JP4326883B2 - Control device for electric power steering device - Google Patents

Description

  The present invention relates to a control device for an electric power steering device, and more particularly to a control device for an electric power steering device that can correctly control the output value of a torque sensor that detects the steering torque of a steering wheel even if the output value is abnormal.

  An electric power steering device that applies a steering assist force to a steering device of an automobile by the rotational force of a motor is a steering assist force applied to a steering shaft or a rack shaft by a transmission mechanism such as a gear or a belt via a speed reducer. Is supposed to be granted. A simple configuration of such an electric power steering apparatus will be described with reference to FIG. A shaft 102 of the steering handle 101 is connected to a tie rod 106 of a steering wheel via a reduction gear 103, universal joints 104a and 104b, and a pinion rack mechanism 105. The shaft 102 is provided with a torque sensor 107 that detects the steering torque of the steering handle 101, and a motor 108 that assists the steering force of the steering handle 101 is connected to the shaft 102 via the reduction gear 103. . The motor control of the electric power steering apparatus is controlled by the control unit 109 using the torque value detected by the torque sensor 107, the vehicle speed detected from a vehicle speed sensor (not shown), the rotation angle of the motor detected by the hall sensor 110, etc. as input values. Is done. The control unit 109 is mainly a CPU, and motor control is executed by a program inside.

  FIG. 10 shows an example of a motor control block diagram for controlling the motor 108 of the electric power steering apparatus having such a configuration. In FIG. 10, a torque value detected by the torque sensor 107 is input, a current command value calculation unit 120 calculates a current command value Iref, a difference from the detected motor current value is calculated by a subtraction unit 121, and current control is performed. The duty ratio is determined by the unit 122, and the motor driving unit 123 drives the motor 108 by executing PWM control according to the duty ratio.

  In such an electric power steering apparatus, control of the electric power steering apparatus is executed on the assumption that the torque value detected by the torque sensor 107 is correctly detected. However, in actuality, when the torque sensor 107 also fails and an abnormal torque detection value is input, there is a risk of causing an abnormal operation with respect to the handle operation. Has been applied.

  For example, in Patent Document 1, a control method as shown in FIG. 11 is adopted to deal with an abnormality in the torque value output from the torque sensor. When the torque value output from the torque sensor becomes abnormal, if the abnormality continues for a certain time (tA), the auxiliary steering force command value that is the output value of the current control calculation based on the torque value is cut off. This is a control method in which the motor drive power supply is shut off when the abnormality continues for a longer period of time (tB). FIG. 12 shows the relationship between the torque value and the motor current when the torque sensor has a ground fault in such a control method and the torque value, which is the output of the torque sensor, becomes zero. In the case of this control method, since the calculation is performed based on the output value of the abnormal torque sensor during the determination time tA, the torque generated by the motor also becomes abnormal, and the steering wheel moves unintended by the driver. Furthermore, if the abnormality continues for the determination time (tB) or longer, the motor power supply is shut off. Therefore, if a large torque is applied to the handle, the torque changes suddenly, which is not preferable.

  As another countermeasure, there is a control method as in Patent Document 2. In Patent Document 2, when a serious abnormality such as a voltage drop or a momentary interruption of the torque sensor power supply occurs, the fail switch is opened, and the torque value that is the torque sensor output before the fail switch is opened is held. The auxiliary steering force command value is obtained by multiplying the held value by the output gain. Further, since the subsequent auxiliary steering force is controlled to gradually attenuate, the auxiliary steering force does not change suddenly. FIG. 13 shows the relationship between the torque value, which is the output of the torque sensor when the ground fault of the torque sensor fails, and the motor current when the control method of Patent Document 2 is used. The maximum negative current flows through the motor from the occurrence of the failure to the detection of the failure. However, since the motor current is gradually decreased from the torque immediately before the occurrence of the failure after the failure is detected, a sudden torque change as in Patent Document 1 occurs. do not do.

  However, when a ground fault occurs while the torque value as shown in FIG. 14 causes chattering, a value such as a black circle may be sampled when the output value of the torque sensor is sampled by the AD converter. If these values do not fall below the ground fault detection threshold, it cannot be detected that a ground fault has occurred, and the control is continued as it is. After detecting the ground fault, the motor current is gradually reduced from the torque value immediately before the occurrence of the failure, but the motor current is gradually reduced from the unstable torque value due to chattering. Since the decrease starts from the reverse torque, it is not preferable.

  In the method of Patent Document 2, an abnormal current flows through the motor during the determination period from the occurrence of a failure to the detection of the failure, so that the failure detection time cannot be made too long. However, in order to prevent erroneous detection of failure detection and to ensure failure detection, there is a contradiction that it is desired to make the failure detection time as long as possible.

JP 2000-318633 A JP 2000-329628 A

  When the torque value, which is the output of the torque sensor, becomes abnormal, in the conventional control method, the output torque of the motor becomes abnormal because control is performed based on the abnormal torque value until the torque sensor detects failure. . Further, even when a substitute value is used instead of an abnormal torque value, there is a problem that an appropriate substitute value is not calculated. As a result, when the output of the torque sensor becomes abnormal, the steering wheel moves unintended by the driver, and there is a problem that the driver feels uncomfortable with the steering wheel operation. Further, since an abnormal current flows through the motor during the failure period, the failure detection time cannot be made long, and as a result, there is a problem that erroneous detection is caused with respect to the failure detection of the torque sensor.

  The present invention has been made under the circumstances as described above. The object of the present invention is to provide a failure detection period that is long enough to prevent erroneous detection of a torque sensor failure even when the output value of the torque sensor becomes abnormal. It is an object of the present invention to provide a control device for an electric power steering apparatus that can secure a safe steering operation without giving a sense of incongruity to the steering wheel operation.

The present invention includes an electric motor that provides a steering assist force to a steering system of a vehicle and a torque sensor that detects a steering force acting on a steering wheel, and controls the motor based on an output value of the torque sensor. The present invention relates to a control device for a power steering device, and the object of the present invention is to provide a torque abnormality detection means for detecting an abnormality in the output value of the torque sensor, and a past normality before the output value of the torque sensor becomes abnormal. A torque input processing unit comprising an alternative value calculating means for calculating an alternative value based on a plurality of output values of the torque sensor, and determining that the torque sensor is faulty if an abnormality in the output value of the torque sensor continues for a certain period of time and a torque fault detecting means for, when the output value of the torque sensor is abnormal, even before determining said torque sensor is faulty, the torque sensor It is achieved by controlling the motor based on the alternative value instead of the output values. Also, the object of the present invention, the substitute value is the output value of the torque sensor can be achieved by an average value of n (natural number) samples of the output value of the torque sensor immediately before the abnormality. Also, the object of the present invention is achieved by the substitute value being a weighted average value of n (natural number) samples of the output value of the torque sensor immediately before the output value of the torque sensor becomes abnormal. . Further, the object of the present invention is that the substitute value is a value calculated by a least square method from n (natural number) samples of the output value of the torque sensor immediately before the output value of the torque sensor becomes abnormal. Achieved .

  By using the control device for the electric power steering device of the present invention, when the torque value that is the output of the torque sensor becomes abnormal, it is replaced with the abnormal torque value immediately and correctly based on the past detected torque value immediately before the abnormality. Since the electric power steering device is controlled using the predicted substitute value, the torque sensor failure determination time can be kept long enough to prevent false detection, and the correct torque output can be secured even when the torque sensor is abnormal, and the steering wheel can be operated. Therefore, it is possible to provide a control device for an electric power steering apparatus that can ensure a safe steering operation without giving a sense of incompatibility to the vehicle.

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

  FIG. 1 is a control block diagram showing an embodiment of the present invention. The torque value detected by the torque sensor 107 is not directly input to the current command value calculation unit 120 but is input to the torque input processing unit 10, and the output value is input to the current command value calculation unit 120. The current command value calculation unit 120 calculates the current command value Iref, the difference from the detected motor current value is calculated by the subtraction unit 121, the current control unit 122 determines the duty ratio, and the motor drive unit 123 sets the duty ratio. According to the PWM control, the motor 108 is driven.

  When the torque value output from the torque sensor 107 is normal, the torque input processing unit 10 operates so that the torque value is input to the current command value calculation unit 120. When the torque value is abnormal, the torque input processing unit 10 sets an alternative value. The alternative value is calculated and input to the current command value calculation unit 120.

The torque input processing unit 10 includes a torque abnormality detection unit 10-1, an alternative value calculation unit 10-2, and a selection switch 10-4. The torque failure detection means 10-3 considers a failure if the output value of the torque sensor becomes abnormal and the abnormality continues for a certain time. Limiter 11 has a function to narrow down the limit value for gradually decreasing the motor current if it is determined that the failure torque failure detection unit 10-3 (gradually decrease process). The torque failure detection means 10-3 is not necessarily incorporated in the torque input processing unit 10. In this embodiment, since the output result of the torque abnormality detection means 10-1 is used, the torque failure detection means 10-3 is incorporated in the torque input processing unit 10. Further, the method of gradually decreasing the motor current is not limited to the limiter 11. For example, if the current command value Iref, which is the output of the current command value calculation unit 120, is multiplied by the gain G and the gain G is decreased from 1 to 0, the value of G · Iref gradually decreases from Iref to 0. Decrease towards

  The operation of the torque input processing unit 10 will be described with reference to the flowchart of FIG. The torque value T, which is the output value of the torque sensor 107, is read through the AD converter (S1). Next, it is determined whether the torque value T is normal or abnormal (S2). Various normal / abnormal determination values Tref are conceivable. For example, if a normal torque value is greater than or less than a threshold that is not possible, it is determined to be abnormal. Or, if it changes suddenly, it is considered abnormal. Torque value abnormalities include zero output voltage or a fixed power supply voltage, offset abnormalities (abnormalities that are biased by (T + α) and α), and torque amplifier abnormalities ((KT)). Abnormal or operational amplifier failure). If the torque value T is not abnormal, the abnormality detection counter is cleared (S3).

  This abnormality detection counter counts when an abnormality in the torque value T is detected, and even if it is detected even once, it does not immediately determine that the torque sensor has failed. As will be described later, a torque sensor failure is determined only when the count value of the abnormality detection counter becomes equal to or greater than a set value. Next, the past torque value update routine is called to update the values T1, T2, T3, T4, and T5 of the previous n samples, for example, 5 samples as shown in FIG. 3 (S4). Since the torque value is not abnormal, the torque value T is calculated using the torque value as the torque input processing unit 10 (S5). Since the torque value T is not abnormal, the current command value calculation unit 120 calculates the current command value Iref based on the torque value T, not the substitute value.

  On the other hand, if it is determined in S2 that the torque value T is abnormal, the abnormality detection counter is counted up once (S6). Next, it is determined whether the count value N of the abnormality detection counter is equal to or greater than a set value (S7). If the count value is greater than or equal to the set value, it is determined that the torque sensor is malfunctioning. If the count value is less than or equal to the set value, it is not determined that the torque sensor has failed. However, since the torque value is abnormal, the torque value T cannot be used for the current command value calculation unit 120 as the output value of the torque sensor. Therefore, it is necessary to set an alternative value instead of the torque value T (S8).

  Here, the substitute value needs to be the current normal torque value predicted from the past torque value, and there are several methods for calculating the substitute value. The substitute value is calculated using n samples of past normal torque values. However, n is a natural number. For example, as shown in FIG. 4, an expected current value is obtained based on the values of five samples of past normal torque values, and is used as an alternative value (S11). In other words, the torque values of the past five samples are averaged, and the average value Tm = (T1 + T2 + T3 + T4 + T5) / 5 may be used as the substitute value. Other alternative value calculation methods will be described in detail later. Here, it is described that the normal torque value in the past is used, but this is ensured by the past torque value update routine which is the step of S4.

  Then, the substitute value is replaced as the torque value instead of the abnormal torque value (S9). And this alternative value is input into the electric current command value calculation part 120 as an output value of a torque sensor (S5). By controlling the motor with this alternative value, it is possible to avoid the output torque of the motor that was generated when the motor was controlled with an abnormal torque value.

  Another important point is that even before it is determined that the torque sensor is in failure, the abnormal torque value is not used for control, but is controlled using an alternative value. Conventionally, since the motor control is executed by substituting an alternative value after determining a torque sensor failure, control is performed based on an abnormal torque value before determining the failure, and the abnormal motor output torque is It was generated and the handle operation was uncomfortable.

  If the abnormality of the torque sensor continues, it is determined that the torque value is abnormal (S2), the abnormality detection counter is counted, and the count value is increased (S6). If the abnormality of the torque sensor further continues and the count value of the abnormality detection counter exceeds the set value N, it is determined that the torque sensor has failed (S7). If it is determined that the torque sensor has failed, a control for gradually decreasing the motor current is executed to prevent a sudden change in the output torque of the motor (S10). As a method of gradually attenuating the motor current, the alternative value is kept constant, the limiter 11 is provided at the output of the current command value calculation unit 120, and the limiter value of the limiter 11 is gradually reduced to gradually reduce the motor current. The motor current may be gradually attenuated by gradually decreasing the alternative torque value.

  FIG. 5 is a diagram showing the relationship between the torque value that is the output of the torque sensor and the motor current when the output value of the torque sensor suddenly becomes zero, using the torque input processing unit 10 of the present embodiment. . Even if the torque value suddenly becomes zero, the substitute value is immediately used instead of the abnormal torque value, so that the motor current maintains the value immediately before the torque value becomes abnormal. The motor current maintains the previous value until it is determined that the torque sensor has failed, and the motor current gradually attenuates after it is determined that the torque sensor has failed. Compared with FIG. 12 and FIG. 13 of the result by the conventional control method, the motor current does not reverse the polarity immediately before the torque value becomes abnormal, and the steering operation does not give a sense of incongruity.

  FIG. 6 shows the torque value (worst case) that is the output of the torque sensor when the output value of the torque sensor malfunctions due to chattering using the torque input processing unit 10 of this embodiment, and the motor current. The figure showing the relationship is shown. If the torque value causes chattering and it is determined that the torque value is abnormal, a substitute value is calculated using a past normal torque value, and the motor current is controlled based on the substitute value. Therefore, the motor current is output that is not significantly different from the motor current immediately before the chattering is generated. Furthermore, the motor current is gradually attenuated after the failure is detected. This result is compared with FIG. 14 of the result of control by the conventional control method. In the case of the conventional control method, a motor current having a polarity opposite to that before the motor current becomes an abnormality in the torque sensor output is generated, and then the result is unfavorable for the driver. Although it is preferable to gradually attenuate the motor current after the failure is detected, it is not preferable because the motor current immediately before the attenuation is attenuated from the current having the opposite polarity. Obviously, the control method of this embodiment is more preferable for steering the steering wheel even in the worst case.

  In the above embodiments, the case where the substitute value uses a simple average of the past five samples has been described. As a substitute value calculation method, the following equation is calculated from the least squares method and the past n sample values. There are a method for calculating the current value and a weighted average method, which will be described below. However, n is a natural number.

First, a method for calculating an alternative value by creating the following equation (n-1) from past n samples will be described. For example, the following calculation is performed to create a quadratic expression from the past three samples (T ₀ , T ₁ , T ₂ ) as shown in FIG. 7 and predict the current value T ₃ .

とした場合、ａ，ｂ，ｃを算出するには、数２の連立方程式を求める必要がある。

In order to calculate a, b, and c, it is necessary to obtain simultaneous equations of Formula 2.

よって、現在値Ｔ３は数３のように算出される。

Therefore, the current value T3 is calculated as shown in Equation 3.

実際の計算では逆行列部分は予め計算することができる。例えば、過去３サンプルの場合の逆行列部分は数４のようになる。

In actual calculation, the inverse matrix portion can be calculated in advance. For example, the inverse matrix portion in the case of the past three samples is as shown in Equation 4.

次に、最小自乗法を用いた代替値の算出方法について説明する。
過去のトルク値の直帰のｎサンプルから１次式を最小自乗法により作成して、現在値を予測し代替値を設定する。上述した代替値をｎ次式で求める方法の場合、過去のトルク値にノイズが含まれているので、厳密にｎ次式にフィッテイングすると最適な現在値を得られない場合がある。そこで、最小自乗法によって各係数を計算する。例えば、過去３サンプルから１次式を作成して現在値を予測する場合は以下の計算をすれば良い。

Next, a method for calculating an alternative value using the least square method will be described.
A linear expression is created by the least square method from n samples of bounces of past torque values, a current value is predicted, and an alternative value is set. In the case of the method for obtaining the substitute value by the n-order equation described above, noise is included in the past torque value, and therefore, if the fitting is strictly performed to the n-order equation, an optimal current value may not be obtained. Therefore, each coefficient is calculated by the method of least squares. For example, when a linear expression is created from the past three samples and the current value is predicted, the following calculation may be performed.

  First, obtaining the current value means obtaining the torque value T3 at the current time point t3 from the torque values T0, T1, T2 at the past t0, t1, t2 in FIG.

ここで、係数のａ，ｂを求めるには、数６の連立方程式を解ければ良い。

Here, in order to obtain the coefficients a and b, the simultaneous equations of Equation 6 may be solved.

そこで、過去３サンプルの場合は、逆行例を利用して数７のようになる。

Therefore, in the case of the past three samples, Equation 7 is obtained using a retrograde example.

実際の計算では逆行列は、予め計算することができる。その結果、各係数は以下数８のようになる。

In actual calculation, the inverse matrix can be calculated in advance. As a result, each coefficient is as shown in Equation 8 below.

最小自乗法でも、ｎ次式を用いる方法でも、代替値の最終的に計算する形はＴ＝ａＴ１＋ｂＴ２＋ｃＴ３＋ｄＴ４などの係数と過去トルク値との積和なのでＣＰＵにとって計算の負担は多くない。

Regardless of the method of least squares or the method using the n-order formula, the calculation form of the substitute value is finally the product sum of the coefficient such as T = aT1 + bT2 + cT3 + dT4 and the past torque value, so that the calculation burden on the CPU is not great.

  Finally, the weighted average will be described. The weighted average weights the torque values shown in FIG. 6 in order from the past. For example, T1, T2, T3, T4, and T5 in the oldest order, and the weights are, for example, a, b, c, d, and e.

である。ここで、ａ，ｂ，ｃ，ｄ，ｅをそれぞれ、例えば、８，４，２，１，１とすると数９は数１０のようになる。

It is. Here, when a, b, c, d, and e are set to 8, 4, 2, 1, and 1, for example, Expression 9 becomes Expression 10.

となる。

It becomes.

According to the embodiment described above, when the torque value that is the output of the torque sensor becomes abnormal, the motor of the electric power steering device is immediately replaced with the correctly predicted alternative value instead of the abnormal torque value. Since the motor is controlled, the electric power steering apparatus can be correctly controlled without the fact that the motor outputs an abnormal torque even in one cycle. Furthermore, using the present embodiment, it can be prevented even unusual since Torr does not output a click even take longer time determination for the failure detection such as a torque sensor erroneously no problem detection, even for one cycle.

  In the conventional control method, control is performed using an abnormal torque value until an abnormal output of the torque sensor is detected, so that the output torque of the motor becomes abnormal or the alternative value is not correctly predicted as the current value. Therefore, there has been a problem that the output torque of the motor becomes abnormal. Further, since the output of the motor becomes abnormal, it is not possible to take a long time for detecting abnormality such as a torque sensor, and there is a problem that causes erroneous detection of a torque sensor failure. Conventional problems can be solved.

It is a control block diagram which is one Example of this invention. It is a flowchart which shows operation | movement of the torque input process part of this invention. It is a flowchart of the update operation | movement of a past torque value. It is a flowchart which substitutes the present value estimated from the past torque value as a substitute value. It is a figure which shows the output result of the motor current at the time of the torque sensor ground fault at the time of using this invention. It is a figure which shows the output result of the motor current at the time of the failure where the torque sensor at the time of using this invention caused the chattering phenomenon. It is a figure which shows the principle of the present value estimation using a n-th order type | formula. It is a figure which shows the principle of the present value estimation using the least square method. It is a figure which shows the structure of an electric power steering apparatus. It is a control block diagram of the conventional electric power steering device. It is a control block diagram of the conventional electric power steering device corresponding to a torque sensor ground fault It is a figure which shows the output result of the motor current by the conventional control at the time of a torque sensor ground fault failure. It is a figure which shows the output result of the motor current by the conventional improved control at the time of a torque sensor ground fault failure. It is a figure which shows the output result of the motor current by the conventional control at the time of a torque sensor chattering failure.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Torque input process part 10-1 Torque abnormality detection means 10-2 Alternative value calculation means 10-3 Torque failure detection means 10-4 Selection switch 11 Limiter 107 Torque sensor 108 Motor 120 Current command value calculation part 121 Subtraction part 122 Current control Part 123 motor drive part

Claims (4)

An electric power steering apparatus comprising: a motor that applies a steering assist force to a steering system of a vehicle; and a torque sensor that detects a steering force acting on a steering wheel, and controls the motor based on an output value of the torque sensor. In the control device,
Torque abnormality detection means for detecting an abnormality in the output value of the torque sensor, and an alternative value calculation that calculates an alternative value based on a plurality of past output values of the normal torque sensor before the output value of the torque sensor becomes abnormal A torque input processing unit comprising means ,
A torque failure detection means for determining that the torque sensor is malfunctioning if an abnormality in the output value of the torque sensor continues for a certain period of time ;
When the output value of the torque sensor is abnormal, the electric power controls the motor based on the alternative value instead of the output value of the torque sensor even before determining that the torque sensor is in failure Control device for steering device. The control device for an electric power steering apparatus according to claim 1, wherein the substitute value is an average value of n (natural number) samples of the output value of the torque sensor immediately before the output value of the torque sensor becomes abnormal. The control device for an electric power steering apparatus according to claim 1, wherein the substitute value is a weighted average value of n (natural number) samples of the output value of the torque sensor immediately before the output value of the torque sensor becomes abnormal. 2. The electric power steering apparatus according to claim 1, wherein the substitute value is a value calculated by a method of least squares from n (natural number) samples of the output value of the torque sensor immediately before the output value of the torque sensor becomes abnormal. Control device.

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