JP5130685B2 - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device capable of storing history information necessary and sufficient for investigation of causes of assist shortage related to steering assist. <P>SOLUTION: A control part 8 calculates a target current value of an electric current to be fed to a motor 6 at normal time and a limit current value of an electric current to be fed to the motor 6 during protection control at the time of continuation of high load or during overheat protection control. When the target current value successively exceeds the limit current value, the control part 8 stores, in an EEPROM 9, only the latest three pieces of predetermined history information regarding the limit current value corresponding to the maximum value of a subtraction result obtained by subtracting the limit current value from the target current value until the limit current value successively exceeds a predetermined threshold value. Thus, the history information necessary and sufficient for investigation of causes of assist shortage can be stored in the EEPROM 9 with a small storage capacity. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to an electric power steering apparatus that assists steering by a rotational force of a motor that is driven and controlled based on a detection result of steering torque applied to a steering member.

  An electric power steering device that drives a motor to assist steering and reduces the burden on the driver includes an input shaft that is connected to a steering member (steering wheel, steering wheel), and an output shaft that is connected to a steering wheel by a pinion, a rack, etc. And a connecting shaft that connects the input shaft and the output shaft, and a torque sensor detects a steering torque applied to the input shaft based on a torsion angle generated in the connecting shaft, and a steering that connects to the output shaft based on the detected steering torque value. Drive control of the auxiliary motor.

  In such an electric power steering device, by carrying out two current limiting controls of high load continuation protection control and overheat protection control, excessive current consumption is avoided, and malfunctions due to overheating of the motor and the motor drive circuit are obviated. There is something to prevent.

In the high load continuation protection control, for example, the current flowing to the motor is temporarily limited when the high load state is reached near the end position of the steering member, and the current is quickly limited when the high load state stops. In order to avoid overheating by avoiding excessive current consumption at high load, the overheat protection control is prevented from reaching early.
On the other hand, in the overheat protection control, for example, the temperature of the motor and the motor drive circuit is estimated based on the integrated amount of the current flowing to the motor, and when the estimated temperature exceeds a predetermined temperature, the current flowing to the motor is changed for a relatively long time. The limit is made, and when the restriction of the current is released, it is gradually released.

In Patent Document 1, in order to keep the driver's steering feeling good when the current limit is released, an electric motor that allows an increase in the current flowing through the motor when the steering torque value detected by the torque sensor is equal to or greater than a predetermined value. A power steering device is disclosed.
JP 2001-171540 A

In the overheat protection control, the current flowing through the motor is limited for a long time by the current limiting control, so that the output of the steering assist motor is insufficient (assist is insufficient), and the steering force is extremely heavy for a long time. For this reason, it may be pointed out by the user that the same phenomenon occurs as when the fail-safe function is activated (for example, the steering wheel is heavy or power steering does not work).
Investigate the phenomenon of insufficient assist, point out whether overheat protection control worked or fail-safe function worked, and to identify the cause, if history information about current limit is stored Easy to analyze.

In the electric power steering device of Patent Document 1, when the current flowing through the motor is largely restricted by current restriction control, the difference between the restricted current value and the unrestricted current value is stored as history information. I have to do it.
However, in this case, since the history information is stored every time the current flowing through the motor is greatly limited, unnecessary history information is stored and the amount of information increases. It is necessary to increase the storage capacity.

  The present invention has been made in view of such circumstances, and its main object is that the target current value of the current to be passed through the motor exceeds the limit current value of the current to be passed through the motor under predetermined conditions. In this case, the minimum history information necessary and sufficient for investigating the cause is saved by adopting a configuration for storing predetermined history information related to the limit current value corresponding to the maximum difference between the target current value and the limit current value. Accordingly, an object of the present invention is to provide an electric power steering apparatus capable of reducing the storage capacity of the storage means for storing history information.

  Another object of the present invention is that, when the target current value continuously exceeds the limit current value, a subtraction result obtained by subtracting the limit current value from the target current value until the limit current value continuously exceeds a predetermined threshold value. An object of the present invention is to provide an electric power steering apparatus capable of storing history information necessary and sufficient for investigating the cause of lack of assisting by storing predetermined history information corresponding to the maximum value.

  Another object of the present invention is to provide an electric power steering system capable of preventing the storage of history information unnecessary for investigating the cause of insufficient assistance by adopting a configuration in which history information is not stored when the vehicle speed is equal to or higher than a predetermined vehicle speed. To provide an apparatus.

  Still another object of the present invention is a configuration in which, when a predetermined number of history information is stored, the history information with the oldest time-series information included in the history information is deleted when new history information is stored. Thus, an object of the present invention is to provide an electric power steering apparatus that can prevent the storage of history information that is unnecessary for investigating the cause of insufficient assist.

An electric power steering device according to a first aspect of the invention is based on a torque sensor for detecting a steering torque value applied to a steering member, a motor for assisting steering, and a steering torque value detected by the torque sensor. A current setting means for determining a target current value related to a power current; and a current limiting means for determining a limit current value related to the current under a predetermined condition, the target current value determined by the current setting means or the current setting means In the electric power steering apparatus that assists steering by flowing a current based on the limit current value determined by the motor to the motor, when the target current value exceeds the limit current value, the target current value and the limit current corresponding to the maximum difference between the values, comprising a history storage means for storing a predetermined history information on the limited current value, as subsequent history storage means, the target electric A first comparison means for comparing the value and the limit current value, a threshold having a value equal to or greater than the target current value, a second comparison means for comparing the limit current value, and the first comparison means, the target current A first number determination means for determining whether or not it has been determined M times (M is a natural number of M> 1) that the value has exceeded the limit current value; and the second comparison means includes the limit current value A second number determination means for determining whether or not N is determined to have exceeded the threshold continuously (N is a natural number where N> 1), and a subtraction result obtained by subtracting the limit current value from the target current value From the time when the subtracting means for obtaining the value and the first number of times determining means determine that M has been determined consecutively until the second number of times determining means determines that N has been determined continuously. Maximum value calculating means for obtaining the maximum value of the subtraction result obtained by the subtracting means, and the maximum value Corresponds to the maximum value means calculated out, characterized Rukoto and storage means for storing a predetermined history information on the limited current value.

The electric power steering apparatus according to the second aspect of the present invention includes vehicle speed detection means for detecting a vehicle speed, and when the vehicle speed detected by the vehicle speed detection means is equal to or higher than a predetermined vehicle speed, the storage means is prohibited from storing history information. It is characterized by that.

In the electric power steering apparatus according to a third aspect of the invention, the history information includes time-series information corresponding to the maximum value, and a number determination unit that determines whether or not a predetermined number of history information is stored in the storage unit. When the number determination unit determines that a predetermined number is stored, when the storage unit stores new history information, the history information with the oldest time-series information included in the history information is stored. And erasing means for erasing.

  In the case of the electric power steering device according to the first aspect of the present invention, when current limit control is performed, the history corresponding to the maximum difference between the target current value and the limit current value is representative history information regarding one current limit control. Since the information is stored and no other history information is stored, the history information necessary and sufficient for investigating the cause of the lack of assist can be saved.

  The case where the difference between the target current value and the limit current value is the largest is the case where the current to be supplied to the motor is most limited, that is, the case where the worst shortage of assist occurs for one current limit control. For this reason, by storing history information regarding this case (at least the maximum difference between the target current value and the limit current value, or the history of both the target current value and the limit current value), the failure of the electric power steering apparatus will be performed later. It is possible to appropriately perform the presence / absence of the occurrence of failure and the analysis of the occurrence of failure.

  As a result, the storage capacity of the storage means for storing the history information can be reduced, and the cause of the lack of assist indicated by the user can be smoothly investigated based on the necessary and sufficient history information.

In the case of the electric power steering device according to the present invention, when current limit control is performed, as representative history information regarding one current limit control, the maximum value of the subtraction result obtained by subtracting the limit current value from the target current value is used. storing the corresponding history information, since it does not store other historical information, it is possible to save the necessary and sufficient historical information to investigate the cause of the assist shortage.

In the case of the electric power steering apparatus according to the second aspect of the invention, even when current limit control is performed, history information corresponding to vehicle speeds higher than a predetermined vehicle speed is not stored, so history information unnecessary for investigating the cause of insufficient assistance is stored. Can be prevented.

In the case of the electric power steering apparatus according to the third aspect of the invention, since the latest history information of a predetermined number or less is stored, it is possible to prevent the history information unnecessary for investigating the cause of the lack of assist.

As a result, the electric power steering devices of the second and third inventions can further reduce the storage capacity of the storage means for storing the history information, and the user has been pointed out by omitting unnecessary history information. The cause of the lack of assistance can be investigated more smoothly.

  Hereinafter, the present invention will be described in detail with reference to the drawings illustrating embodiments thereof.

FIG. 1 is a schematic diagram showing a configuration of an electric power steering apparatus EPS according to the present invention.
This electric power steering device EPS is a steering member 27 for steering, a steering assist motor 6 driven in accordance with the steering of the steering member 27, and the rotation of the motor 6 via the reduction gear mechanism 17. A transmission means 24 for transmitting to the mechanisms 23 and 23 and a control device 1 for controlling the motor drive circuit 5 of the motor 6 are provided.

The steering member 27 is connected to the input shaft 26, and the steering angle sensor 18 that detects the rotation angle of the steering member 27 is disposed on the input shaft 26. The steering angle detected by the steering angle sensor 18 is given to the control device 1.
The transmission means 24 includes an output shaft 29 connected to the input shaft 26 via a torsion bar (not shown), a connecting shaft 30 connected to the output shaft 29 via a universal joint, and a connecting shaft 30 via a universal joint. A pinion shaft 31 to be connected and a rack shaft 32 having rack teeth meshing with the pinion of the pinion shaft 31 and connected to the left and right steered wheels A and A via the steering mechanisms 23 and 23 are provided. Yes.
Such an input shaft 26 and transmission means 24 constitute a steering shaft 25.

Around the input shaft 26, there is disposed a torque sensor 21 that detects a steering torque value applied to the input shaft 26 by operating the steering member 27 based on a twist generated in the torsion bar. The steering torque value detected by the torque sensor 21 is given to the control device 1.
The control device 1 is configured to control the motor drive circuit 5 based on the steering torque value given from the torque sensor 21.

  The reduction gear mechanism 17 includes a worm connected to the output shaft of the motor 6 and a worm wheel fitted in the middle of the output shaft 29, and transmits the rotation of the motor 6 from the worm and the worm wheel to the output shaft 29. It is constituted as follows.

In the electric power steering apparatus EPS configured as described above, the steering operation force by the operation of the steering member 27 is transmitted via the input shaft 26, the torsion bar (not shown), the output shaft 29, the connecting shaft 30, and the pinion shaft 31. This is transmitted to the rack shaft 32, the rack shaft 32 is moved in the axial direction, and the steering mechanisms 23, 23 are operated.
Further, based on the steering torque value detected by the torque sensor 21, the control device 1 controls the motor drive circuit 5 to drive the motor 6, and transmits the driving force of the motor 6 to the output shaft 29. Assist the steering force and reduce the labor burden.

FIG. 2 is a block diagram showing a main configuration of the electric power steering apparatus EPS.
The control device 1 of the electric power steering apparatus EPS includes a control unit 8 using an MPU, and a calculation unit 12 that performs a calculation based on a value given from another part and gives a calculation result to the other part.

The steering torque value detected by the torque sensor 21 is sampled by the interface 20, and the sampled steering torque value T is given to the control unit 8 and the calculation unit 12 of the control device 1.
Similarly, the vehicle speed value V detected by the vehicle speed sensor 3 that detects the traveling speed of the vehicle on which the electric power steering device EPS is mounted and sampled by the interface 4 is also given to the control unit 8 and the calculation unit 12.
Further, the motor current detection value Is output from the motor current detection circuit 7 that detects the current flowing through the motor 6 that assists steering is also given to the control unit 8 and the calculation unit 12.

Furthermore, the steering angle detected by the steering angle sensor 18 is sampled by the interface 19, and the sampled steering angle value θ is given to the control unit 8 of the control device 1.
Similarly, the counting result counted by the IG (ignition) counter 10 that stores the vehicle life accumulation counter (the number of times the ignition is turned on) is given to the control unit 8 of the control device 1 via the interface 11.
An EEPROM 9 is connected to the control unit 8, and the control unit 8 reads and writes various values with respect to the EEPROM 9 and erases various values stored in the EEPROM 9.

  As shown in FIG. 2, when the steering torque value T exceeds a predetermined dead zone, the calculation unit 12 increases the motor current value I as the steering torque value T increases, and further increases the steering torque value T to a predetermined value or more. Then, a function that saturates the motor current value I is variably determined according to the vehicle speed value V (where V1 <V2 <V3...). This function is determined so that the ratio of the motor current value I to the steering torque value T becomes smaller and the saturation value of the motor current value I becomes smaller as the vehicle speed values V1, V2, V3,. There are many cases.

In the present embodiment, the calculation unit 12 is controlled by the control unit 8, and a target current value Ia to be described later is determined and given to the control unit 8 based on the function.
The calculation unit 12 obtains a differential current value based on the vehicle speed value V and the steering torque value T that are respectively given, the obtained differential current value, a target current value Ia or a limit current value Ib described later, and a motor. Based on the detected current value Is, a PWM signal which is a motor current command value is obtained using PID calculation, and the obtained PWM signal is given to the motor drive circuit 5.
The motor drive circuit 5 drives the motor 6 by the given PWM signal.

  Here, the target current value Ia is a current value related to the current to be supplied to the motor 6, and the limited current value Ib is a limited current value related to the current to be supplied to the motor 6 under a predetermined condition. More specifically, the limit current value Ib is a limit current value used when high load continuous protection control or overheat protection control is performed, and the target current value Ia is a case where such protection control is not performed. It is a normal current value used for. Under conditions where high load continuous protection control or overheat protection control is required, target current value Ia> limit current value Ib, and under conditions where high load continuous protection control and overheat protection control are unnecessary, target current value Ia ≦ Limit current value Ib (see FIG. 4).

  Based on the given steering angle value θ, steering torque value T, and target current value Ia, the control unit 8 determines, for example, whether or not there is a high load state near the end position of the steering member 27, and the high load state. If so, high load continuation protection control that temporarily limits the current to be supplied to the motor 6 is executed. When the load is no longer high, the current limit is released immediately.

The control unit 8 obtains an integrated amount of the given motor current detection value Is, estimates the temperatures of the motor 6 and the motor drive circuit 5 based on the obtained integrated amount, and when the estimated temperature exceeds a predetermined value. Then, the overheat protection control for gradually limiting the current to be supplied to the motor 6 is executed by a predetermined calculation method.
Note that, instead of the estimated temperature, a temperature sensor may be provided and an actually measured temperature may be used.

  The electric power steering device EPS is supplied with power from the battery B through the power switch circuit 2.

FIG. 3 is a flowchart illustrating the procedure of the steering assist process executed by the control unit 8.
First, the control unit 8 reads the steering torque value T detected by the torque sensor 21 and sampled by the interface 20 (S1), detected by the steering angle sensor 18 and read the steering angle value θ sampled by the interface 19. (S2).

Next, the control unit 8 reads the vehicle speed value V detected by the vehicle speed sensor 3 and sampled by the interface 4 (S3), and reads the motor current detection value Is detected by the motor current detection circuit 7 (S4).
Next, the control unit 8 calculates the target current value Ia based on the steering torque value T and the vehicle speed value V in the calculation unit 12 (S5). Further, the control unit 8 performs a current limiting process for the high load continuation protection control or the overheat protection control based on the steering torque value T, the steering angle value θ, the motor current detection value Is, the time measurement result of the time measuring means (not shown), and the like. When the current limiting process is being executed, various calculations are performed to determine whether or not to cancel the current limiting process (S6), and the current limiting process is performed based on the calculation result in S6. It is determined whether or not to perform it and whether or not to cancel (S7).

  When it is determined that the current limiting process is not performed or when it is determined that the current limiting process should be canceled (NO in S7), the control unit 8 actually sets the target current value Ia calculated in S5 to the motor. The command motor current value to be applied to the current to be passed is determined (S8), the PWM signal is calculated by the calculation unit 12 based on the command motor current value determined in S8 (S9), and the obtained PWM signal is supplied to the motor drive circuit 5. Output (S10), and return the process to S1.

When it is determined that the current limiting process is to be performed, or when it is determined that the current limiting process is being performed and should not be released (YES in S7), the control unit 8 limits the current to be supplied to the motor 6. A predetermined process is performed to calculate the limit current value Ib (S11). In S11, the control unit 8 is provided in advance in the calculation unit 12 in order to obtain the limit current value Ib based on, for example, the steering angle value θ, the steering torque value T, the vehicle speed value V, the target current value Ia, and the like. The limit current value Ib is obtained from the table that is not to be stored, and further, which one of the high load continuation protection control and the overheat protection control is executed is stored.
Then, the control unit 8 determines whether or not the overheat protection control has been performed (S12). If the high load continuation protection control has been performed (S12: NO), the process proceeds to S8 and the overheat protection control is performed. Is performed (S12: YES), a subroutine (see FIG. 6) for performing a history saving process described later is called and executed (S13).

After completion of S13, the control unit 8 moves the process to S8, determines whether the current limiting process determined to be performed in S6 is the high load continuation protection control or the overheat protection control, the target current value Ia and the limit current Based on the magnitude relationship with the value Ib, the target current value Ia or the limit current value Ib is determined as the command motor current value applied to the current that should actually flow through the motor.
Finally, in S9, the control unit 8 calculates a PWM signal in the calculation unit 12 based on the command motor current value determined in S8, and outputs the obtained PWM signal to the motor drive circuit 5 in S10. To do.

  As a result of the steering assist process as described above, two current limit controls, that is, a high load continuation protection control and an overheat protection control, are executed. For this reason, excessive current consumption can be avoided, and failure due to overheating of the motor 6 and the motor drive circuit 5 can be prevented in advance.

That is, the electric power steering apparatus EPS includes a torque sensor 21 that detects a steering torque value applied to the steering member 27 and the steering assist motor 6.
In addition, the control unit 8 and the calculation unit 12 in the process of S5 function as a current setting unit that determines a target current value Ia related to a current to be supplied to the motor 6 based on the steering torque value detected by the torque sensor 21. Furthermore, the control unit 8 and the calculation unit 12 in the process of S11 function as a current limiting unit that determines the limited current value Ib related to the current under a predetermined condition.

  The electric power steering device EPS assists steering by causing the motor 6 to pass a current based on the target current value Ia determined by the current setting means or the limited current value Ib determined by the current setting means.

FIG. 4 is a characteristic diagram showing temporal changes in the target current value Ia and the limit current value Ib, and FIG. 5 is an enlarged view of a region E shown in FIG. 4 and 5, the horizontal axis is the time axis, and the vertical axis indicates the current value (Arms).
In the figure, Iu is a maximum current value, and the maximum current value Iu is a current value corresponding to the rated maximum current (system maximum current) value of the motor 6.

The target current value Ia shows a substantially regular time change according to the steering torque value T and the vehicle speed value V, and does not exceed the maximum current value Iu.
On the other hand, the limit current value Ib shows an irregular time change according to not only the steering torque value T and the vehicle speed value V but also the load state of the steering member 27, the temperature of the motor 6 and the motor drive circuit 5, and the like. The maximum current value Iu may be exceeded.

  As described above, the target current value Ia> the limit current value Ib under the condition that the high load continuous protection control or the overheat protection control is required, and the high load continuous protection control and the overheat protection control are unnecessary. Target current value Ia ≦ limit current value Ib. That is, when the limit current value Ib> the maximum current value Iu, the high load continuation protection control and the overheat protection control are unnecessary, and therefore, the current exceeding the rated maximum current based on the limit current value Ib exceeding the maximum current value Iu. Is not sent to the motor 6.

Next, storage of history information related to current limit control will be described.
History information regarding the current limit control is stored in the EEPROM 9. Specifically, the history information uses the counting result counted by the IG counter 10 as information indicating the time when the assist shortage related to the steering assist occurs, and the vehicle speed as information indicating the situation where the assist shortage occurs. The value V, the target current value Ia, the limit current value Ib, the estimated temperature of the motor 6 and the motor drive circuit 5, the voltage value of the battery B, and the like are used, and these are counted as one set of history information.

  One set of history information is stored once or a plurality of times by the control unit 8, and only the latest three times of the stored history information are left, and others are deleted. For this reason, the number of times history information is stored (the number of times history information storage conditions are satisfied; hereinafter referred to as history storage count) is also stored in the EEPROM 9 by the control unit 8. The number of times of history storage indicates how many times the current limit control has occurred.

6 and 7 are flowcharts showing a subroutine of the history saving processing procedure executed by the control unit 8. When the electric power steering apparatus EPS is shipped from the factory, each variable and flag described later is reset to “0”.
First, the control unit 8 determines whether or not the vehicle speed value V read in S3 is equal to or higher than a predetermined vehicle speed (for example, 100 km / h) (S21). If the vehicle speed value V is equal to or higher than the predetermined vehicle speed (S21: YES) ), End the history saving process and return.
On the other hand, when the vehicle speed value V is less than the predetermined vehicle speed (S21: NO), the control unit 8 executes the process of S22.

  If YES in S21, the processing from S22 onward is not executed, so that the history information of the current limit control performed when the vehicle speed value V is equal to or higher than the predetermined vehicle speed, that is, unnecessary history information is prevented from being saved. .

  The control unit 8 determines whether or not the target current value Ia calculated in S5 exceeds the limit current value Ib calculated in S11 (S22).

  When the target current value Ia> the limit current value Ib (S22: YES) as indicated by points P3, P5, P6, and P8 shown in FIG. 5, the control unit 8 satisfies the target current value Ia> the limit current value Ib. The first counter C1 for counting the number of times is incremented (C1 ← C1 + 1) (S23), and a second counter C2 described later is reset to “0” (C2 ← 0) (S24).

  Then, the control unit 8 determines whether or not the first counter C1 is equal to or greater than a predetermined constant M (M is a natural number of M> 1) described later (S25).

When the first counter C1 ≧ M (S25: YES) as indicated by points P6 and P8 shown in FIG. 5, “1” is set to the flag F (S26), and the processing from S27 onward is executed.
Here, the flag F is a flag indicating whether or not the system is in the current limit control state. When the flag F = “1”, the control unit 8 determines that the system is in the current limit control state, and the flag F When “= 0”, it is determined that the system is not in the current limit control state (recovered from the current limit control state).

The constant M is determined in advance in consideration of sampling intervals such as the steering torque value T and the vehicle speed value V. When sampling of the steering torque value T, the vehicle speed value V, etc. is executed M times, the time T1 elapses (FIG. 5).
When the state where the target current value Ia> the limit current value Ib continues for T1 time, the control unit 8 determines that the system is in the current limit control state and the history information storage condition is satisfied.

  If the first counter C1 <M as indicated by points P3 and P5 shown in FIG. 5 (S25: NO), the history information storage condition is not satisfied, so the history storage process is terminated and the process returns.

After the processing of S26 is completed, the control unit 8 calculates a subtraction result X = Ia−Ib obtained by subtracting the limit current value Ib from the target current value Ia (S27), and the subtraction result X calculated in S27 is the maximum difference described later. It is determined whether or not Xn or more (S28).
When the subtraction result X ≧ maximum difference Xn (S28: YES), the control unit 8 assigns the subtraction result X to the maximum difference Xn (Xn ← X) and updates the value of the maximum difference Xn (S29).
That is, the maximum difference Xn is the maximum value of the subtraction result X calculated in S27. For example, between the subtraction result X related to the point P6 in FIG. 5 and the subtraction result X related to the point P8, the subtraction result X related to the point P8 becomes the maximum difference Xn.

After the processing of S29 is completed, the control unit 8 stores the history information such as the target current value Ia and the limit current value Ib used for the determination in S22, that is, history information corresponding to the maximum difference Xn in the EEPROM 9 as temporary storage history information. Store (S30).
In S30, a flag indicating temporary storage is set in the history information stored in the EEPROM 9. The history information in which this flag is set is overwritten and erased when new history information is stored in S30.
After the process of S30 is completed, the control unit 8 ends the history storage process and returns.

  When subtraction result X <maximum difference Xn (S28: NO), since subtraction result X calculated in S27 is not the maximum value, control unit 8 ends the history storage process without performing the processes of S29 and S30. And return.

If the target current value Ia ≦ the limited current value Ib (S22: NO) as indicated by points P1, P2, P4, P7, and P9 to P11 shown in FIGS. It is determined whether or not “1” (S31).
When the flag F = “0” as indicated by points P1, P2, and P4 shown in FIGS. 4 and 5 (S31: NO), the system is not in the current limit control state. C1 is reset to “0” (S32), the history saving process is terminated, and the process returns.

  When the flag F = “1” as in points P7 and P9 to P11 shown in FIGS. 4 and 5 (S31: YES), the system is in the current limit control state, but the history information storage condition is satisfied. Therefore, the control unit 8 determines whether or not the limited current value Ib exceeds the maximum current value Iu (S41).

  When the limit current value Ib ≦ maximum current value Iu (S41: NO) as indicated by points P7 and P9 shown in FIGS. 4 and 5, the control unit 8 has not recovered from the current limit control state. Then, the second counter C2 is reset to “0” (S42), the history storing process is terminated, and the process returns.

  When the limit current value Ib> the maximum current value Iu (S41: YES) as indicated by points P10 and P11 shown in FIG. 4, the control unit 8 counts the number of times that the limit current value Ib> the maximum current value Iu. The second counter C2 is incremented (S43), and it is determined whether or not the second counter C2 is equal to or greater than a predetermined constant N (N is a natural number of N> 1) described later (S44).

Here, the constant N is determined in advance in consideration of sampling intervals such as the steering torque value T and the vehicle speed value V. When sampling of the steering torque value T, the vehicle speed value V, etc. is executed N times, T2 time elapses (FIG. 4).
When the state of limited current value Ib> maximum current value Iu continues for T2 time, the control unit 8 determines that the system has recovered from the current limit control state.
When the second counter C2 <N times as indicated by a point P10 shown in FIG. 4 (S44: NO), since the system has not recovered from the current limit control state, the control unit 8 ends the history storage process. And return.

If the second counter C2 ≧ N (S44: YES) as indicated by a point P11 shown in FIG. 4, the system has recovered from the current limit control state, and therefore the control unit 8 sets the first counter C1 and the second counter C2 to each other. It is reset to “0” (S45), the flag F is reset to “0” (S46), and the maximum difference Xn is reset to “0” (S47).
And the control part 8 performs the process below S48, and preserve | saves, deletes, etc. history information.

The control unit 8 determines whether or not three sets of history information are already stored (described later) in the EEPROM 9 (S48).
When the three sets of history information are permanently stored (S48: YES), the control unit 8 counts the oldest history information among the history information already stored in the EEPROM 9, specifically, the IG counter 10 counts. The history information having the smallest count result value is erased (S49), and the history information temporarily stored in S30 is permanently stored (S50).

  Here, “main saving” means that the temporarily stored history information is left as the history information to be saved without being erased, and the flag indicating temporary saving is reset for the history information. Then, a flag indicating that the book is stored is set. The history information in which this flag is set is not overwritten and erased even when new history information is stored in S30, but may be erased in the process of S49.

When the history information of two sets or less is not actually stored (S48: NO), the control unit 8 shifts the process to S50 and stores the history information temporarily stored in S30.
As a result, for example, history information unnecessary for investigating the cause of lack of assistance, such as history information related to P6 shown in FIG. 5, is prevented, and causes of lack of assistance such as history information related to P8 The history information necessary for the investigation is stored in the EEPROM 9 for the latest three necessary and sufficient times.
That is, as representative history information regarding one current limit control, one set of history information corresponding to the maximum difference Xn is stored, and a total of three sets of history information are stored regarding the latest three current limit controls.
In addition, the structure which preserve | saves for the latest 1 time or 2 times, or 4 times or more may be sufficient.

Then, after the process of S50 is completed, the control unit 8 increases the value of the history storage count stored in the EEPROM 9 by “1” (S51).
After the process of S51 is completed, the control unit 8 ends the history storage process and returns.

  In S22 of the history storage process as described above, the control unit 8 functions as a first comparison unit that compares the target current value Ia and the limited current value Ib. In S41, the control unit 8 functions as a second comparison unit that compares a threshold value (maximum current value Iu) having a value equal to or greater than the target current value Ia and the limited current value Ib.

  In S <b> 25, the control unit 8 functions as a first number determination unit that determines whether or not the first comparison unit continuously determines M times that the target current value Ia exceeds the limit current value Ib. In S <b> 44, the control unit 8 functions as a second number determination unit that determines whether or not the second comparison unit continuously determines N times that the limited current value Ib exceeds the maximum current value Iu. .

In S27, the control unit 8 functions as a subtracting unit that obtains a subtraction result X obtained by subtracting the limit current value Ib from the target current value Ia.
In S29, the control unit 8 determines that the first number of times determination means has determined M times continuously (since it becomes YES in S25), and then the second number of times determination means continues N times. Until it is determined that it has been determined (until YES in S44), it functions as a maximum value calculation means for obtaining the maximum difference Xn of the subtraction result X obtained by the subtraction means.
In S50, the EEPROM 9 controlled by the control unit 8 corresponds to the maximum difference Xn obtained by the maximum value calculation means and functions as a storage means for storing predetermined history information related to the limit current value Ib.

  In the first comparison unit, the second comparison unit, the first number determination unit, the second number determination unit, the subtraction unit, the maximum value calculation unit, and the storage unit, the target current value Ia exceeds the limit current value Ib. In this case, it corresponds to the maximum difference between the target current value Ia and the limit current value Ib, and functions as history storage means for storing predetermined history information related to the limit current value Ib.

  Further, the electric power steering device EPS includes a vehicle speed sensor 3 as a vehicle speed detection means for detecting the vehicle speed. When the vehicle speed detected by the vehicle speed detection means is equal to or higher than a predetermined vehicle speed (YES in S21), the control unit 8 performs S22. By not performing the subsequent processing, the storage means is prohibited from storing history information.

The history information includes a counting result counted by the IG counter 10 as time-series information corresponding to the maximum difference Xn. In S48, the control unit 8 determines whether a predetermined number (three) of history information is stored in the storage unit. It functions as a number determination means for determining whether or not.
In S49, when the control unit 8 determines that the predetermined number is stored, when the storage unit stores new history information, the time series information included in the history information is stored. It functions as an erasing means for erasing the oldest history information.

The electric power steering device EPS as described above can store the minimum history information necessary for investigating the cause of the lack of assist related to steering assist, and can reduce the storage capacity of the EEPROM 9.
Then, by reading the history information stored in the EEPROM 9, the operator can specify the cause of the lack of assist accurately and promptly.

  Instead of the counting result of the IG counter 10, the travel distance information may be stored in the EEPROM 9 as time series information.

It is a mimetic diagram showing the composition of the electric power steering device concerning the present invention. It is a block diagram which shows the principal part structure of the electric power steering apparatus which concerns on this invention. It is a flowchart which shows the procedure of the steering assistance process which the control part of the electric power steering device which concerns on this invention performs. It is a characteristic view which shows the time change of the target electric current value of the electric power steering device which concerns on this invention, and a limiting electric current value. It is the elements on larger scale of the area | region E of FIG. It is a flowchart which shows the subroutine of the log | history preservation | save processing procedure which the control part of the electric power steering device which concerns on this invention performs. It is a flowchart which shows the subroutine of the log | history preservation | save processing procedure which the control part of the electric power steering device which concerns on this invention performs.

Explanation of symbols

  21 torque sensor, 27 steering member, 3 vehicle speed sensor (vehicle speed detection means), 6 motor, 8 control unit, 9 EEPROM (storage means), EPS electric power steering device

Claims (3)

A torque sensor for detecting a steering torque value applied to the steering member;
A steering assist motor;
Current setting means for determining a target current value related to a current to be passed through the motor based on a steering torque value detected by the torque sensor;
Current limiting means for determining a current limit value related to the current under a predetermined condition, and
In the electric power steering apparatus for assisting steering by passing a current based on a target current value determined by the current setting means or a limited current value determined by the current setting means to the motor,
History storage means for storing predetermined history information related to the limit current value corresponding to a maximum difference between the target current value and the limit current value when the target current value exceeds the limit current value Prepared ,
As the history storage means,
First comparison means for comparing the target current value and the limit current value;
A threshold having a value equal to or greater than the target current value, and second comparison means for comparing the limit current value;
A first number determination means for determining whether or not the first comparison means continuously determines M times (M is a natural number of M> 1) that the target current value exceeds the limit current value;
A second number determination means for determining whether or not the second comparison means continuously determines that the limit current value exceeds the threshold value N times (N is a natural number of N>1);
Subtracting means for obtaining a subtraction result obtained by subtracting the limit current value from the target current value;
The subtraction obtained by the subtracting means from the time when the first number of times determining means determines that it has been determined M times continuously until the time of the second number of times determining means determining that N times is determined continuously. A maximum value calculating means for obtaining the maximum value of the result;
Storage means for storing predetermined history information related to the limit current value corresponding to the maximum value obtained by the maximum value calculation means;
An electric power steering apparatus according to claim Rukoto equipped with. Vehicle speed detection means for detecting the vehicle speed,
If vehicle speed detected is vehicle speed detecting means is equal to or higher than a predetermined vehicle speed, the electric power steering apparatus according to claim 1, characterized in that said storage means are to be prohibited storing history information. The history information includes time series information corresponding to the maximum value,
A number determination means for determining whether or not a predetermined number of history information is stored in the storage means;
When the number determination unit determines that a predetermined number is stored, when the storage unit stores new history information, the history information having the oldest time-series information included in the history information is deleted. the electric power steering apparatus according to claim 1 or 2, characterized in that it comprises an erasing unit.

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