JP2006240479A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device having excellent steering feeling which is capable of reducing vibrations and noise of a steering wheel in a steering holding state, and ensuring the steering performance in a normal steering state. <P>SOLUTION: The electric power steering device comprises a motor, a current command value determination means to determine the current command value based on the vehicle speed and the torque, a current detection means to detect the motor current, and a current control means to output the voltage command value, and further comprises a steering state detection means to detect the steering state of a steering wheel, output the steering holding signal to the current control means when the steering state is detected to be the steering holding state, and prevent the output of the steering holding signal when the steering state is detected to be the normal steering state. The current control means changes the current control responsiveness according to the steering state detected by the steering state detection means with the deviation between the current command value and the motor current being an input, and determines the voltage command value based on the current control responsiveness after the change and the deviation. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electric power steering device, and in particular, can reduce steering vibration and noise during steering (hereinafter also referred to as steering noise) and ensure steering performance in a normal steering state (during normal steering). The present invention relates to an electric power steering apparatus with good steering feeling.

  An electric power steering device that applies an assisting force (steering assisting force) to a steering device of an automobile by a rotational force of a motor is a steering shaft or rack shaft by a transmission mechanism such as a gear or a belt via a reduction gear. An auxiliary force is given to the. 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. A torque sensor 107 that detects the steering torque of the steering handle 101 is provided on the shaft 102, 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. Yes.

  Control of the electric power steering apparatus configured as described above will be described with reference to FIG. First, the torque T detected by the torque sensor 107 and the vehicle speed V detected by a vehicle speed sensor (not shown) are input to the assist map 190, and a steering assist command value is calculated. Further, compensation values calculated by the compensation value calculation unit 194, for example, compensation values such as convergence and inertia calculated by the convergence calculation unit 191 and the inertia calculation unit 192 are added by the addition units 195, 196, and 197. The torque command value Tref is determined by adding to the command value. Then, the current command value calculation unit 200 determines the current command value Iref based on the torque command value Tref.

  In the brushless motor, in addition to the torque command value Tref, the rotor angle of the rotor is also input to the current command value calculation unit 200 to determine the current command value Iref. Here, the processing part (the part surrounded by the broken line B) until the current command value Iref is determined based on the torque T, the vehicle speed V, and the compensation value is referred to as a current command value determination unit B for convenience.

  On the other hand, the motor current Im supplied to the motor 108 is detected by the current detector 202 and input to the subtraction unit 204 together with the current command value Iref. In the subtraction unit, the deviation ΔI = Iref−Im is calculated.

  Next, the deviation ΔI is input to a proportional-integral control unit as current control means A surrounded by a broken line A. In this example, the proportional term 208 as the proportional gain Kp and the integral term 206 as the integral gain Ki are input. The output of the proportional term 208 and the output of the integral term 206 are added by the adder 210 to output a voltage command value Vref.

  The PWM control unit 212 receives the voltage command value Vref and outputs a PWM signal to the inverter circuit 214, whereby the PWM signal based on the voltage command value Vref is instructed to the inverter circuit 214. The inverter circuit 214 supplies the motor current Im to the motor 108 based on the PWM signal.

  The above is an explanation regarding an example in which proportional integral control is used for the current controller A in the control of the electric power steering apparatus. Here, the gain Gi related to the proportional integration is expressed by the following equation (1).

つまり、偏差ΔＩが小さい値であっても、ゲインＧｉが無限大になるために、ハンドル保舵時や、ゆっくりした操舵時にも電圧指令値Ｖｒｅｆは大きな値として出力され、以下のような問題が発生する。

That is, even if the deviation ΔI is a small value, the gain Gi becomes infinite, so that the voltage command value Vref is output as a large value even during steering of the steering wheel or during slow steering. appear.

  In other words, recent electric power steering devices have increased capacity, that is, increased current, but AD converters and the like used in control devices mainly composed of CPUs have a resolution of 10 bits. The resolution has become relatively coarse. The calculation error such as noise generated by the roughness of the resolution is amplified by the feedback gain that becomes infinite when the deviation ΔI at the time of steering or slow steering is small, and the vibration or noise of the steering wheel is increased. As a result, there is a problem that makes the driver feel uncomfortable.

  By the way, in the current control of the electric power steering apparatus, integral control (I control), proportional integral control (PI control) and proportional integral derivative control (PID control) are generally used. However, the current control including the integral term has an infinite gain in the steady state, so that the steady state or the steady state of the electric power steering device or vibrations via the steering wheel during slow steering. There is a problem that the steering wheel feels uncomfortable due to noise.

Therefore, in Patent Document 1, in order to solve this problem, in feedback control, the deviation ΔI = Iref−Im between the current command value Iref and the actual motor current Im is adjusted before being input to the current control system including the integral term. A gain is provided so that the adjustment gain is reduced when the deviation ΔI is small and the adjustment gain is increased when the deviation ΔI is large.
JP 2000-108916 A

  However, in the above-described conventional electric power steering device, the design (threshold value) for determining the adjustment gain that changes in accordance with the deviation of the current feedback is difficult, and the gain of the integral term is infinite. Even if it is made small, the total gain becomes large, and the problem of feeling the vibration and noise generated during steering of the steering wheel and slow steering is not solved.

  In addition, there is a problem in which discrete time, fixed-point arithmetic, and the like, which are mounting problems when using a CPU as a control device for an electric power steering device, are not taken into consideration.

  The present invention has been made under the circumstances described above, and an object of the present invention is to reduce the vibration and noise of the steering wheel at the time of steering, and to ensure the steering performance at the time of normal steering. It is to provide an electric power steering device with good quality.

  The present invention relates to a motor that applies a steering assist force to a vehicle steering system, a torque sensor that detects a steering force acting on a steering wheel, a current command based on a vehicle speed and a torque that is an output value of the torque sensor. The present invention relates to an electric power steering apparatus comprising a current command value determining means for determining a value Iref, a current detecting means for detecting a motor current Im, and a current control means for outputting a voltage command value Vref. Steering state detection means for detecting a steering state of the steering wheel, outputting a steering holding signal to the current control means when the steering holding state is detected, and not outputting a steering holding signal when the normal steering state is detected. The current control means further includes a deviation between the current command value Iref and the motor current Im as an input, and responds to the steering state detected by the steering state detection means. Switching the current control response Te effectively achieved by determining the voltage command value Vref on the basis of said deviation current control response after the switching.

  Further, the object of the present invention is that the steering state detecting means uses at least one of the torque, the current command value Iref, the vehicle speed, the rotation angle of the motor, and the rotation angular velocity of the motor to Or the current control means comprises a current controller, changes the time constant of the current controller, switches the current control responsiveness, or the current control means Is composed of a current controller and a gradual gain, and by changing the gradual gain, switching the current control responsiveness, or in the current control means, the gradual gain is controlled by the current control. Or by providing the gradual gain on the output side of the current controller, or in the current control means, or Flow controller is more effectively accomplished by being constituted from lead lag function.

  Further, the above object of the present invention is that in the current control means, the current controller is constituted by a lead / lag function (L · s + R) / (T · s + a), where L is an inductance value of the motor and R Is a resistance value of the motor, T is a time constant of the current controller, a is a constant, and by gradually changing the gradual gain, by switching the current control responsiveness, or In the current control means, the constant a is gradually changed to 0 or a small value in accordance with a gradual change of the gradual change gain to a small value in the steered state, and in the normal steering state. This is effectively achieved by gradually changing the reduced constant a to the original value of a while the gradually changing gain that has been reduced is gradually changed to the original value.

  According to the electric power steering apparatus of the present invention, the steering state is determined using at least one of the torque T, the current command value Iref, the vehicle speed V, the motor angle θ, and the rotational angular velocity ω of the motor. Since the current control response is changed according to the steering state, the vibration and noise of the steering wheel during steering can be remarkably reduced and the steering performance during normal steering can be ensured. There is an excellent effect of being obtained.

  In the electric power steering apparatus of the present invention, more specifically, when the current control response is changed according to the steering state, that is, the steering holding state or the normal steering state, the steering of the current control means is described. Since the gain is gradually changed when switching the gain in the state (hereinafter also referred to as the steered state gain) and the gain in the normal steering state of the current control means (hereinafter also referred to as the normal steering state gain), Even if the steering is started from the steering holding state or the steering holding is started from the normal steering state, the steering assist force can be prevented from suddenly decreasing or increasing, and the steering feeling can be further improved.

  In the electric power steering apparatus of the present invention, at least one of the torque T, the current command value Iref, the vehicle speed V, the motor angle θ, and the rotational angular velocity ω of the motor is used as an input parameter of the steering state detecting means, and the steering state detecting means is used. It is one point to detect the steering state and change the current control response in accordance with the detected steering state (steering state or normal steering state).

  As another point of the present invention, when the current control responsiveness is changed depending on whether the steering state is the normal steering state or not, the gain in the steering state of the current control means (hereinafter referred to as “maintenance state”) will be described. The gain is gradually changed when switching between a gain in a normal steering state of the current control means (hereinafter also referred to as a normal steering state gain).

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

  FIG. 1 shows a control block diagram of the electric power steering apparatus of the first embodiment.

  First, the overall configuration of the electric power steering apparatus according to the first embodiment will be described. As shown in FIG. 1, the current command value determination unit B determines the current command value Iref with the torque T detected by the torque sensor 107 and the vehicle speed V detected by a vehicle speed sensor (not shown) as inputs. On the other hand, the motor current Im supplied to the motor 108 is detected by the current detector 202 and input to the subtraction unit 204 together with the current command value Iref. In the subtraction unit, the deviation ΔI = Iref−Im is calculated.

  Next, the deviation ΔI and the steering holding signal when there is a steering holding signal output from the steering state detector 30 which is an example of the steering state detection means are the current control means A (current controller 20 in this example). ). Here, as a specific example of the current controller 20, for example, it is configured by an advance / delay function. As an example of the advance / delay function, (L · s + R) / (T · s + a) is used. Here, L is an inductance value of the motor 108, R is a resistance value of the motor 108, T is a time constant of the current controller, and a is a constant.

  Here, the steering state detector 30 will be described. In the steering state detector 30, the steering state is determined using at least one of the torque T, the current command value Iref, the vehicle speed V, the motor angle θ, and the rotational angular velocity ω of the motor. The steering holding signal is output, and on the other hand, when the normal steering state is detected, the steering holding signal is not output. Further, the rotor position signals such as the motor angle θ and the rotational angular velocity ω of the motor can be detected by a rotor position detection sensor such as a resolver or a hall sensor.

  Next, current control of the electric power steering apparatus of the present invention will be described. In the first embodiment, the current control means A is composed of only the current controller 20. The current controller 20 outputs the voltage command value Vref based on the presence / absence of the steering holding signal and the input deviation ΔI.

  Specifically, when a steering signal from the steering state detector 30 is input to the current controller 20, that is, when it is determined that the steering wheel is in the steering state, the time constant T of the current controller 20 is set. By increasing the value, the current control response is lowered to the current control response in the steered state. In other words, the gain of the current control means (hereinafter also simply referred to as control gain) is lowered from the normal steering state gain to the steered state gain.

  On the other hand, when there is no steering holding signal from the steering state detector 30, that is, when it is determined that the steering wheel is in the normal steering state, the current control responsiveness is reduced by reducing the time constant T of the current controller. Is returned to the current control response in the normal steering state. In other words, the gain (control gain) of the current control means is increased from the steering state gain to the normal steering state gain.

  Further, the PWM control unit 212 receives the voltage command value Vref, which is the output of the current control means A, and outputs a PWM signal to the inverter circuit 214, whereby the PWM signal based on the voltage command value Vref is converted to the inverter circuit 214. Is directed to. The inverter circuit 214 supplies the motor current Im to the motor 108 based on the PWM signal.

  As described above, in the electric power steering apparatus configured as shown in FIG. 1, the current control responsiveness is changed by changing the time constant T of the current controller according to the steering state of the steering wheel. . That is, when it is determined that the steering wheel is in the holding state, the steering control gain (control gain) of the current control means is switched to the holding state gain having a small value. ) Can be secured. On the other hand, when it is determined that the steering wheel is in the normal steering state, the steering performance can be ensured because the gain (control gain) of the current control means is switched to the normal steering state gain having a large value.

  Next, FIG. 2 shows a control block diagram of the electric power steering apparatus of the second embodiment.

  As shown in FIG. 2, the electric power steering apparatus according to the second embodiment is different from the electric power steering apparatus according to the first embodiment only in the current control means A. Therefore, only the current control means A of Example 2 will be described. For the description of other parts of the electric power steering apparatus of the second embodiment, refer to the description of the first embodiment.

  As shown in FIG. 2, in the electric power steering apparatus according to the second embodiment, a gradual gain 21 is provided between the subtraction unit 204 and the current controller 20.

  The current control of the electric power steering apparatus according to the second embodiment will be described. In the second embodiment, the current control means A includes a current controller 20 and a gradual gain 21. The current control means A outputs the voltage command value Vref based on the presence / absence of the steering holding signal and the input deviation ΔI.

  Specifically, when the steering signal from the steering state detector 30 is input to the gradual gain 21, that is, when it is determined that the steering wheel is in the steering state, the gradual gain 21 is decreased. The current control responsiveness is lowered to the current control responsiveness in the steering state. In other words, the gain of the current control means (hereinafter also simply referred to as control gain) is lowered from the normal steering state gain to the steered state gain.

  On the other hand, when there is no steering holding signal from the steering state detector 30, that is, when it is determined that the steering wheel is in the normal steering state, the gradual change gain 21 is increased so that the current control responsiveness is changed to the normal steering state. Return to the current control response. In other words, the gain (control gain) of the current control means is increased from the steering state gain to the normal steering state gain.

  As described above, in the electric power steering apparatus configured as shown in FIG. 2, the current control responsiveness is changed by changing the gradual change gain 21 in accordance with the steering state of the steering wheel. That is, when it is determined that the steering wheel is in the holding state, the steering control gain (control gain) of the current control means is switched to the holding state gain having a small value. ) Can be secured. On the other hand, when it is determined that the steering wheel is in the normal steering state, the steering performance can be ensured because the gain (control gain) of the current control means is switched to the normal steering state gain having a large value.

  Next, FIG. 3 shows a control block diagram of the electric power steering apparatus of the third embodiment.

  As shown in FIG. 3, the electric power steering apparatus of the third embodiment is different from the electric power steering apparatus of the first embodiment only in the current control means A. Therefore, only the current control means A of the third embodiment will be described. For the description of other parts of the electric power steering apparatus of the third embodiment, refer to the description of the first embodiment.

  As shown in FIG. 3, in the electric power steering apparatus of the second embodiment, a gradual gain 21 is provided between the current controller 20 and the PWM control unit 212.

  The current control of the electric power steering apparatus according to the third embodiment will be described. Also in the third embodiment, the current control means A is composed of the current controller 20 and the gradual gain 21, but unlike the second embodiment, the gradual gain 21 is provided on the output side of the current controller 20. Yes. The current control means A outputs the voltage command value Vref based on the presence / absence of the steering holding signal and the input deviation ΔI. More precisely, the voltage command value Vref is output from the gradual change gain 21.

  Specifically, when the steering signal from the steering state detector 30 is input to the gradual gain 21, that is, when it is determined that the steering wheel is in the steering state, the gradual gain 21 is decreased. The current control responsiveness is lowered to the current control responsiveness in the steering state. In other words, the gain of the current control means (hereinafter also simply referred to as control gain) is lowered from the normal steering state gain to the steered state gain.

  On the other hand, when there is no steering holding signal from the steering state detector 30, that is, when it is determined that the steering wheel is in the normal steering state, the gradual change gain 21 is increased so that the current control responsiveness is changed to the normal steering state. Return to the current control response. In other words, the gain (control gain) of the current control means is increased from the steering state gain to the normal steering state gain.

  As described above, in the electric power steering apparatus configured as shown in FIG. 3, the current control responsiveness is changed by changing the gradual change gain 21 in accordance with the steering state of the steering wheel. That is, when it is determined that the steering wheel is in the holding state, the steering control gain (control gain) of the current control means is switched to the holding state gain having a small value. ) Can be secured. On the other hand, when it is determined that the steering wheel is in the normal steering state, the steering performance can be ensured because the gain (control gain) of the current control means is switched to the normal steering state gain having a large value.

  Although three preferred embodiments of the present invention have been described above, specific examples of how to change the current control response in the present invention will be described.

FIG. 4 is a circuit diagram showing a specific example of the current controller 20 as the current control means A in the first embodiment of FIG. The time constant T of the current controller 20 can be changed using the circuit of FIG. In the current controller 20 to which the circuit of FIG. 4 is applied, if the intermediate variable (W _n−1 ) of integration is calculated so that the output becomes constant before and after the change of the current control response, the current control response is rapidly increased. The output does not change suddenly even if it is changed to.

A specific example of the intermediate variable (W _n-1 ) reset can be expressed by the following formula.

よって、数３において、ｙ_ｎに前回出力ｙ_ｎ−１を代入すれば、今回の出力ｙ_ｎがｙ_ｎ−１に等しくなる。

Therefore, the number 3, by substituting the previous output _{y n-1} to _{y n,} the current output _{y n} is equal to _{y n-1.}

  FIG. 5 is a schematic diagram for explaining the principle of changing the current control response (current control response switching logic) in the electric power steering apparatus according to the third embodiment. As shown in FIG. 5, for example, when the current command value Iref is 10A, there is a current waveform as shown, and the current detection value Im has a current waveform as 10A as shown. The deviation ΔI between the current command value Iref and the detected current value Im has a current waveform of 0 A as shown in the figure. The deviation ΔI is input to the PI controller, the steering signal from the steering state detector is input to the gradually changing gain, and the voltage command value Vref is output from the gradually changing gain. When it is determined that the steering state is maintained, that is, when the steering signal is input to the gradual gain from the steering state detector, the response of the current control means is lowered, that is, by reducing the gradual gain, vibration is generated. It becomes smaller and the steering noise is improved.

  Next, FIG. 6 is a schematic diagram for explaining the timing for switching the gain of the current control means and how to switch the gain in the electric power steering apparatus of the present invention. In FIG. 6, the steering state is detected using the Hall sensor change signal.

  As shown in FIG. 6, when the hall sensor change signal is detected in the normal steering state and the predetermined steering hold determination time threshold has elapsed, it is determined that the steering state has been changed from the normal steering state, and the current control means When the gain (control gain) is lowered from the normal steering state gain to the steered state gain with a fixed slope within the predetermined descending gradual change time, then held as it is, and the Hall sensor change signal is detected again Then, it is determined that the steering state has changed to the normal steering state, and the gain (control gain) of the current control means is increased from the steering state gain to the normal steering state gain at a fixed slope within a predetermined gradual increase time. In other words, in the electric power steering apparatus of the present invention, when changing the current control response, that is, when changing the gain (control gain) of the current control means, the control gain is gradually changed instead of suddenly changing. Yes.

  FIG. 7 is a schematic diagram for explaining frequency characteristics of current control response in the electric power steering apparatus of the present invention. As shown in FIG. 7, as the frequency increases, both the current control responsiveness (normal steering state gain) in the normal steering state and the current control responsiveness (maintenance state gain) in the steered state tend to decrease. However, the steered state gain is smaller than the normal steering state gain at a predetermined frequency. In short, in the electric power steering apparatus of the present invention, the current control responsiveness (normal steering state gain) in the normal steering state ensures the steering performance, and the current control responsiveness (steering state gain) in the steered state is maintained. Rudder sound performance is secured.

  Furthermore, in the present invention, the current control responsiveness in the normal steering state is, for example, reducing the time constant T of the current controller of the first embodiment or increasing the gradual gain in the second and third embodiments. Is realized. Further, the current control responsiveness in the steered state is realized, for example, by increasing the time constant T of the current controller of the first embodiment or by decreasing the gradual gain in the second and third embodiments. The

  In the second embodiment and the third embodiment, as a specific example of the current controller 20, for example, when it is configured by an advance / lag function, the current control responsiveness can be switched as follows. Here, (L · s + R) / (T · s + a) is used as an example of the advance / delay function constituting the current controller 20. However, L is an inductance value of the motor 108, R is a resistance value of the motor 108, T is a time constant of the current controller, and a is a constant.

  That is, when the current controller 20 is configured by the advance / delay function (L · s + R) / (T · s + a), as shown in FIG. 7, the steady-state (low frequency) gain decreases, and the gradual gain 21 When the value is lowered, the phenomenon of further decreasing occurs, and the current decreases when the current is large. In order to prevent this, in the electric power steering apparatus of the present invention, when the current control response is switched, when it is determined that the steering wheel is in the steered state, that is, the gradual gain 21 is gradually decreased to a small value during the steered state. In accordance with the change, the value of the constant a (> 0) is gradually changed to 0 or a small value. Further, when it is determined that the steering wheel is in the normal steering state, that is, when the steering wheel is returned to the normal steering state, the gradually changing gain 21 is gradually changed to the original value. At the same time, the value of the reduced constant a may be gradually changed toward the original value of a.

  As described above, in the steering state detector of the present invention, the steering state is determined using at least one of the torque T, the current command value Iref, the vehicle speed V, the motor angle θ, and the rotational angular velocity ω of the motor. Yes. In other words, the steering state detector of the present invention outputs a steering holding signal to the current control unit when the steering holding state is detected, and outputs no signal to the current control unit when the normal steering state is detected. Like that.

  Here, in the present invention, the steered state determination condition, which is a specific condition for determining that the steered state has been switched from the normal steered state to the steered state in the steering state detector 30 serving as the steering state detecting means, will be described.

For example,
(A1) The differential value (time variation) of the torque T is equal to or less than a predetermined value.
(A2) The torque T belongs to the predetermined value range. That is, T ₁ <T <T ₂ is satisfied.
(A3) The vehicle speed V is not more than a predetermined value. For example, when V ≦ 8 kph.
(A4) When there is no change in the motor angle θ, that is, when there is no change in the signal of the sensor that detects the motor angle. For example, when a Hall sensor is used as the motor angle sensor, the Hall IC pattern duration time ≧ 0.2 seconds.
(A5) The differential value of the motor angle θ is not more than a predetermined value.
(A6) The rotational angular velocity ω of the motor is not more than a predetermined value.
(A7) The current command value Iref belongs to a predetermined value range. That is, Iref ₁ <Iref <Iref ₂ is established. For example, 2A <Iref <93A.
The steering condition determination condition is as follows.

  That is, among the above-described steering state determination conditions (A1 to A7), a logical product is obtained by combining several determination conditions, and when the result is TRUE, the steering state detector maintains the steering state from the normal steering state. It is determined that the state has been switched, and a steering holding signal is output to the current control means.

  In cases other than the above-mentioned steered state determination conditions (A1 to A7), or when the result of the logical product is FALSE, the steering state detector determines that the steering state has returned to the normal steered state, and the steered signal Is not output.

  For example, when the vehicle speed V is high, the current control responsiveness is always the current steering responsiveness in the normal steering state in order to ensure the steering performance during traveling. Further, when the current command value Iref is small, the current control responsiveness is changed from the current control responsiveness in the steered state to the normal steering state in order to secure the steering performance in the vicinity of the steering wheel neutral position (the position of the steering wheel in the straight traveling state). Return to current control response. Further, when the current command value Iref is large, for example, in the electric power steering apparatus of FIG. 1, when some value is entered in a of the current controller 20, if the current control responsiveness is lowered, the gain also decreases, Since the output down in a large region is large, the current control response is returned from the current control response in the steering state to the current control response in the normal steering state.

  In the above description, whether the motor used in the electric power steering apparatus is a single-phase motor or a three-phase motor, and in the case of a three-phase motor, the current control of the motor is a three-phase control. Needless to say, the effects of the present invention can be obtained even with d and q control.

It is a control block diagram of Example 1 of the present invention. It is a control block diagram of Example 2 of the present invention. It is a control block diagram of Example 3 of the present invention. In Example 1 of this invention, it is a circuit diagram which shows the specific example of the current controller as a current control means. In Example 3 of this invention, it is a schematic diagram for demonstrating the change of a current control responsiveness. In the electric power steering device of the present invention, it is a schematic diagram for explaining the timing of switching the gain of the current control means and how to switch the gain. In the electric power steering device of the present invention, it is a schematic diagram for explaining the frequency characteristic of the current control response. It is a general block diagram of the conventional electric power steering device. It is a control block diagram of the conventional electric power steering apparatus shown in FIG.

Explanation of symbols

A current control means B current command value determination unit 20 current controller 21 gradual gain 30 steering state detector 108 motor 202 current detector 204 subtraction unit 212 PWM control unit 214 inverter circuit

Claims (9)

A motor that applies a steering assist force to the steering system of the vehicle, a torque sensor that detects the steering force acting on the steering wheel, and a current command value Iref based on the vehicle speed and the torque that is the output value of the torque sensor. An electric power steering apparatus comprising: current command value determining means for performing current detection means for detecting motor current Im; and current control means for outputting voltage command value Vref,
Steering state detecting means for detecting a steering state of the steering wheel, outputting a steering holding signal to the current control means when the steering holding state is detected, and not outputting a steering holding signal when the normal steering state is detected. Further comprising
In the current control means, the deviation between the current command value Iref and the motor current Im is input, the current control response is switched according to the steering state detected by the steering state detection means, and the current control response after switching The electric power steering apparatus, wherein the voltage command value Vref is determined based on the characteristics and the deviation.   2. The steering state detection unit according to claim 1, wherein the steering state detection unit detects the steering state using at least one of the torque, the current command value Iref, the vehicle speed, the rotation angle of the motor, and the rotation angular velocity of the motor. Electric power steering device.   The electric power steering apparatus according to claim 2, wherein the current control unit includes a current controller, and switches the current control response by changing a time constant of the current controller.   The electric power steering apparatus according to claim 2, wherein the current control means includes a current controller and a gradually varying gain, and the current control response is switched by changing the gradually varying gain.   The electric power steering apparatus according to claim 4, wherein the current control means is provided with the gradually changing gain on an input side of the current controller.   The electric power steering apparatus according to claim 4, wherein the current control means provides the gradually changing gain on an output side of the current controller.   The electric power steering apparatus according to any one of claims 3 to 6, wherein the current controller is configured by an advance / delay function. In the current control means, the current controller is configured by a lead / lag function (L · s + R) / (T · s + a), where L is an inductance value of the motor, R is a resistance value of the motor, and T Is the time constant of the current controller, a is a constant,
The electric power steering apparatus according to any one of claims 4 to 6, wherein the current control response is switched by gradually changing the gradually changing gain.   In the current control means, the constant a is gradually changed to 0 or a small value as the gradually changing gain is gradually changed to a small value in the steering holding state. 9. The electric power steering apparatus according to claim 8, wherein the constant a that has been reduced is gradually changed to the original value a while the gradually changing gain that has been reduced to the original value is gradually changed to the original value. .

Images