JP2002347635A - Electric power steering device - Google Patents

Abstract

(57) [Problem] To improve the accuracy of detecting an abnormal state of a steering assist circuit that outputs a steering assist instruction current to an electric motor that applies a steering assist force, and to prevent unnecessary stoppage of a device due to erroneous determination. To provide an electric power steering device that can operate. Kind Code: A1 A difference value calculating means for calculating a difference value between an actual current detected by a current detecting means and a steering assist instruction current output from a steering assist circuit, and a difference value calculating means for calculating a difference value. Abnormality detecting means d for detecting abnormality of the steering assist circuit when a difference value between the actual current and the steering assist instruction current output from the steering assist circuit a exceeds a predetermined abnormality detection threshold value; Command current change rate calculating means e for calculating the change rate of the motor, and when the change rate of the steering assist command current calculated by the command current change rate calculating means e is equal to or more than a predetermined value, the abnormality detection means d is prohibited from detecting the abnormality. Abnormality detection inhibiting means f.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric power steering device for applying a steering assist force by an electric motor to a steering shaft, and more particularly, to an abnormality in a steering assist circuit for outputting a steering assist instruction current to an electric motor for applying a steering assist force. And a technology for detecting the same.

[0002]

2. Description of the Related Art As a conventional electric power steering apparatus equipped with this kind of abnormality detecting means, for example, an electric power steering apparatus described in JP-A-63-180567 is known. That is, in general, in the electric power steering device, when an abnormality occurs in the steering assist circuit, such as a short circuit of the power element of the power element unit that controls the current and the direction of the current supplied to the electric motor that applies the steering assist force, In the related art, in order to prevent such a problem that the wiring is burned out or a problem such as inability to use the battery occurs.
As shown in the time chart of FIG. 9, a steering assist instruction current calculated based on a steering torque signal detected by a torque sensor for driving the electric motor, and the electric motor is actually supplied to the electric motor based on the steering assist instruction current. When the difference from the actual current flowing exceeds a predetermined abnormality detection threshold and the state continues for a certain period of time, it is determined that the steering assist circuit such as the power element unit is abnormal, and each power element is turned off as abnormality processing. It was intended to be switched.

[0003]

However, in the conventional power steering apparatus, as described above, the difference between the steering assist command current for the electric motor and the actual current actually flowing in the electric motor is a predetermined abnormality. Since the abnormality was determined based on whether the detection threshold was exceeded,
There were the following problems.

[0004] That is, when the turning speed is low, there is no problem. However, when the turning speed is high, the rate of change (= differential value) of the steering assist instruction current is large. The value cannot immediately follow the change in the steering assist command current, and therefore, the difference between the steering assist command current value and the actual current value may temporarily increase. As a result, the steering assist circuit such as the power element unit is determined to be abnormal although it is normal, and the device is unnecessarily stopped.

[0005] As described above, the steering assist command current is calculated based on the steering torque signal detected by the torque sensor, as shown in the time chart of FIG.
Input (disturbance) from the road surface is detected by the torque sensor,
This causes the steering assist instruction current to fluctuate rapidly irrespective of the actual steering torque, thereby causing the same problem as in the case where the steering speed is high.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and improves the accuracy of detecting an abnormal state of a steering assist circuit that outputs a steering assist instruction current to a motor that applies a steering assist force. An object of the present invention is to provide an electric power steering device that can prevent unnecessary stoppage of a device due to erroneous determination.

[0007]

In order to achieve the above object, an electric power steering apparatus according to claim 1 of the present invention detects a torque acting on a steering shaft as shown in a claim correspondence diagram of FIG. A torque sensor, a motor that applies a steering assist force to the steering shaft, and a steering assist circuit a that outputs a steering assist instruction current to the motor based on a torque signal acting on the steering shaft detected by the torque sensor.
Current detection means b for detecting an actual current actually input to the motor; calculating a difference value between the actual current detected by the current detection means b and a steering assist instruction current output from the steering assist circuit a; A difference value calculating means for detecting the abnormality of the steering assist circuit when a difference value between the actual current calculated by the difference value calculating means c and the steering assist instruction current exceeds a predetermined abnormality detection threshold value. In the electric power steering apparatus provided with abnormality detecting means d, a command current change rate calculating means e for calculating a change rate of the steering assist command current, and a steering assist command calculated by the command current change rate calculating means e. Abnormality detection inhibiting means f for inhibiting the abnormality detection by the abnormality detecting means d when the current change rate is equal to or more than a predetermined value.

According to a second aspect of the present invention, there is provided the electric power steering apparatus according to the first aspect, wherein the abnormality detecting means includes an actual current calculated by the difference value calculating means, a steering assist instruction current, When a state in which the difference value exceeds a predetermined abnormality detection threshold value continues for a predetermined time, an abnormality of the steering assist circuit a is detected. A means configured to prohibit abnormality detection by stopping the continuous counting of the predetermined time in the abnormality detection means when the rate of change of the steering assist instruction current calculated by the means e is equal to or more than a predetermined value; did.

According to a third aspect of the present invention, in the electric power steering apparatus according to the first or second aspect, the abnormality detection threshold value of the steering assist circuit a is variably set according to the steering assist instruction current. Means for setting a threshold value.

According to a fourth aspect of the present invention, in the electric power steering apparatus according to any one of the first to third aspects, the command current change rate calculating means e is provided.
Is a means configured to be calculated based on a difference between the current value and the n-th previous value of the steering assist instruction current.

[0011]

According to the first aspect of the present invention, as described above, the difference value between the actual current calculated by the difference value calculation means c and the steering assist instruction current exceeds a predetermined abnormality detection threshold value. In this case, the abnormality detection means d detects an abnormality in the steering assist circuit a. However, when the change rate of the steering assist instruction current calculated by the instruction current change rate calculation means e is equal to or more than a predetermined value, the abnormality detection inhibition means f In the process, the process of prohibiting the abnormality detection by the abnormality detecting means d is performed.
As a result, erroneous determination of abnormality detection due to a high steering speed or road surface input (disturbance) can be prevented, and unnecessary stoppage of the device can be avoided.

In the electric power steering apparatus according to the second aspect, the abnormality detecting means d determines a difference value between the actual current calculated by the difference value calculating means c and the steering assist instruction current at a predetermined abnormality detection threshold value. The abnormality detection prohibiting means f is configured to detect an abnormality of the steering assist circuit a only when the state of exceeding the predetermined time continues for a predetermined time. Is a process for prohibiting abnormality detection by stopping the continuous counting of the predetermined time in the abnormality detecting means d. This makes it possible to detect an error when the steering speed is high or when abnormality is detected due to road surface input (disturbance). The judgment prevention effect is enhanced,
The effect of avoiding unnecessary stoppage of the device can be enhanced.

In the electric power steering apparatus according to the third aspect, as described above, the threshold value setting means variably sets the abnormality detection threshold value of the steering assist circuit a in accordance with the steering assist instruction current. Accurate abnormality detection can be performed.

In the electric power steering apparatus according to the fourth aspect, as described above, the command current change rate calculating means c is
By using the means for calculating the difference between the previous value and the current value of the steering assist command current, the command current change rate can be calculated without using a special sensor.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. (Embodiment 1) First, Embodiment 1 of the present invention
Corresponds to the invention of claims 1 to 4,
The configuration will be described with reference to FIGS.

FIG. 2 is an overall schematic diagram showing the electric power steering apparatus according to Embodiment 1 of the present invention. As shown in FIG. 2, when the steering wheel 1 is manually rotated, the rotation is changed to the steering shaft (input). Shaft) 2, a steering shaft (output shaft) 5, a universal joint 6, an intermediate shaft 7, and a universal joint 8 to be transmitted to a pinion shaft 9, and the pinion shaft 9 is screwed into the rack shaft 10 to rotate the pinion shaft 9. Is converted into a linear motion of the rack shaft 10, and this linear motion changes (steers) the directions of the left and right front wheels via the tie rods 11a and 11b. And the steering shaft (input shaft) 2
The steering shaft (output shaft) 5 is configured to be rotatable via the speed reducer 4 by an electric motor 12 provided between the steering shaft (output shaft) 5 and the steering shaft (output shaft) 5, thereby assisting the manual steering force. It has become.

The motor 12 is subjected to steering assist control by a steering assist circuit incorporated in a control unit 13 mounted on the vehicle, based on a signal from a torque sensor 3 for detecting a manual steering force. , The steering force is manually assisted. The steering assist circuit of the control unit 13 includes a vehicle speed sensor 14.
Is input. Note that in FIG.
5 is an ignition switch, and 16 is a battery mounted on the vehicle.

Next, the specific configuration of the control unit 13 will be described with reference to a control system block diagram of FIG. 3. A steering torque calculating means 13a calculates a steering torque based on an input signal from the torque sensor 3. On the other hand, the vehicle speed calculating means 13b calculates the vehicle speed based on the input signal from the vehicle speed sensor. Then, the following command current calculating means 13c calculates a steering assist command current (hereinafter simply referred to as a command current) icmd to be output to the electric motor 12, according to the steering torque signal and the vehicle speed signal.

In the following PWM duty determining means 13d, the on-duty ratio in the PWM (pulse width modulation) operation of the motor 12 is determined based on the command current icmd and the actual current i detected by the motor current detecting means described later. P of determined on-duty ratio
The WM signal is output to the power element driving means 13f. The power element driving means 13f drives the gates of the power elements 13i, 13j, 13k, and 131 of the power element section P based on the PWM signal of the on-duty ratio to drive the power elements 13i, 13j, 13k, 13l
Is switched, whereby an energizing direction instruction to the electric motor 12 and an ON / OFF instruction for controlling the energizing current value are issued.

Incidentally, the steering torque calculating means 13
a, vehicle speed calculating means 13b, command current calculating means 13c, P
WM duty determining means 13d, power element driving means 1
A steering assist circuit that outputs a command current icmd to the electric motor 12 is configured by 3f and the power element unit P.

In the current detecting means 13e, the motor 1
A voltage difference is taken out from both ends of a shunt resistor 13h constituting a current sensor inserted in series in the middle of the second drive power supply line L, and an actual current flowing to the electric motor 12 is based on this voltage difference (voltage drop value). The current i is detected, and the actual current i is output to the PWM duty determining means 13d and the abnormality detecting means 13g.

The abnormality detecting means 13g detects an abnormality in the PWM duty determining means 13d, the power element driving means 13f, and the power element section P in the steering assist circuit. More specifically, the abnormality detection unit 13g creates an abnormality determination threshold value and detects an abnormality.

Next, a method of creating an abnormality determination threshold value and an abnormality determination method in the abnormality detection means 13g will be described with reference to FIG.
This will be described in detail based on the flowchart of FIG. First, in step S101, the command current icmd output from the command current calculation unit 13c is read, and in step S102 (command current change rate calculation unit), the command current icmd read from the command current icmd read in step S101 is read. The rate of change (dicmd / dt) is determined.

FIG. 5 is a block diagram showing a method of calculating the indicated current change rate, and FIG. 6 is a control block diagram showing further details thereof. First, a high-pass filter HPF (fc = 50
Hz), the current value icmd of the indicated current is differentiated, and a high-frequency component is removed by a low-pass filter LPF (fc = 200 Hz).
dicmd / dt is required. In FIG. 6, icmd (n)
Is the current value of the command current, icmd (n-1) is the value immediately before the command current, and K1 and K2 are transfer functions τ of the high-pass filter HPF.
s (1 + τs) is converted to a bilinear transform T (1-Z ⁻¹ ) / 2 (1-
Coefficients when discretized by Z ^-1 ), K3 and K4 are coefficients when transfer function 1 (1 + τs) of low-pass filter LPF is discretized by bilinear transformation in the same manner as HPF, and Z ^-1 is a high-pass filter HPF. One time before the output of each low-pass filter LPF, T represents a sample time.

In the following step S103, the command current icmd
After performing the process of converting the rate of change (dicmd / dt) into the absolute value | dicmd / dt |, the process proceeds to step S104.

In this step S104, it is determined whether or not the absolute value | dicmd / dt | of the indicated current change rate is less than a count-up suspension threshold Thd, and YES (| dicmd / d
When t | <Thd), the process proceeds to step S105 to perform the abnormality determination process.

In step 105, after reading the actual current i actually flowing through the motor 12 detected by the motor current detecting means 13e, the process proceeds to step S106 (difference value calculating means), where the command current icmd and the actual current i are calculated. Absolute difference id of
ef (= | idef-i |) is calculated.

In the following step 107, the absolute difference value idef
Is compared with the current abnormality detection threshold value Thi, and the absolute difference id
It is determined whether or not ef is greater than or equal to the current abnormality detection threshold value Thi. If YES (idef ≧ Thi), there is a possibility that an abnormality has occurred in the steering assist circuit. After incrementing the error counter Cerr of the timer by 1, the process proceeds to step S109.

In this step S109, it is determined whether or not the error counter Cerr of the abnormality detection timer is equal to or greater than the timer threshold Thr, and if YES (Cerr ≧ Thr),
It is determined that some abnormality has occurred in the steering assist circuit,
After proceeding to step S110, the abnormality detection flag f_ierr is set to 1, and then proceeding to step S111, abnormality processing is performed, and one flow is completed.

In step S104, NO (| dic
If md / dt | ≧ Thd), the abnormality counter Cerr is not set to 0 when the turning speed is high or as temporary due to road surface input (disturbance), and the error counter Cerr is set to 0.
Is reset to “1”.
After resetting f_ierr to 0, this ends one flow.

The determination in step S107 is NO.
When (idef <Thi), since the steering assist circuit is operating normally, the process proceeds to step S112 to reset the error counter Cerr to 0, and then resets the abnormality detection flag f_ierr to 0 in step S113. This completes one flow.

If the determination in step S109 is NO
If (Cerr <Thr), it is determined that this is due to a temporary fluctuation of the actual current i, and the process proceeds to step S113 (abnormality detection prohibiting means) to reset the abnormality detection flag f_ierr to 0. Ends the flow.

Next, the operation and effect of the first embodiment of the present invention will be described with reference to the time chart of FIG. In the electric power steering apparatus according to Embodiment 1 of the present invention, as described above, the difference value calculating means (Step S1)
06) When the absolute difference value idf between the actual current i and the command current icmd calculated in step 06) exceeds a predetermined abnormality detection threshold value Thi, it is highly likely that an abnormality has occurred in the steering assist circuit. However, as shown in the time chart of FIG. 7, there is a possibility that the command current icmd temporarily fluctuates (increases) when the steering speed is high or due to road surface input (disturbance).
That is, as described above, the command current icmd is calculated based on the steering torque signal detected by the torque sensor 3, and the input from the road surface is detected by the torque sensor 3, whereby the actual steering torque and Causes the command current icmd to vary independently.

Therefore, in such a case, the command current change rate calculated by the command current change rate calculating means (step S102) is used.
It is determined whether or not the absolute value | dicmd / dt | of the rate of change of icmd (dicmd / dt) is less than the count-up suspension threshold Thd,
It is determined that there is a possibility of an abnormality in the steering assist circuit only when the steering speed is less than the threshold value. When the steering speed is higher than the threshold value, it is determined that the steering speed is high or due to road surface input (disturbance). By performing the process of prohibiting abnormality detection, erroneous determination of abnormality detection due to a high steering speed or road surface input (disturbance) can be prevented, whereby unnecessary stoppage of the device can be avoided.

In the abnormality detecting means, the absolute difference value idef between the actual current i and the command current icmd calculated by the difference value calculating means (step S106) exceeds a predetermined abnormality detection threshold value Thi. When the state (error counter Cerr) continues for a predetermined time (timer threshold Thr) (Cerr ≧ Thr)
First, an abnormality of the steering assist circuit is configured to be detected for the first time (step S109), and the abnormality detection inhibiting means (steps S104, S112) sets the absolute value of the rate of change (dicmd / dt) of the command current icmd to | When dicmd / dt | is greater than or equal to the count-up hold threshold Thd, the abnormality detecting means stops the continuous counting of the abnormality detection timer to prevent the error counter Cerr from exceeding the abnormality determination threshold Thi. By performing the process of prohibiting abnormality detection, the effect of preventing erroneous determination of abnormality detection due to a high turning speed or road surface input (disturbance) is enhanced, and the effect of avoiding unnecessary stoppage of the device is enhanced. Will be able to do it.

As described above in detail, in the electric power steering apparatus according to the first embodiment of the present invention, the accuracy of detecting an abnormal state of the steering assist circuit that outputs the steering assist instruction current to the electric motor that applies the steering assist force. And it is possible to prevent unnecessary stoppage of the apparatus due to erroneous determination.

Next, another embodiment of the present invention will be described.
In describing other embodiments of the present invention,
The same components as those in the first embodiment of the invention are omitted from the drawings and description, or the same reference numerals are given and the description is omitted, and only different points will be described.

(Embodiment 2) An electric power steering apparatus according to Embodiment 2 of the present invention is different from Embodiment 1 in that an instruction in step S102 (instruction current change rate calculating means) of FIG. The calculation method of the current change rate dicmd / dt is different.

FIG. 8 is a control block diagram showing a method of calculating the indicated current change rate according to the second embodiment of the present invention. As shown in FIG. 8, a moving average process for removing the high frequency component of the indicated current icmd is performed twice. , The calculation of the instruction current change rate is performed. That is, the current value icmd (n) of the command current is calculated from the sum of the current value icmd (n) of the command current and the immediately preceding value icmd (n-1) of the command current.
(n) The value icmd (nm) m times before and the value icmd m times before the indicated current
(nm) is subtracted from the previous value icmd (nm-1).
m) The change rate of the command current icmd is calculated by calculating the change value of the command current icmd over time and multiplying the change value by a gain K (1 / dt corresponding to (nm) time). It was made.

As described above, in the second embodiment of the present invention, the command current change rate calculating means is a means for calculating the difference between the previous value and the current value of the command current icmd,
Indication current change rate dicmd / dt without using special sensor
Can be calculated, thereby making it possible to reduce the size of the device and reduce the cost.

Although the embodiments of the present invention have been described with reference to the drawings, the specific configuration is not limited to those embodiments of the present invention, and there are design changes and the like without departing from the scope of the present invention. Are also included in the present invention.

For example, in the embodiment of the invention, the abnormality determination threshold value Thi is fixed, but the threshold value setting means variably sets the abnormality detection threshold value according to the steering assist instruction current. More accurate abnormality detection can be performed.

[0043]

As described above, in the electric power steering apparatus according to the first aspect of the present invention, as described above, the actual current detected by the current detection means and the steering assist instruction current output from the steering assist circuit are provided. A difference value calculating means for calculating a difference value between the steering assist circuit and a steering assist circuit when a difference value between the actual current calculated by the difference value calculating means and the steering assist instruction current exceeds a predetermined abnormality detection threshold value. An electric power steering apparatus comprising: an abnormality detection unit that detects an abnormality; a command current change rate calculation unit that calculates a change rate of the steering assist command current; and a steering assist calculated by the command current change rate calculation unit. Means for prohibiting abnormality detection by the abnormality detecting means when the rate of change of the command current is equal to or greater than a predetermined value. An erroneous determination of abnormality detection due to (disturbance) is prevented, whereby an effect is obtained that unnecessary stoppage of the device can be avoided.

According to the second aspect of the present invention, as described above, the abnormality detecting means detects a predetermined abnormality in the difference value between the actual current calculated by the difference value calculating means and the steering assist instruction current. When the state exceeding the threshold value continues for a predetermined time, an abnormality of the steering assist circuit is detected, and the abnormality detection prohibiting means detects the rate of change of the steering assist instruction current calculated by the instruction current change rate calculating means. When the steering speed is high, or when road surface input (disturbance) occurs, the abnormality detection means stops the continuous count for a predetermined period of time to prohibit abnormality detection. As a result, the effect of preventing erroneous determination of abnormality detection can be enhanced, and the effect of avoiding unnecessary device stoppage can be enhanced.

According to a third aspect of the present invention, there is provided an electric power steering apparatus comprising a threshold setting means for variably setting an abnormality detection threshold of a steering assist circuit in accordance with the steering assist command current. More accurate abnormality detection according to the change in the instruction current can be performed.

According to a fourth aspect of the present invention, in the electric power steering apparatus, the command current change rate calculating means is configured to be calculated based on a difference between a previous value and a n-th previous value of the steering assist command current. By doing so, it becomes possible to calculate the indicated current change rate without using a special sensor, thereby making it possible to reduce the size and cost of the device.

[Brief description of the drawings]

FIG. 1 is a diagram corresponding to claims of the present invention.

FIG. 2 is an overall schematic diagram showing the electric power steering device according to the first embodiment of the present invention.

FIG. 3 is a system block diagram illustrating the electric power steering device according to the first embodiment of the present invention;

FIG. 4 is a flowchart showing a method for determining an abnormality in the electric power steering device according to the first embodiment of the present invention.

FIG. 5 is a block diagram illustrating a method of calculating an abnormality determination threshold value in the electric power steering device according to the first embodiment of the present invention.

FIG. 6 is a control block diagram illustrating a method for calculating an abnormality determination threshold value in the electric power steering device according to the first embodiment of the present invention.

FIG. 7 is a time chart showing operation contents of abnormality detection means in the electric power steering device according to the first embodiment of the present invention.

FIG. 8 is a control block diagram illustrating a method for calculating an abnormality determination threshold value in the electric power steering device according to the second embodiment of the present invention.

FIG. 9 is a time chart showing the operation of an abnormality detecting means in the conventional electric power steering apparatus.

[Explanation of symbols]

 Reference Signs List 1 steering wheel 2 steering shaft 3 torque sensor 4 speed reducer 5 steering shaft 6 universal joint 7 intermediate shaft 8 universal joint 9 pinion shaft 10 rack shaft 11a tie rod 11b tie rod 12 electric motor 13 control unit 14 vehicle speed sensor 15 ignition switch 16 battery L drive power supply Line P Power element

Claims (4)

[Claims] A torque sensor that detects a torque acting on a steering shaft; an electric motor that applies a steering assist force to the steering shaft; and a motor that outputs a torque to the electric motor based on a torque signal detected by the torque sensor that acts on the steering shaft. A steering assist circuit that outputs a steering assist command current; a current detecting unit that detects an actual current that is actually input to the electric motor; a steering current that is detected by the current detecting unit and a steering that is output from the steering assist circuit A difference value calculating means for calculating a difference value between the assist instruction current and the steering operation when the difference value between the actual current calculated by the difference value calculation means and the steering assist instruction current exceeds a predetermined abnormality detection threshold value An electric power steering apparatus comprising: an abnormality detection unit that detects abnormality of an auxiliary circuit; an instruction current change rate calculation unit that calculates a change rate of the steering assist instruction current; An electric power steering system comprising: an abnormality detection prohibiting unit that prohibits the abnormality detection unit from detecting an abnormality when a change rate of the steering assist instruction current calculated by the conversion ratio calculation unit is equal to or more than a predetermined value. apparatus. 2. The apparatus according to claim 1, wherein the abnormality detecting means is provided when a state in which a difference value between the actual current calculated by the difference value calculating means and the steering assist instruction current exceeds a predetermined abnormality detection threshold value has continued for a predetermined time. The abnormality detection inhibiting means is configured to detect an abnormality of the steering assist circuit, and the abnormality detection prohibiting means is configured to detect the abnormality in the abnormality detection means when a change rate of the steering assist instruction current calculated by the instruction current change rate calculation means is equal to or more than a predetermined value 2. The electric power steering apparatus according to claim 1, wherein the abnormality detection is prohibited by stopping the continuous counting of the predetermined time. 3. A threshold setting means for variably setting an abnormality detection threshold of the steering assist circuit according to the steering assist command current.
The electric power steering device according to claim 1. 4. The control device according to claim 1, wherein the command current change rate calculating means is configured to calculate the steering assist command current based on a difference between an n-times preceding value and a current value of the steering assist command current. The electric power steering device according to any one of the above.