JP4581537B2 - Electric power steering device - Google Patents

Description

  The present invention relates to an electric power steering apparatus, and more particularly to an electric power steering apparatus having a good steering feeling with less vibration and noise of a steering wheel.

An electric power steering device that applies an assisting force to the steering device of an automobile by the rotational force of the motor applies an assisting force to the steering shaft or the rack shaft by a transmission mechanism such as a gear or a belt via a speed reducer. It is supposed to be. 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. Yes.

Control of the electric power steering apparatus configured as described above will be described with reference to FIG . First, the torque value 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 to calculate a steering assist command value. 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, 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, for the sake of convenience, the processing part (the part surrounded by the broken line B) until the current command value Iref is determined based on the torque value T, the vehicle speed V, and the compensation described above is referred to as the current command value determination unit B (current command value). It is called a calculation means.

  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 204 serving as a deviation calculating means, the deviation ΔI = Iref−Im is calculated.

  Next, the deviation ΔI is input to a proportional-integral control unit serving as a current controller A surrounded by a broken line A that is a current control unit. 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 steady-state gain Gi regarding the proportional integration is expressed by the following equation (1).

つまり、偏差ΔＩが小さい値でも、定常ゲインＧｉが無限大であるために、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 when the deviation ΔI is small, the steady gain Gi is 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, causing the following problems. .

  In other words, recent electric power steering devices have increased output, that is, increased current. However, since the AD converter used for the control device mainly composed of the CPU is, for example, the 10 bits described above, a large current is required. As a result, the resolution becomes relatively coarse. A calculation error such as a quantization error caused by the roughness of the resolution is amplified by a feedback gain at which the steady-state gain becomes infinite when the deviation ΔI during steering or slow steering is small. There is a problem that the driver feels uncomfortable due to vibration and noise.

  As described above, in the control of the electric power steering apparatus, integral control (I control), proportional integral control (PI control) and proportional integral differential control (PID control) are generally used as current control means including an integral term. . However, in the control including the integral term, since the gain becomes infinite in the steady state, the vibration and noise are controlled via the steering wheel when the electric power steering apparatus is in a steady state or when the steering is slowly performed. There is a problem that the steering wheel feels uncomfortable.

  Therefore, in Patent Document 1, in order to solve this problem, in feedback control, an adjustment gain is input before a deviation ΔI = Iref−Im between the current command value Iref and the actual motor current Im is input to a control system including an integral term. 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 apparatus, the design (threshold value) for determining the adjustment gain that changes in accordance with the deviation of the current feedback is difficult, and the steady gain of the integral term is infinite. However, the total gain becomes large, and the problem of feeling vibrations and noises generated during steering of the steering wheel and slow steering cannot be 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, are not taken into consideration.

  The present invention has been made under the circumstances as described above, and an object of the present invention is to handle the steering wheel even when the steering wheel is held or when the steering wheel is slowly operated, particularly in a large capacity (high output) electric power steering apparatus. It is an object of the present invention to provide an electric power steering device that does not generate vibrations and noises and that can be expected to handle steering with a good steering feeling.

The present invention relates to a motor that applies a steering assist force to a steering system of a vehicle, a torque sensor that detects a steering force acting on a steering wheel, a current detector that detects a current Im of the motor, and the torque sensor. Current command value calculating means for calculating a current command value Iref determined based on the output value of the current, and current control means for controlling the motor based on the current command value Iref and the current Im of the motor. The present invention relates to an electric power steering apparatus, and the object of the present invention is to smooth a quantization error generated during AD conversion of an analog signal used in a current control system including the motor current Im and the electric power steering apparatus. It is achieved by provided with the flat smooth filter.
Further, the object of the present invention is to provide the current control system with deviation calculating means for calculating a deviation (Iref−Im) between the current command value Iref and the motor current Im, and the smoothing using the deviation as an input. And is achieved by controlling the motor based on the output of the current control means.
The present invention also includes a motor that applies a steering assist force to a vehicle steering system, a torque sensor that detects a steering force that acts on a steering wheel, and a current detector that detects a current Im of the motor. The object of the present invention is to provide a current command value calculating means for calculating a current command value Iref determined based on an output value of the torque sensor, the current command value Iref and the Deviation calculating means for calculating a deviation (Iref-Im) from the motor current Im , and for smoothing a quantization error generated at the time of AD conversion of an analog signal used as an input and used in the electric power steering apparatus. flat smooth and the filter is composed of a current control means including an integral term for receiving the output of the smoothing filter, based on an output of said current control means It is made reach by to control the motor.
Further, the object of the present invention is to provide a voltage command value calculating means for calculating a first voltage command value Vref1 based on an output of the torque sensor, a motor calculated from a current Im of the motor and a model of the motor. as input a deviation between the voltage and the second voltage command value Vref2, and the flat smooth filter for smoothing the quantization error generated at the time of AD conversion of the analog signal used in the electric power steering apparatus, the smoothing filter This is achieved by including addition means for adding the output and the first voltage command value Vref1 to calculate the second voltage command value Vref2.
The above object can be achieved more effectively by adjusting the parameter of the smoothing filter in accordance with the vehicle speed of the vehicle or the rotational speed of the motor.

  According to the electric power steering apparatus of the present invention, when the steering is performed slowly or when the steering is kept, the deviation value between the current command value and the motor current is very small, and thus occurs when the detected motor current is quantized. Even if the quantization error is greatly reflected in the value of the deviation, the error is smoothed by the smoothing filter and is not output as a torque ripple of the motor. Can do.

  Further, according to the electric power steering apparatus of the present invention, the value of the deviation between the second voltage command value and the motor voltage calculated from the motor current is very small when the steering is slowly performed or the steering is maintained. Even if a quantization error that occurs during quantization of the detected motor current is largely reflected in the value of the deviation, the error is smoothed by the smoothing filter and is not output as a motor torque ripple. It is possible to obtain an effect that does not generate time vibration and noise.

  In addition, by adjusting the smoothing filter parameters according to the vehicle speed and motor rotation speed, the steering wheel vibration and noise during slow steering and holding at low speeds of the vehicle can be suppressed, while high speeds at high speeds of the vehicle can be achieved. Steering can also be enabled.

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

In FIG. 1, a current command value determination unit B, which is an example of a current command value calculation unit, receives a torque value T detected by the torque sensor 107, a vehicle speed V detected by a vehicle speed sensor (not shown), and an auxiliary value. Thus, the current command value Iref is determined. On the other hand, after the motor current Im supplied to the motor 108 is detected by the current detector 202, it is AD-converted by a 10-bit AD converter 202A as an example, and the bit shift unit 202B increases the bit scale from 10 bits to 12 bits. It is done. The reason for increasing the bit scale from 10 bits to 12 bits (increasing the position of the fixed point) is to perform current control by improving the resolution in terms of software. Then, the 12-bit motor current Im is input to the subtraction unit 204 which is an example of a deviation calculating means together with the current command value Iref. The subtraction unit 204 calculates the deviation ΔI = Iref−Im.

  Next, the deviation ΔI is input to the smoothing filter 10 which is a main part of the present invention. The smoothing filter 10 is a filter that smoothes a stepped signal having a high resolution in terms of software. The output of the smoothing filter 10 is input to a current controller A including an integral term which is an example of a current control unit, for example, a proportional integrator 206 such as a function (Kp + Ki / s). The value Vref is output.

  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.

  In FIG. 1, the current control system refers to the AD converter 202A, the digit shift unit 202B, the subtraction unit 204, the smoothing filter 10, and the current controller A (based on the motor current Im detected by the current detector 202. PI controller 206), PWM controller 212, inverter circuit 214 for supplying motor current Im, and motor 108.

  The control feature of the electric power steering apparatus configured as described above is that the deviation ΔI becomes a very small value (1 to 2 bits) when the steering wheel is steered slowly or held, and as a result, the current detector 202 The quantization error that occurs when the motor current Im detected in step 1 is quantized greatly affects the value of the deviation ΔI. If the smoothing filter 10 does not exist, the stepped error is greatly amplified by the steady gain of the current controller including the integral term (theoretically infinite gain) and appears as a torque ripple of the motor output. The vibration and noise generated in the steering wheel are generated. However, the presence of the smoothing filter 10 smoothes the motor current quantization error included in the deviation ΔI and prevents the current controller from being oversensitive. it can. As a result, the torque ripple contained in the output of the motor is greatly reduced, and vibrations and noises through the handle are not felt, and an excellent effect of not feeling uncomfortable with the handle operation can be expected. In particular, a large effect can be expected in a high-output electric power steering apparatus having a large current value per bit (rough resolution).

  FIG. 2A is a discretized expression of a function (K / (T2 · s + 1)) which is an embodiment of the smoothing filter 10, and FIG. 2B is a function (K / (T2) that is more preferable in terms of calculation accuracy. A configuration example of s + 1)).

In FIG. 2A, the input of the smoothing filter 10 is first input to the subtracter 30-1, and the output is input to the delay unit 30-5 and the gain unit 30-2 having the gain b0. The output of the delay unit 30-5 is input to the gain unit 30-6 having the gain a1 and the gain unit 30-8 having the gain b1. The output of the gain units 30-6, are input to the shifter ^{30-7, 2-8} are rounded, the other input of the subtractor 30-1.

On the other hand, the outputs of the gain units 30-8 of gain device 30-2 are added by the adder 30-3, the output of the adder 30-3 is a shifter 30-4 ^2-8 rounded output Is done. The smoothing filter 10, there is a problem of calculation accuracy is poor because it is performed after the subtraction of the subtractor 30-1 and the adder 30-3 is rounded ^2-8 of shifters 30-7.

  Compared to the smoothing filter of FIG. 2A, the smoothing filter of FIG. 2B is an embodiment in which the calculation accuracy is improved. In FIG. 2B, the input of the smoothing filter 10 is input to the gain unit 30-2 and the delay unit 30-5 having the gain b0. Next, the output of the delay unit 30-5 is input to the gain unit 30-8 having the gain b0, and the output of the gain unit 30-8 and the output of the gain unit 30-2 are added by the adder 30-3. .

The output of the adder 30-3 is then input to the subtracter 30-1. The output of the subtractor 30-1 is input to the shifter ^{30-4, 2-8} rounding is performed. The output of the shifter 30-4 is the output of the smoothing filter 10, but is also used as the input of the delay unit 30-9. The output of the delay unit 30-9 is input to the gain unit 30-6 having the gain a1, and the output of the gain unit 30-6 is the other input of the subtracter 30-1.

  In the smoothing filter 10 in FIG. 2B described above, the delay unit 30-9 is increased by one as compared with the smoothing filter in FIG. 2A, but the shifter 30-7 is eliminated. It can be executed on a scale and has an excellent effect of improving the accuracy of calculation.

  With reference to FIG. 3, another embodiment of the present invention will be described. The first embodiment of FIG. 1 is feedback control of the motor current Im, but the second embodiment of FIG. 3 is a combination control of feedforward and disturbance observer.

  First, in FIG. 3, the current command value Iref is determined by the current command value determination unit B with the torque value T detected by the torque sensor 107, the vehicle speed V detected by the vehicle speed sensor (not shown), and the auxiliary value as inputs. Is done. Next, the current command value Iref is input to the advance / delay function unit 20 which is an example of the voltage command value calculation means, and the first voltage command value Vref1 is calculated. As an example of this advance / delay function, (L · s + R) / (T1 · s + a) is used. Here, L is an inductance value of the motor 108, R is a resistance value of the motor 108, 1 / T1 is a break frequency, and a is a constant. A voltage command value calculation unit C is a portion surrounded by a broken line C in a portion where the current command value determination unit B and the advance / delay function unit 20 are connected in series.

  The first voltage command value Vref becomes one input of the adding unit 22 that is an adding means. Another input of the adding unit 22 is an output of a disturbance observer described later. The output of the adding unit 22 is the second voltage command value Vref2. The second voltage command value Vref is input to the PWM control unit 212. The PWM control unit 212 outputs a PWM signal based on the second voltage command value Vref2, and the inverter circuit 214 outputs the motor current Im according to the PWM signal. Is supplied to the motor 108.

  Next, the disturbance observer will be described. After being detected by the current detector 202, AD conversion is performed by the 10-bit AD converter 202A, and the bit scale is increased from 10 bits to 12 bits by the digit shift unit 202B. The 12-bit motor current Im is transferred to a transfer function unit 24 having a transfer function (L · s + R) composed of a motor inductance value L and a motor winding resistance value R, which is a motor model of the motor 108. The motor voltage Vm calculated from the motor current Im is calculated as the output of the transfer function unit 24. The subtractor 26 calculates a deviation ΔV between the motor voltage Vm and the second voltage command value Vref2 that is an input value of the PWM controller 212. Next, the smoothing filter 12, which is the main part of the present invention, for example, the function (K / (T2 · s + 1)) is arranged at the output of the subtracting unit 26, and the output of the smoothing filter 12 is the output of the adding unit 22 described above. Another input.

  In the disturbance observer configured as described above, when the steering wheel is slowly steered or when the steering wheel is held, the motor voltage Vm derived from the second voltage command value Vref2 and the motor current Im detected by the current detector 202 Is a very small value (about 1 to 2 bits) close to zero. In addition, the quantization error when the detected motor current Im is quantized is greatly reflected in the motor voltage Vm, and the deviation ΔV is a very small value. give.

  Here, if the smoothing filter 12 does not exist, the noise at the time of quantization greatly affects the second voltage command value Vref2, and finally appears as a torque ripple of the motor output. As uncomfortable. However, since the smoothing filter 12 is present, even when the steering wheel is steered slowly or when the steering wheel is held, the ripple Δ is smoothed by the deviation ΔV caused by the error in the quantization of the detected motor current Im. The torque ripple of the motor output can be reduced, and as a result, the vibration and noise of the handle can be greatly reduced.

  Embodiments in which the high-speed steering performance of the electric power steering apparatus is improved by adding the vehicle speed and the rotation speed of the motor 108 to the above-described Embodiments 1 and 2 will be described. The degree to which the driver and passengers feel discomfort due to the vibration and noise of the steering wheel varies depending on the vehicle speed and the rotational speed of the motor. In other words, when the car is traveling at high speed or the motor is rotating at high speed, vibration and noise are not so noticeable, but when the car is traveling at low speed or the motor is rotating at low speed. The handle vibrations and noises are particularly uncomfortable.

  Therefore, when the vehicle speed is high or when the motor rotation speed is high, the smoothing filter parameters are adjusted to reduce the degree of smoothing, ensuring high response speed and suppressing steering vibration and noise. It is intended to secure the high-speed steering performance of the steering wheel by reducing the degree. On the other hand, when the vehicle is traveling at a low speed or when the motor is rotating at a low speed, the vibration and noise generated on the steering wheel can be felt sensitively. Therefore, the smoothness is increased by adjusting the parameters of the smoothing filter. The control focuses on the suppression of vibration and noise rather than steering.

  Specifically, an example in which the vehicle speed and the rotation speed of the motor are added to the example 1 is the example of FIG. In FIG. 4, the angular velocity ω that is the rotational speed of the motor is detected by installing the resolver 40 in the motor 108. On the other hand, although not shown, the vehicle speed V can be detected by a vehicle speed sensor. Then, the parameters of the smoothing filter 10 are adjusted according to the vehicle speed V and the motor angular speed ω. If the smoothing filter 10 is composed of, for example, a first-order lag function (K / (T2 · s + 1)), when the vehicle speed V and the angular speed ω are fast, the gain K and time constant T2, which are parameters, are set to the cutoff frequency. The parameter is set to be higher, the degree of smoothing is weakened, and the smoothing filter parameter focuses on the high-speed steering performance of the electric power steering apparatus. On the other hand, when the vehicle speed or the rotational angular speed of the motor is low, the cutoff frequency of the gain K and the time constant T is lowered with an emphasis on smoothing the quantization error that causes the vibration and noise of the steering wheel. Set to. It is also effective to set the gain K <1. By adjusting the parameters of the smoothing filter, it is possible to achieve both high-speed steering performance of the electric power steering device and suppression of vibration and noise of the steering wheel.

  Next, an embodiment in which the vehicle speed and the rotation speed of the motor are added to the embodiment 2 is the embodiment of FIG. The vehicle speed V detected by the vehicle speed sensor and the angular velocity ω of the motor detected by the resolver 40 are input to the smoothing filter 12 (function is K / (T2 · s + 1)), and the gain K and time constant T2 which are parameters of the smoothing filter 12 are input. Is adjusted as described above. This parameter adjustment makes it possible to achieve both high-speed steering performance of the electric power steering apparatus and vibration and noise suppression of the steering wheel. Note that the transfer function unit 24A (function = (L · s + R) / (T3 · s + 1) denominator and transfer function unit 28 (function = (1 / (T3 · s + 1))), which did not exist in the second embodiment, Although there is a first-order lag function (1 / (T3 · s + 1)), it has been omitted because the explanation in the second embodiment places emphasis on the principle description, but in an actual device, a first-order lag function as a noise filter is omitted. Generally, (1 / (T3 · s + 1)) exists.

  As described above, when the present invention is used, an excellent electric power steering system that can suppress torque ripple caused by quantization error of the current control system that occurs during slow steering or steering, that is, vibration and noise of the steering wheel. Equipment can be provided.

It is a control block diagram of the present invention It is an example of 1 structure of a smoothing filter. It is another Example of this invention. It is the Example of this invention which considered vehicle speed. It is another Example of this invention which considered the vehicle speed. It is a block diagram of an electric power steering device. It is a control block diagram of the conventional electric power steering device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Smoothing filter 12 Smoothing filter 20 Lead / lag function part 22 Addition part 24, 24A Transfer function part 26 Subtraction part 28 Transfer function part 40 Resolver A Current controller B Current command value determination part C Voltage command value calculation part

Claims (5)

A motor configured to apply a steering assist force to a vehicle steering system, a torque sensor that detects a steering force acting on a steering wheel, a current detector that detects a current Im of the motor, and an output value of the torque sensor Electric power steering apparatus comprising: current command value calculating means for calculating a current command value Iref determined based on; and current control means for controlling the motor based on the current command value Iref and the motor current Im. In
The current control system including a current Im of the motor, the electric power electric power steering, characterized in that the quantization error occurring during AD conversion of the analog signals used in the steering apparatus comprises a flat smooth filter for smoothing apparatus. The current control system includes a deviation calculating means for calculating a deviation (Iref-Im) between the current command value Iref and the motor current Im, and the smoothing filter having the deviation as an input. The electric power steering apparatus according to claim 1, wherein the motor is controlled based on the output of the motor. In an electric power steering apparatus comprising: a motor that applies a steering assist force to a steering system of a vehicle; a torque sensor that detects a steering force acting on a steering wheel; and a current detector that detects a current Im of the motor. ,
Current command value calculation means for calculating a current command value Iref determined based on the output value of the torque sensor, and deviation calculation for calculating a deviation (Iref−Im) between the current command value Iref and the motor current Im. means and the integral term as input the deviation, and the input and the flat smooth filter for smoothing the quantization error generated at the time of AD conversion of the analog signal used in the electric power steering apparatus, the output of the smoothing filter And an electric power steering device that controls the motor based on an output of the current control unit. In an electric power steering apparatus comprising: a motor that applies a steering assist force to a steering system of a vehicle; a torque sensor that detects a steering force acting on a steering wheel; and a current detector that detects a current Im of the motor. ,
Voltage command value calculating means for calculating a first voltage command value Vref1 based on the output of the torque sensor, a motor voltage calculated from the motor current Im and the motor model, and a second voltage command value Vref2 the difference as an input, and the electric power and the flat smooth filter for smoothing the quantization error generated at the time of AD conversion of the analog signals used in the steering system, the first voltage command and the output of the smoothing filter with Adding means for adding the value Vref1 to calculate the second voltage command value Vref2,
An electric power steering apparatus comprising: The electric power steering apparatus according to any one of claims 1 to 4, wherein a parameter of the smoothing filter is adjusted according to a vehicle speed of the vehicle or a rotation speed of the motor.

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