JP4923521B2 - Control device for electric power steering device - Google Patents

Description

  The present invention relates to a control device for an electric power steering apparatus in which a steering assist force by a motor is applied to a steering system of an automobile or a vehicle. In particular, when there is an input exceeding a maximum current, frequency phase compensation is advanced. The present invention relates to a control device for an electric power steering device that is switched.

  An electric power steering device that biases an automobile or a vehicle steering device with an auxiliary load by the rotational force of a motor assists the steering shaft or rack shaft with a transmission mechanism such as a gear or a belt via a reduction gear. The load is energized.

  Such a conventional electric power steering apparatus performs feedback control of motor current in order to accurately generate assist torque (steering assist torque). Feedback control adjusts the motor applied voltage so that the difference between the current control value, which is the target value, and the detected motor current value is small. The adjustment of the motor applied voltage is generally performed by PWM (pulse width modulation). This is done by adjusting the duty ratio of the control.

  Here, the general configuration of the electric power steering apparatus will be described with reference to FIG. 4. The column shaft 2 of the handle 1 is connected to the tie rod 6 of the traveling wheel via the reduction gear 3, the universal joints 4A and 4B, and the pinion rack mechanism 5. It is connected. The column shaft 2 is provided with a torque sensor 10 that detects the steering torque of the handle 1, and a motor 20 that assists the steering force of the handle 1 is connected to the column shaft 2 via the reduction gear 3. Electric power is supplied from the battery 14 to a control unit (ECU) 30 that controls the power steering device, and an ignition key signal is input from the ignition key 11. The control unit 30 calculates the current command value I of the assist command based on the steering torque T detected by the torque sensor 10 and the vehicle speed V detected by the vehicle speed sensor 12, and based on the calculated current command value I. The current supplied to the motor 20 is controlled.

  The control unit 30 is mainly composed of a CPU (or 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 with reference to FIG. 5. The steering torque T detected by the torque sensor 10 and the vehicle speed V detected by the vehicle speed sensor 12 are input to the assist map 31 of the look-up table, and the assist map. The steering assist command value Ir calculated at 31 is phase compensated by the phase compensator 32 in order to enhance the stability of the steering system, and the phase compensated steering assist command value Ira is input to the robust stabilization compensator 33. . The robust stabilization compensator 33 is a compensator as disclosed in JP-A-8-290778, and a characteristic expression G (s) = (s ² + a1 · s + a2) / (s ² + b1 · s + b2), and removes the peak value of the resonance frequency of the resonance system consisting of the inertia element and the spring element included in the detected torque, and shifts the phase of the resonance frequency that impairs the stability and responsiveness of the control system. Is compensated. Note that a1, a2, b1, and b2 in the characteristic equation G (s) are parameters determined by the resonance frequency of the resonance system.

  The steering assist command value Irb compensated by the robust stabilization compensator 33 is limited in maximum current by the maximum current limiter 34, and the current command value I subjected to current limit is input to the subtractor 35. Further, the current i of the motor 20 is detected by the current detector 21, and the detected motor current i is input to the subtractor 35 and fed back. The deviation (= I−i) obtained by the subtractor 35 is input to the PI control unit 36 for improving the characteristics of the steering operation, and the voltage control value Vref PI-controlled by the PI control unit 36 is input to the PWM control unit 37. Then, the motor 20 is PWM driven via an inverter circuit 38 as a drive unit.

In such a configuration, the steering torque T and the vehicle speed V are input to the assist map 31 to calculate the steering assist command value Ir, and predetermined compensation is performed by the phase compensator 32 and the robust stabilization compensator 33 to obtain the maximum current. The maximum current is limited by the maximum current limiter 34 and is input to the subtractor 35. The deviation from the motor current i is obtained by the subtractor 35 and input to the PI control unit 36, and the voltage control value Vref PI-controlled by the PI control unit 36 is input to the PWM control unit 37, and an inverter circuit as a drive unit Steering assist is performed by driving the motor 20 through the control unit 38.
JP 2003-31509 A

In the control device of the conventional electric power steering apparatus shown in FIG. 5, the phase compensation unit 32 and the robust stabilization compensation unit 33 have the effect of phase delay, and the current value in the maximum current limiting unit 34 installed in the subsequent stage. The maximum value of is to be limited. For example, if the maximum current value is limited in the assist map 31, a transient response occurs in the subsequent dynamic characteristics, so that the maximum current limit unit 34 is calculated with the maximum current.

  Here, in the above control device, as shown in FIG. 6, when the steering assist current is turned back from the end contact (time 0 to t1) that is equal to or greater than the maximum current, and the steering assist current indicated by the characteristic A is equal to or less than the maximum current (time) t2) There is a delay as shown by the characteristic B from the start of switching until the current command value actually starts decreasing. The delay time has a relationship as shown in FIG. That is, as the steering torque T increases, the delay time increases exponentially. Due to this delay, a so-called “feeling of sticking” that is sticking to the magnet is generated in the steering operation, which makes the driver uncomfortable.

  In addition, a control device disclosed in Patent Document 1 (Japanese Patent Application Laid-Open No. 2003-31509) that gradually lowers the gain before the maximum current has been proposed. There is a problem that becomes large.

  The present invention has been made under the circumstances described above, and the object of the present invention is to apply a large calculation load with a simple configuration even when the steering wheel is turned to the rack end at the time of stationary, low speed, and then turned back. It is an object of the present invention to provide a control device for an electric power steering apparatus that does not require sticking feeling.

The present invention includes a phase compensation unit that compensates the phase of the steering assist command value Ir calculated based on the steering torque and the vehicle speed, and a robust stabilization that compensates the steering assist command value Ira compensated by the phase compensation unit. Electric power provided with a compensation unit and a drive control unit that controls the motor based on the steering assist command value Irb compensated by the robust stabilization compensation unit and applies steering assist force to the steering system by driving the motor The present invention relates to a control device for a steering device, and the object of the present invention is to limit a maximum value of the steering assist command value Ira and a switchback determination unit that determines whether to turn the steering wheel based on the steering torque and the steering assist command value Irb. the robust and an input limiting unit is provided for inputting to the stability compensation unit, only when the turning-back determining section determines the turning-back, the phase of the phase compensator It is achieved by the body.

  According to the control device for the electric power steering apparatus according to the present invention, when there is an input exceeding the maximum current, the phase compensation of the frequency is switched to the advance, so that the delay time is offset by the advance compensation. It becomes smaller and there is no feeling of sticking even when turning over.

In the case of only phase switching, it is calculated internally with a value exceeding the maximum current, and values such as center response and inertia compensation are added / subtracted later, but in a region exceeding the maximum current limit value. Even if it is calculated, there is no meaning and it is cut at the maximum current limit value. For example, when the maximum current limit value is 100 A, assuming that 200 A has been calculated internally, even if compensation of, for example, about ± 50 A is performed in the subsequent addition and subtraction, an output of 100 A is eventually obtained. That is, it is performed to reflect the effect of the compensation value. When switching back from the vicinity of the rack end, the compensation value is further subtracted from the vicinity of the maximum current value due to the input restriction, so that a switching back effect is obtained. If there is input limit as in the present invention, 100A + <is 100A, when there is no input restrictions, 200A + compensation value (-50A) = 150A> compensation value (-50 A) = 50A is 100A, the input It is cut to 100A by the limiting part .

  As a method of removing the feeling of sticking to the handle, it is conceivable to stop the calculation by detecting the maximum current of the calculation system, but there is a problem that vibration occurs due to a sudden change in frequency. The principle of the present invention is that the phase compensation is switched from the delay compensation to the advance compensation in order to remove the feeling of sticking of the handle that occurs at the time of turning back, such as turning the handle to the rack end at stationary or very low speed, and then turning back. The overall delay time is compensated, and the input to the robust stabilization compensator is limited to reduce the delay ratio.

  Hereinafter, an example of an embodiment of the present invention will be described with reference to the drawings.

  In the present invention, as shown in FIG. 1, a turn-back determining unit 300 that determines the turning of the handle and an input limiting unit 310 that restricts the input of the robust stabilization compensator 33 are provided. Phase delay and advance with respect to 32A are switched. The turning determination unit 300 receives the steering assist T and the steering assist command value Irb that is the output of the robust stabilization compensator 33, and outputs a turning signal SF when turning is determined. The switching signal SF1 is input to the phase compensation unit 32A.

  FIG. 2 shows an example of the characteristics of the input limiting unit 310. When the input current command value Ira exceeds ± Ir1, the output is limited to a constant value.

  In such a configuration, the switching determination unit 300 determines switching (current value over) based on the steering torque T and the steering assist command value Irb. If the switching is not switched, the current compensated by the phase compensation unit 32A. The value Ira is input limited by the input limiting unit 310, and the same assist process as described in FIG. 5 is executed. That is, normal assist control is performed.

When the switching determination unit 300 determines that the switching is performed, the switching signal SF1 is input to the phase compensation unit 32A, and the phase delay in the phase compensation unit 32A is switched to advance as shown in FIG. The output of the phase compensation unit 32A is input to the input limiting unit 310, and the current command value Ira ′ whose maximum value is limited is input to the robust stabilization compensator 33. Therefore, the input of the robust stabilization compensator 33 is the maximum current. Since the value is less than or equal to the value, the ratio of the delay time is reduced and no vibration is generated.

  The switching determination in the switching determination unit 300 may save the calculation time, and the switching signal SF1 may be output when the maximum current value + α is exceeded. The reason for not using the steering torque T is that even if the calculation is slightly different at the maximum current value or more, it is not a problem in terms of specifications because it is not output in the end. That is, if the maximum current value + α is exceeded even during round-up, the phase parameter of the phase compensator 32A is switched forward. If α is too large, the feeling of sticking will not be reduced, and if it is too small, the maximum current value may not be output. Such phase compensation control can also be applied to control in which the phase is switched by a change in vehicle speed.

  In the above description, the input restriction unit 310 and the robust stabilization compensator 33 are separately provided. However, the input restriction unit may be provided in the robust stabilization compensator 33.

It is a block block diagram which shows an example of the control apparatus of the electric power steering apparatus which concerns on this invention. It is a characteristic view which shows the example of a characteristic of an input control part. It is a characteristic view of phase lead compensation. It is a figure showing an example of composition of a general electric power steering device. It is a block block diagram which shows an example of a control unit. It is a characteristic view for demonstrating the operation example of a conventional apparatus. It is a characteristic view for demonstrating the operation example of a conventional apparatus.

Explanation of symbols

1 Handle 2 Column shaft 3 Reduction gear 10 Torque sensor 11 Ignition key 12 Vehicle speed sensor 14 Battery 20 Motor 30 Control unit 31 Assist map 32, 32A Phase compensator 33 Robust stabilization compensator 34 Maximum current limiter 36 PI controller 37 PWM Control unit 38 Inverter circuit 300 Cutback determination unit 310 Input restriction unit

Claims (2)

A phase compensation unit that compensates the phase of the steering assist command value Ir calculated based on the steering torque and the vehicle speed, and a robust stabilization compensation unit that robustly compensates the steering assist command value Ira compensated by the phase compensation unit; Control of an electric power steering apparatus including a drive control unit that controls a motor based on a steering assist command value Irb compensated by the robust stabilization compensator and applies a steering assist force to a steering system by driving the motor. In the device
A turning determination unit for determining turning of the steering wheel based on the steering torque and the steering assist command value Irb;
An input limiting unit that limits the maximum value of the steering assist command value Ira and inputs the maximum value to the robust stabilization compensator;
The control device for an electric power steering apparatus, wherein the phase compensation unit is advanced in phase only when the switching determination unit determines the switching. A phase compensation unit that compensates the phase of the steering assist command value Ir calculated based on the steering torque and the vehicle speed, and a robust stabilization compensation unit that robustly compensates the steering assist command value Ira compensated by the phase compensation unit; Control of an electric power steering apparatus including a drive control unit that controls a motor based on a steering assist command value Irb compensated by the robust stabilization compensator and applies a steering assist force to a steering system by driving the motor. In the device
A turning determination unit that determines turning of the steering wheel based on the maximum value + α of the steering assist command value Irb;
An input limiting unit that limits the maximum value of the steering assist command value Ira and inputs the maximum value to the robust stabilization compensator;
The control device for an electric power steering apparatus , wherein the phase compensation unit is advanced in phase only when the switching determination unit determines the switching .

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