JP2006142960A - Control device of electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control device for an electric power steering device with an enhanced performance by lessening the behavior of the motor current even in case where recovery is made from wire disconnection in the motor to determination of the failed condition. <P>SOLUTION: The control device of the electric power steering device is equipped with a motor to give a steering assist force to the steering system of a vehicle and a torque sensor to sense the steering force acting on a steering wheel, in which the motor is controlled on the basis of the output of the torque sensor, wherein the arrangement includes a failure sensing means to sense a failure and recovery of the motor driving system, torque system or the power supply voltage and a current limiting means to limit the current in the motor control in accordance with the output of the failure sensing means. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a control device for an electric power steering device that controls a steering assist force by a motor based on current control, and in particular, an electric motor that reduces the behavior of a motor current when the control system returns to normal from an abnormal state to failure determination. The present invention relates to a control device for a power steering device.

  An electric power steering device that assists an automobile or a vehicle steering device with an auxiliary load by the rotational force of a motor is a steering shaft or rack that transmits the driving force of the motor by a transmission mechanism such as a gear or a belt via a reduction gear. An auxiliary load is applied to the shaft. Such a conventional electric power steering apparatus performs feedback control of motor current in order to accurately generate assist torque (steering assist force). In the feedback control, the motor applied voltage is adjusted so that the difference between the current command value and the motor current detection value becomes small. Generally, the adjustment of the motor applied voltage is a duty of PWM (pulse width modulation) control. This is done by adjusting the tee ratio.

  Here, the general configuration of the electric power steering apparatus will be described with reference to FIG. It is connected to the tie rod 6. The column shaft 2 is provided with a torque sensor 10 that detects the steering torque of the steering handle 1, and a motor 20 that assists the steering force of the steering handle 1 is connected to the column shaft 2 via the reduction gear 3. ing. The control unit 30 that controls the power steering device is supplied with electric power from the battery 14 via the ignition key 11 and the relay 13, and the control unit 30 is detected by the steering torque T detected by the torque sensor 10 and the vehicle speed sensor 12. The steering assist command value I of the assist command is calculated based on the vehicle speed V, and the current supplied to the motor 20 is controlled based on the calculated steering assist command value I.

  The control unit 30 is mainly composed of a CPU (including an MPU). FIG. 5 shows general functions executed by a program inside the CPU.

  The function and operation of the control unit 30 will be described. The torque value T detected and input by the torque sensor 10 and the vehicle speed V from the vehicle speed sensor are input to the current command value calculation unit 31 that calculates the current command value Iref. . The current command value calculation unit 31 determines a current command value Iref that is a control target value of the current to be supplied to the motor 20 based on the input torque value T and vehicle speed V. The current command value Iref is input to the subtractor 32, a deviation I (Iref-Im) from the fed back motor current value Im is calculated, and the deviation is input to the PI control unit 33 for improving the characteristics of the steering operation. Is done. The steering assist command value Vref whose characteristics have been improved by the PI control unit 33 is input to the PWM control unit 34, and the motor 20 is PWM driven via an inverter circuit 35 as a drive unit. The current value Im of the motor 20 is detected by the motor current detector 36 and fed back to the subtractor 32. The inverter circuit 35 is composed of an FET as a drive element.

  In such an electric power steering apparatus, when the disconnection state of the motor 20 occurs, the motor assist is normally stopped and manual steering is performed. In manual steering, the steering wheel becomes heavy because the steering wheel becomes heavier, especially during turning-holding and turning-back steering, and the driver increases the steering torque. Along with this, the current command value increases, but the motor is disconnected, so that it is not reflected in the actual current. In this state, when the failure state is not determined and the normal state is restored from the disconnection state, a large current is reflected as it is in the current command value, resulting in an excessive assist state.

  FIG. 6 shows an operation example at the time of motor disconnection and return, and shows a case where the disconnection of the motor 20 occurs at time t1 and the disconnection returns at time t2. Accordingly, as shown in FIG. 6A, the motor line state is normal (normal assist steering) before time t1 and after time t2, and is abnormal (manual steering) between time points t1 and t2. . When the motor disconnection occurs at time t1, the steering torque of the driver, that is, the torque value T increases as a result of manual steering as shown in FIG. Further, as shown in FIG. 6C, the current command value Iref is based on the torque value T (vehicle speed V) even though the motor current value Im is 0 because of the disconnection. Rise to be calculated in.

When the disconnection returns to the normal state at time t2, the current command value Iref that has been calculated by the current command value calculation unit 31 until then is applied immediately, so that the motor current as shown in FIG. The behavior of the value Im increases.
JP-A-11-263240

  As described above, the conventional control device has a problem that when the motor is disconnected from the disconnected state before the failure is determined, the behavior of the motor current Im becomes large, which gives the driver anxiety and discomfort.

  The same applies to not only the motor disconnection but also the failure of the FET constituting the inverter circuit 35, the torque system abnormality, the power supply voltage abnormality, etc. There is a problem that the driver becomes uncomfortable and uncomfortable.

  The present invention has been made under the circumstances described above, and the object of the present invention is to make the driver feel uneasy and uncomfortable by reducing the behavior of the motor current even when the motor is disconnected until the failure is confirmed. It is an object of the present invention to provide a control device for an electric power steering device that has improved performance without imparting any of the above.

  The present invention includes an electric power steering system that includes 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 of the torque sensor. The above object of the present invention relates to a control device for an apparatus, the abnormality detection means for detecting abnormality and recovery of the motor drive system, the torque system or the power supply voltage, and the motor control according to the output of the abnormality detection means. This is achieved by providing current limiting means for limiting the current.

  The object of the present invention is to output an abnormal signal when the abnormality detecting means detects the abnormality, and to output a return signal when detecting the return, and the current limiting means gradually decreases with the input of the abnormal signal. The gradual increase in response to the input of the return signal, or the gradual decrease is larger than the gradual increase, or the gradual decrease and the gradual increase are variable. Or by increasing the current after the gradual decrease of the current limiting means to 0 or larger than 0, or because the abnormality of the motor drive system is a disconnection of the motor or a failure of the drive element of the motor, Achieved more effectively.

  According to the control device for the electric power steering apparatus according to the present invention, when the motor disconnection is detected, the output is limited to the current command value, so that an excessive motor current flows when the motor disconnection is restored. Nor. This improves the performance of the power steering device without giving the driver anxiety or discomfort.

  In the present invention, the disconnection of the motor (harness disconnection, etc.), the failure of the FET as the motor drive element, the abnormality of the torque system including the torque sensor, the abnormality of the power supply voltage, etc. are detected. When the current is gradually decreased and the current is restored before the failure is determined, the current command value is gradually increased to reduce the behavior of the motor current at the time of return. As a result, a high-performance electric power steering device can be realized without causing anxiety or discomfort to the driver.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a block diagram showing an embodiment of the present invention corresponding to FIG. 4, and a motor disconnection detecting unit as an abnormality detecting means for detecting disconnection and return of a motor 20 and outputting a disconnection signal and a return signal. 40, and a current limiting unit 41 as current limiting means for limiting or returning the steering assist command value Vref from the PI control unit 33 based on the disconnection signal and the return signal from the motor disconnection detection unit 40. . The limited current command value Vrefa output from the current limiting unit 41 is input to the PWM control unit 34.

The motor disconnection detection unit 40 detects disconnection of the motor 20 based on the following principle, and outputs a disconnection signal when the disconnection is detected. That is, when the motor 20 is disconnected, the relationship between the motor terminal voltage Vm and the power supply voltage (VR voltage) is expressed by the following equation (1). Therefore, equation (1) is the first condition for detecting disconnection of the motor 20.

Motor terminal voltage Vm> VR voltage (1)

In addition, when the motor is disconnected, the current detected by the current detector 36 becomes 0. At the same time, the motor current Im from the current detector 36 needs to be equal to or less than a predetermined value (for example, 5.5 A). It is. That is, the following equation (2) is the second condition for detecting the disconnection of the motor 20.

Motor current Im <predetermined value (2)

The motor disconnection detection unit 40 determines that the motor 20 is disconnected when the two conditions of the expressions (1) and (2) are satisfied at the same time, and outputs a disconnection signal. Then, when the above two conditions are not satisfied until the failure is confirmed separately, a return signal is output as the motor disconnection is recovered. That is, when one or both of the conditions (1) and (2) are not satisfied, a return signal is output.

  On the other hand, the current limiting unit 41 has a current limiting characteristic as shown in FIG. That is, when the disconnection signal is input, the gain gradually decreases from the gain 1 with the slope A, and reaches the minimum gain after a predetermined time Ta, and when the return signal is input, the gain gradually increases to the gain 1 with the slope B. In FIG. 2, the minimum gain is set to be larger than 0, but may be 0.

  Here, in the present invention, the gradual change time of the current limit is made different between the time of disconnection (inclination A) and the case of returning from the disconnection (inclination B), and the gradually decreasing inclination is increased. That is, the inclination A> the inclination B. When the motor is disconnected, the assist cannot be performed, and the current command value gradually decreases in the current limit = 0 state. This is because, since the motor current becomes 0 simultaneously with the motor disconnection, it is desirable to perform the gradual reduction process of the current limit with the same time constant as much as possible. Further, it is desirable that the gradual increase process at the time of disconnection recovery is gradually increased as much as possible in order to reduce the behavior of the motor current.

  There are two possible gradual changes, torque gradual change and current limit as in the present invention, but the current limit is better. The reason is as follows. That is, the main cause of the increase in the behavior of the motor current Im when the disconnection is restored is an increase in the steering torque, so that the torque can be gradually changed. However, the reason why the current is narrowed by the current limit is that the factor that cannot be assisted is not the torque. When the output is limited when the motor is disconnected by gradually changing the torque, the output Iref of the current command value calculation unit 31 can be suppressed, but the current flowing through the motor 20 cannot be suppressed by the feedback of the current detector 36. For this reason, the current limitation is superior to the gradual torque change.

  The operation of the configuration as described above will be described with reference to FIG.

  In FIG. 3, the disconnection of the motor 20 occurs at time T <b> 1, which is detected by the motor disconnection detection unit 40, and the disconnection signal is input to the current limiting unit 41. A case where a return signal is input to the restriction unit 41 is shown. When the disconnection signal is input to the current limiting unit 41, the gain is gradually reduced with the characteristic of the slope A as shown in FIG. 2, so that the current command value Vrefa output from the current limiting unit 41 is as shown in FIG. become. FIG. 3C shows the conventional current command value Vref shown in FIG. 5, and the magnitude of the current command value is smaller than that of the conventional one. When the disconnection returns to the normal state at time T2, a return signal is input from the motor disconnection detection unit 41 to the current limiting unit 41, and the characteristics of the current limiting unit 41 are inclined from the minimum gain value as shown in FIG. Since it gradually increases at B, the behavior of the motor current value Im can be reduced as shown in FIG.

  In the above-described embodiment, the current limiting unit is gradually decreased or increased by a linear expression (straight line), but may be gradually decreased or increased by a curve characteristic such as a quadratic expression. It is also possible to make the inclination and the like variable from the outside. Further, the current after gradual decrease is set to be larger than 0 in the above embodiment, but may be 0.

  Furthermore, although the motor disconnection has been described above as an example of the motor drive system, the abnormal state such as a failure of a drive element such as an FET, a failure of a torque system including a torque sensor, or a decrease in power supply voltage is similarly described. It is possible to limit the current by detecting the return.

  According to the control device for an electric power steering apparatus according to the present invention, when an abnormality in a drive system such as a motor disconnection, an abnormality in a torque system or a power supply voltage is detected, an output restriction is applied to a current command value. As a result, excessive motor current does not flow even when normal operation is restored before the failure is confirmed. For this reason, it is possible to realize a high-performance power steering device without causing the driver anxiety or discomfort.

It is a block block diagram which shows one Example of this invention. It is a figure which shows the example of a characteristic of the current limiting part of this invention. It is a timing chart which shows the operation example of this invention. 1 is a structural diagram showing an outline of a general electric power steering apparatus. It is a block block diagram which shows an example of a controller. It is a timing chart which shows the operation example at the time of a motor disconnection.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steering handle 2 Column shaft 3 Reduction gear 10 Torque sensor 11 Ignition key 12 Vehicle speed sensor 13 Relay 14 Battery 20 Motor 30 Control unit 31 Current command value calculating part 33 PI control part 34 PWM control part 35 Inverter circuit 36 Current detector 40 Motor disconnection detector 41 Current limiter

Claims (6)

A control device for 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 of the torque sensor. The motor drive system, the torque system, or an abnormality detection means for detecting an abnormality and recovery of the power supply voltage, and a current limiting means for limiting the motor control current according to the output of the abnormality detection means. A control device for an electric power steering device. When the abnormality detection unit detects the abnormality, an abnormality signal is output, and when the recovery is detected, a recovery signal is output. The current limiting unit gradually decreases with the input of the abnormality signal, and the recovery signal is input. The control device for an electric power steering device according to claim 1, wherein the control device has a characteristic of gradually increasing. The control device for an electric power steering apparatus according to claim 2, wherein the gradually decreasing inclination is larger than the gradually increasing inclination. 4. The control device for an electric power steering apparatus according to claim 3, wherein the gradually decreasing inclination and the gradually increasing inclination are variable. The control device for an electric power steering apparatus according to any one of claims 2 to 4, wherein the current after the current limiting means gradually decreases is 0 or larger than 0. 6. The control device for an electric power steering apparatus according to claim 1, wherein the abnormality of the motor drive system is a disconnection of the motor or a failure of a drive element of the motor.

Images