JP5122258B2 - Electric power steering control device - Google Patents

Description

  The present invention relates to an electric power steering control device that reduces a steering force applied to a steering wheel by a driver by control for assisting steering by using an electric motor.

  In a general electric power steering control device, a detection sensor for steering torque is used, and this torque detection sensor detects a steering torque applied to a steering system by a driver of a car. The steering torque output is calculated using a table that stores in advance the torque command value corresponding to the output of the low-pass filter based on the output of the low-pass filter after the high-frequency component is removed by the low-pass filter. A differential command value or the like based on the output from the low-pass filter is added to determine a target value of the drive current for the electric motor. The electric motor is driven based on the target value of the drive current, and provides a steering assist force for the steering torque by the driver. When an abnormality occurs in the steering torque, the abnormality detection means detects the abnormality based on the output signal of the torque detection sensor, and gradually decreases the gain (proportional gain) so as to lower the target value of the drive current for the electric motor. To do.

  The electric power steering control device described in Patent Document 1 receives the detected torque signal from the torque detecting means, and generates an auxiliary torque signal in accordance with the change in the detected torque signal. The auxiliary torque signal is generated so as to coexist with the detected torque signal, and when the abnormality detection means generates an abnormality detection output, a protection operation is performed in response to the selection of the auxiliary torque signal. The auxiliary torque signal includes a follow-up signal that follows the detected torque signal when the detected torque signal changes, and a return signal that returns the auxiliary steering force to 0 level when an abnormality detection output is generated. The follow-up signal is generated by calculation so as to gradually change toward the detected torque signal and the return signal toward zero level. As a result, the delay time from when an abnormality is detected in the torque detection means until the transition to the protective operation by the auxiliary torque signal is shortened, and fluctuations in the auxiliary steering force during this delay time are suppressed.

JP 2004-345569 A

  However, in the electric power steering control device as described above, immediately after the abnormality detection unit detects an abnormality in the steering torque based on the output signal of the torque detection sensor, the current operation value is changed by a control operation for changing the current command value for the electric motor. There is a problem that the command value changes rapidly and the vehicle becomes unstable.

  In the present invention, in view of the above-described problems, immediately after the abnormality detection unit detects an abnormality in the steering torque based on the output signal of the torque detection sensor, the current command value changes suddenly and the vehicle becomes unstable. An object of the present invention is to provide an electric power steering control device that can be eliminated.

  An electric power steering control device according to the present invention includes a torque sensor that detects steering torque of a steering, a filter that removes a high-frequency component of an output from the torque sensor, and a current that calculates a current command value based on the output from the filter. Command value calculating means, drive control means for driving an electric motor for assisting steering based on a current command value, and abnormality detecting means for detecting an abnormality of the steering torque based on an output from a torque sensor The time constant of the filter is changed based on the fact that the abnormality detecting means detects the abnormality of the steering torque.

  In this way, when the abnormality detection means detects an abnormality in the steering torque, the current command value changes abruptly immediately after the occurrence of the abnormality in the steering torque as in the conventional case, and the vehicle becomes inoperative. Stability can be improved. Further, the same effect can be obtained when the noise disappears immediately after the erroneous determination that the steering torque is abnormal because the noise is temporarily mixed, and the normal determination is returned.

  In the present invention, in the electric power steering control device described above, when the abnormality detection unit detects an abnormality in the steering torque and then no longer detects the abnormality, the time constant changed in the filter may be restored. Good.

  According to this, when the steering torque returns to normal after detecting the abnormality of the steering torque, it is possible to promptly shift to the original normal control.

  In the present invention, the electric power steering control device includes a vehicle speed detection unit that detects a vehicle speed, and when the abnormality detection unit detects an abnormality in the steering torque, the filter of the filter is based on the vehicle speed detected by the vehicle speed detection unit. The time constant may be changed.

  According to this, the electric motor can be controlled with a time constant suitable for the vehicle speed at any vehicle speed from high speed to low speed.

  According to the present invention, in the electric power steering control device described above, when the abnormality detection unit detects an abnormality in the steering torque for a certain period of time, the abnormality determination unit determines the abnormality, and the drive control unit determines the abnormality. When the means determines abnormality, the gain for the current command value may be changed.

  According to this, since the gain changes after the abnormal state continues for a certain period of time and the abnormality is confirmed, it is possible to avoid the fluctuation of the gain due to the instantaneous abnormality and the operation of the electric motor becoming unstable. .

  According to the present invention, when the abnormality detection means detects an abnormality in the steering torque, the current command value changes abruptly immediately after the occurrence of the abnormality in the steering torque as in the prior art by changing the time constant of the filter, It is possible to improve the instability of the vehicle. Further, the same effect can be obtained when the noise disappears immediately after the erroneous determination that the steering torque is abnormal because the noise is temporarily mixed, and the normal determination is returned.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram of an electric power steering control apparatus 100 according to an embodiment of the present invention. The electric power steering control device 100 according to the embodiment of the present invention has the following configuration. The steering torque sensor 1 is a sensor that detects the steering torque of the steering. The low-pass filter 2 is composed of a first-order lag system having a predetermined time constant, and removes a high-frequency component of the output Tq from the steering torque sensor 1. Based on the output ATq from the low-pass filter 2 and the vehicle speed information from the vehicle speed detection means 10, the torque command calculation unit 3 calculates a current command value Tref using a table to be described later.

  The differential command calculation unit 8 calculates a differential value of the output ATq from the low-pass filter 2 and calculates a differential command value Dref with reference to vehicle speed information from the vehicle speed detection means 10. The convergence command calculation unit 9 calculates a convergence command value KVref for improving the steering operation feeling and the like based on the vehicle speed information from the vehicle speed detection means 10, the rotational speed of the electric motor 6, and the like. The current command value Tref output from the torque command calculation unit 3, the differential command value Dref output from the differentiation command calculation unit 8, and the convergence command value KVref output from the convergence command calculation unit 9 are added by adders 11 and 12. The current command value Iref1 is determined and input to the gain variable unit 4. The current command value Iref2, which is the output of the gain variable section 4, is input to the motor drive means 5, and the motor drive means 5 drives the electric motor 6 that assists steering.

The abnormality determination means 7 detects various abnormalities in the steering torque system based on the output Tq from the steering torque sensor 1, and an abnormality detection flag Err1 = for changing the time constant of the low-pass filter 2 when an abnormality is detected. 1 is output. When Err1 = 1 is input, the low-pass filter 2 changes the time constant from the normal time constant τ _OK to the abnormal time constant τ _NG . Here, τ _OK and τ _NG have a relationship of τ _OK <τ _NG . In addition, the abnormality determination unit 7 outputs a flag Err1 = 0 that changes the time constant of the low-pass filter 2 when normal is detected after detection of abnormality. When Err1 = 0 is input, the low-pass filter 2 changes the time constant from the time constant τ _NG at the abnormal time to the time constant τ _OK at the normal time.

When the abnormality determination unit 7 determines abnormality, the low-pass filter 2 changes the time constant τ _NG based on the vehicle speed signal detected by the vehicle speed detection unit 10. In addition, the abnormality determination unit 7 outputs an abnormality confirmation flag Err2 = 1 to the gain variable unit 4 when various abnormality of the steering torque system is confirmed. When the abnormality confirmation flag Err2 = 1 is input, the gain variable unit 4 gradually changes the gain Gn (proportional gain), which was 1 level when normal, to 0 level. Further, when Err2 = 0 is input from the state of the abnormality confirmation flag Err2 = 1, the gain Gn that has been at 0 level is gradually changed to 1 level.

  In the configuration of FIG. 1, the torque command calculation unit 3 is an embodiment of a current command value calculation unit in the present invention, and the gain variable unit 4 and the motor drive unit 5 are an embodiment of the drive control unit in the present invention. Yes, the abnormality determination means 7 is an embodiment of the abnormality detection means and abnormality determination means in the present invention. The low-pass filter 2, the torque command calculation unit 3, the gain variable unit 4, the abnormality determination unit 7, the differential command calculation unit 8, and the convergence command calculation unit 9 are configured by a CPU, and the motor drive unit 5 is configured by, for example, an FET bridge, 6 can be constituted by a brushless motor, for example.

  FIG. 2 is a flowchart when an abnormality is detected in the steering torque signal of the electric power steering control device according to the embodiment of the present invention. First, the abnormality determination means 7 detects the output Tq from the steering torque sensor 1 (S1). Next, it is determined whether or not Tq exceeds a preset upper limit abnormality threshold (S2). If it exceeds (Yes in S2), an abnormality detection flag Err1 = 1 is set (S4). If Tq does not exceed the upper limit abnormality threshold (No in S2), it is determined whether Tq is less than the preset lower limit abnormality threshold (S3). If Tq is less (Yes in S3), the abnormality detection flag Err1 = 1 (S5). If Tq is not less than the lower limit abnormality threshold (No in S3), the abnormality detection flag Err1 = 0 is set (S6).

  Note that this algorithm is an example of steering torque system diagnosis, which assumes circuit abnormality and noise contamination, and does not depend on the type of abnormality.

FIG. 3 is a flowchart showing a time constant changing algorithm of the low-pass filter when abnormality of the steering torque signal is detected. First, it is determined whether the abnormality detection flag Err1 determined by the torque signal abnormality detection algorithm is 1 or 0 (S11). If the abnormality detection flag Err1 = 1 (Yes in S11), the time constant of the low-pass filter 2 is set to the time constant τ _NG at the time of abnormality (S12). If the abnormality detection flag Err1 = 0 (No in S11), the time constant of the low-pass filter 2 is set to the normal time constant τ _OK (S13).

FIG. 4 is a timing chart showing the time constant changing operation of the low-pass filter when the steering torque signal abnormality is detected. The time constant of the low-pass filter 2 is set to a normal time constant τ _OK when the abnormality detection flag Err1 = 0 is normal. When the abnormality of the torque signal is detected and the abnormality detection flag changes to Err1 = 1, in the present invention, the time constant of the low-pass filter 2 is changed to the time constant τ _NG at the time of abnormality as shown by the solid line. On the other hand, in the prior art, the time constant of the low-pass filter 2 is not changed as shown by the dotted line. Next, when the torque signal becomes normal again and the abnormality detection flag changes to Err1 = 0, the time constant of the low-pass filter 2 is set again to the normal time constant τ _OK .

  FIG. 5 is a flowchart showing an algorithm for determining an abnormality in the steering torque signal. First, the abnormality determination means 7 determines whether or not the abnormality detection flag Err1 = 1 continues for a preset time (abnormality determination time) (S21). If it continues (Yes in S21), the abnormality confirmation flag Err2 = 1 is set (S22). If it is not continued (No in S21), the abnormality confirmation flag Err2 is not changed. Next, it is determined whether or not the abnormality detection flag Err1 = 0 continues for a preset time (abnormality release time) (S23). If it continues (Yes in S23), the abnormality confirmation flag Err2 = 0 is set (S24). If not continued (No in S23), the abnormality confirmation flag Err2 is not changed.

  FIG. 6 is a timing chart showing the operation of the gain variable unit 4. In a normal state where the abnormality detection flag Err1 = 0 and the abnormality detection flag Err2 = 0, the gain Gn of the gain variable unit 4 is maintained at 1 level. Next, when an abnormality occurs in the steering torque signal and the abnormality detection flag Err1 = 1, the gain Gn remains at 1 level as long as the abnormality detection flag Err2 = 0. If the state of the abnormality detection flag Err1 = 1 continues for the abnormality confirmation time, the abnormality confirmation flag Err2 = 1 is set, the gain Gn gradually decreases from the first level, and the electric motor 6 decelerates. Then, when a preset gain lowering time elapses, the gain Gn becomes 0 level, and the auxiliary steering by the electric motor 6 is stopped. While the state of the abnormality detection flag Err1 = 1 and the abnormality confirmation flag Err2 = 1 continues, the gain Gn maintains the 0 level. That is, the electric motor 6 is in a stopped state.

  Next, when the abnormality of the steering torque signal disappears and the abnormality detection flag Err1 = 0, the abnormality confirmation flag Err2 = 1, and the gain Gn maintains the 0 level. When the state of the abnormality detection flag Err1 = 0 continues for the abnormality confirmation release time, the abnormality confirmation flag Err2 = 0, the gain Gn gradually increases from the 0 level, the electric motor 6 rotates, and auxiliary steering is started. When a preset gain increase time elapses, the gain Gn becomes 1 level.

FIG. 7 is a timing chart for explaining changes in the time constant of the low-pass filter, each command value, and the like when an abnormality occurs in the steering torque signal. In the figure, the control method according to the present invention is indicated by a solid line, and the conventional control method is indicated by a dotted line. First, when the steering torque Tq, which is an output from the steering torque sensor 1, is at a neutral level and is normal, the abnormality detection flag Err1 = 0, the abnormality confirmation flag Err2 = 0, and the time constant of the low-pass filter 2 is normal. is set to a constant tau _OK when the gain Gn of the gain variable section 4 is 1 level, the control torque ATq is output from the low-pass filter 2, the torque command value Tref is the output from the torque command calculation portion 3, a differential The differential command value Dref which is an output from the command calculation unit 8, the current command value Iref1 which is an input of the gain variable unit 4, and the current command value Iref2 which is an output are all 0 level.

Next, when a torque under-abnormality in which the steering torque Tq becomes 0 torque level occurs, the abnormality detection flag Err1 = 1 is set, and the time constant of the low-pass filter 2 is changed to the time constant τ _NG (> τ _OK ) at the time of abnormality. . That is, the time constant of the low pass filter 2 is increased. The gain Gn of the gain variable unit 4 is kept at 1 level. The control torque ATq and the torque command value Tref have increased rapidly in the conventional control method, but in the case of the control method of the present invention, the time constant starts to increase more gradually than in the conventional method. The differential command value Dref rises and then falls, but the change is slow compared with the conventional control method. The current command value Iref1 and the current command value Iref2 have risen sharply according to the control method of the present invention, although they have risen sharply in the conventional control method (portions surrounded by a one-dot chain line).

That is, by changing the time constant of the low-pass filter 2 to the time constant τ _NG at the time of abnormality, it is possible to delay the saturation of the current command value Iref2 to the motor 6 to the maximum value. The control operation until the auxiliary steering stop (at the time when the gain Gn decreases and reaches the 0 level) that sometimes occurs in the past is suppressed, and the unstable operation of the vehicle is improved. In addition, the unstable operation of the vehicle, which has occurred in the past, is improved even when noise is temporarily mixed in the steering torque signal and then disappears and returns to normal.

  Next, when the state of the abnormality detection flag Err1 = 1 reaches the abnormality confirmation time (FIG. 6), the abnormality confirmation flag Err2 = 1 is set, and the gain Gn is gradually reduced from the first level, and the gain falling time (FIG. 6). When it reaches, it becomes 0 level. While the state of the abnormality detection flag Err1 = 1 and the abnormality confirmation flag Err2 = 1 continues, the gain Gn maintains the 0 level. Meanwhile, the control torque ATq and the torque command value Tref continue to rise moderately as compared with the conventional control method. The differential command value Dref is kept near 0 level. The current command value Iref1 continues to rise gently, and the current command value Iref2 gradually shifts to the 0 level as compared with the conventional control method.

Next, when the steering torque Tq returns to normal, the abnormality detection flag Err1 = 0, and the time constant of the low-pass filter 2 is changed from the time constant τ _NG at the time of abnormality to the time constant τ _OK at the time of normal operation. That is, the time constant is restored. Although the gain Gn is maintained at the 0 level, the control torque ATq and the torque command value Tref are gradually decreased as compared with the conventional control method. The differential command value Dref falls and then rises, but the change is slow compared to the conventional control method. The current command value Iref1 has fallen sharply according to the control method of the present invention, while it has fallen sharply with the conventional control method. Current command value Iref2 is kept at 0 level.

  Next, when the state of the abnormality detection flag Err1 = 0 reaches the abnormality confirmation release time (FIG. 6), the abnormality confirmation flag Err2 = 0 is set, the gain Gn gradually increases from the 0 level, and the gain rise time (FIG. 6). ) Reaches 1 level.

  FIG. 8 is a diagram showing a vehicle speed sensitive steering torque command table. The torque command calculation unit 3 forms a torque command table for each representative vehicle speed (0, 50, 100 km / h in this embodiment). As the control torque ATq on the horizontal axis increases, the torque command value Tref on the vertical axis increases at an acceleration, but saturates when it reaches a certain level for each representative vehicle speed. As the vehicle speed increases from a vehicle speed of 0 km / h to a vehicle speed of 50 km / h and a vehicle speed of 100 km / h, the value of the torque command value Tref decreases, and the saturation level also decreases.

FIG. 9 is a diagram showing a table of time constants τ _NG when the vehicle speed sensitive low-pass filter is abnormal. When the vehicle speed on the horizontal axis is small, the time constant τ _NG of the low-pass filter 2 on the vertical axis is constant. However, when the vehicle speed exceeds a predetermined value, the time constant τ _NG increases at a constant rate, and the vehicle speed further changes to another predetermined value. When it exceeds, it becomes constant again. The normal time constant τ _OK of the low-pass filter 2 is constant at a value lower than the abnormal time constant τ _NG even if the vehicle speed changes. Of course, these characteristics may be designed so as to constitute another linear or curved table.

  In the present invention, various embodiments other than those described above can be adopted. For example, in the above embodiment, a low-pass filter is used as a filter, but a band-pass filter or the like may be used.

1 is a block diagram of an electric power steering control device according to an embodiment of the present invention. It is a flowchart at the time of abnormality detection of the steering torque signal of the electric power steering control device according to the embodiment of the present invention. It is a flowchart which shows the time constant change algorithm of a low-pass filter at the time of abnormality detection of a steering torque signal. It is a timing chart which shows the time constant change operation | movement of a low-pass filter at the time of steering torque signal abnormality detection. It is a flowchart which shows the algorithm which determines abnormality of a steering torque signal. It is a timing chart which shows operation | movement of a gain variable part. It is a timing chart for demonstrating change of the time constant of each low-pass filter, each command value, etc. when abnormality of a steering torque signal occurs. It is a figure which shows a steering torque command table. It is a figure which shows a low-pass filter time constant table.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steering torque sensor 2 Low pass filter 3 Torque command calculation part 4 Gain variable part 5 Motor drive means 6 Electric motor 7 Abnormality judgment means 8 Differential command calculation part 9 Convergence command calculation part 10 Vehicle speed detection means 100 Electric power steering control apparatus

Claims (4)

A torque sensor for detecting the steering torque of the steering;
A filter for removing high frequency components of the output from the torque sensor;
Current command value calculating means for calculating a current command value based on an output from the filter;
Drive control means for driving an electric motor for assisting steering of the steering based on the current command value;
An abnormality detecting means for detecting an abnormality of the steering torque based on an output from the torque sensor,
An electric power steering control device characterized in that the time constant of the filter is changed based on the fact that the abnormality detecting means detects an abnormality in steering torque. In the electric power steering control device according to claim 1,
An electric power steering control device that returns the changed time constant of the filter to the original when the abnormality detection means detects no abnormality in the steering torque and then detects no abnormality. In the electric power steering control device according to claim 1,
Vehicle speed detection means for detecting the vehicle speed,
An electric power steering control device, wherein when the abnormality detection means detects an abnormality in steering torque, the time constant of the filter is changed based on the vehicle speed detected by the vehicle speed detection means. In the electric power steering control device according to claim 1,
When the abnormality detection means detects the abnormality of the steering torque continuously for a predetermined time, the abnormality detection means comprises an abnormality confirmation means for determining the abnormality.
The electric power steering control device, wherein the drive control means changes a gain with respect to the current command value when the abnormality confirmation means confirms an abnormality.

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