JP2009173180A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device capable of minimizing an influence on steering assist, by detecting abnormality and corresponding to that before developing to CPU runway. <P>SOLUTION: An ECC function or a parity check function which is a failure detecting-error correcting function possessed by a hardware of a microcomputer is used for steering assisting control. When a memory of the microcomputer, an arithmetic logical unit (ALU), or a register detects a temporary failure such as a bit error temporary occurred, error correction is carried by an ECC function or a re-try processing. When the error detection-correction is executed, an electric motor 12 is controlled by using a torque instruction value Ir computed in previous sampling. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

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

In the conventional electric power steering device, when an abnormality of the assist control means is detected, the assist control is stopped by stopping the rotation control of the electric motor, and the running stability when the abnormality occurs is ensured.
As such an electric power steering device, when abnormality of the assist control means is detected, the rotation control of the electric motor is interrupted, and then when the abnormality of the assist control means is recovered, the vehicle is stopped or immediately before It is known that the rotation control of the electric motor by the assist control means is restarted on the condition that the vehicle is stopped (for example, see Patent Document 1). Here, a watchdog timer is built in, and normality and abnormality of the microcomputer unit such as program runaway are detected, and when the abnormality is detected, a reset signal is output to the CPU to restart the CPU.
Japanese Patent No. 3412581

By the way, in recent years, with the increase in size of vehicles equipped with electric power steering, the output of electric power steering devices has increased, and the increase in motor torque and the increase in current have accelerated.
In such a large vehicle, since steering becomes difficult when the assist control is stopped as compared with a light vehicle or the like, it is desired that the steering assist can be continued even if an abnormality occurs.
However, in the electric power steering device described in Patent Document 1, since the abnormality cannot be detected unless the CPU runs away, the steering assist cannot be maintained after the abnormality is detected.

Further, since the CPU is reset when an abnormality is detected, steering assist is completely lost. At this time, the steering assist cannot be gradually reduced and stopped.
Therefore, an object of the present invention is to provide an electric power steering apparatus that can minimize the influence on steering assist by detecting and dealing with an abnormality before developing into a CPU runaway.

In order to solve the above-described problem, an electric power steering apparatus according to a first aspect of the present invention includes a steering torque detection unit that detects a steering torque input to a steering mechanism that steers a steered wheel, and a steering assist force that is applied to the steering mechanism. An electric power steering apparatus comprising: an electric motor to be applied; and a control unit that calculates a current command value based on the steering torque and controls the electric motor based on the calculated current command value,
An abnormality detection means for detecting an abnormality occurring in the control means, and an abnormality correction means for correcting the abnormality when the abnormality detection means detects an abnormality, the control means correcting the abnormality by the abnormality correction means Is executed, the electric motor is controlled based on the current command value calculated in the previous sampling.

  According to a second aspect of the present invention, there is provided an electric power steering apparatus according to the first aspect of the invention, wherein the control means is constituted by a microcomputer, and the abnormality detection means is a bit of data based on an ECC function of the microcomputer. An error is detected, and the abnormality correcting means is configured to automatically correct the bit error using the ECC function when an abnormality is detected by the abnormality detecting means.

  Furthermore, the electric power steering apparatus according to a third aspect is the invention according to the first or second aspect, wherein the control means is constituted by a microcomputer, and the abnormality detecting means is based on a parity check function of the microcomputer. A bit error of data is detected, and the abnormality correcting means is configured to correct the bit error by retrying the process of the part where the abnormality is detected when the abnormality detecting means detects the abnormality. It is characterized by.

According to a fourth aspect of the present invention, in the electric power steering apparatus according to the second or third aspect of the present invention, at least one of the memory, the arithmetic unit, and the register of the microcomputer includes the abnormality detecting unit.
Furthermore, the electric power steering apparatus according to claim 5 is the invention according to any one of claims 1 to 4, wherein the control means performs the previous sampling when the abnormality correction is executed by the abnormality correction means. The electric motor is controlled by using the current command value calculated in step 1 as the current command value output in the current sampling.

  According to a sixth aspect of the present invention, in the electric power steering apparatus according to any one of the first to fourth aspects of the present invention, the control means is based on the current command value calculated in the previous sampling. A current command value complementary calculation means for estimating a current command value output by sampling, and when the abnormality correction is executed by the abnormality correction means, based on the current command value estimated by the current command value complement calculation means; The electric motor is controlled.

  According to the electric power steering apparatus of the present invention, an abnormality detection function for detecting an abnormality such as a bit error temporarily generated in the control means and an abnormality correction function for correcting the abnormality are provided. A previous small error can be detected and corrected. As a result, the CPU runaway can be prevented, the arithmetic processing by the control means can be continued, and the steering assist can be continued.

  In addition, the sampling with the above error correction causes a calculation delay, so the calculation result of the sampling is discarded and the electric motor is controlled using the calculation result of the previous sampling. It is possible to continue the assist while suppressing the influence on the steering assist such as a system failure caused by continuing.

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 the present invention. In the figure, symbol SM denotes a steering mechanism. The steering mechanism SM has a steering shaft having an input shaft 2a to which a steering force applied from a driver is transmitted to the steering wheel 1 and an output shaft 2b connected to the input shaft 2a via a torsion bar (not shown). 2 is provided. The steering shaft 2 is rotatably mounted on the steering column 3, one end of the input shaft 2a is connected to the steering wheel 1, and the other end is connected to a torsion bar (not shown).

The steering force transmitted to the output shaft 2b is transmitted to the intermediate shaft 5 via the universal joint 4 composed of the two yokes 4a and 4b and the cross connecting portion 4c for connecting them, It is transmitted to the pinion shaft 7 through a universal joint 6 composed of yokes 6a and 6b and a cross connecting portion 6c for connecting them.
The steering force transmitted to the pinion shaft 7 is transmitted to the left and right tie rods 9 via the steering gear mechanism 8, and the left and right steered wheels WL and WR are steered by these tie rods 9. Here, the steering gear mechanism 8 is configured in a rack and pinion type having a pinion 8b connected to the pinion shaft 7 and a rack shaft 8c meshing with the pinion 8b in the gear housing 8a, and is transmitted to the pinion 8b. The rotational motion obtained is converted into a linear motion in the vehicle width direction by the rack shaft 8 c and transmitted to the tie rod 9.

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 brushless motor that generates a steering assist force connected to the reduction gear 11.
A steering torque sensor 14 serving as a steering torque detecting means is disposed in a housing 13 connected to the steering wheel 1 side of the reduction gear 11. The steering torque sensor 14 detects a steering torque applied to the steering wheel 1 and transmitted to the input shaft 2a. For example, 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 converted into a torsional angular displacement, the torsional angular displacement is detected as a magnetic change or a resistance change, and converted into an electrical signal.

  The steering torque detection value T output from the steering torque sensor 14 is input to a controller 15 constituted by a microcomputer (hereinafter referred to as a microcomputer), as shown in FIG. In addition to the torque detection value T, the controller 15 detects the vehicle speed detection value V detected by the vehicle speed sensor 16, the motor currents Iu to Iw flowing through the electric motor 12, and the rotation angle sensor 17 constituted by a resolver, encoder, and the like. The rotation angle θ of the electric motor 12 is also input.

The controller 15 calculates a steering assist torque command value Iref that causes the electric motor 12 to generate a steering assist force according to the input torque detection value T and the vehicle speed detection value V, and with respect to the calculated steering assist torque command value Iref. After performing various compensation processes such as convergence compensation, inertia compensation, self-aligning torque compensation based on the motor angular velocity ω and motor angular acceleration α calculated based on the rotation angle θ, the dq axis current command value Id ^* , Iq ^* .

Further, the motor currents Iu to Iw are three-phase / two-phase converted to calculate dq-axis motor currents Id and Iq. The drive current supplied to the electric motor 12 is feedback-processed based on the dq-axis current command values Id ^* and Iq ^* and the dq-axis motor currents Id and Iq, and the result is expressed as two-phase / 3-phase. The motor currents Iu, Iv and Iw for driving and controlling the electric motor 12 are output after conversion.

That is, the controller 15 includes a steering assist torque command value calculation unit 21 that calculates a steering assist torque command value Iref based on the steering torque T and the vehicle speed V, and a command value compensation unit that compensates the calculated steering assist torque command value Iref. 22, a complementary calculation unit 23 that performs a complementary calculation process on the torque command value Iref ′ compensated by the command value compensation unit 22, and a dq-axis current command value based on the torque command value Ir after the complementary calculation. The motor current control unit 24 calculates Id ^* and Iq ^* and generates motor currents Iu to Iw based on these command currents.

In the steering assist torque command value calculation unit 21, first, the torque command value calculation unit 41 refers to the steering assist torque command value calculation map shown in FIG. 3 based on the steering torque T and the vehicle speed V to obtain a current command value. A steering assist torque command value Iref is calculated.
As shown in FIG. 3, the steering assist torque command value calculation map is a parabolic curve with the steering torque T on the horizontal axis, the steering assist torque command value Iref on the vertical axis, and the vehicle speed V as a parameter. The steering assist torque command value Iref is maintained at “0” while the steering torque T is between “0” and a set value Ts1 in the vicinity thereof, and the steering torque T is set at the set value Ts1. When it exceeds, the steering assist torque command value Iref increases relatively slowly with the increase of the steering torque T, but when the steering torque T further increases, the steering assist torque command value Iref increases sharply with the increase. The characteristic curve is set so that the inclination becomes smaller as the vehicle speed increases.

Then, the phase compensation unit 42 performs phase compensation on the steering assist torque command value Iref, and outputs the steering assist torque command value Iref after phase compensation to an adder 38 described later. Further, the torque differentiating circuit 43 differentiates the steering torque T to calculate the steering torque change rate ΔT and outputs it to the adder 38 described later.
The command value compensator 22 differentiates the motor rotation angle θ detected by the rotation angle sensor 17 to calculate the motor angular velocity ω, and differentiates the motor angular velocity ω calculated by the angular velocity calculator 31. The angular acceleration calculation unit 32 that calculates the motor angular acceleration α, the convergence compensation unit 33 that compensates for the convergence of the yaw rate based on the motor angular velocity ω calculated by the angular velocity calculation unit 31, and the angular acceleration calculation unit 32 An inertia compensation unit 34 that compensates for the torque equivalent generated by the inertia of the electric motor 12 on the basis of the motor angular acceleration α and prevents deterioration of the feeling of inertia or control responsiveness, and a self-aligning torque (SAT) And a SAT estimation feedback unit 35 for estimation.

Here, the convergence compensation unit 33 receives the motor angular velocity ω calculated by the angular velocity calculation unit 31 and applies a brake to the operation in which the steering wheel 1 swings in order to improve the yaw convergence of the vehicle. Thus, the convergence compensation value Ic is calculated.
Further, the SAT estimation feedback unit 35 receives the steering torque T, the motor angular velocity ω, the motor angular acceleration α, and the steering assist torque command value Iref calculated by the steering assist torque command value calculation unit 21, and based on these, the self-aligning is performed. The torque SAT is estimated and calculated.

The principle of calculating the self-aligning torque SAT will be described with reference to FIG. 4 showing the state of torque generated between the road surface and the steering.
That is, when the driver steers the steering wheel 1, a steering torque T is generated, and the electric motor 12 generates an assist torque Tm according to the steering torque T. As a result, the wheel W is steered and a self-aligning torque SAT is generated as a reaction force. Further, at that time, torque serving as a steering resistance of the steering wheel 1 is generated by the inertia J and friction (static friction) Fr of the electric motor 12. Considering the balance of these forces, the following equation of motion can be obtained:

  J · α + Fr · sign (ω) + SAT = Tm + T (1)

  Here, when the above equation (1) is Laplace transformed with the initial value zero and the self-aligning torque SAT is solved, the following equation (2) is obtained.

  SAT (s) = Tm (s) + T (s) −J · α (s) −Fr · sign (ω (s)) (2)

  As can be seen from the above equation (2), the inertia J and static friction Fr of the electric motor 12 are obtained in advance as constants, so that the self-aligning torque is obtained from the motor angular velocity ω, rotational angular acceleration α, assist torque Tm, and steering torque T. The SAT can be estimated. Here, since the assist torque Tm is proportional to the steering assist torque command value Iref, the steering assist torque command value Iref is applied instead of the assist torque Tm.

  Then, the inertia compensation value Ii calculated by the inertia compensation unit 34 and the self-aligning torque SAT calculated by the SAT estimation feedback unit 35 are added by the adder 36, and the addition output of the adder 36 and the convergence compensation unit 33 are added. Is added by an adder 37 to calculate a command compensation value Icom, and this command compensation value Icom is output from the steering assist torque command value calculation unit 21. Is added by the adder 38 to calculate a post-compensation torque command value Iref ′, and this post-compensation torque command value Iref ′ is output to the complementary calculation unit 23.

  The complementary calculation unit 23 receives a temporary failure detection signal S, which will be described later, and performs a complementary calculation on the current command value of the electric motor 12 in accordance with the temporary failure detection signal S. Here, the temporary failure detection signal S is a signal that indicates whether or not a temporary failure such as a bit error (bit corruption) has been detected in the microcomputer memory, register, or arithmetic unit (ALU). Is output by the fault detection / correction function implemented in the above.

FIG. 5 is a block diagram illustrating a specific configuration of the complementary calculation unit 23. As shown in FIG. 5, in the complementary calculation unit 23, the switch A is switched by the input of the temporary failure detection signal S.
That is, the switch A is in a state indicated by a solid line when a temporary failure detection signal S having a logical value “0” indicating that a temporary failure has not occurred, and the temporary failure has occurred. When a temporary failure detection signal S having a logical value “1”, which means that there is an error, is input, the state is switched to a state indicated by a broken line.

With such a configuration, when the temporary failure detection signal S having the logical value “0” is input, the complement calculating unit 23 directly uses the compensated torque command value Iref ′ calculated by the adder 38 after the complement calculation. The torque command value Ir is output to the motor current control unit 24.
On the other hand, when the temporary failure detection signal S having the logical value “1” is input, the complementary calculation unit 23 discards the compensated torque command value Iref ′ calculated in the current sampling and used it in the previous sampling. The torque command value Ir is output to the motor current control unit 24 as the current sampling calculation result.

Further, the motor current control unit 24 includes a motor current detector 60 that detects motor currents Iu, Iv, and Iw supplied to the phase coils Lu, Lv, and Lw of the electric motor 12, and a dQ from the torque command value Ir. A current command value calculation unit 61 for calculating shaft current command values Id ^* and Iq ^* , a three-phase / two-phase conversion unit 62 for converting motor currents Iu, Iv and Iw to dq-axis motor currents Id and Iq, Subtractors 61d and 61q for individually subtracting dq axis motor currents Id and Iq from dq axis current command values Id ^* and Iq ^* to obtain respective phase current deviations ΔId and ΔIq, and respective phase current deviations ΔId, A current control unit 63 that calculates voltage command values Vd and Vq by performing proportional-integral control on ΔIq, and the voltage command values Vd and Vq are input to calculate three-phase voltage command values Vu, Vv, and Vw. 2-phase / 3-phase converter 64 These voltage command values Vu, and a duty ratio calculation unit 65 for calculating the duty of each phase ratio by performing the duty operation on the basis of the Vv and Vw.

  Further, the motor current control unit 24 performs pulse width modulation based on the duty ratio output from the duty ratio calculation unit 65 to obtain a pulse width modulation signal, and based on the pulse width modulation signal, the three-phase motor current Iu, An inverter 66 that outputs Iv and Iw to the electric motor 12 is provided.

Next, a failure detection function implemented for each part of the microcomputer will be described.
The failure that occurs in the microcomputer is a permanent failure that occurs fixedly due to internal factors of the hardware of the microcomputer, such as a semiconductor junction failure, circuit short circuit, disconnection, etc., and electromagnetic noise, temperature change, vibration, etc. There are two types of temporary failures that occur temporarily due to external factors.
Permanent failure is a physical destruction of the hardware of the microcomputer, so it is unlikely that it will be recovered even if a retry is performed after the failure is detected, such as disconnecting the failed circuit and implementing alternative control with a redundant circuit. Although it is necessary to deal with it, a temporary failure is likely to be recovered.

Improving the reliability of an arithmetic control device such as a microcomputer is very important for improving the reliability of an electric power steering device. As techniques for improving the reliability of a microcomputer, a parity check function for detecting a bit error, which is a representative example of a temporary failure, and an ECC (Error Correction Code) function for detecting and correcting the bit error are known.
The parity check function is a function that enables detection of a bit error in data by checking a parity bit that is an error correction code added to the data.

  The ECC function is a function that detects a bit error in the data and enables automatic correction of the bit error. Specifically, it has at least a memory array unit for storing normal data and an error correction code (ECC) for error correction of the data, and an ECC circuit for error correction of the data based on the ECC, and a memory Even if a part of the data in the array is destroyed, it is recovered to correct data by the ECC circuit.

In this embodiment, the memory in the microcomputer has an error correction function using error ECC or the like, and the register and the arithmetic unit (ALU) in the microcomputer have an error detection function using parity or the like.
In other words, the memory of the microcomputer according to the present embodiment forms an ECC of the write data input from the data input / output terminal, and stores this ECC together with the write data in the memory array. When reading data, the ECC circuit checks the data based on the data read from the memory array and the ECC, and corrects the data when an error has occurred in the data. Output more.

Further, when an error bit is detected and corrected by the ECC circuit, a temporary failure detection signal S is formed and output from a predetermined output terminal to the above-described complementary calculation unit 23.
Note that the memory is a circuit that is prone to a temporary failure called a soft error in which a data error temporarily occurs at an unspecified location, and therefore a plurality of failure detection and error correction functions are implemented.

FIG. 6 is a flowchart showing a memory failure detection / correction processing procedure.
First, an ECC check is performed in step S1, and then in step S2, it is determined whether or not a bit error has occurred in the data based on the check result in step S1. When it is determined in step S2 that an abnormality has occurred, the process proceeds to step S3, where the bit error is automatically corrected using the ECC function, and the temporary failure detection signal S = 1 is complemented. Are transferred to step S4.

If it is determined in step S2 that no bit error has occurred in the data due to the ECC check, the process proceeds to step S6 described later.
In step S4, it is determined whether or not the automatic correction by the ECC function is completed. If it is determined that the automatic correction is not normally performed, the process proceeds to step S5, and if it is determined that the automatic correction is normally completed. Shifts to step S6 to be described later.

In step S5, after outputting an abnormality signal indicating that an abnormality has occurred in the data, the failure detection / correction process is terminated.
In step S6, a parity check is performed to refer to the parity bit of the data. Next, in step S7, it is determined whether or not a bit error has occurred in the data based on the check result in step S6. If it is determined in step S7 that an abnormality has occurred, the process proceeds to step S8 to retry the operation instruction (Read / Write) to the memory, and to add the temporary failure detection signal S = 1 to the complementary calculation unit. 23, and the process proceeds to step S9.

In step S9, it is determined whether or not the retry process has been completed. If it is determined that the retry is not normally performed and the correction of the data error is not completed, the process proceeds to step S5, and the retry is normally completed. If it is determined that the data error has been corrected properly, the process proceeds to step S10.
If it is determined in step S7 that no bit error has occurred in the data based on the parity check result, the process proceeds to step S10.

In step S10, a normal signal indicating that the data is normal is output, and then the failure detection / correction process is terminated.
As a result, when a 1-bit error has occurred in the memory data, the error is automatically corrected using the ECC function, and when a multi-bit error that cannot be corrected by the ECC function has occurred, Error correction is performed by retrying the operation command.

In FIG. 6, the processes in steps S1, S2, S6 and S7 correspond to the abnormality detecting means, and the processes in steps S3 and S8 correspond to the abnormality correcting means.
An arithmetic unit (ALU) of the microcomputer is a circuit that actually executes an instruction, and a register is a circuit that temporarily stores data to be executed by the arithmetic unit. Temporary errors such as bit errors can be detected by a parity check function (abnormality detection means). A fault is detected. Since a method for detecting a data error using a parity bit is well known, detailed description thereof is omitted here.

If an error is detected in the register by this parity check function, the data is re-read from the memory and the process is retried. If an error is detected in the arithmetic unit (ALU), the data is read from the register. Shall be re-read and processing should be retried. Each retry process corresponds to the abnormality correcting means.
In addition, even when error detection / retry is performed in a register or an arithmetic unit (ALU), a temporary failure detection signal S having a logical value “1” is output to the complementary operation unit 23.
That is, in these arithmetic units (ALUs) and registers, processing except steps S1 to S4 in FIG. 6 is performed as failure detection / correction processing.

Next, the operation of the controller 15 will be described with reference to the flowchart of FIG.
First, the steering torque T from the torque sensor 14, the vehicle speed V from the vehicle speed sensor 16, and the motor rotation angle θ from the rotation sensor 17 are read (step S101).

  Next, a steering assist torque command value Iref corresponding to the steering torque T and the vehicle speed V is calculated with reference to the steering assist torque command value calculation map shown in FIG. 3 based on the input steering torque T and the vehicle speed V (step S102). Further, the angular velocity calculation unit 31 calculates the angular velocity ω of the electric motor 12 based on the motor rotation angle θ from the rotation sensor 17, and the angular acceleration calculation unit 32 calculates the angular acceleration α (step S103).

  Next, based on the steering torque T, the steering assist torque command value Iref, the motor angular velocity ω, and the motor angular acceleration α, the calculation of the equation (2) is performed to detect the self-aligning torque SAT (step S104).

  Next, a convergence compensation value Ic for compensating the convergence of the yaw rate is calculated based on the motor angular velocity ω, and the inertial feeling or the torque equivalent generated by the inertia of the electric motor 12 is compensated based on the motor angular acceleration α. An inertia compensation value Ii that prevents deterioration of control responsiveness is calculated (step S105), and a compensation value Icom is calculated by adding the convergence compensation value Ic, the inertia compensation value Ii, and the self-aligning torque SAT (step S106). .

The compensation value Icom thus calculated is added to the steering assist torque command value Iref to calculate a post-compensation steering assist torque command value Iref ′ (step S107).
Then, a complementary calculation process is performed on the calculated post-compensation steering assist torque command value Iref ′ to calculate a torque command value Ir after the complementary calculation (step S108). Here, when a data error has occurred in any of the memory, register, and arithmetic unit (ALU), and the temporary failure detection signal S having a logical value “1” is input, the torque command used in the previous sampling is used. When the value Ir is set as the torque command value Ir after the complementary calculation, and no data error has occurred, and the temporary failure detection signal S having the logical value “0” is input, after the compensation calculated by the current sampling The steering assist torque command value Iref ′ is set as the torque command value Ir after the complement calculation.

Next, the d-axis current command value Id ^* is calculated based on the torque command value Ir, the q-axis current command value Iq ^* is calculated (step S109), and then the dq-axis current command values Id ^* and Iq are calculated. Each phase current deviation ΔId, ΔIq is calculated by subtracting the dq axis motor currents Id, Iq obtained from the motor currents Iu, Iv, Iw by three-phase / 2-phase conversion from ^* (step S110). ).

  Then, PI control processing is performed on these current deviations ΔId and ΔIq to calculate voltage command values Vd and Vq (step S111). Finally, the voltage command values Vd and Vq are converted into two-phase / 3-phase. The obtained voltage command values Vu, Vv, and Vw are subjected to pulse width modulation to form a pulse width modulation signal, and the formed pulse width modulation signal is output to the inverter 66 (step S112).

  Thereby, three-phase motor drive currents Iu, Iv, and Iw are output from the inverter 66 to the electric motor 12, and the electric motor 12 is driven and controlled, so that the optimum steering assist force according to the steering torque T and the vehicle speed V is obtained. The steering assist force is transmitted to the steering shaft 2 via the reduction gear 11.

  At this time, if no data error occurs in the memory, register, and arithmetic unit (ALU) of the microcomputer, the complementary arithmetic processing unit 23 obtains the post-compensation steering assist torque command value Iref ′ calculated by the current sampling. The torque command value Ir after the complement calculation is adopted, and the electric motor 12 is driven and controlled based on the torque command value Ir. Therefore, normal steering assist control is performed, and the driver's steering operation of the steering wheel 1 can be accurately assisted.

  From this state, for example, if a 1-bit error occurs in the memory, it is determined in the failure detection / correction process shown in FIG. 6 that a data error has occurred due to the ECC check, and the 1-bit error is detected using the ECC function. Automatically correct errors. At this time, a temporary failure detection signal S = 1 is formed and output to the complementary calculation processing unit 23.

  For this reason, in the complementary calculation processing unit 23, the torque command value Ir used in the previous sampling is set as the current torque command value Ir as it is. The electric motor 12 is driven and controlled based on the torque command value Ir.

As described above, since a temporary failure such as a bit error which is a small error before the CPU runaway is detected and corrected, the CPU runaway can be prevented and the arithmetic processing of the steering assist control can be continued.
In addition, since the calculation delay occurs in the sampling in which the data error is detected and corrected, the steering assist control is continued using the calculation result of the previous sampling in the sampling in which the error detection and correction is performed. As a result, it is possible to continue the assist while minimizing the influence on the assist, such as preventing a system failure caused by continuing the calculation with the delay.

  Since the delay time due to the correction function such as retry is short for the control of the motor, the assist torque output from the motor hardly changes even when the control is performed using the previous torque command value. Accordingly, the steering assist can be continued without causing the driver to feel uncomfortable.

  By the way, as a method of detecting a temporary failure such as a bit error, a method of performing the same operation in two systems and comparing the results is known. However, in this case, although it is possible to detect a mismatch between the calculation results, it is not possible to determine which calculation result is correct, and thus the assist cannot be continued.

Therefore, it is conceivable that the correct calculation result is selected by carrying out three systems of calculations and taking a majority decision, and the assist is continued. In this case, however, the calculation load becomes large.
On the other hand, in this embodiment, since the failure detection / correction function of the microcomputer hardware is used, a data error can be detected / corrected without increasing the calculation load, thereby improving the reliability of the microcomputer. be able to.

And the reliability of an electric power steering apparatus can also be improved by utilizing the said failure detection and correction function for control of an electric power steering apparatus.
In addition, by applying an ECC function as an abnormality detection means for detecting a temporary failure, if a 1-bit error has occurred in the data, the bit error can be automatically corrected using this ECC function.

Furthermore, by applying a parity check function as an abnormality detection means for detecting a temporary failure, it is possible to detect a bit error in data without requiring a complicated calculation.
Here, the process of FIG. 7 corresponds to the control means, of which the process of step S102 corresponds to the steering assist torque command value calculation unit 21, the processes of steps S103 to S106 correspond to the command value compensation unit 22, The process of S108 corresponds to the complementary calculation unit 23, and the processes of steps S109 to S112 correspond to the motor current control unit 24.

  In the above embodiment, when any error detection / correction of the memory, register, or arithmetic unit (ALU) of the microcomputer is performed, the complementary operation unit 23 uses the torque command value Ir used in the previous sampling this time. The torque command value Ir is output as the current torque command value Ir. However, the current torque command value is calculated based on the torque command value calculated in the previous sampling, such as a complementary calculation based on the previous torque command value and the previous torque command value. The command value may be estimated and calculated and output. That is, the complementary calculation unit 23 may be configured as shown in FIG. The complementary calculation unit 23 shown in FIG. 8 corresponds to current command value complementary calculation means.

  Furthermore, in the above embodiment, the case where the present invention is applied to a column-type electric power steering apparatus in which an electric motor is connected to a steering shaft via a speed reduction mechanism has been described. The present invention can also be applied to a pinion type electric power steering apparatus that connects an electric motor or a rack type electric power steering apparatus that connects an electric motor to a rack shaft via a speed reducer.

  Furthermore, although the case where the present invention is applied to a brushless motor has been described in the above embodiment, the present invention can also be applied to a motor with a brush. In this case, for example, the motor angular velocity ω may be estimated from the back electromotive force of the motor.

1 is a schematic configuration diagram of an electric power steering apparatus according to an embodiment of the present invention. It is a block diagram which shows the structure of the controller in this embodiment. It is a steering assist torque command value calculation map. It is a schematic diagram with which it uses for description of the self-aligning torque. It is a block diagram which shows the specific structure of a complement calculating part. It is a flowchart which shows an error correction processing procedure. It is a flowchart which shows an example of the process sequence of a controller. It is a block diagram which shows the other example of a complement calculating part.

Explanation of symbols

  SM ... steering mechanism, 1 ... steering wheel, 2 ... steering shaft, 3 ... steering column, 4, 6 ... universal joint, 5 ... intermediate shaft, 8 ... steering gear, 10 ... steering assist mechanism, 11 ... reduction gear, 12 ... Electric motor, 14 ... steering torque sensor, 15 ... controller, 16 ... vehicle speed sensor, 17 ... rotation sensor, 21 ... steering assist torque command value calculation unit, 22 ... command value compensation unit, 23 ... complementation calculation unit, 24 ... motor current Control unit

Claims (6)

Steering torque detection means for detecting a steering torque input to a steering mechanism for turning steered wheels; an electric motor for applying a steering assist force to the steering mechanism; and a current command value based on the steering torque; An electric power steering device having control means for controlling the electric motor based on the calculated current command value,
An abnormality detection means for detecting an abnormality occurring in the control means, and an abnormality correction means for correcting the abnormality when the abnormality detection means detects an abnormality, the control means correcting the abnormality by the abnormality correction means Is executed, the electric motor is controlled based on the current command value calculated by the previous sampling.   The control means is constituted by a microcomputer, the abnormality detection means detects a data bit error based on an ECC function of the microcomputer, and the abnormality correction means detects an abnormality by the abnormality detection means. The electric power steering apparatus according to claim 1, wherein the bit error is automatically corrected using the ECC function.   The control means is constituted by a microcomputer, the abnormality detection means detects a data bit error based on a parity check function of the microcomputer, and the abnormality correction means detects an abnormality by the abnormality detection means. 3. The electric power steering apparatus according to claim 1, wherein the bit error is corrected by retrying processing of a part where an abnormality is detected.   4. The electric power steering apparatus according to claim 2, wherein at least one of a memory, an arithmetic unit, and a register of the microcomputer includes the abnormality detection unit.   When the abnormality correction is performed by the abnormality correction unit, the control unit controls the electric motor using the current command value calculated in the previous sampling as a current command value output in the current sampling. The electric power steering apparatus according to any one of claims 1 to 4.   The control means includes a current command value complement calculation means for estimating a current command value output in the current sampling based on the current command value calculated in the previous sampling, and the abnormality correction means corrects the abnormality. The electric power steering apparatus according to any one of claims 1 to 4, wherein when the operation is executed, the electric motor is controlled based on a current command value estimated by the current command value complement calculation means. .

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