Steering control device, power steering system and steering control method

Abstract

To provide a steering control device capable of suppressing noises, vibrations and shocks corresponding to the frequency components of a natural frequency and of enhancing the stability of a system regardless of a steering angular speed.SOLUTION: A steering control device includes: a basic assist torque calculating unit that calculates a basic assist torque value based on a torsion bar torque value and on a vehicle speed; a phase compensation torque calculating unit that calculates a phase compensation torque value based on the torsion bar torque value and on the basic assist torque value; and a higher-order filter that performs a higher-order filter process on a total torque value obtained by adding the basic assist torque value to the phase compensation torque value. The higher-order filter outputs an assist torque value that has a suppressed frequency component of a natural frequency in accordance with a steering angular speed by performing a first filter process by a filter transfer function in accordance with the steering angular speed of a handle on the total torque value, and a second filter process by a filter transfer function in accordance with a vehicle speed on the first filter process output.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a steering control device, a power steering system, and a steering control method that assist a driver in steering a vehicle. [Background technology]

[0002] As a conventional power steering system, an electric power steering device disclosed in Patent Document 1 is known. For example, the abstract of this document states that "By improving the phase compensation process for the torque signal, the delay in the inertia compensation control is compensated for, and the steering feeling is improved." As a solution, it states that "the correction value calculation unit 27 calculates the steering angular acceleration dω h A correction value Ic is determined according to the target current value Ia / dt. The target current value Ia is corrected by this correction value Ic, thereby performing inertia compensation. The gain of the phase compensation processing unit 40, which performs phase compensation processing on the torque signal output by the torque sensor 5, is determined according to the vehicle speed V and the operation angular velocity ω h That is, when a fast steering operation is performed, the steering angular velocity ω h When takes a large value, the gain of the phase compensation processing unit 40 becomes large, and the response is improved."

[0003] In this way, in Patent Document 1, fast steering is performed and the steering angular velocity ω h This paper discloses an electric power steering device that increases the gain of a phase compensation processor to compensate for the delay in inertia compensation control when the steering angle velocity (hereinafter referred to as steering angular velocity) takes a large value, thereby increasing responsiveness and improving steering feel. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-276636 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the electric power steering device of Patent Document 1 only improves responsiveness when fast steering is performed, and does not suppress the frequency components of the natural frequency of the electric power steering device that change according to the steering angular speed.

[0006] Therefore, in the electric power steering device of Patent Document 1, noise, vibration, and impact corresponding to the frequency components of the natural frequency may deteriorate the steering feel for the driver or cause discomfort to the driver.

[0007] Therefore, an object of the present invention is to provide a steering control device, a power steering system, and a steering control method that can suppress noise, vibration, and impact corresponding to frequency components of the natural frequency regardless of the steering angular speed, thereby improving the stability of the system. [Means for solving the problem]

[0008] In order to solve the above problems, the steering control device of the present invention is a steering control device that calculates an assist torque value of a power steering system, and includes a basic assist torque calculation unit that calculates a basic assist torque value based on a torsion bar torque value and a vehicle speed, a phase compensation torque calculation unit that calculates a phase compensation torque value based on the torsion bar torque value and the basic assist torque value, and a high-order filter that performs high-order filtering on a combined torque value of the basic assist torque value and the phase compensation torque value, wherein the high-order filter performs a first filtering process on the combined torque value using a filter transfer function that corresponds to the steering angular velocity of the steering wheel, and a second filtering process on the output of the first filtering process using a filter transfer function that corresponds to the vehicle speed, thereby outputting an assist torque value in which the frequency component of the natural frequency that corresponds to the steering angular velocity is suppressed. [Effects of the Invention]

[0009] According to the steering control device, power steering system, and steering control method of the present invention, it is possible to suppress noise, vibration, and impact corresponding to frequency components of the natural frequency regardless of the steering angular velocity, thereby improving the stability of the system. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a functional block diagram of a power steering system according to an embodiment of the present invention. [Figure 2] FIG. 2 is a functional block diagram of the filter processing unit in FIG. 1. [Figure 3] 10 is a control flowchart of a filtering process using a third-order filter that depends on a steering angle velocity. [Figure 4A] 10 is an example of a table used to identify the first coefficient set. [Figure 4B] 10 is an example of a table used to identify the first coefficient set. [Figure 5] 10 is an example of a table used to identify the second coefficient set. [Figure 6] An example of a table used to identify the third coefficient set. [Figure 7] An example of a Bode plot for the function Gf3. [Figure 8] An example of a Bode plot of the function Gf1. [Figure 9] An example of a Bode plot of the function Gf2. [Figure 10] An example of a Bode plot of the filter transfer function Gf. [Figure 11] 10 is an example of a graph showing input and output signals of a third-order filter depending on a steering angle velocity. [Figure 12] 4 is a graph showing an example of the relationship between steering angular velocity and damping central frequency ω1. [Figure 13] 10 is a graph showing an example of the relationship between steering angular velocity and cutoff frequency ω2. DETAILED DESCRIPTION OF THE INVENTION

[0011] An embodiment of a power steering system according to the present invention will now be described with reference to the accompanying drawings.

[0012] 1 is a functional block diagram of a power steering system 100 according to one embodiment. The power steering system 100 is an in-vehicle system that assists a driver in steering the vehicle, and includes a steering control device 1, a motor 2, a motor driver 3, a rotation angle sensor 5, a torque sensor 6, and the like.

[0013] Motor 2 is a power source that provides an assist force to the rack bar of the steering mechanism that steers the steering wheels of the vehicle in response to the driver's steering operation. Motor driver 3 is a power source that supplies power to motor 2 in response to commands from steering control device 1. Vehicle speed sensor 4 is a sensor equipped on the vehicle that measures the rotational speeds of the left and right wheels of the vehicle and sends this to steering control device 1 via CAN. Rotation angle sensor 5 is a sensor that measures the rotation angle of motor 2 and sends this to steering control device 1. Torque sensor 6 is a sensor that measures the torsion bar torque generated in a torsion bar that connects the steering wheel and steering mechanism and sends the torsion bar torque value to steering control device 1.

[0014] The steering control device 1 is a computer that transmits to the motor driver 3 a command corresponding to an appropriate assist torque value calculated based on the outputs of the vehicle speed sensor 4, the rotation angle sensor 5, and the torque sensor 6. In this steering control device 1, a calculation device such as a CPU executes a predetermined program loaded into a storage device such as a semiconductor memory, thereby realizing the respective functional units of a vehicle speed calculation unit 11, a steering angle velocity calculation unit 12, a boost curve torque calculation unit 13, a phase compensation torque calculation unit 14, and a high-order filter 15.

[0015] The vehicle speed calculation unit 11 is a functional unit that calculates the vehicle speed based on the left and right wheel speeds received from the vehicle speed sensor 4, etc.

[0016] The steering angular velocity calculation unit 12 is a functional unit that calculates the steering angular velocity ω of the steering wheel based on the rotation angle of the motor 2 received from the rotation angle sensor 5. Note that the steering angular velocity ω may be directly acquired from a steering angular velocity sensor provided on the steering wheel or the torsion bar.

[0017] The basic assist torque calculation unit 13 is a functional unit that calculates a basic assist torque value based on the torsion bar torque value measured by the torque sensor 6 and the vehicle speed calculated by the vehicle speed calculation unit 11. When calculating the basic assist torque value, a well-known basic assist torque calculation method may be used, such as specifying the basic assist torque value based on a boost curve map that defines the relationship between the combination of the torsion bar torque value and the vehicle speed and the basic assist torque value.

[0018] The phase compensation torque calculation unit 14 is a functional unit that calculates a phase compensation torque value based on the torsion bar torque value measured by the torque sensor 6 and the basic assist torque value calculated by the basic assist torque calculation unit 13. Note that when calculating the phase compensation torque value, a well-known phase compensation torque calculation method may be used, such as multiplying a high-pass filtered torque value obtained by performing phase advance processing (high-pass filter processing) on the torsion bar torque value by a phase compensation gain according to the ratio between the basic assist torque value and the torsion bar torque value.

[0019] The high-order filter 15 is a functional unit that reduces the frequency components of the natural frequency of the power steering system 100 by performing third-order filtering depending on the steering angular velocity and third-order filtering depending on the vehicle speed on the combined torque value of the basic assist torque value and the phase compensation torque value.

[0020] 2 is a functional block diagram of the high-order filter 15. As shown here, the high-order filter 15 has a third-order filter 15a that depends on the steering angle velocity and a third-order filter 15b that depends on the vehicle speed.

[0021] The steering angle velocity dependent third-order filter 15a calculates a filter transfer function G f The details of this filtering process will be described later.

[0022] The vehicle speed-dependent third-order filter 15b performs third-order filtering using a filter transfer function according to the vehicle speed on the output of the steering angle velocity-dependent third-order filter 15a. Since this filtering is the same as that of the prior art, detailed description thereof will be omitted below.

[0023] <Filtering by the steering angle velocity dependent third-order filter 15a> The filter transfer function G used in the steering angle velocity dependent third-order filter 15a f is expressed by the following (Equation 1).

[0024]

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[0025] In this (Equation 1), the function G on the right side f1 , G f2 , G f3 are expressed by the following (Equation 2), (Equation 3), and (Equation 4). In each equation, ω1 is the attenuation width of the steering angular velocity, ω2 is the cutoff frequency of the steering angular velocity, ω3 is the cutoff frequency of the steering angular velocity, and ω n is the damping center frequency of the steering angular velocity, and ζ is the damping degree of the steering angular velocity.

[0026]

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[0027]

number

[0028]

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[0029] When (Equation 2), (Equation 3), and (Equation 4) are each subjected to discrete equations and partial fraction expansion processing, the function G f1 , G f2 , G f3can be transformed into the following (Equation 5), (Equation 6), and (Equation 7).

[0030]

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[0031]

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[0032]

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[0033] As shown in (Equation 5), the transformed function G f1 includes coefficients A1, B0, D0, and D1. Hereinafter, these will be referred to as the first coefficient group. Similarly, hereinafter, the function G f2 The coefficients E1 and F0 included in the second coefficient group are called the second coefficient group, and the function G f3 The coefficients G1 and H0 included in are called the third coefficient group.

[0034] Next, the details of the filtering process by the steering angular velocity dependent third-order filter 15a will be described with reference to the flowchart of FIG.

[0035] <<Step S1>> First, in step S1, the steering control device 1 determines the coefficients of (Equation 5), (Equation 6), and (Equation 7) based on the steering angular velocity ω calculated by the steering angular velocity calculation unit 12. Here, FIGS. 4A and 4B are examples of tables for determining a first set of coefficients according to the current steering angular velocity ω, with FIG. 4A(a) being a table for determining coefficient A1, FIG. 4A(b) being a table for determining coefficient B0, FIG. 4B(a) being a table for determining coefficient D0, and FIG. 4B(b) being a table for determining coefficient D1. FIG. 5 is an example of a table for determining a second set of coefficients according to the current steering angular velocity ω, with FIG. 5(a) being a table for determining coefficient E1, and FIG. 5(b) being a table for determining coefficient F0. FIG. 6 is an example of a table for determining a third set of coefficients according to the current steering angular velocity ω, with FIG. 6(a) being a table for determining coefficient G1, and FIG. 6(b) being a table for determining coefficient H0.

[0036] <<Step S2>> Next, in step S2, the steering control device 1 calculates a function G that changes according to the steering angular velocity ω for the combined torque value of the basic assist torque value and the phase compensation torque value. f3 Filtering is performed using the following method.

[0037] As can be seen from (Equation 4), the function G f3 is a first-order low-pass filter. Since most of the high-frequency signals of the total torque value are noise, the function G f3 A cutoff frequency ω3 is set to a value that cuts off high frequency signals corresponding to noise.

[0038] For example, if the third coefficient group (coefficients G1 and H0) is set to a cutoff frequency ω3 = 500 Hz, the function G f3 The characteristic of the function G is shown in the Bode diagram in Figure 7. f3 By using this filter processing, it is possible to remove signals in the high frequency range corresponding to the noise frequency from the total torque value, as shown in the upper graph of Fig. 7.

[0039] <<Step S3>> In step S3, the steering control device 1 calculates a function G that changes according to the steering angular velocity ω for the output of step S2. f1 Filtering is performed using the following method.

[0040] As can be seen from (Equation 2), the function G f1 is a filter including a second-order differential element. A differential element filter has the effect of amplifying high-frequency noise, so normally, using a differential element filter would deteriorate the stability of the high-frequency region. However, in this embodiment, since the noise in the high-frequency region is cut in step S2, the stability of the high-frequency region will not deteriorate as a result of the processing in this step.

[0041] That is, after the gain and phase in the high frequency region are lowered in step S2, the phase in the operating frequency region is raised in this step, and therefore, by processing this step, the phase margin in the operating frequency region is increased, thereby improving the stability of the power steering system 100.

[0042] Figure 8 shows the appropriate ω1, ω n , ζ, the first coefficient group (coefficients A1, B0, D0, D1) corresponding to the function G f1 This is a Bode diagram showing the characteristics of the function G f1 By using this filter processing, the phase of the signal in the region corresponding to the operating frequency region can be increased, as shown in the upper graph of Figure 8.

[0043] <<Step S4>> In step S4, the steering control device 1 calculates a function G that changes according to the steering angular velocity ω for the output of step S3. f2 Filtering is performed using the following method.

[0044] As can be seen from (Equation 3), the function G f2 is a first-order low-pass filter. Since most of the low-frequency signals of the total torque value are vibrations caused by mechanical elements such as resonance, the function G f2 A cutoff frequency ω2 is set to a value that cuts off low frequency signals corresponding to vibrations caused by mechanical elements.

[0045] For example, if the second coefficient group (coefficients E1, F0) is set to correspond to the cutoff frequency ω2 = 37 Hz, the function G f2 The characteristic of the function G is shown in the Bode diagram in Figure 9. f2 By using this filter, it is possible to cut signals in the low frequency range corresponding to the vibration frequency of the mechanical elements, as shown in the upper graph of Figure 9.

[0046] As explained above with reference to Figs. 3 to 9, the function G f3 , function G f1 , function G f3 When the filtering processes are performed in this order, the filter transfer function G of the third-order filter 15a dependent on the steering angle velocity is f As shown in the Bode diagram of Fig. 10, the filter has the characteristics of cutting out the frequency components of the noise frequency, the natural frequency according to the steering angular velocity, and the resonance frequency of the mechanical elements, and extracting the frequency components in the operating frequency range.

[0047] FIG. 11 shows the filter transfer function G f 11(a) is a graph showing an example of the input and output of the steering angle velocity-dependent third-order filter 15a equipped with the steering angle velocity-dependent filter transfer function G f By this filtering process, the total torque value is corrected to a smooth value with the natural frequency noise removed, as shown in Fig. 11(b).

[0048] Therefore, if filtering processing is performed only by the vehicle speed-dependent tertiary filter 15b without using the steering angular velocity-dependent tertiary filter 15a, an assist torque value containing natural frequency noise is generated, and as a result of the assist of the power steering system 100, minute vibrations of the steering wheel occur, deteriorating the driver's operational feel. On the other hand, by using the steering angular velocity-dependent tertiary filter 15a of this embodiment, an assist torque value not containing natural frequency noise is generated, and a power steering system 100 with good steering feel can be realized.

[0049] <How to set various parameters> The various parameters described above may be set appropriately depending on the characteristics of the power steering system 100, and may be set, for example, as follows.

[0050] Figure 12 shows the relationship between the steering angular velocity ω and the damping central frequency ω n 1 is a graph showing an example of the relationship between the function G f1 The attenuation center frequency ω determines the filter characteristics n is set to 20Hz in the low steering angular velocity range, and 13Hz above 600deg / s. This allows the damping degree and damping width at low steering angular velocities in Figure 10 to be set appropriately.

[0051] Fig. 13 is a graph showing an example of the relationship between steering angular velocity and cutoff frequency ω when a first-order LPF is used instead of a high-order filter. In this example, the cutoff frequency ω is set to 200 Hz at low steering angular velocity, 100 Hz at 600-1000 deg / s, and 50 Hz at high steering angular velocity. The cutoff frequency ω is set in this way to avoid the possibility that the assist torque value will be excessively reduced when steering suddenly if the cutoff frequency ω is set too low.

[0052] <Effects of this Example> As described above, the power steering system of this embodiment can suppress noise, vibration, and shock corresponding to the frequency components of the natural frequency regardless of the steering angular speed, thereby improving the stability of the system. As a result, it is possible to suppress deterioration of the steering feel and discomfort to the driver caused by noise, vibration, and shock corresponding to the frequency components of the natural frequency. [Explanation of symbols]

[0053] 100 Power Steering System 1 Steering control device 11 Vehicle speed calculation section 12 Steering angle speed calculation unit 13 Basic assist torque calculation unit 14 Phase compensation torque calculation section 15 High-order filters 15a Steering angle velocity dependent third order filter 15b Vehicle speed dependent third order filter 2 motors 3 Motor drivers 4 Vehicle speed sensor 5 Rotation angle sensor 6 Torque Sensor

Claims

1. A steering control device that calculates an assist torque value of a power steering system, a basic assist torque calculation unit that calculates a basic assist torque value based on the torsion bar torque value and the vehicle speed; a phase compensation torque calculation unit that calculates a phase compensation torque value based on the torsion bar torque value and the basic assist torque value; a high-order filter that performs high-order filtering on a combined torque value of the basic assist torque value and the phase compensation torque value, The high-order filter is a first filtering process for the combined torque value using a filter transfer function according to a steering angular velocity of a steering wheel; and performing a second filtering process using a filter transfer function according to the vehicle speed on the output of the first filtering process, A steering control device that outputs an assist torque value in which the frequency component of the natural frequency corresponding to the steering angular velocity is suppressed.

2. 2. The steering control device according to claim 1, The first filtering process includes: Function G that cuts out high frequency signals that correspond to noise ｆ３ First-order low-pass filtering by Function G that increases the phase margin in the operating frequency range ｆ１ Second-order differential element filtering by Function G that cuts low-frequency signals corresponding to vibrations caused by mechanical elements ｆ２ First-order low-pass filtering by A steering control device characterized by sequentially performing the above processes.

3. 3. The steering control device according to claim 2, The function G ｆ３ , the function G ｆ１ , and the function G ｆ２ The coefficient is determined in accordance with the steering angular velocity.

4. The steering control device according to any one of claims 1 to 3, A steering control device characterized in that the torsion bar torque value is input from a torque sensor that measures torque generated in a torsion bar that connects a steering wheel and a steering mechanism.

5. 5. The steering control device according to claim 4, 10. A steering control device according to claim 9, wherein the steering angular velocity is calculated based on the output of a rotation angle sensor that measures the rotation angle of a motor that applies an assist force to a rack bar of the steering mechanism.

6. 5. The steering control device according to claim 4, 10. A steering control device, wherein the steering angular velocity is input from a steering angular velocity sensor provided on the steering wheel or the torsion bar.

7. a steering mechanism for steering the steering wheels; a motor for powering a rack bar of the steering mechanism; A power steering system including a steering control device that calculates power to be applied to the rack bar based on a driver's steering operation, The steering control device includes: a basic assist torque calculation unit that calculates a basic assist torque value based on the torsion bar torque value and the vehicle speed; a phase compensation torque calculation unit that calculates a phase compensation torque value based on the torsion bar torque value and the basic assist torque value; a high-order filter that performs high-order filtering on a combined torque value of the basic assist torque value and the phase compensation torque value, The high-order filter is a first filtering process for the combined torque value using a filter transfer function according to a steering angular velocity of a steering wheel; and performing a second filtering process using a filter transfer function according to the vehicle speed on the output of the first filtering process, A power steering system that outputs an assist torque value in which the frequency component of the natural frequency corresponding to the steering angular velocity is suppressed.

8. A steering control method for a power steering system, comprising: a basic assist torque calculation step of calculating a basic assist torque value based on the torsion bar torque value and the vehicle speed; a phase compensation torque calculation step of calculating a phase compensation torque value based on the torsion bar torque value and the basic assist torque value; a high-order filtering step of performing high-order filtering on a combined torque value of the basic assist torque value and the phase compensation torque value, The high-order filter step includes: a first filtering step of filtering the combined torque value using a filter transfer function according to a steering angular velocity of a steering wheel; and performing a second filtering step using a filter transfer function according to the vehicle speed on the output of the first filtering step, A steering control method comprising: outputting an assist torque value in which the frequency component of the natural frequency corresponding to the steering angular velocity is suppressed.

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