JP2011088486A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device capable of reliably preventing a sense of congruity from being given to a driver without generating discontinuous output when differential compensation is made using a torque signal. <P>SOLUTION: Steering auxiliary control is usually performed based on a gain twice torque detection value obtained by multiplying a main torque detection value detected in a main torque detection part by n times, and the steering auxiliary control is performed based on the main torque detection value when the gain twice torque detection value is abnormal. When the gain twice torque detection value is abnormal, variable rate limiter processing for restricting the main torque detection value to a restriction value according to a variation amount of the main torque detection value in every predetermined period is performed by a torque restriction part. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

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

  As this type of electric power steering device, for example, a main torque input value obtained by A / D conversion of a main torque signal from a torque sensor, and a gain multiplied torque input value obtained by A / D conversion after multiplying the main torque signal by a first gain. And a steering assist force control means for controlling a motor that applies a steering assist force to the steering mechanism based on the sub-torque signal from the torque sensor, and an electric power steering apparatus that performs a fail-safe function. The control device includes a gain multiplier that multiplies the main torque input value by a second gain, and switch means that switches the output of the gain multiplier and the gain multiple torque input value to input to the steering assist force control device. A control device for an electric power steering device is known (for example, see Patent Document 1).

A steering torque detection means for detecting a steering torque input to the steering system and outputting a steering torque detection signal; an amplifier circuit for amplifying the steering torque detection signal output from the steering torque detection means; A control device for an electric power steering apparatus, comprising: a steering assist control unit that controls an electric motor that applies a steering assist force to the steering system based on an amplified steering torque signal amplified by an amplifier circuit; Amplifying circuit abnormality detecting means for detecting an abnormality is provided, and the steering assist control means detects steering abnormality without using the amplified steering torque signal of the amplifier circuit when the amplifier circuit abnormality detecting means detects abnormality of the amplifier circuit. There is also known a control device for an electric power steering device in which control is continued.
(For example, refer to Patent Document 2).

JP 2002-308136 A JP 2006-123775 A

In the conventional examples described in Patent Documents 1 and 2, the gain double torque detection signal including a digital value obtained by A / D converting the gain double torque detection signal obtained by amplifying the main torque signal by the amplifier circuit becomes abnormal. Sometimes, the steering assist control is continued using the main torque signal. However, since the main torque signal used for the steering assist control is the main torque signal after A / D conversion of the main torque signal input from the torque sensor, the A / D converter performs the A / D conversion. The resolution cannot be utilized to the maximum, and the resolution becomes coarser than that of the gain double torque signal amplified by the amplifier circuit. Therefore, normally, the torque signal is directly input to the steering assist command value calculation unit that calculates the steering assist command value, and the control responsiveness near the neutral point of the steering is improved to realize smooth and smooth steering. Therefore, it is also directly input to the center responsiveness control unit, and when the center responsiveness control unit performs the differential compensation function, it becomes overcompensation and discontinuous compensation by changing the main torque signal. There is an unsolved problem of outputting a value and giving the driver a sense of incongruity.
Therefore, the present invention has been made paying attention to the unsolved problems of the above-described conventional example, and when performing differential compensation using a torque signal, a discontinuous output is not generated and the driver feels uncomfortable. It is an object of the present invention to provide an electric power steering apparatus that can reliably prevent the occurrence of the problem.

  In order to achieve the above object, an electric power steering apparatus according to an aspect includes a torque detection apparatus including at least a main torque detection unit that detects torque transmitted to a steering system and outputs a main torque detection signal; A gain double torque output unit that outputs a gain double torque detection value obtained by multiplying the main torque detection signal by n times, a torque abnormality determination unit that detects abnormality of the gain double torque output unit, and the main torque detection signal for each predetermined period When it is determined by the torque limiting unit that outputs a torque limit output value limited according to the amount of change in the main torque detection signal and the torque abnormality detection unit, the gain multiple torque output unit is normal, When a gain double torque detection value is selected and it is determined that the gain double torque output unit is abnormal, a torque limit output value is selected. A selection unit; an electric motor that generates a steering assist force for the steering system; a steering assist command value control unit that calculates a steering assist command value based on at least a torque detection value selected by the torque selection unit; And a motor drive control unit that drives and controls the electric motor based on a steering assist command value.

In the electric power steering apparatus according to another aspect, the torque selection unit receives the main torque detection signal and the gain multiplied torque detection value after A / D conversion, and inputs the main torque detection signal after the A / D conversion. A value obtained by multiplying the torque detection value by n is used as a main torque detection signal.
Furthermore, an electric power steering apparatus according to another aspect is characterized in that the torque limiting unit is configured by a variable rate limiter.

Furthermore, in the electric power steering apparatus according to another aspect, the variable rate limiter is a value obtained by subtracting a gain multiplied main torque detection value before n periods corresponding to the gain multiple n from the current value of the main torque detection signal. Is divided by a gain multiple n to calculate a limit value, and the calculated limit value is added to the previous limit torque output value to calculate the limit torque output value.
Still further, in the electric power steering apparatus according to another aspect, the gain multiple torque output unit is characterized in that the gain multiple n is set to a value that can effectively use the resolution at the time of the A / D conversion. .

  According to the present invention, when the gain double torque output unit becomes abnormal, the steering assist control is continued using the main torque detection value. At this time, the main torque detection value for each predetermined period is determined by the torque limiting unit. When the limited torque output value limited according to the amount of change is used as the torque detection value, the rate of change of the torque detection value is suppressed and differential compensation is performed based on the torque detection value. By calculating the above, it is possible to reliably prevent the driver from feeling uncomfortable.

It is a schematic structure figure showing a 1st embodiment of the present invention. FIG. 2 is a block diagram illustrating a specific configuration of the controller in FIG. 1. It is a functional block diagram which shows the specific structure of a controller. It is a functional block diagram which shows the specific structure of the torque signal switching part of FIG. It is a characteristic diagram which shows a steering auxiliary current command value calculation map. It is a block diagram which shows the specific structure of a center response improvement part. It is a flowchart which shows an example of the torque signal selection processing procedure performed with a controller. It is a flowchart which shows an example of the steering assistance control processing procedure performed with a controller. It is a signal waveform diagram with which it uses for description of a variable rate limiter function.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram showing an embodiment of an electric power steering apparatus according to the present invention. In FIG. 1, 1 is a steering wheel, and a steering force applied by a driver to the steering wheel 1 is input. It is transmitted to a steering shaft 2 having a shaft 2a and an output shaft 2b. The steering shaft 2 has one end of the input shaft 2a connected to the steering wheel 1 and the other end connected to one end of the output shaft 2b via a steering torque sensor 3 as a steering torque detector.

The steering force transmitted to the output shaft 2 b is transmitted to the lower shaft 5 via the universal joint 4 and further transmitted to the pinion shaft 7 via the universal joint 6. The steering force transmitted to the pinion shaft 7 is transmitted to the tie rod 9 via the steering gear mechanism 8 to steer a steered wheel (not shown). Here, the steering gear mechanism 8 is configured in a rack and pinion type having a pinion 8a connected to the pinion shaft 7 and a rack shaft 8b meshing with the pinion 8a, and the rotational motion transmitted to the pinion 8a is transmitted to the rack shaft. In 8b, it is converted to a straight motion.
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 an electric motor 12 composed of, for example, a three-phase brushless motor as an electric motor that generates a steering assist force connected to the reduction gear 11. ing.

  The steering torque sensor 3 detects the steering torque applied to the steering wheel 1 and transmitted to the input shaft 2a. For example, the steering torque sensor 3 is a torsion bar (not shown) in which the steering torque is interposed between the input shaft 2a and the output shaft 2b. It is configured to convert to a torsional angular displacement and detect this torsional angular displacement with a non-contact magnetic sensor or the like. The steering torque sensor 3 includes a main torque detector 3M and a sub torque detector 3S. The main torque signal Tm and the sub torque signal Ts output from the main torque detection unit 3M and the sub torque detection unit 3S are input to the controller 14 to which electric power is supplied from the battery B through the ignition switch IG.

In addition to the steering torque T, the controller 14 includes a vehicle speed detection value Vs detected by the vehicle speed sensor 15, a motor rotation angle θm detected by the rotation angle sensor 19, and a motor current flowing in the electric motor 12 detected by the motor current detection circuit 20. The detection values Ia to Ic are also input, a steering assist current command value Iref for generating the steering assist force in the electric motor 12 according to the input torque detection value T and the vehicle speed detection value Vs is calculated, and the calculated steering assist command value Based on the Iref and the motor current detection value Im, the drive current supplied to the electric motor 12 is subjected to feedback control processing, and various compensation processing is performed based on the motor angular velocity ωm to drive the electric motor 12 after compensation. Iaref is calculated.
As shown in FIG. 2, the controller 14 receives a main torque detection signal output from the main torque detection unit 3M of the steering torque sensor 3 via a noise removing low-pass filter (LPF) 16a. It is input to 17 A / D conversion input terminals ta.

The main torque detection signal output from the main torque detection unit 3M is supplied to an amplification circuit 18 as a gain multiplication torque output unit, and is multiplied by a gain multiple n (n is an integer of 1 or more). The gain n-fold torque signal is input to the A / D conversion input terminal tb of the central processing unit 17 through a low-pass filter (LPF) 16b for noise removal.
Further, a sub-torque detection signal Ts output from the sub-torque detection unit 3S of the steering torque sensor 3 is input to the A / D conversion input terminal tc of the central processing unit 17 via the noise removing low-pass filter 16c.

  Further, the vehicle speed detection value Vs output from the vehicle speed sensor 15 is input to the central processing unit 17, and the motor rotation angle detected by the rotation angle sensor 19 such as a resolver that detects the rotation angle of the electric motor 12. θm is input to the A / D conversion input terminal td. Further, in the central processing unit 17, the motor current Im supplied to the electric motor 12 detected by the motor current detection circuit 20 is input to the A / D conversion input terminal te.

Here, a schematic configuration of the central processing unit 17 will be described with reference to a functional block diagram shown in FIG.
That is, the central processing unit 17 is input to the A / D converter 21a for A / D converting the main torque detection signal Tm input to the A / D conversion input terminal ta and to the A / D conversion input terminal tb. An A / D converter 21b for A / D converting the gain double torque detection signal Tnm input from the amplifier circuit 18, and a sub torque detection signal Ts input from the sub torque detector 3S input to the A / D conversion input terminal tc. Is input to the A / D converter 21c.

  Further, the central processing unit 17 receives the main torque detection signal Tmd, the gain double torque detection signal Tnmd, and the sub torque detection signal Tsd converted into digital signals by the A / D converters 21a, 21b, and 21c, and based on them. A torque sensor abnormality check unit 22 that performs a torque sensor abnormality check. When the correlation between the main torque detection signal Tmd and the sub torque detection signal Tsd is normal, the torque sensor abnormality check unit 22 determines that the steering torque sensor 3 is normal, for example, a logical value “0” indicating normality. "When the gain double torque detection signal Tnmd is within the allowable torque range, the main torque signal gain Gm is set to 0% and the gain double torque signal gain Gg is set to 100%. When the gain double torque detection signal Tnmd is outside the allowable torque range, the main torque signal gain Gm is set to 100%, and the gain double torque signal gain Gg is set to 0%. Further, when the correlation between the main torque detection signal Tmd and the sub torque detection signal Tsd is normal, but the gain double torque detection signal Tnmd is abnormal, for example, a logical value “1” indicating an abnormality of the gain double torque detection signal Tnmd. ", The main torque signal gain Gm is set to 100%, and the gain multiplied torque signal gain Gg is set to 0%. Further, when the correlation between the main torque detection signal Tmd and the sub torque detection signal Tsd is abnormal, a control prohibiting signal for prohibiting the steering assist control is output.

  The central processing unit 17 receives the main torque detection signal Tmd output from the A / D converter 21a and the gain double torque detection signal Tnmd output from the A / D converter 21b, and detects torque abnormality. A torque signal switching unit 23 to which a main torque signal gain Gm and a gain double torque signal gain Gg output from a torque sensor abnormality check unit 22 as a unit are input. As shown in FIG. 4, the torque signal switching unit 23 includes an n-times amplifying unit 23a that adjusts the unit of the main torque detection signal Tmd to a gain n-times of the amplifier circuit 18, and an output of the n-times amplifying unit 23a. A gain multiplier 23b that multiplies the detection signal gain Gm, a gain multiplier 23c that multiplies the gain double torque detection signal Tmdd by the gain double torque signal gain Gg, and an addition that adds the outputs of the gain multiplier 23b and the gain multiplier 23c 23d and a torque selection unit 23f to which the torque selection signal Tss as an addition output of the addition unit 23d is directly input and the torque selection signal Tss is input via the variable rate limiter unit 23e.

Here, in the variable rate limiter unit 23e, the torque selection signal Tss output from the adder unit 23d is set as the input signal Tin, the output signal is set as Tout, and the output signal at the previous sampling is set as Tout _−1. When the input signal at the time of sampling n times corresponding to the gain multiple n of 18 is Tin- _n , the output signal Tout is calculated by performing the calculation represented by the following equation (1), and the torque selection unit 23f Output.
Tout = Tout ₋₁ + (Tin−Tin _−n ) / n (1)

The torque selection unit 23f selects the torque selection signal Tss directly input from the addition unit 23d and selects the torque detection value T when the abnormality signal Sa input from the torque sensor abnormality check unit 22 is a logical value “0”. When the logical value is “1”, the output signal Tout of the variable rate limiter 23e is selected and output as the torque detection value T.
Further, the central processing unit 17 is detected by the steering assist command value calculation unit 24 and the center response improvement unit 25 to which the torque detection value T output from the torque signal switching unit 23 is individually input, and the rotation angle sensor 19. The motor angular velocity calculation unit 26 that calculates the motor angular velocity ωm by differentiating the motor rotation angle θm, and the yaw rate convergence control unit that calculates the convergence compensation value Ic based on the motor angular velocity ωm calculated by the motor angular velocity calculation unit 26 27 and an addition unit 28 for adding the outputs of the steering assist command value calculation unit 24, the center response improvement unit 25, and the yaw rate convergence control unit 27.

Here, the steering assist command value calculation unit 24 refers to the steering assist current command value calculation map shown in FIG. 5 based on the input torque detection value T and the vehicle speed detection value Vs detected by the vehicle speed sensor 15. A steering assist current command value Iref is calculated and output to the adding unit 28.
Here, as shown in FIG. 5, the steering assist command value calculation map has a parabolic shape with the detected torque T on the horizontal axis, the steering assist current command value Iref on the vertical axis, and the vehicle speed Vs as a parameter. It is composed of a characteristic diagram represented by a curve. The steering assist current command value Iref is maintained at “0” while the torque detection value T is between “0” and a set value Ts1 in the vicinity thereof, and the torque detection value T is When the set value Ts1 is exceeded, initially, the steering assist current command value Iref increases relatively slowly as the torque detection value T increases, but when the torque detection value T further increases, the steering assist current command value increases. The value Iref is set so as to increase steeply, and this characteristic curve is set so that the inclination becomes smaller as the vehicle speed Vs increases.

  Further, the center responsiveness improvement unit 25 increases the control responsiveness near the neutral point of the steering to realize smooth and smooth steering. For example, as shown in FIG. The detected torque detection value T is differentiated by the difference calculation unit 25a and the amount of change in steering torque per unit time is divided by the unit time to differentiate the torque detection value T, and the steering torque differential value T ′ is filtered by the low-pass filter 25b. Then, the filter output of the low-pass filter 25b is supplied to the vehicle speed Vs-sensitive compensation gain unit 25c, and the center response compensation value Ir is calculated by multiplying by the compensation gain that changes according to the vehicle speed detection value Vs. The center responsiveness compensation value Ir is output to the adder 28.

The yaw rate convergence control unit 27 estimates the yaw rate of the vehicle based on the motor angular velocity ωm, and in order to improve the convergence of the estimated yaw rate, the convergence control value for braking the operation of the steering wheel 1 swinging. Ic is calculated, and the calculated convergence compensation value Ic is output to the adder 28.
The adder 28 adds the steering assist current command correction value Iaref, the center response compensation value Ir, and the convergence control value Ic to calculate the compensated steering assist current command value Iref ′, and calculates the compensated steering assist current. The command value Iref ′ is supplied to the robust stabilization compensator 29.

This robust stabilization compensator 29 has a transfer function G (s) = (s ² + a 1 · s + a 2) / (s ² + b 1 · s + b ² ) with s as a Laplace operator, and is included in the detected torque value T. A peak at the resonance frequency of the resonance system composed of the inertia element and the spring element is removed to compensate for a phase shift of the resonance frequency that hinders the stability and responsiveness of the control system. The output of the robust stabilization compensator 29 is supplied to the adder 30. A motor inertia compensation value Ii calculated by the motor inertia compensation unit 31 based on the motor angular velocity ωm input from the motor angular velocity calculation unit 26 is input to the addition unit 30.

  Then, the addition output of the addition unit 30 is supplied to the dq axis command value calculation unit 32 as the current command value It. In the dq axis command value calculation unit 32, the d axis current command value Idref and the q axis current are calculated based on the motor rotation angle θm detected by the rotation angle sensor 19 and the motor angular velocity ωm calculated by the motor angular velocity calculation unit 26. The command value Iqref is calculated, and the calculated d-axis current command value Idref and q-axis current command value Iqref are converted into three-phase current command values Iaref, Ibref, and Icref by the two-phase / three-phase conversion unit 33, and the subtraction unit 34a , 34b and 34c are supplied separately. The motor currents Ia, Ib, and Ic detected by the motor current detection circuit 20 are input to the subtractors 34a, 34b, and 34c, and their current deviations ΔIa, ΔIb, and ΔIc are PI (proportional / integral) currents. The voltage command values Varef, Vbref and Vcre are calculated by PI control calculation supplied to the control unit 35, and these voltage command values Varef, Vbref and Vcref are output to the motor drive circuit 40.

In this motor drive circuit 40, pulse width modulation is performed based on the voltage command values Varef, Vbref and Vcref to form a gate drive signal, and the formed gate drive signal is applied to, for example, six switching elements constituting a three-phase inverter circuit. By supplying, three-phase motor currents Ia, Ib and Ic are formed by the three-phase inverter circuit, and these three-phase motor currents Ia, Ib and Ic are output to the electric motor 12.
The above is the description of the functional block diagram of the central processing unit 17, but in the central processing unit 17, by executing the torque command value selection processing program and the steering assist calculation processing program stored in the ROM (not shown), The voltage command values Varef to Vcref for the motor drive circuit 40 are calculated.

  Here, the torque command value selection process is executed as a timer interrupt process for the main program for each sampling period of the A / D conversion function corresponding to the A / D converters 21a to 21c. First, as shown in FIG. In step S1, the A / D converted main torque detection signal Tmd, the gain double torque detection signal Tnmd, and the sub torque detection signal Tsd are read. Then, the process proceeds to step S2, and the main torque detection signal Tmd and the sub torque detection signal Tsd It is determined whether or not the correlation is normal. If the determination result is abnormal, the process proceeds to step S3, and a torque command is set after setting a steering assist prohibition flag for prohibiting steering assist control to “1”. The value selection process ends.

  If the determination result in step S2 indicates that the correlation between the main torque detection signal Tmd and the sub-torque detection signal Tsd is normal, the process proceeds to step S4, where the correlation between the main torque detection signal Tmd and the gain multiplied torque detection signal Tmdd. It is determined whether or not the relationship is normal. If the correlation is normal, it is determined that the steering torque sensor 3 is normal, and the process proceeds to step S5.

  In this step S5, it is determined whether or not the value of the gain double torque detection signal Tnmd is within the allowable torque range (−Tp ≦ Tnmd ≦ + Tp). If it is within the allowable torque range, the process proceeds to step S6. The main torque detection signal gain Gm is set to 0%, the gain multiplied torque detection signal gain Gg is set to 100%, and the abnormality flag Fa is reset to “0” indicating normality, and then the process goes to step S9. Transition.

  On the other hand, if the determination result in step S5 is that the value of the gain multiple torque detection signal Tnmd is outside the allowable torque range (Tnmd <−Tp or Tnmd> + Tp), the process proceeds to step S7, and the main torque detection signal gain Gm is set. Then, the gain multiplied torque detection signal gain Gg is set to 0%, and the abnormality flag Fa is reset to “0” indicating normality, and then the process proceeds to step S9.

On the other hand, when the correlation between the main torque detection signal Tmd and the gain multiple torque detection signal Tnmd is abnormal as a result of the determination in step S4, the process proceeds to step S8, the main torque signal gain Gm is set to 100%, Further, the gain double torque signal gain Gg is set to 0%, and the abnormality flag Fa is set to “1” indicating an abnormality of the gain double torque detection signal Tnmd, and then the process proceeds to step S9.
In step S9, the torque selection signal Tss is calculated by performing the calculation of the following equation (2).
Tss = n · Tmd · Gm + Tnmd · Gg (2)

Next, the process proceeds to step S10, where the calculated torque selection signal Tss is set as the input signal Tin, and Tin _−n from the last stage of the so-shift register area of the gain multiple n stages of the amplification circuit 18 formed in the RAM (not shown). Is calculated, and the torque output signal Tout is calculated by performing the calculation of the above-described equation (1).
Next, the process proceeds to step S11, where the calculated torque output signal Tout is updated and stored in a torque output signal storage area formed in a RAM (not shown) as Tout _-1 , and the input signal Tin is stored in the gain multiple n stage of the amplifier circuit 18. After the data is stored in the shift register area, the process proceeds to step S12.

  In this step S12, it is determined whether or not the abnormality flag Fa is set to “1”. When the abnormality flag Fa is reset to “0”, the process proceeds to step S13, and the torque selection signal Tss is changed to the torque. When the detected value T is updated and stored in the torque detected value storage area of the RAM (not shown), the timer interrupt process is terminated and the program returns to the predetermined main program. When the abnormality flag Fa is set to “1”, step S14 is performed. Migrate to

In step S14, the torque output signal Tout calculated in step S9 is updated and stored in the torque detection value storage area of the RAM (not shown) as the torque detection value T, and then the timer interrupt process is terminated and the program returns to the predetermined main program. .
In the torque signal selection process of FIG. 7, the process of step S4 corresponds to the torque abnormality determination unit, the processes of steps S6 to S9 and S12 to S14 correspond to the torque selection unit, and the processes of steps S10 and S11 are torque limiting. The processing of step S10 corresponds to the variable rate limiter.

  As shown in FIG. 8, in the steering assist control process, in step S21, the torque detection value T stored in the torque detection value storage area of the RAM, the vehicle speed detection value Vs detected by the vehicle speed sensor 15, and the rotation angle sensor 19 are used. Various detection values such as the detected motor rotation angle θm and the motor currents Ia to Ic detected by the motor current detection circuit 20 are read, and then the process proceeds to step S22, where the above-mentioned is based on the torque detection value T and the vehicle speed detection value Vs. The steering assist current command value Iref is calculated with reference to the steering assist current command value calculation map shown in FIG.

  Next, the process proceeds to step S23, and the center response compensation value calculation process corresponding to the center response improvement unit 25 described above is executed. In this center response compensation value calculation process, the rate of change of the torque detection value T per unit time, that is, the steering torque differential value T ′ obtained by differentiating the torque detection value T is low-pass filtered, and the steering torque differential value T after filtering is processed. The center response compensation value Ir (= Gr · T ′) is calculated by multiplying ′ by a compensation gain Gr that is changed according to the vehicle speed detection value Vs.

Next, the process proceeds to step S24, where the motor angular speed ωm is calculated by differentiating the motor rotation angle θm, and then the process proceeds to step S25, where the yaw rate convergence control value Ic and the motor inertia are based on the calculated motor angular speed ωm. A compensation value Ii is calculated.
Next, the routine proceeds to step S26, where the steering assist current command value Iref, the center response improvement value Ir, and the yaw rate convergence control value Ic are added to calculate a post-compensation steering assist current command value Iref ′. In step S27, a robust stabilization compensation process for multiplying the calculated post-compensation steering assist current command value Iref ′ by the transfer function G (s) described above is performed to calculate a post-compensation steering assist current command value Iref ″. .

Next, the process proceeds to step S28, and the motor inertia compensation value Ii is added to the post-compensation steering assist current command value Iref ″ to calculate the current command value It (= Iref ″ + Ii).
Next, the process proceeds to step S29, where the d-axis current command value Idref and the q-axis current command value Iqref are calculated based on the calculated current command value It, the motor rotation angle θm and the motor angular velocity ωm, and then in step S30. Then, the calculated d-axis current command value Idref and q-axis current command value Iqref are subjected to a two-phase / three-phase conversion process to calculate three-phase current command values Iaref, Ibref, and Icref.

Next, the process proceeds to step S31, and motor current detection values Ia, Ib and Ic are subtracted from the calculated three-phase current command values Iaref, Ibref and Icref to calculate current deviations ΔIa, ΔIb and ΔIc, and then to step S32 Then, the calculated current deviations ΔIa, ΔIb, and ΔIc are subjected to PI (proportional / integral) control processing to calculate voltage command values Varef, Vbref, and Vcref.
Next, the process proceeds to step S33, and the calculated voltage command values Varef, Vbref, and Vcref are output to the motor drive circuit 40, and then the process returns to step S21.
The steering assist control process of FIG. 8 corresponds to the steering assist command value control unit.

Next, the operation of the above embodiment will be described.
Now, it is assumed that the vehicle is stopped in a steering neutral position, that is, in a straight traveling state, with the ignition switch IG turned off.
When the ignition switch IG is turned on while the vehicle is stopped, the power is supplied from the battery B to the controller 14 accordingly, and the central processing unit 17 and the motor drive circuit 40 are put into operation.

At this time, the correlation between the main torque detection signal Tm detected by the main torque detection unit 3M of the steering torque sensor 3 and the sub torque detection signal Ts detected by the sub torque detection unit 3S is normal, and the main torque detection value Tm 7 and the gain double torque detection signal Tnm calculated by the amplifier circuit 18 are normal, when the torque signal selection process of FIG. 7 is executed, the process goes to steps S5 through S1, S2, and S4. When the gain double torque detection signal Tnmd is within the allowable range, that is, −Tp ≦ Tnmd ≦ + Tp, it is determined that the gain double torque detection signal Tnmd is normal, and the flow proceeds to step S6. In step S6, the main torque signal gain Gm is set to 0%, the gain multiple torque signal gain Gg is set to 100%, and the abnormality flag Fa is reset to “0”.
For this reason, as the torque selection signal Tss calculated in step S9, the gain double torque detection signal Tnmd is selected as it is.

In step S10, the torque selection signal Tss is used as the input signal Tin, and Tim _−n is read from the final stage of the shift register area formed in the RAM, and the above-described calculation of the expression (1) is performed. An output torque signal Tout is calculated.
The calculated output torque signal Tout is updated and stored in the output torque signal storage area formed in the RAM, and the input signal Tin is stored in the first stage of the shift register area formed in the RAM, and each stage is shifted one by one ( Step S11).

Further, since the abnormality flag Fa is reset to “0”, the process proceeds from step S12 to step S13, and the torque selection signal Tss is updated and stored in the torque detection value storage area formed in the RAM as the torque detection value T. Then, the timer interrupt process is terminated and the process returns to the predetermined main program.
Thus, when the gain double torque detection signal Tnmd output from the amplifier circuit 18 is normal, the gain double torque detection signal Tnmd is selected as the torque detection value T, so that the resolution of the A / D conversion function is effective. Can be used.

Then, in the steering assist control process shown in FIG. 8 based on the selected torque detection value T, the steering assist current command value Iref is calculated, the center response improvement value Ir is calculated, and both are added. The yaw rate convergence control value Ic calculated based on the motor angular velocity ωm obtained by differentiating the motor rotation angle θm is added to calculate the steering assist current compensation value Iref ′ (step S26).
The steering assist current compensation value Iref ′ is multiplied by the transfer function G (s) by a robust stabilization process to calculate a compensated steering assist current command value Iref ″ (step S27), and the calculated aftercompensation steering assist current command value is calculated. A motor command value It is calculated by adding the motor inertia compensation value Ii to Iref ″ (step S28).

Then, a dq-axis current command value calculation process is performed based on the current command value It to calculate a d-axis current command value Idref and a q-axis current command value Iqref (step S29), and the calculated d-axis current command value The Idref and the q-axis current command value Iqref are subjected to 2-phase / 3-phase conversion processing to calculate the 3-phase motor current command values Iaref, Ibref, and Icref (step S30).
Then, current deviations ΔIa, ΔIb, and ΔIc are calculated by individually subtracting the motor currents Ia, Ib, and Ic detected by the motor current detection circuit 20 from the calculated three-phase motor current command values Iaref, Ibref, and Icref (step S31). ), The voltage command values Varef, Vbref, and Vcref are calculated by subjecting the calculated current deviations ΔIa, ΔIb, and ΔIc to PI control calculation processing (step S32).

Then, by outputting the calculated voltage command values Varef, Vbref and Vcref to the motor drive circuit 40, the motor drive circuit 40 performs pulse width modulation based on the voltage command values Varef, Vbref and Vcref to generate a gate drive signal. The three-phase motor currents Ia, Ib and Ic are formed by driving and controlling the six switching elements constituting the inverter with the gate drive signal, and these three-phase motor currents Ia, Ib and Ic are generated by the electric motor 12. , The electric motor 12 is driven to rotate, and a steering assist force corresponding to the detected torque value T is generated.
The steering assist force generated by the electric motor 12 is transmitted to the output shaft 2b of the steering shaft via the reduction gear 11, so that the steering wheel 1 can be steered with a light steering force.

  When the gain torque detection signal Tnmd output from the amplifier circuit 18 is outside the allowable torque range with the steering torque sensor 3 in a normal state, the process proceeds from step S5 to step S7 in the torque signal selection process of FIG. Then, the main torque signal gain Gm is set to 100%, and the gain multiplied torque signal gain Gg is set to 0%. Therefore, a signal obtained by multiplying the main torque detection signal Tmd by a gain multiple n is selected as the torque selection signal Tss as the torque selection signal Tss calculated by the equation (2), and the abnormality flag Fa is set to “0”. Therefore, the torque selection signal Tss, that is, the main torque detection signal n · Tmd multiplied by the gain is updated and stored in the torque detection value storage area of the RAM as the torque detection value T. Based on this torque detection value T, the steering assist control process of FIG.

Further, when the correlation between the main torque detection signal Tmd and the sub torque detection signal Tsd is normal and the gain double torque detection signal Tnmd output from the amplifier circuit 18 becomes abnormal, the main torque detection signal Tmd And the gain multiplied torque detection signal Tnmd are lost, and the process proceeds from step S4 to step S8 in the torque signal selection process of FIG. In step S8, the main torque signal gain Gm is set to 100%, the gain multiplied torque signal gain Gg is set to 0%, and the abnormality flag Fa is set to “1”.
For this reason, the main torque detection signal n · Tnmd multiplied by n is selected as the torque selection signal Tss (step S9), the torque selection signal Tss is set as the input signal Tin, and the (1) The operation constituting the variable rate limiter of the equation is executed to calculate the output torque signal Tout.

Since the abnormality flag Fa is set to “1”, the calculated output torque signal Tout is selected as the torque detection value T and is updated and stored in the torque detection value storage area of the RAM. Based on this, the steering assist control process shown in FIG. 8 is executed.
At this time, the torque detection value calculated in the torque command value selection process is as shown in FIGS. 9A to 9C, and the input torque is the main torque signal n · Tmd multiplied by n as the input signal. An output torque signal Tout that suppresses a rapid change in the signal Tin can be obtained.

That is, for example, when the gain multiple n is set to “4”, for example, the absolute value of the input torque signal Tin is, for example, “0” to “16” at the time t0 as shown by the solid line in FIG. When this state continues for two sampling cycles of the A / D conversion function and then suddenly returns to “0”, the input torque signal Tin 4 sampling cycles before the time t0. _{Since −n} is “0” and the previous output torque Tout ₋₁ is also “0”, the output torque signal Tout shown in the broken line is
Tout = 0 + (16-0) / 4 = 4
It becomes.

Next, at the time point t1, Tin continues to be “16” and Tin ₋₄ is still “0”, but since the previous output torque signal Tout ₋₁ is “4”, the output torque signal Tout is ,
Tout = 4 + (16-0) / 4 = 8
It becomes.
At time t2, the input torque signal Tin becomes “0”, the input torque signal Tin ₋₄ before 4 sampling periods is also “0”, and the previous output torque signal Tout ₋₁ is “8”. The signal Tout is
Tout = 8 + (0-0) / 4 = 8
It becomes.

Since the time t3 is the same as the time t2, the output torque signal Tout continues to be “8”. At the time t4, the previous output torque signal Tout ₋₁ is “8”, and the input torque signal Tin before the four sampling periods _-4 is “16”, so the output torque signal Tout is
Tout = 8 + (0-16) / 4 = 4
Thus, the output torque signal Tout decreases as shown by the broken line.

Similarly, at time t5, as in time t4, the input torque signal Tin- ₄ before the four sampling periods is “16”, but the previous output torque signal Tout- ₁ is “4”, so the output torque signal Tout is
Tout = 4 + (0-16) / 4 = 0
Thus, the output torque signal Tout returns to “0”.

  In this way, even if the input torque signal Tin, which is the main torque detection signal Tmd multiplied by n, suddenly changes, the torque detection value T can be gradually changed by exhibiting the variable rate limiter function. For this reason, when the center response improvement process accompanied by the differentiation process is performed as in the conventional example, the center response improvement value can be reliably prevented from being a discontinuous value, and the main torque detection signal By interpolating the roughness of the resolution of Tmd, it is possible to reliably suppress the influence of the roughness of the resolution on the steering feeling.

Further, the case where the input torque signal Tin composed of the main torque detection signal n · Tmd multiplied by n is further increased by “20” as shown by the solid line at time t2 and then returned to “0” at time t3 as shown in FIG. b), with respect to the case of FIG. 9A described above, it increases by “9” according to the increase of the input torque signal Tin at the time point t2, and then the input torque signal Tin is “0” at the time point t3. , The output torque signal Tout maintains the value at the time point t2, and then the output torque signal Tout gradually decreases after the time point t4 and returns to “0” at the time point t6.
Also in this case, even if the input torque signal Tin, which is the main torque detection signal Tmd multiplied by n, suddenly changes, the torque detection value T can be gradually changed by exhibiting the variable rate limiter function, and the main torque detection By interpolating the roughness of the resolution of the signal Tmd, it is possible to reliably suppress the influence of the roughness of the resolution on the steering feeling.

Further, as shown by the solid line in FIG. 9C, when the input torque signal Tin does not return to “0” at the time point t3 but once decreases and then increases further, the output torque signal Tin As shown in the broken line in FIG. 9C, Tout changes gradually while following the change of the input torque signal Tin, and the main torque detection signal Tmd multiplied by n is obtained as in FIGS. 9A and 9B. Even if the input torque signal Tin is changed suddenly, the torque detection value T can be changed gently by exercising the variable rate limiter function, and the resolution resolution of the main torque detection signal Tmd is interpolated. It is possible to reliably suppress the roughness of the wheel from affecting the steering feeling.
As described above, by demonstrating the variable rate limiter function, it is possible to follow the change in the main torque signal Tmd while suppressing the rate of change in the main torque signal Tnd, as is apparent from FIGS. The limit torque output value Tout that can ensure responsiveness can be obtained.

  If the correlation between the main torque detection signal Tmd and the sub torque detection signal Tsd is not normal, the process proceeds from step S2 to step S3 in the torque signal selection process of FIG. By setting to “1”, when the steering assist control process of FIG. 8 is executed, the process ends in step S20, and the steering assist control based on an inaccurate torque detection value is prohibited.

  Thus, according to the above embodiment, when the gain double torque detection signal Tnm output from the amplifier circuit 18 is normal by the torque signal selection process, the gain double torque detection signal Tnm is used to perform A / D. The resolution of the conversion function can be used effectively, and when the gain double torque detection signal Tnm becomes abnormal, the main torque detection signal Tmd is detected by the variable rate limiter function even if the main torque detection signal Tmd having a low resolution is used. The torque detection value T that suppresses a sudden change in the value can be obtained, and it is possible to reliably prevent a discontinuous value due to the center response improvement process accompanied by the differentiation process.

Moreover, since the variable rate limiter function is applied to limit the rate of change of the main torque detection signal Tmd, the limit torque output that follows the main torque detection signal while limiting the rate of change of the main torque detection signal Tmd. A value can be obtained.
In the above embodiment, the case where the variable rate limiter is applied to limit the rate of change of the main torque detection signal Tmd has been described. However, the present invention is not limited to this, and the case where the upper limit value of the rate of change is exceeded. It is also possible to apply a normal limiter that restricts to.

In the above embodiment, when the main torque signal Tmd and the gain double torque detection signal Tnmd are selected, either the main torque signal gain Gm or the gain double torque signal gain Gg is set to 0% and the other is set to 100%. Although the case where the setting is made has been described, the present invention is not limited to this, and the selection switch may be used for selection.
Furthermore, the present invention can be applied to all electric power steering devices regardless of the type of electric power steering device (column type, pinion type, rack type) and the type of motor (with brush, brushless, etc.).

  DESCRIPTION OF SYMBOLS 1 ... Steering wheel, 2 ... Steering shaft, 3 ... Steering torque sensor, 8 ... Steering gear mechanism, 12 ... Electric motor, 13 ... Steering angle sensor, 14 ... Controller, 15 ... Vehicle speed sensor, 18 ... Amplifier circuit, 19 ... Rotational angle sensor, 20 ... motor current detection circuit, 21a to 21c ... A / D converter, 22 ... torque sensor abnormality check unit, 23 ... torque signal switching unit, 24 ... steering auxiliary current command value calculation unit, 25 ... center response Improvement unit, 26 ... motor angular velocity calculation unit, 27 ... yaw rate convergence control unit, 28 ... addition unit, 29 ... robust stabilization compensation unit, 30 ... addition unit, 31 ... dq axis current command value calculation unit, 32 ... 2 phase / 3 phase conversion unit, 33 ... subtraction unit, 34 ... PI current control unit, 40 ... motor drive circuit

Claims (5)

A torque detection device having at least a main torque detection unit for detecting torque transmitted to the steering system and outputting a main torque detection signal;
A gain double torque output unit for outputting a gain double torque detection value obtained by multiplying the main torque detection signal by n times;
A torque abnormality determination unit for detecting an abnormality of the gain double torque output unit;
A torque limiter that outputs a torque limit output value in which the main torque detection signal is limited according to a change amount of the main torque detection signal for each predetermined period;
When the torque abnormality detecting unit determines that the gain double torque output unit is normal, the gain double torque detection value is selected, and when the gain double torque output unit is determined to be abnormal. A torque selector for selecting the torque limit output value;
An electric motor that generates a steering assist force for the steering system;
A steering assist command value controller that calculates a steering assist command value based on at least the torque detection value selected by the torque selector;
An electric power steering apparatus comprising: a motor drive control unit that drives and controls the electric motor based on the steering assist command value.   The torque selection unit receives the main torque detection signal and the gain multiplied torque detection value after A / D conversion and inputs a value obtained by multiplying the main torque detection value after the A / D conversion by n. The electric power steering apparatus according to claim 1, wherein the electric power steering apparatus is configured as follows.   The electric power steering apparatus according to claim 1, wherein the torque limiting unit is configured by a variable rate limiter.   The variable rate limiter calculates a limit value by dividing a value obtained by subtracting a gain multiplied main torque detection value before n periods corresponding to the gain multiple n from a current value of the main torque detection signal by a gain multiple n, The electric power steering apparatus according to claim 3, wherein the calculated limit value is added to the previous limit torque output value to calculate the limit torque output value.   5. The electric motor according to claim 1, wherein the gain multiple torque output unit is configured such that the gain multiple n is set to a value that can effectively use the resolution at the time of the A / D conversion. Power steering device.

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