proceeds to step S26. Here, the minute angle offset value (± Δθ _OFS ) is an angle amount that does not give the driver a feeling of strangeness by assist control using the offset motor rotation angle θm, and is set to the target motor rotation angle θt. Set in consideration of the addition period until it reaches.

  Direction to offset the motor rotational angle θ, which may be kept as one in which either, so that the motor rotational angle θ does not exceed the steering limit as a result of the offset of the motor rotational angle θ for load balancing For example, in order to prevent the angle from being advanced in only one direction by causing the motor current to phase-commutate, in the present embodiment, settings are made as shown in Table 1, for example.

The conditions for offsetting the motor rotation angle and causing the motor current to phase commutate to perform load distribution are not limited to those in Table 1 above, but the optimum pattern according to the characteristics of the electric power steering device. Is preferably determined.
In step S26, the angle θ _OFS after adding the minute angle offset value Δθ _OFS to the current motor rotation angle θ is stored in the memory, and the process proceeds to step S27.

In step S27, the offset addition timer T _OFS for measuring the timing of offset addition is initialized, and in step S28, the offset addition flag OFS is set to “1”, and then the offset addition processing is ended.
On the other hand, when it is determined in the step S22 that OFS = 1, it is determined that the offset is being added, and the process proceeds to step S29.

In step S29, it is determined whether or not the offset addition cancellation condition is satisfied. If the offset addition cancellation condition is not satisfied, the process proceeds to step S30. If the offset addition cancellation condition is satisfied, the process proceeds to step S35 described later. Transition.
Here, the state where the offset addition cancellation condition is satisfied indicates a case where so-called phase commutation is performed in which a phase in which current is supplied to the motor is switched.

In step S30, it is determined whether or not the offset addition timer T _OFS is equal to or longer than a predetermined time T _TH (eg, 100 msec). If T _OFS ≧ T _TH , the process proceeds to step S31, and T _OFS <T _TH . If there is, the offset addition process is terminated.
In step S31, it is determined whether or not the current motor rotation angle θ matches the target angle θ _OFS after addition of the minute angle offset stored in the memory. If θ = θ _OFS , the process proceeds to step S32. When θ ≠ θ _OFS , the process _proceeds to step S34 described later.

In step S32, an offset addition process is performed on the current motor rotation angle θ, the result is output as the motor rotation angle θm, and the process proceeds to step S33.
At this time, it is determined whether or not the motor rotation speed ω is equal to or less than a predetermined value ω _TH . If ω ≦ ω _TH , a minute angle offset value Δθ _OFS is added to the current motor rotation angle θ. Is output as the motor rotation angle θm. In this way, when ω ≦ ω _TH , the offset addition value (angle added to the initial angle θ ₀ ) is gradually increased by the minute angle Δθ _OFS .

On the other hand, when ω> ω _TH , an offset value smaller than the minute angle offset value Δθ _OFS is added to the current motor rotation angle θ, and this is output as the motor rotation angle θm. In this way, the offset addition process is performed by reducing the offset value to be added from the normal offset value (Δθ _OFS ). If ω> _ωTH , the offset value may be “0”.
Here, the predetermined value ω _TH is set to a motor rotation speed at which the motor current is expected to result in phase commutation.

In step S33, the angle θ _OFS after adding the minute angle offset value Δθ _OFS to the current motor rotation angle θ is stored in the memory, and the process _proceeds to step S34.
In step S34, the offset addition timer T _OFS is initialized, and then the offset addition process is terminated.
In step S35, the offset addition flag OFS is reset to “0” and the offset addition timer T _OFS is initialized, and then the offset addition process is terminated.

In FIG. 4, the motor stop determination unit 51 corresponds to the motor stop state detection unit, the phase current monitoring unit 52 corresponds to the load distribution state detection unit, and the offset addition processing unit 53 corresponds to the load distribution processing unit.
In FIG. 7, the processes in steps S25, S26, and S30 to S33 correspond to the gradual change means, and the processes in steps S29 and S35 correspond to the load distribution process release means.

Next, the operation and effect of the first embodiment will be described.
Assuming that the vehicle is turning on a curved road and the three-phase brushless motor 12 is not in a stopped state, the motor stop determination unit 51 outputs a motor stop state flag MS = 0. Thereby, in the integration processing units 52a to 52c, No is determined in step S3 in FIG. 5, the process proceeds to step S2, and the integrated value I _{add of} each phase current is reset. Further, since the high load state determination unit 52d determines No in step S13 of FIG. 6, the high load state detection signal F is not output. Therefore, the switches A and B in FIG. 4 are in a state indicated by solid lines, and the motor angle output unit 32 outputs the actual motor rotation angle θ detected by the rotor position detection circuit 13 as it is as the motor rotation angle θm. Auxiliary control is implemented.

Therefore, the steering arithmetic unit 23 determines each phase current command value Iu ^* based on the steering torque T detected by the torque sensor 3, the vehicle speed Vs detected by the vehicle speed sensor 21, and the motor rotation angle θ detected by the rotor position detection circuit 13 ^. , Iv ^* and Iw ^* are calculated, and current feedback processing is performed using the phase current command values Iu ^* , Iv ^* and Iw ^* and the motor current detection values Iud, Ivd and Iwd detected by the motor current detection circuit 22. The phase voltage commands Vu, Vv and Vw are calculated. Then, PWM signals PWMua to PWMwb calculated based on the phase voltage commands Vu, Vv and Vw are output to the FET gate drive circuit 25.

The FET gate drive circuit 25 controls the gate current of the field effect transistor of the motor drive circuit 24 based on the PWM signal. As a result, the torque generated by the three-phase brushless motor 12 is converted into the rotational torque of the steering shaft 2 via the reduction gear 11, and the driver's steering force is assisted.
From this state, when a large current is continuously applied to a specific phase, and the rate of change of the motor rotation angle θ is equal to or less than a predetermined value for a predetermined time, the motor stop determination unit 51 sets the motor stop state flag MS = 1. Output. Then, the integration value I _add of each phase current is calculated by the integration processing units 52a to 52c. At this time, assuming that a large current is continuously applied to the U phase of the three-phase brushless motor 12, the high load state determination unit 52d performs an integrated value of the U phase current in the sorting process in step S12 of FIG. Iu _add is selected as the maximum integrated value. If this maximum integrated value is greater than or equal to the high load determination threshold value, the process proceeds from step S13 to step S14, where it is determined that the three-phase brushless motor 12 is in the stopped state and in the high load state, and in step S14 the high load is determined. A state detection signal F is output.

Therefore, the switches A and B in FIG. 4 are in a state indicated by broken lines, and the motor angle output unit 32 outputs the output result of the offset addition processing unit 53 as the motor rotation angle θm.
Since the high load state detection signal F is output, the offset addition processing unit 53 first determines Yes in step S21 of FIG. 7 and proceeds to step S22. At this time, since the offset addition process is not started and the offset addition flag OFS = 0, the process proceeds from step S22 to step S23, and the current motor rotation angle θ is set to the motor rotation angle at the start of the offset addition process. (Initial angle) θ ₀ is stored in the memory. Then, in step S24, the calculated target motor rotational angle θt based on the maximum offset value and the initial angle theta ₀ according to the load state of the three-phase brushless motor 12, and then proceeds to step S25, the motor rotation angle theta On the other hand, a value obtained by adding the minute angle offset value Δθ _OFS is output as the motor rotation angle θm.

Thus, the steering calculation device 23 performs steering based on the steering torque T detected by the torque sensor 3, the vehicle speed Vs detected by the vehicle speed sensor 21, and the motor rotation angle θm after offset addition output from the offset addition processing unit 53. Auxiliary control is implemented.
Thereafter, by adding a minute angle Δθ _OFS to the actual motor rotation angle θ every predetermined time T _TH, the motor drive control is performed by incrementally adding an offset toward the target motor rotation angle θt. At this time, even if the process of changing the angle step by step is a minute angle, the angle used in the motor drive control is randomly updated without confirming whether the actual motor rotation angle θ follows. Since the magnetic field vector may deviate and cause torque fluctuation (in some cases, unintended steering assistance), the actual motor rotation angle θ follows the target angle θ _OFS after adding the minute angle offset in step S31. Perform offset addition while confirming that

  As described above, the motor is driven with a value obtained by adding the minute offset value to the actual angle θ, and the motor rotation angle θ detected by the rotor position detection circuit 13 reaches the target motor rotation angle θt calculated in the step S24. When the phase commutation of current is performed, the offset release condition is satisfied and it is determined Yes in step S29, so the offset addition process is terminated and the normal steering assist control is resumed.

As described above, when it is determined that the three-phase brushless motor 12 is in the stopped state and the high load state, the steering assist control is performed by adding a small offset value Δθ _OFS to the actual motor rotation angle θ used for the steering assist control. And by slightly rotating the actual motor rotation angle θ of the motor 12, the phase (between the coil and the driving element) in which a large current is energized and becomes a high load can be switched as a result. Can be realized.

Also, when offsetting the motor rotation angle θ, by repeating the process of adding the minute angle offset value Δθ _OFS to the actual motor rotation angle θ and changing the actual motor rotation angle θ to the target angle θ _OFS , Since the actual motor rotation angle θ is changed very gently to the final target angle θt, it is possible to reliably distribute the load without giving a sense of incongruity to the steering feeling.

Furthermore, the offset value added to the motor rotation angle θ is changed according to the motor rotation speed ω. That is, when the motor rotation speed ω is equal to or less than the predetermined value ω _TH and the change in the motor rotation angle θ is small, the offset value is set to the normal minute angle Δθ _OFS , and the motor rotation speed ω is greater than the predetermined value ω _TH. In this case, the offset value is made smaller (or 0) than the normal minute angle Δθ _OFS .

In this way, when the motor rotation speed ω is relatively high, the motor rotation angle θ is updated without performing the offset addition process, resulting in phase commutation and limiting (or stopping) the offset addition process. )can do.
In addition, when the motor current phase commutation is performed, it is determined that the offset release condition is satisfied, so that the motor is rotated by the driver's steering operation or the road surface reaction force, resulting in energization of the motor. Even when the current is commutated, the offset release condition is satisfied, and it is possible to shift to normal steering assist control according to the driver's steering operation, and to reliably provide a steering assist without any sense of incongruity. It is possible to reliably distribute the load.

  By the way, in an inverter that controls a multiphase AC motor, when a large current is continuously supplied to a single phase, some elements generate abnormally heat. Therefore, there is a method of estimating the temperature of the element that generates heat based on the presence or absence of rotation of the motor and implementing overheat protection. However, in this case, overheating of the element itself cannot be prevented, and the time during which the steering assist control can be continued cannot be extended without limiting the maximum assist force as compared with when the motor rotates. Moreover, it is necessary to use a plurality of temperature estimation blocks, which is complicated.

One way to improve this is to reduce the PWM duty ratio from excessive energization to one phase (including drive elements and motors) that occurs during steering near the stopper end in order not to overheat certain elements. There is something to reduce. However, in this case, since the amount of current flowing in one phase is only reduced, the effect of dispersing the heat generation sites is small.
Further, although a limited area near the rack end is protected, the area where the protective operation is activated is unclear, which may cause a decrease in steering feeling performance. Furthermore, when the road surface friction resistance is large, the intended effect may not be obtained.

Also, during assembly work at the factory, there are things that assemble a brushless motor and resolver so that the three-phase current is less than the maximum current value near the stopper end, but in this case, the total man-hour for the work is (number of ECUs × The number of work steps per unit) is required, and in the case of mass production, the overall cost increases.
In contrast, in this embodiment, when the three-phase brushless motor 12 is determined to be in a stopped state and a high load state, the phase through which a large current is passed is switched by slightly rotating the motor 12. Local overheating of a one-phase coil / element or the like can be reliably prevented, and the load state can be distributed to each phase. Moreover, since the temperature estimation logic can be simplified, software can be simplified.

As described above, in the first embodiment, when it is determined that the electric motor is in the stopped state and in the high load state, the process of distributing the load from the electric motor to the electric motor drive circuit is performed. Thus, local overheating of a coil or element of a specific phase can be prevented.
Further, when it is determined that the electric motor is in a stopped state and in a high load state, the motor drive control is performed by adding a predetermined offset value to the motor rotation angle. Therefore, by slightly rotating the electric motor, With a simple configuration, it is possible to switch the phase in which a large current is energized reliably, preventing the energization of a specific phase continuously without deteriorating the steering feeling, It is possible to prevent local overheating of coils and elements, and to disperse the load state in each phase.

Furthermore, since the maximum offset value is set according to the load state of the electric motor, the motor rotation angle can be changed to the angle at which the phase commutation is performed reliably.
In addition, since the maximum offset value is set according to the number of phases of the electric motor, for example, in the case of a three-phase motor, it is possible to reliably perform phase commutation by setting an integer multiple of 60 deg to the maximum offset value. .

Furthermore, since the offset addition value is gradually changed to the maximum offset value, the electric motor can be rotated slowly, and the deterioration of the steering feeling due to the instantaneous rotation of the electric motor can be reliably prevented. Can do.
Further, when the motor rotation speed is less than or equal to a predetermined value, the offset addition value is increased by adding a minute angle offset value to the actual motor rotation angle, and when the motor rotation speed is greater than the predetermined value, the offset value to be added is Since the motor rotation speed is relatively large and the offset addition process is substantially unnecessary, the offset addition process can be limited or stopped when the motor rotation speed is relatively large. The load can be appropriately distributed according to the necessity of processing.

  Furthermore, since the load distribution process is canceled when a predetermined condition is satisfied, the motor rotates when a phase commutation of the motor current is performed or when the driver's steering operation or road reaction force is received. When the energizing current to the phase commutates, it is possible to cancel the offset addition process and prevent the offset addition process from being performed unnecessarily, and steering without a sense of incongruity according to the driver's steering Assist can be provided.

If the motor position after adding the maximum offset value is expected to reach the steering limit, the offset value to be added in the offset addition process is set in the direction opposite to the steering limit. It is possible to reliably prevent deterioration of the steering feeling due to the offset.
In the first embodiment, the case where the motor is determined to be in the stopped state and the high load state when the integrated value of the phase current is equal to or greater than the predetermined high load determination threshold has been described. When the current value or the average value of the phase current detected when determined to be equal to or greater than a certain value is greater than or equal to a certain value, it may be determined that the motor is in a stopped state and a high load state. Further, it may be determined that the motor is in a stopped state and in a high load state when the integrated value of the square of the phase current or the average value thereof is a certain value or more.

In the first embodiment, the case where the integrated value of the motor phase current is calculated after determining the motor stop state has been described. However, the integrated value is calculated from the state in which the rate of change of the motor rotation angle is equal to or less than a predetermined value. A value can also be calculated. Thereby, it is possible to more appropriately determine the high load state of the motor.
Further, in the first embodiment, the phase commutation completion flag is turned on when the offset addition cancellation condition is satisfied in step S29 of FIG. 7, and after the phase commutation completion flag is turned on, for example, 1 sec elapses. When a large current is supplied to the specific phase again, the offset direction in the next offset addition process can be determined based on Table 1 above.

In the first embodiment, when the offset addition process is executed in step S31 of FIG. 7, it is determined that the actual angle θ follows the target angle θ _OFS when θ = θ _OFS. However, even if there is a magnetic field vector deviation between the rotor and the stator of the motor 12, if the torque fluctuation caused by the magnetic field vector deviation does not give the driver a sense of incongruity, θ≈θ _OFS. Alternatively, the offset addition process may be executed.

In this case, if the release condition is satisfied during the offset addition process (Yes in step S29), the process of step S35 is executed, and then the deviation between the actual angle θ and the target angle θ _OFS is returned stepwise. Such processing can also be added.
In the first embodiment, when it is determined that the three-phase brushless motor 12 has reached the steering limit and has stopped, or when the maximum offset value is added, the motor position is expected to reach the steering limit. Load distribution processing prohibiting means for prohibiting the operation of the offset addition processing can be provided. Thereby, the offset addition process can be operated only under an appropriate condition, and the steering feeling can be further improved.

Furthermore, in the first embodiment, when it is determined that the three-phase brushless motor 12 has reached the steering limit and has stopped, the offset value added in the offset addition process is set in the direction opposite to the steering limit. You can also. Also in this case, the steering feeling can be further improved.
Further, in the first embodiment, the case where the current integration is not performed while the offset value is added to the actual angle for phase commutation has been described, but the offset addition for phase commutation is being performed. Also, it is possible to perform more effective load distribution processing by monitoring the load state of each phase by accumulating current values and changing the sign of the angle to be offset according to the situation.

Next, a second embodiment of the present invention will be described.
In the second embodiment, in the first embodiment described above, the motor is determined to be in a high load state when the integrated value of the phase current is equal to or greater than a certain value. When the value is above a certain value, it is determined that the motor is in a high load state.
That is, in the phase current monitoring unit 52 of the second embodiment, the torque detection value T detected by the torque sensor 3 is input and the load state determination process shown in FIG. 8 is executed. Except for the processing of the phase current monitoring unit 52, the same processing as that of the first embodiment described above is executed, and therefore the description will focus on the different parts of the processing.

First, in step S41 of FIG. 8, it is determined whether or not the offset addition flag OFS set by the offset addition processing unit 53 is set to “1” meaning that offset addition is being performed, and OFS = 1. If so, the load state determination process is terminated.
On the other hand, when it is determined in step S41 that the offset addition flag OFS has been reset to “0” meaning that the offset addition is not being performed, the process proceeds to step S42.

In step S42, it is determined whether or not the motor stop state flag MS output from the motor stop determination unit 51 is set to “1” which means that the motor is stopped. The process proceeds to step S43, and when MS = 0, the load state determination process is terminated as it is.
In step S43, the detected torque value T detected by the torque sensor 3 is read, and the process proceeds to step S44.

In step S44, it is determined whether or not the absolute value of the detected torque value T read in step S43 is equal to or greater than a predetermined torque threshold value T1. Here, the torque threshold T1 is set to a value that allows the driver to perform a large steering operation and determine that the three-phase brushless motor 12 is in a high load state.
When it is determined in this step S44 that | T | ≧ T1, it is determined that the three-phase brushless motor 12 is in a stopped state and a high load state, and the process proceeds to step S45, where | T | <T1. If it is determined, the load state determination process is terminated.

In step S45, the high load state detection signal F is output, the process proceeds to step S46, the offset value of the motor rotation angle is determined, and the load state determination process is terminated. Here, the offset value is set according to the high load state of the motor and the number of phases of the motor.
Next, operations and effects of the second embodiment will be described.
It is assumed that the vehicle is traveling straight ahead and the torque detection value T detected by the torque sensor 3 is substantially zero. In this case, even if the motor stop determination unit 51 determines that the three-phase brushless motor 12 is in the stopped state, the phase current monitoring unit 52 determines No in step S44 of FIG. Since it is determined that the phase brushless motor 12 is not in the high load state, the high load state detection signal F is not output.

Therefore, the switches A and B in FIG. 4 are in a state indicated by solid lines, and the motor angle output unit 32 outputs the actual motor rotation angle θ detected by the rotor position detection circuit 13 as it is as the motor rotation angle θm. Auxiliary control is implemented.
On the other hand, when the driver is performing a relatively large steering operation, the absolute value of the torque detection value T detected by the torque sensor 3 is equal to or greater than the predetermined value T1, so the motor stop determination unit 51 uses the three-phase brushless motor. If it is determined that 12 is in a stopped state, the phase current monitoring unit 52 determines Yes in step S44 of FIG. 8, and outputs a high load state detection signal F in step S45.

Accordingly, the switches A and B in FIG. 4 are in a state indicated by broken lines, and the motor angle output unit 32 outputs a value obtained by performing the offset addition process on the actual motor rotation angle θ as the motor rotation angle θm. Then, steering assist control is performed based on the motor rotation angle θm.
As described above, in the second embodiment, when the absolute value of the steering torque value when it is determined that the electric motor is in the stopped state is greater than or equal to the predetermined value, it is determined that the motor is in the high load state. Thus, the logic for determining the load state of the electric motor can be simplified.

Next, a third embodiment of the present invention will be described.
In the third embodiment, in the first and second embodiments described above, the motor energization phase is switched by offsetting the motor rotation angle used in the steering assist force control, whereas the steering assist force control is performed. The motor energization phase is switched by offsetting the steering torque used in FIG.

  That is, as shown in FIG. 9 for the specific configuration of the control arithmetic device 23 of the third embodiment, in the control arithmetic device 23 of the first and second embodiments described above, the motor angle output unit 32 is deleted, The electrical angle converter 33 outputs the electrical angle θe and the electrical angular velocity ωe based on the motor rotation angle θ (= θm) detected by the rotor position detection circuit 13. Further, when the steering torque T detected by the torque sensor 3 is input and it is determined that the three-phase brushless motor 12 is in a stopped state and a high load state, a steering torque output unit 38 that outputs a value obtained by offsetting the steering torque T. Add Other than that, the same processing as that in FIG. 3 is executed, and therefore, different portions of the processing will be mainly described.

In the steering torque output unit 38, whether or not the three-phase brushless motor 12 is in a stopped state and a high load state, similarly to the motor stop determination unit 51 and the phase current monitoring unit 52 of the first or second embodiment described above. Is determined, and the steering torque T detected by the torque sensor 3 is output to the steering assist current command value calculation unit 31 as it is.
On the other hand, when it is determined that the vehicle is in a stopped state and a high load state, a value obtained by multiplying the steering torque T detected by the torque sensor 3 by the gain G is output to the steering assist current command value calculation unit 31.

Here, when the motor rotational speed ω is “0”, the gain G is reduced with respect to its initial value (for example, G = 1) according to the time during which this state continues. If 0 <ω ≦ ω _TH , the previously calculated gain is maintained.
The gain G, using the rotational speed threshold omega _TH is smaller than the rotational speed threshold .omega.1, when the motor rotation speed omega is 0 ≦ ω ≦ ω1, to its initial value according to the time the condition persists smaller for the case the motor rotation speed omega is ω1 <ω ≦ ω _TH, it may be to maintain the gain calculated previously.

The gain multiplication process for the steering torque T is canceled (G = 1) when a predetermined high load state cancellation condition is satisfied. Here, the state where the high load state cancellation condition is satisfied means a state where the motor rotational speed ω is larger than the rotational speed threshold ω _TH .
When this high load state cancellation condition is satisfied, the gain G multiplied by the steering torque T detected by the torque sensor 3 is returned to “1”. When the gain G is returned to “1”, if there is a certain difference or more from the gain before the return, and if the gain G is instantaneously returned to “1”, there is a possibility that a steering discomfort may be caused. The gain G is gradually returned to “1” using functions such as the torque T, the gain continuation time, and the offset value.

Note that a rapid gain change may be prevented by using a gain G change limiter.
Next, operations and effects of the third embodiment will be described.
It is assumed that the rate of change of the motor rotation angle θ is “0” for a predetermined time and it is determined that the motor is in a stopped state. At this time, if the driver is performing a relatively large steering operation and the torque threshold value | T | of the steering torque T is greater than or equal to the predetermined value T1, the three-phase brushless motor 12 is in a stopped state and a high load state. It is judged.

At this time, since the motor rotation speed ω is “0”, the steering torque output unit 38 calculates the gain G to be smaller than the initial value and multiplies the steering torque T detected by the torque sensor 3 with the gain G. The value is output to the steering assist current command value calculation unit 31. Therefore, the steering assist force control is performed based on the steering torque T multiplied by the gain G and the vehicle speed Vs.
If the state of ω = 0 continues thereafter, the steering torque output unit 38 calculates the gain G to be gradually smaller than the initial value. As a result, the steering torque T output from the steering torque output unit 38 gradually increases with respect to the steering torque T detected by the torque sensor 3.

Thereafter, when the motor rotational speed ω gradually increases and exceeds the rotational speed threshold value ω _TH , it is determined that the high load state release condition is satisfied, and processing for returning the gain G to the initial value “1” is performed. Thus, the normal steering assist force control is restored, and the steering torque T detected by the torque sensor 3 is used as it is for the steering assist force control.
As described above, in the third embodiment, when it is determined that the electric motor is in the stopped state and the high load state, the electric motor is rotated by multiplying the steering torque used for the steering assist force control. It is possible to switch the phase through which a large current is passed with certainty with a simple configuration.

  In the third embodiment, the case where the amount of the steering torque T is gradually increased by gradually decreasing the gain G with respect to the initial value has been described. However, the gain G is increased with respect to the initial value. By gradually increasing the amount, the amount with respect to the steering torque T can be gradually increased. Further, the changing direction of the gain G can also be determined according to the changing direction of the steering torque T before the gain multiplication process.

1 is a schematic configuration diagram of a vehicle in an embodiment of the present invention. It is a block diagram which shows an example of a steering assistance control apparatus. It is a block diagram which shows the specific structure of the control arithmetic unit of FIG. It is a block diagram which shows the specific structure of the motor angle output part of FIG. It is a flowchart which shows the integration process performed in an integration process part. It is a flowchart which shows the load state judgment process performed in a high load state judgment part. It is a flowchart which shows the offset addition process performed with an offset addition process part. It is a flowchart which shows the load condition judgment process performed with the phase current monitoring part of 2nd Embodiment. It is a block diagram which shows the specific structure of the control arithmetic unit in 3rd Embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Steering wheel, 2 ... Steering shaft, 3 ... Torque sensor, 10 ... Steering assistance mechanism, 11 ... Reduction gear, 12 ... Three-phase brushless motor, 13 ... Rotor position detection circuit, 20 ... Steering assistance control device, 21 ... Vehicle speed Sensors 31... Steering auxiliary current command value calculation unit 32... Motor angle output unit 34... D-axis command current calculation unit 35 35 dq-axis voltage calculation unit 36 36 q-axis command current calculation unit 37. Phase / three-phase conversion unit, 38 ... steering torque output unit, 42 ... PI control unit, 43 ... PWM control unit, 51 ... motor stop determination unit, 52 ... phase current monitoring unit, 52a to 52c ... integration processing unit, 52d ... High load state determination unit, 53... Offset addition processing unit

Claims (10)

An electric motor for applying a steering assist force to reduce a steering burden on the driver to the steering system, a motor rotation angle detecting means for detecting a rotation angle of the electric motor, and a steering torque for detecting a steering torque transmitted to the steering system A steering assist command value is calculated based on the detection means and at least the steering torque detected by the steering torque detection means, and based on the calculated steering assist command value and the motor rotation angle detected by the motor rotation angle detection means, An electric power steering apparatus comprising: motor control means for performing motor drive control for driving and controlling an electric motor;
Motor stop state detection means for detecting that the electric motor is in a stopped state, and load distribution state detection means for detecting a load distribution state from the electric motor to the electric motor drive circuit, the motor control means, The load that is detected by the motor stop state detecting means that the electric motor is in a stopped state and the load distribution state detecting means is in a high load state from the electric motor to the electric motor drive circuit. An electric power steering apparatus comprising load distribution processing means for distributing a load from the electric motor to the electric motor drive circuit when it is detected that the electric power is in a distributed state.   The load distribution processing means is configured to perform the motor drive control by adding a predetermined offset value to the motor rotation angle detected by the motor rotation angle detection means. Item 4. The electric power steering device according to Item 1.   2. The load distribution processing unit is configured to perform the motor drive control by adding a predetermined offset value to the steering torque detected by the steering torque detection unit. The electric power steering device described in 1.   4. The electric power steering apparatus according to claim 2, wherein the load distribution processing unit sets a maximum offset value according to the load distribution state detected by the load distribution state detection unit.   The electric power steering apparatus according to claim 4, wherein the maximum offset value is set according to the number of phases of the electric motor.   6. The electric power steering apparatus according to claim 4, wherein the load distribution processing unit includes a gradual change unit that gradually changes an offset addition value to the maximum offset value.   When the change rate of the motor rotation angle is equal to or less than a predetermined value, the gradual change means gradually increases the offset addition value by adding minute offset values, and the change rate of the motor rotation angle is larger than the predetermined value. The electric power steering apparatus according to claim 6, wherein the minute offset value is reduced or made zero.   The electric power steering apparatus according to any one of claims 1 to 7, further comprising a load distribution process canceling unit that cancels a load distribution process by the load distribution processing unit when a predetermined condition is satisfied.   When it is determined that the electric motor has reached the steering limit and has stopped, or when the position of the electric motor after adding the maximum offset value determined by the load distribution processing means is expected to reach the steering limit The electric power steering apparatus according to any one of claims 2 to 8, further comprising load distribution processing prohibiting means for prohibiting load distribution processing by the load distribution processing means.   When the load distribution processing unit determines that the electric motor has reached a steering limit and has stopped, or the position of the electric motor after adding the maximum offset value determined by the load distribution processing unit is steered 9. The electric power steering apparatus according to claim 2, wherein when the limit is expected to be reached, an offset value added in the load distribution process is set in a direction opposite to the steering limit.

Images