JP4581299B2 - Control device for electric power steering device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a control device for an electric power steering device that applies a steering assist force by a motor to a steering system of an automobile or a vehicle, and more particularly to a control device for an electric power steering device that reduces noise.
[0002]
[Prior art]
An electric power steering device for energizing an automobile or vehicle steering device with an auxiliary load by the rotational force of a motor is an auxiliary load applied to a steering shaft or a rack shaft by a transmission mechanism such as a gear or a belt via a speed reducer. It comes to be energized. Such a conventional electric power steering apparatus performs feedback control of motor current in order to accurately generate assist torque (steering assist torque). The feedback control adjusts the motor applied voltage so that the difference between the current control value and the motor current detection value becomes small. The adjustment of the motor applied voltage is generally performed by a PWM (pulse width modulation) control duty. This is done by adjusting the tee ratio.
[0003]
Here, the general configuration of the electric power steering apparatus will be described with reference to FIG. 6. The shaft 2 of the steering handle 1 is connected to the tie rod of the steering wheel via the reduction gear 3, the universal joints 4 a and 4 b, and the pinion rack mechanism 5. 6. The 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 coupled to the shaft 2 via the reduction gear 3. . Electric power is supplied from the battery 14 via the ignition key 11 to the control unit 30 that controls the power steering device. The control unit 30 detects the steering torque T detected by the torque sensor 10 and the vehicle speed V detected by the vehicle speed sensor 12. Based on the above, the steering assist command value I of the assist command is calculated, and the current supplied to the motor 20 is controlled based on the calculated steering assist command value I.
[0004]
The control unit 30 is mainly composed of a CPU, and FIG. 7 shows general functions executed by a program inside the CPU (or MCU). For example, the phase compensator 31 does not indicate a phase compensator as independent hardware, but indicates a phase compensation function executed by the CPU (or MCU).
[0005]
The function and operation of the control unit 30 will be described. The steering torque T detected and input by the torque sensor 10 is phase-compensated by the phase compensator 31 in order to improve the stability of the steering system, and the phase-compensated steering torque. TA is input to the steering assist command value calculator 32. The vehicle speed V detected by the vehicle speed sensor 12 is also input to the steering assist command value calculator 32. The steering assist command value calculator 32 determines a steering assist command value I that is a control target value of the current supplied to the motor 20 based on the input steering torque TA and vehicle speed V. The steering assist command value I is input to the subtractor 30A, and is also input to the feedforward differential compensator 34 for increasing the response speed. The deviation (Ii) of the subtractor 30A is input to the proportional calculator 35. At the same time, it is input to an integration calculator 36 for improving the characteristics of the feedback system. The outputs of the differential compensator 34 and the integral compensator 36 are also added to the adder 30B, and the current control value E, which is the addition result of the adder 30B, is input to the motor drive circuit 37 as a motor drive signal. The motor current value i of the motor 20 is detected by the motor current detection circuit 38, and the motor current value i is input to the subtractor 30A and fed back.
[0006]
On the other hand, as shown in FIG. 8, the widely used hydraulic power steering apparatus has a characteristic that the friction of the cylinder portion increases in proportion to the cylinder pressure P (the horizontal axis T is the steering torque). It has hysteresis due to its characteristics, for example, it prevents the steering wheel from being suddenly returned by self-aligning torque during cornering, and helps to improve the driver's steering feeling. FIG. 9 shows such a situation. When the steering torque T changes abruptly by ΔT, the cylinder pressure P1 changes when there is no hysteresis, but when there is hysteresis, P2 (<P1 ) Change. Therefore, if there is hysteresis, the change in the cylinder pressure P can be made moderate with respect to the change in the steering torque T. Here, it is known that the hysteresis width changes according to the magnitude of the friction. In the rubber packing of the hydraulic cylinder, the rubber is compressed as the cylinder pressure increases, so that the Coulomb friction increases and the hysteresis is increased. The width increases. It is important for the driver to feel a strong self-aligning torque near the neutral point and not to feel the self-aligning much during cornering. In this sense, ideally, it is desirable that the friction (hysteresis) is small in a region where the steering angle θ is small and the friction (hysteresis) is large in a region where the steering angle θ is large, as in a hydraulic power steering device.
[0007]
On the other hand, the electric power steering apparatus has a constant friction regardless of the assist torque T as shown in FIG. In the case of the electric power stearin device, the coulomb friction of the motor is dominant, and therefore it has a characteristic of having a constant friction characteristic regardless of the steering force. Therefore, as shown in FIG. It becomes a characteristic. However, the hysteresis width is narrower than the hysteresis width at the time of high torque of the hydraulic power steer apparatus. Therefore, in the electric power steer device, the friction characteristic is emphasized in the region where the steering torque T is small, and the friction is compensated. However, in the case of such compensation, the friction becomes too small in the region where the steering torque T is large, and as a result, when the steering torque T is large during cornering or the like, a stable steering feeling is lost.
[0008]
As a control device that solves the above-mentioned problems, for example, there is one disclosed in Japanese Patent Laid-Open No. 9-156526. The vehicle steering control apparatus includes a steering torque detection unit that detects a steering torque, and controls an assist amount of an electrical power assist unit based on a detection signal output from the steering torque detection unit. An adjustment means for providing hysteresis to the detection signal of the torque detection means is provided.
[0009]
By providing the adjusting means, hysteresis can be given to the detection signal of the steering torque detecting means. Therefore, since the hysteresis characteristic of the power assist means that operates can be varied according to the steering state based on the detection signal of the steering torque, the torque assist amount can be optimized. However, this conventional apparatus has the drawbacks that an intermittent feeling remains in the steering operation, the torque control system is unstable, and a new hardware configuration is added, resulting in an increase in cost.
[0010]
Further, as disclosed in Japanese Patent Application Laid-Open No. 2000-95131 by the present applicant, a negative differential gain is applied at the time of returning the handle to prevent a sudden decrease in the assist amount, and a positive differential gain is applied at the time of increasing the responsiveness. As a result, there is a technique that gives a large hysteresis characteristic in the high torque region and a small hysteresis characteristic in the low torque region near the neutral point. However, this apparatus has a problem that an unnatural steering feeling occurs when the negative and positive differential gains are separated too much by switching between the negative and positive differential gains by the steering wheel return and the additional steering pattern.
[0011]
Further, as a device for obtaining a comfortable steering feeling regardless of the traveling speed and the steering angle of the steering wheel, there is one disclosed in Japanese Patent Application Laid-Open No. 10-291481. However, since attention is paid only to the stability of the control system, the assist torque There is a problem in terms of responsiveness. In addition, a device for removing or minimizing the influence of motor inertia is also important.
[0012]
As a solution to the above problems, there is Japanese Patent Application No. 2000-274525 by the present applicant. That is, FIG. 11 is a block diagram of the control function. The steering torque T1 (main) is input to the steering assist command value calculation unit 100, the steering torque T2 (sub) is input to the center response improvement unit 101, each output is input to the adder 102, and the addition result is the torque. It is input to the control calculation unit 103. The output signal of the torque control calculation unit 103 is input to the motor loss current compensation unit 104, and the output is input to the maximum current limiting unit 106 via the adder 105, and the maximum current value is limited and input to the current control unit 110. . The output of the current control unit 110 is input to the current drive circuit 112 via the H bridge characteristic compensation unit 111, thereby driving the motor 113.
[0013]
The motor current i of the motor 113 is input to the motor angular speed estimation unit 121, the current drive switching unit 122 and the current control unit 110 via the motor current offset correction unit 120, and the motor terminal voltage Vm is input to the motor angular speed estimation unit 121. . The angular velocity ω estimated by the motor angular velocity estimation unit 121 is input to the motor angular acceleration estimation unit / inertia compensation unit 123, the motor loss torque compensation unit 124, and the yaw rate estimation unit 125, and the output of the yaw rate estimation unit 125 is input to the convergence control unit 126. The outputs of the convergence control unit 126 and the motor loss torque compensation unit 124 are added by the adder 127, and the addition result is input to the adder 102. The motor loss torque compensator 124 provides assist equivalent to loss torque in the direction in which the loss torque of the motor 113 is generated, that is, the rotation direction of the motor 113, and the convergence controller 126 controls the steering wheel to improve the yaw convergence of the vehicle. The brakes are applied to the movement of the swaying.
[0014]
Also, a current dither signal generator 130 that generates a dither signal for minutely vibrating the motor 113 to the extent that the driver does not feel is provided. The current dither signal generator 130 and the motor angular acceleration estimation unit / inertia compensation unit 123 are provided. These outputs are added by the adder 131, and the addition result is input to the adder 105. Then, the addition result in the adder 105 is input to the maximum current limiting unit 106.
[0015]
In such a configuration, as shown in FIG. 12, the center response improvement unit 101 is composed of a phase lead compensation unit 101A, an approximate differentiation unit 101B, and a gain setting unit 101C, and the phase lead compensation unit 101A has a frequency shown in FIG. The approximate differentiation unit 101B has the frequency characteristics shown in FIG. As a result, the combined characteristic of the phase lead compensation and the approximate derivative is as shown in FIG. 15, and a phase characteristic without a phase delay can be obtained.
[0016]
The gain setting unit 101C switches and sets the gain according to the vehicle speed V and the steering torque T. Furthermore, in order to reduce the uneasy steering feeling that the steering wheel is suddenly returned and to stabilize the steering, the steering torque is increased and the steering torque change rate is increased, and the gain is decreased in the steering torque decreasing direction.
[0017]
In the calculation of the assist amount in the steering assist command value calculation unit 100, assist characteristics based on three representative vehicle speeds (0, 30, 254 Km / h) are set as basic characteristics, and at other vehicle speeds, each basic characteristic is set according to the vehicle speed interpolation gain. Interpolation is performed every 2 km / h of vehicle speed. The vehicle speed setting range of assist characteristics is 0 to 254 km / h and the resolution is 2 km / h.
[0018]
Here, detailed configurations of the steering assist command value calculation unit 100 and the center response improvement unit 101 will be described with reference to FIG. The calculation of the steering assist command value I by the steering assist command value calculation unit 100 is calculated and output with a function characteristic as shown in the block 100 of FIG. 16, and ΔI / ΔT = K, and K∝T for simplification. Assume the following relationship. The transfer function of the approximate differentiation unit 101B is as shown in the block 101B of FIG. 16 with the gain set to “1”, and the gain Kdd of the gain setting unit 101C connected to the subsequent stage changes according to the vehicle speed V and the steering torque T. It has become. T1 is an integration time constant, and s is a Laplace variable. From the block diagram of FIG. 16, when there is no phase advance compensation unit 101A, the following equation (1) holds for the current command value Iref.
[0019]
Iref = K + Kdd · s / (T1 · s + 1)
= (K ・ T1 ・ s + K + Kdd ・ s) / (T1 ・ s + 1)
= {(K ・ T1 + Kdd) s + K} / (T1 ・ s + 1)
= {K / (T1 · s + 1)} {(K · T1 + Kdd) s / K + 1} …… (1)
Here, Equation (2) below is established.
[0020]
(K · T1 + Kdd) / K> T1 (2)
Therefore, the frequency characteristic of the above equation (1) is as shown in FIG.
[0021]
As shown in FIG. 17, when the assist characteristic gain K is small and when the assist characteristic gain K is large, the assist characteristic gain K is obtained in the band of the frequency a or higher when the assist characteristic gain K is large. Regardless of the size, the difference in gain G is small.
That is, in the band of frequency a or higher, almost constant response is obtained regardless of the magnitude of the assist characteristic gain K. As shown in FIG. 18, the steering assist command value I, which is the output of the steering assist command value calculation unit 100, has a small assist characteristic gain K when the steering torque T is small, and an assist characteristic when the steering torque T is large. The gain K is large. As a result, when the steering torque T is small, the responsiveness is lower than when the steering torque T is large. Therefore, by providing the characteristics as shown in FIG. 17, it is possible to maintain the responsiveness in the high frequency band and compensate the influence of the friction and inertia of the motor.
[0022]
[Problems to be solved by the invention]
As described above, the center torque sensor signal is used as an input signal of the MCU, and the center response improvement unit is configured through the combination of the signal with approximate differentiation or phase compensation, which is realized by software. Here, since noise is mixed in the A / D input signal of the MCU, the noise is expanded by the approximate differential or phase lead compensator, and the gain or phase lead component of the approximate differential cannot be increased in terms of noise mixing. There is. For this reason, the degree of freedom of tuning of the control system is limited, resulting in a disadvantage that good steering feeling cannot be obtained.
[0023]
The present invention has been made under the circumstances as described above, and the object of the present invention is to provide continuous hysteresis characteristics with an adjustable width in a mixed configuration of hardware and software. It is an object of the present invention to provide a control device for an electric power steering device that provides a comfortable steering feeling, is not affected by motor inertia, and has improved steering performance of the steering wheel.
[0024]
[Means for Solving the Problems]
The present invention controls the motor that applies a steering assist force to a steering mechanism based on a current control value calculated from a steering assist command value calculated based on a steering torque generated in a steering shaft and a current value of the motor. The above-mentioned object of the present invention is to differentiate the steering torque signal and add it to the steering assist command value, and to compensate for the phase advance in the differentiation. This is achieved by including a center response improving unit for performing the above and performing the differentiation by a hardware differentiation circuit.
[0025]
Further, the object of the present invention is to provide a center response improving unit that differentiates the steering torque signal and adds the differentiated steering torque signal to the steering assist command value, and compensates for the phase advance in the differentiation. Compensation is achieved by a hardware phase compensator.
[0026]
Further, the object of the present invention is to input a steering torque signal to the control device as main signals 1 and 2 and a sub signal, and insert a hard compensator to the main signal 1 or 2. Alternatively, the steering torque signal is input to the control device as a main signal and a sub signal, the main signal is amplified by an amplifier and input to the control device, and the main signal is compensated by a hard compensator. This is achieved by inputting to the control device.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, a part of functions (approximate differentiation, phase compensation, or a combination thereof) of the center response improvement unit realized by conventional software is realized by hardware. The analog signal generates quantization noise due to A / D conversion at the MCU input. However, according to the present invention, since the hardware configuration differentiation circuit and phase compensator are used, the quantization noise is not enlarged. As a result, the gain can be increased and the degree of tuning can be increased.
[0028]
Embodiments of the present invention will be described below with reference to the drawings.
[0029]
As shown in FIG. 1, the center response improvement unit of the present invention also includes an approximate differentiation unit 200 (including a gain unit 201), a phase compensation unit 203, and a gain setting unit 204. (Including the gain unit 201) is configured by hardware, and the phase compensation unit 203 and the gain setting unit 204 are configured by software. An A / D converter 202 is provided at the boundary between hardware and software.
[0030]
The transfer function of the entire center response improvement unit is expressed by the following equation (3), for example.
Gcen (s) = Gd (s) x Gld (s) x Kdd (3)
The transfer function Gkd (s) of the approximate differentiation unit 200 is
Gkd (s) = T1 ・ s / (T1 ・ s + 1) (4)
Considering the gain kd of the gain unit 201,
Gkd (s) = kd ・ T1 ・ s / (T1 ・ s + 1) ...... (5)
It becomes. The transfer function Gld (s) of the phase compensation unit 203 is
Gld (s) = (T2 ・ s + 1) / (T3 ・ s + 1) (6)
And the transfer function (constant) of the gain setting unit is Kdd / kd.
[0031]
Here, the case where only the approximate differentiation unit 200 (including the gain unit 201) is configured by hardware will be described with reference to FIG. In order to make maximum use of the resolution of the A / D converter 202, the output signal of the hardware approximate differentiation is taken into the input range (for example, 0V to 5V) of the A / D converter 202 in consideration of the amplitude and frequency of the input signal. It is necessary to suppress. From the input signal of the steering torque signal (torque sensor signal T) of the assumed steering pattern, the output of the transfer function Gkd (s) of the approximate differentiator 200 exceeds the input range of the A / D converter 202, or the input range If it is much smaller, gain adjustment is necessary. Therefore, the transfer function of hardware approximate differentiation is expressed by the following equation (7).
[0032]
Gkdp (s) = kd x Gkd (s) (7)
That is, the torque sensor signal T is input to the RC approximate differentiation circuit 200A through the buffer. The transfer characteristic of the approximate differentiation circuit 200A is
Gkd (s) = T1 ・ s / (T1 ・ s + 1) = RC ・ s / (RC ・ s + 1) (8)
It is. The output of the approximate differentiation circuit 200A is output through a synchronous amplifier (gain unit) 201A of kd times (= (R2 + R1) / R1). Since the input / output of the kd = (R2 + R1) / R1 signal of the synchronous amplifier 201A is required centering on 2.5V, the center voltage is 2.5V by dividing the power supply voltage Vdd (5V) and the resistance (R, 2 × R1). Is configured. The output of the synchronous amplifier (gain unit) 201A is input to the A / D converter 202 via a noise removing low-pass filter (LPF) made of RC.
[0033]
On the other hand, FIG. 3 shows an embodiment in which the phase compensation unit 203 has a hardware configuration. In this case, the torque sensor signal T is input to the phase compensator 203A, and then input to the A / D converter via the low pass filter 203B. The transfer function G (s) of the phase compensator 203A is expressed by the following equation (9).
[0034]
G (s) = R ₂ / (R ₁ + R ₂ ) ・ (R ₁ C ₁・ s + 1) / (R ₁ R ₂ / (R ₁ + R ₂ ) ・ (C ₁ + C ₂ ) ・ s + 1} …… (9)
In the electric power steering apparatus to which the present invention can be applied, in addition to the main torque sensor signal and the sub torque sensor signal, the main signal of the torque sensor signal can be input to the MCU (control device) 40 through the hardware compensator 41. . FIG. 4 shows such an example. Normally, control and fail-safe processing are performed using the main torque sensor signal (main 1) and the sub torque sensor signal (sub), but the compensator 41 is realized by hardware. For this purpose, it is input to the MCU 40 through the main torque sensor signal (main 2).
[0035]
By the way, normally, in order to increase accuracy, the torque sensor signal (main 1) is amplified and input to the MCU 40 after increasing the resolution of torque detection. However, if the amplified signal is input to the MCU 40 through the hard compensator 41 of the present invention, there is a possibility that the signal will be saturated when suddenly steered. When the saturation signal is input to the hard compensator (differentiation or phase advance) 41, a large signal change occurs in the output of the hard compensator 41, and the change signal adversely affects the steering feeling. For this reason, in order not to saturate the input signal of the hard compensator 41, the signal before amplification of the torque sensor signal is used as the input signal of the hard compensator 41 as shown in FIG.
[0036]
In FIG. 11, the output of the center response improvement unit 101 is added to the adder 102, but it may be added to the adder 105, or may be added between the adders 102 and 105. It is also possible to configure both approximate differentiation and phase compensation with hardware and configure only the gain with software.
[0037]
【The invention's effect】
In the present invention, for the purpose of improving the response of the assist torque and the stability of the torque control system, a value proportional to the derivative of the steering torque with respect to the assist amount (steering assist command value) is set to the magnitude of the steering torque and the vehicle speed. The differential gain is changed according to the above, and is added to enhance the response and stability. Further, since the configuration is composed of a mixture of hardware and software, a noise steering signal is not enlarged, and a control device for a power steering device with low vibration, low noise, and good steering feeling can be provided.
[0038]
Furthermore, since phase advance compensation is inserted for the steering assist command value, motor inertia can be compensated, and both responsiveness near neutrality and a sharp decrease in the amount of assist during cornering can be achieved, and An unnatural steering feeling can be prevented and a comfortable steering feeling can be obtained. Further, since noise can be reduced, the phase lead component or gain of the compensator can be increased, and as a result, the degree of freedom in tuning can be improved.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration example of the present invention.
FIG. 2 is a connection diagram illustrating a hardware configuration example of an approximate differentiation unit;
FIG. 3 is a connection diagram illustrating a hardware configuration example of a phase compensator;
FIG. 4 is a block diagram showing another configuration example of the present invention.
FIG. 5 is a block diagram showing another configuration example of the present invention.
FIG. 6 is a block diagram showing an example of an electric power steering apparatus. FIG. 7 is a block diagram showing a general internal structure of a control unit.
FIG. 8 is a diagram illustrating an operation example of a hydraulic power steering apparatus.
FIG. 9 is a diagram for explaining the effect of hysteresis characteristics;
FIG. 10 is a diagram illustrating an operation example of the electric power steering apparatus.
FIG. 11 is a block configuration diagram of a control device for a power steering apparatus having a center response improvement unit.
FIG. 12 is a block configuration diagram of a center response improvement unit.
FIG. 13 is a diagram illustrating a characteristic example of a phase lead compensation unit.
FIG. 14 is a diagram illustrating an example of characteristics of an approximate differentiation unit.
FIG. 15 is a diagram illustrating a combined characteristic of a phase lead compensation unit and an approximate differentiation unit.
FIG. 16 is a transfer function block diagram showing the main part of the center response improvement unit.
FIG. 17 is a diagram for explaining the operation of the center response improvement unit;
FIG. 18 is a diagram illustrating an example of characteristics of a steering assist calculation unit.
[Explanation of symbols]
100 steering assist command value calculation unit 101 center response improvement unit 101A phase advance compensation unit 101B approximate differentiation unit 101C gain setting unit 103 torque control calculation unit 104 motor loss current compensation unit 106 maximum current limiting unit 110 current control unit 113 motor 121 motor angular velocity Estimator 125 Yaw rate estimator 130 Dither signal generator

Claims (6)

The motor that provides steering assist force to the steering mechanism is controlled based on a current control value calculated from the steering assist command value calculated by the calculation means based on the steering torque generated in the steering shaft and the current value of the motor. The control device for the electric power steering apparatus according to the present invention further comprises a center response improving unit that differentiates the steering torque signal and adds the differentiated steering torque signal to the steering assist command value, and performs phase advance compensation for the differentiation. A control device for an electric power steering apparatus, wherein the differentiation is performed by a differentiation circuit having a hardware configuration. The control device for an electric power steering apparatus according to claim 1, wherein the differentiation is performed before the phase compensation. The motor that provides steering assist force to the steering mechanism is controlled based on a current control value calculated from the steering assist command value calculated by the calculation means based on the steering torque generated in the steering shaft and the current value of the motor. The control device for the electric power steering apparatus according to the present invention further comprises a center response improving unit that differentiates the steering torque signal and adds the differentiated steering torque signal to the steering assist command value, and performs phase advance compensation for the differentiation. And a controller for an electric power steering apparatus, wherein the phase compensation is performed by a phase compensator having a hardware configuration. 4. The control device for an electric power steering apparatus according to claim 3, wherein the differentiation is also performed by a hardware configuration, and the gain is realized by software. The motor that provides steering assist force to the steering mechanism is controlled based on a current control value calculated from the steering assist command value calculated by the calculation means based on the steering torque generated in the steering shaft and the current value of the motor. In the control apparatus for the electric power steering apparatus, the steering torque signal is input to the control apparatus as main signals 1 and 2 and a sub signal, and a hard compensator is used for the main signal 1 or 2 A control device for an electric power steering device, characterized in that The motor that provides steering assist force to the steering mechanism is controlled based on a current control value calculated from the steering assist command value calculated by the calculation means based on the steering torque generated in the steering shaft and the current value of the motor. In the control device for the electric power steering device, the steering torque signal is input to the control device as a main signal and a sub signal, and the main signal is amplified by an amplifier and the control device And a controller for the electric power steering apparatus, wherein the main signal is compensated by a hard compensator and input to the controller.

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