Vehicle control system and vehicle control method

Abstract

This vehicle control system, which is a system for controlling a vehicle, comprises a control force calculation unit that calculates a control input, and a frequency response characteristic adjustment unit that adjusts a frequency response characteristic in the control input. The frequency response characteristic adjustment unit adjusts the frequency response characteristic in a fixed-point frequency band determined on the basis of a fixed point at which the magnification of vibration from a disturbance and vehicle body vibration caused by said vibration does not change irrespective of the control input.

Description

Vehicle control system, vehicle control method

[0001] The present invention relates to a vehicle control system and a vehicle control method.

[0002] Generally, suspension control devices mounted on vehicles such as automobiles are known to have a configuration that includes springs and dampers between the vehicle body and each axle, as well as a semi-active suspension with adjustable damping force. In addition to this configuration, there are also known configurations that include springs and dampers, as well as an active suspension that outputs vertical force based on sensor information, and configurations that use drive reaction force as a force generated vertically, similar to an active suspension, instead of an active suspension. If we consider a vehicle as a two-inertia system of the vehicle body and tires, there are two resonance points: the resonance point of the vehicle body (sprung mass) and the resonance point of the tires (unsprung mass). Of these, the unsprung mass resonance point is a fixed point where the vertical force generated from the suspension connecting the vehicle body and tires cannot control the vibration of the vehicle body. Since the fixed point is inversely proportional to the unsprung mass of the vehicle, in vehicles with a large unsprung mass, such as those with in-wheel motors or large wheels and tires, the fixed point is in a lower frequency range than in conventional vehicles.

[0003] Patent Document 1 discloses a suspension control device interposed between a vehicle body and a wheel to suppress vibrations of the vehicle body by generating a damping force between the vehicle body and the wheel, comprising: a control damper that generates the damping force in response to a command signal; motion detection means for detecting the motion of the vehicle body; a feedback controller that calculates a controller output based on the detected vehicle body motion; an observer that calculates the estimated piston speed and unsprung speed of the control damper based on the detected vehicle body motion and the command signal; a ground hook controller that calculates an unsprung vibration damping force according to the unsprung speed calculated by the observer; a target damping force calculator that calculates a target damping force based on the controller output by the feedback controller and the unsprung vibration damping force by the ground hook controller; and a signal outputter that outputs the command signal based on the target damping force calculated by the target damping force calculator and the estimated piston speed by the observer.

[0004] Japanese Patent Application Laid-Open No. 2013-241076

[0005] In the invention described in Patent Document 1, vibration in the frequency region near the fixed point cannot be suppressed.

[0006] A vehicle control system according to a first aspect of the present invention is a vehicle control system that controls a vehicle, and includes a control force calculation unit that calculates a control input, and a frequency response characteristic adjustment unit that adjusts a frequency response characteristic of the control input. The frequency response characteristic adjustment unit adjusts the frequency response characteristic in a fixed point frequency band determined based on a fixed point at which a magnification factor between vibration of an external disturbance and vehicle body vibration caused by the vibration is invariant regardless of the control input. A vehicle control method according to a second aspect of the present invention is a vehicle control method executed by a vehicle control device that is a computer that controls a vehicle, and includes a control input calculation process that calculates a control input, and a frequency response characteristic adjustment process that adjusts a frequency response characteristic of the control input. In the frequency response characteristic adjustment process, the frequency response characteristic is adjusted in a fixed point frequency band determined based on a fixed point at which a magnification factor between vibration of an external disturbance and vehicle body vibration caused by the vibration is invariant regardless of the control input.

[0007] According to the present invention, vibration in the frequency region near the fixed point can be suppressed.

[0008] Block diagram of a vehicle equipped with a vehicle control system, Diagram showing a quarter-car model which is a vehicle model 1, Block diagram expressing the effect of a controller on an external disturbance in an emphasized manner, Diagram showing the correspondence relationship between a sensitivity function and a Nyquist diagram, Diagram showing the classification of the correlation between a vibration deterioration circle and a Nyquist locus, Diagram showing a specific example of a phase adjustment method, Diagram showing a specific example of a phase adjustment method, Diagram showing the sensitivity function of the controller before and after adjustment, Diagram showing the hardware configuration of the vehicle control system

[0009] - First Embodiment - Hereinafter, a first embodiment of a suspension control device which is a vehicle control system will be described with reference to FIGS. 1 to 8. In the present embodiment, a 1 / 4 vehicle body model (quarter-car model), which is often used when targeting the vibration suppression performance of a suspension, will be described as an example, but it can also be applied to other vehicle body models.

[0010] (Vehicle Configuration) Figure 1 is a block diagram of a vehicle 900 equipped with a vehicle control system 10. The vehicle 900 comprises a vehicle model 1 including an active suspension 5, a sprung mass acceleration sensor 6, and a vehicle control system 10. The sprung mass acceleration sensor 6 is an acceleration sensor provided on the vehicle body 2 and measures the vertical acceleration of the vehicle body 2, so-called "sprung mass acceleration." In this embodiment, the vertical acceleration of the tires 3 is not measured. Hereinafter, the vertical acceleration of the vehicle body 2 measured by the sprung mass acceleration sensor 6 will be referred to as the direct output 61. Note that the vertical acceleration of the vehicle body 2 may be calculated using the output of another sensor instead of the sprung mass acceleration sensor 6. The direct output 61 is output to the vehicle control system 10.

[0011] The vehicle control system 10 comprises a sensor noise processing unit 7, a control force calculation unit 8, and a frequency response characteristic adjustment unit 9. The sensor noise processing unit 7 generates a processed output 62 based on the direct output 61 input from the sprung mass acceleration sensor 6. Since the direct output 61 contains noise, the sensor noise processing unit 7 removes the noise and offset from the direct output 61 to generate a processed output 62, which is then output to the control force calculation unit 8. The control force calculation unit 8 uses the processed output 62 to calculate the pre-adjustment control force 71, which is the vertical control force required to make the sprung mass acceleration of the vehicle body 2 zero. The frequency response characteristic adjustment unit 9 adjusts the frequency response to the pre-adjustment control force 71 calculated by the control force calculation unit 8 to generate an adjusted control force 72, which is then input to the active suspension 5.

[0012] (Quarter Car Model) Figure 2 shows the quarter car model, which is vehicle model 1. The quarter car model is a single-wheel model that divides the entire automobile into four parts. The quarter car model models the vehicle 900 with three parts: the tire 3, the suspension 4, and the body 2. The tire 3 acts as a spring that absorbs the changes z0 of fine irregularities in the road surface, and can therefore be modeled with a mass m1 and a spring constant kt. The body weight m2 is 1 / 4 of the total vehicle weight. The sprung displacement, which is the displacement of the body 2, is z2.

[0013] To specifically demonstrate suppressing vertical vibrations in the vehicle 900 using variables, it is necessary to make the sprung mass acceleration, which is the second derivative of z², zero. The suspension 4 connects the vehicle body 2 and the tires 3. The suspension 4 consists of three components connected in parallel: a damper (damping coefficient cs), a spring (spring constant ks), and an active suspension 5. The damper and spring passively generate force based on the difference between the sprung mass displacement and the unsprung mass displacement. The active suspension 5 generates an adjusted control force 72, which is a command value output from the vehicle control system 10.

[0014] In this embodiment, an active suspension 5 is used for the suspension 4, but an actuator capable of actively calculating vertical force, similar to the active suspension 5, may be used instead. For example, a motor may be used instead of the active suspension 5.

[0015] Figure 3 is a simplified block diagram of Figure 1, emphasizing the effect of the vehicle control system 10 on disturbances (road surface irregularities). The vehicle control system 10 receives the difference between the target value of sprung mass acceleration (here, 0) and the sprung mass acceleration y measured by the sensor, and calculates the adjusted control force 72 using the transfer function C.

[0016] (Explanation of fixed points) Based on the quarter car model in Figure 2, the equations of motion for the car body 2 and the tires 3 are expressed by equations 1 and 2, respectively. Here, s is the Laplace operator.

[0017] In Figure 3, P, the transfer function from the vertical force to the sprung acceleration, and Gyd, the transfer function from the disturbance to the sprung acceleration, are expressed by the following equations 3 and 4.

[0018]

[0019] To find the fixed point, we eliminate Fc from equations 1 and 2, which yields equation 5.

[0020]

[0021] When the second term on the left side of equation 5 is 0, it becomes the frequency of the fixed point where no damping effect is obtained at all. If s = jω (j: imaginary number, ω: angular frequency), the fixed point angular frequency ωf, which is the angular frequency of the fixed point, is expressed by the following equation 6.

[0022]

[0023] Since the tire mass m1 and spring constant kt are known, the fixed point angular frequency ωf can be easily calculated. For vibrations at this frequency, the vibration damping effect obtained by the controller will always be zero, regardless of the controller design.

[0024] Based on Figure 3, the transfer function from the disturbance to the sprung acceleration can be found in the following equation 7.

[0025] Here, S(s) = 1 / (1+PC) is called the sensitivity function and represents the effect of the vehicle control system 10. This is because, when there is no controller (i.e., C=0), equation 7 shows that the transfer function from road surface displacement to sprung mass acceleration is Gyd. On the other hand, when the vehicle control system 10 is present, |S|≠1, and the transfer function from road surface displacement to sprung mass acceleration becomes |S| times Gyd. Therefore, if |S|<1, it means that vibration is reduced by the vehicle control system 10, and conversely, if |S|>1, it means that vibration is amplified by the vehicle control system 10.

[0026] (Relationship between sensitivity function and Nyquist diagram) A Nyquist diagram is a diagram used to determine the closed-loop stability of a feedback system. By substituting s = jω for s in the open-loop transfer function PC and continuously varying ω from 0 to infinity, a Nyquist trajectory can be drawn on the complex plane. If this Nyquist trajectory always passes the point (-1, 0) to the left as ω is varied from 0 to infinity, then the feedback system is stable.

[0027] On the other hand, from the definition of the sensitivity function, the sensitivity is greater than 1 when the denominator of the sensitivity function is less than 1, i.e., |1 + PC| < 1. When the left side of this inequality is considered on a Nyquist diagram, it represents the distance between the Nyquist trajectory and the point (-1, 0). Therefore, sensitivity deteriorates when this distance is less than 1. In other words, when the Nyquist trajectory is within a circle with center (-1, 0) and radius 1, the sensitivity at that frequency is greater than 1, and the vibration is amplified by the controller. Conversely, the further the Nyquist trajectory is from the point (-1, 0), the smaller the sensitivity at that frequency becomes, and the damping effect of the controller increases.

[0028] On the other hand, the fixed point coincides with the origin on the Nyquist diagram. This is because the fixed point is a point where no vibration damping effect can be obtained by the controller, so it can be considered as C=0, and at that time the Nyquist trajectory PC becomes 0. Therefore, no matter what transfer function C is used in the vehicle control system 10, the Nyquist trajectory will always pass through the origin. Consequently, unless the Nyquist trajectory is a trajectory that is exactly tangent to the circle at the origin, the trajectory will always pass through a circle with center (-1,0) and radius 1 (vibration deterioration region), so vibration will worsen in the frequency band near the fixed point.

[0029] Figure 4 shows the correspondence between the sensitivity function and the Nyquist plot. In Figure 4, the left side shows the sensitivity function, and the right side shows the Nyquist plot. In the sensitivity function, the vertical axis is 20 log |S|, so when |S| > 1, the value becomes greater than 0 dB. In Figure 4, the region where this vibration is amplified is shown by dot hatching. The dashed line in the left figure shows the general shape of the sensitivity function before applying phase compensation, and it takes a value of 0 dB or more near the fixed point, which is the vibration deterioration region. As will be described later, the solid line is an overview of the sensitivity function after applying phase compensation. In correspondence with Figure 1, the dashed line is the control force 71 before adjustment, and the solid line is the control force 72 after adjustment.

[0030] The vibration aggravation region, where vibrations are amplified on the Nyquist diagram shown on the right side of Figure 4, is illustrated. The vibration aggravation region is a circle with its center at coordinates (-1, 0) and radius 1. Hereafter, this circle will be referred to as the "vibration aggravation circle." Since the fixed point on the Nyquist trajectory is at the origin, it is impossible to create a situation where the Nyquist trajectory and the vibration aggravation circle do not overlap at all. However, the intersection of the Nyquist trajectory with the outer circumference of the vibration aggravation circle and the intrusion of a part of the Nyquist trajectory into the vibration aggravation circle can be avoided by adjusting the frequency characteristics. That is, by applying phase lead compensation or phase lag compensation, the Nyquist trajectory can be adjusted to be tangent to the vibration aggravation circle at the fixed point.

[0031] In the example shown on the right of Figure 4, the dashed line indicated by reference numeral 71 represents the unadjusted control force 71 before phase compensation is applied, and the solid line represents the adjusted control force 72 after phase compensation is applied. The direction of the arrows in the unadjusted control force 71 and the adjusted control force 72 indicates the direction of the Nyquist trajectory corresponding to the increase in frequency. Hereinafter, the point at which the Nyquist trajectory enters the vibration deterioration circle when the frequency is increased will be called the "entry start point," and the point at which the Nyquist trajectory exits the vibration deterioration circle will be called the "entry end point."

[0032] In the example shown in this figure, the adjusted control force 72 is obtained by rotating the trajectory counterclockwise with respect to the pre-adjustment control force 71 through phase lead compensation. By applying the phase compensation designed in this way, the sensitivity function becomes as shown by the solid line in the left figure, and the vibration deterioration near the fixed point is eliminated. Therefore, by adjusting the phase so that the Nyquist trajectory near the fixed point does not enter the vibration deterioration circle, the vibration deterioration near the fixed point can be eliminated.

[0033] Figure 5 shows a classification of the correlation between the vibration deterioration circle and the Nyquist trajectory. The circles shown with hatched dots in Figure 5 are vibration deterioration circles. The solid white circles are Nyquist trajectories at the fixed point angular frequency ωf, and are located at the origin. In Case 1, the Nyquist trajectory is tangent to the vibration deterioration circle at the origin. In this Case 1, the Nyquist trajectory does not penetrate the interior of the vibration deterioration circle; in other words, the Nyquist trajectory does not intersect with the circles that make up the outer perimeter of the vibration deterioration circle, which is an ideal state.

[0034] In Case 2, the Nyquist trajectory intersects the outer circumference of the vibration deterioration circle at the fixed point frequency ff, travels through the interior of the vibration deterioration circle, and exits the exterior at a frequency f2 smaller than ff. In other words, in Case 2, the entry point is the fixed point. In Case 2, applying phase lag compensation can make it the same as Case 1. In Case 3, the Nyquist trajectory intersects the outer circumference of the vibration deterioration circle and enters the interior at an angular frequency f3 smaller than the fixed point frequency ff, and exits the exterior of the vibration deterioration circle at the fixed point frequency ff. In other words, in Case 3, the entry end point is the fixed point. In Case 3, applying phase lead compensation as in Figure 4 can make it the same as Case 1.

[0035] Furthermore, in the following, the frequency band corresponding to a Nyquist trajectory that has entered the vibration aggravation circle and whose entry start or end point is a fixed point will be called the "fixed point frequency band." In Case 2, ff to f2 is the fixed point frequency band, and in Case 3, f3 to ff is the fixed point frequency band. In Case 1, there is no fixed point frequency band. The region of the Nyquist trajectory corresponding to the fixed point frequency will also be called the "specific overlapping region."

[0036] (Specific Example) Figures 6 and 7 show specific examples of phase adjustment methods. Figure 6 shows the Nyquist trajectory before adjustment, and Figure 7 shows the Nyquist trajectory before and after adjustment. However, the right side of Figure 6 will be explained later. Here, we will specifically explain a phase adjustment method when the controller is a controller that uses information on sprung mass acceleration, sprung mass velocity, and sprung mass displacement. In this case, the transfer function C of the vehicle control system 10 is given by the following equation 8.

[0037]

[0038] The dashed line in Fig. 6 is the Nyquist locus when K1 = m2, K2 = cs, and K3 = ks in Equation (8). When this Nyquist locus is changed from 0 Hz to infinity, it proceeds from the origin to the upper left second quadrant, returns to the origin at the frequency corresponding to the fixed point via the first quadrant, the fourth quadrant, and the third quadrant, and further draws an arc in the fourth quadrant. This Nyquist locus penetrates into the interior of the vibration deterioration circle at two locations: the first initial region 91 near 0 Hz immediately after the start and the second initial region 92 near the fixed point. However, since neither the intrusion start point nor the intrusion end point of the first initial region 91 is the fixed point, no countermeasure is taken. The reason is as follows.

[0039] In this embodiment, the purpose is to reduce vibration at frequencies near the fixed point. In principle, it is impossible to reduce vibration in the entire frequency band by adjusting the frequency characteristics, and it is inevitable that the gain becomes greater than 1 in any frequency band. Therefore, when neither the intrusion start point nor the intrusion end point is the fixed point, the occurrence of vibration in the corresponding frequency region is tolerated and no countermeasure is taken.

[0040] On the other hand, the second initial region 92 penetrates into the vibration deterioration circle at 7.3 Hz and exits the vibration deterioration circle at 8.8 Hz, which is the fixed point. That is, since the intrusion end point of the second initial region 92 is the fixed point, the magnitude of the sensitivity function becomes 1 or more in the frequency band from 7.3 Hz to 8.8 Hz, which is the frequency near the fixed point, and vibration is amplified. Therefore, the phase is adjusted for this frequency band.

[0041] As described with reference to Fig. 5, in the example shown in Fig. 6, the phase advance compensation is appropriate. The phase advance compensation K(s) is represented by the following Equation (9), where the angular frequency at which the phase advances the most is ωmax, the maximum value of the phase advance is φmax, and the gain is K.

[0042]

[0043] Here, α and T are obtained by the following Equation (10).

[0044]

[0045] Considering the decrease in controller stability due to the increase in gain in the high-frequency band caused by phase lead compensation, phase lead compensation is applied with ωmax = 8.8 Hz, φmax = 65 degrees, and K = 1. The ωmax, φmax, and K shown here are examples. For ωmax, the larger of the aforementioned 7.3 Hz and 8.8 Hz was adopted. An example of a method for determining φmax will be explained with reference to the right-hand figure in Figure 6.

[0046] The right-hand diagram in Figure 6 is an enlarged view of the area near the origin. In this enlarged view, the hatching of dots indicating the inner circumference of the vibration aggravation circle has been omitted for the sake of drawing convenience. First, in the Nyquist trajectory, we identify the position of approximately 8.0 Hz, which is midway between 7.3 Hz and 8.8 Hz. Next, we draw an auxiliary line 31, which is a straight line connecting this 8.0 Hz position to the origin. Finally, we define the angle 32 between this auxiliary line 31 and the imaginary axis as φmax. By applying phase compensation in this way, the Nyquist trajectory changes as shown in the next diagram.

[0047] Figure 7 shows the Nyquist trajectory after phase adjustment. The left side of Figure 7 shows the Nyquist trajectory before adjustment for comparison, and the right side of Figure 7 shows an ellipse indicating a portion of the adjusted Nyquist trajectory for explanatory purposes. In Figure 7, the dashed line is the Nyquist trajectory before adjustment, as in Figure 6, and the solid line is the Nyquist trajectory after adjustment. In this solid Nyquist trajectory, there is no intersection between the Nyquist trajectory and the vibration deterioration circle near the frequency of the fixed point.

[0048] The three regions shown on the right of Figure 7 are the first region 81, the second region 82, and the third region 83. The first region 81 is the region below 1 Hz where the Nyquist trajectory begins to form. The first region 81 enters the circle of vibration deterioration, but there is no problem as neither the entry point nor the entry point is a fixed point. Neither the second region 82, which is just before the fixed point, nor the third region 83, which is just after the fixed point, intersects the circle of vibration deterioration, and the vibration deterioration near the fixed point is eliminated by phase adjustment.

[0049] Figure 8 shows the sensitivity functions of the controller before and after adjustment. The sensitivity function of the control force 71 before adjustment (before phase adjustment) is shown by a dashed line, and the sensitivity function of the control force 72 after adjustment (after phase adjustment) is shown by a solid line. It can be seen that the deterioration of vibration near the fixed point is eliminated by the phase adjustment. Furthermore, if the fixed point is at a frequency around 10 Hz, which is said to be easily perceived by humans, this phase adjustment reduces the frequency component around 10 Hz, thereby improving ride comfort.

[0050] According to the first embodiment described above, the following effects can be obtained: (1) The vehicle control system 10 controls the suspension 4 of the vehicle 900. The vehicle control system 10 includes a control force calculation unit 8 that calculates a pre-adjustment control force 71 which is a control input, and a frequency response characteristic adjustment unit 9 that adjusts the frequency response characteristics of the pre-adjustment control force 71. The frequency response characteristic adjustment unit 9 adjusts the frequency response characteristics in the fixed point frequency band determined based on a fixed point where the ratio between the vibration of the disturbance and the vibration of the vehicle body caused by the vibration remains constant regardless of the control input. As a result, the vehicle control system 10 can suppress vibrations in the frequency range near the fixed point.

[0051] (2) The frequency response characteristic adjustment unit 9 adjusts the frequency response characteristics so that the Nyquist trajectory, which indicates the control input, and the vibration deterioration circle, which is a circle representing the vibration deterioration region, are tangent at a fixed point, as shown in Figures 4 and 7.

[0052] (3) The adjustment of the frequency response characteristics in the frequency response characteristic adjustment unit 9 is phase adjustment, which involves advancing or delaying the phase of the fixed point frequency band, as shown in Figure 5.

[0053] (4) In phase adjustment, the frequency response characteristic adjustment unit 9 advances the phase when the Nyquist trajectory indicating the control input passes through the vibration deterioration circle, which is a circle indicating the vibration deterioration region, before passing through the fixed point, as in Case 3 of Figure 5. Also, as in Case 2 of Figure 5, the phase is delayed when the Nyquist trajectory passes through the vibration deterioration circle after passing through the fixed point.

[0054] (5) The fixed point frequency band is a frequency that corresponds to a specific overlapping region, which is part of the Nyquist trajectory that indicates the control input. The specific overlapping region is one that overlaps with the vibration deterioration region circle, as shown in the second initial region 92 in Figure 6, and one of its endpoints is a fixed point.

[0055] (Modification 1) In the first embodiment described above, the frequency response characteristic adjustment unit 9 performed only phase compensation. However, the frequency response characteristic adjustment unit 9 may also perform gain adjustment in addition to phase compensation. In this case, as explained with reference to Figure 5 in the first embodiment, phase lag compensation and phase lead compensation are used depending on the situation. The frequency response characteristic adjustment unit 9 then uses a filter to reduce the gain, such as a notch filter, for frequency bands where the gain has increased due to the effect of this phase compensation.

[0056] For example, if the sensitivity is as shown in Figure 8 due to phase compensation, the gain is large around 20 Hz, which is the rightmost point of the figure. In this case, the frequency response characteristic adjustment unit 9 may also use a notch filter that attenuates frequencies from 20 Hz to 30 Hz.

[0057] According to this modified example, in addition to the effects and advantages of the first embodiment, the following effects and advantages can be obtained: (6) The frequency response characteristic adjustment in the frequency response characteristic adjustment unit 9 is phase lead compensation and gain adjustment, and in the gain adjustment, the gain of the high-frequency band amplified by phase compensation is reduced. Therefore, the gain of the fixed point frequency band is reduced by phase compensation, and the gain of the high-frequency band which has become large due to the effect of phase compensation can be reduced.

[0058] (Modification 2) In the first embodiment described above, the operation of the frequency response characteristic adjustment unit 9, i.e., the timing of the execution of phase compensation, was not particularly limited. The frequency response characteristic adjustment unit 9 may be operated at all times or only in specific cases. When the frequency response characteristic adjustment unit 9 is not operated, the vehicle control system 10 outputs the pre-adjustment control force 71, which is the output of the control force calculation unit 8, as is. When the frequency response characteristic adjustment unit 9 is operated only in specific cases, for example, it may be operated only when the road surface vibration is mainly less than 20 Hz. The road surface vibration may be measured by measuring the unsprung displacement, or it may be obtained indirectly by measuring the distance between the road surface and the vehicle body 2 with a distance sensor (not shown). When the road surface vibration is 20 Hz or higher, it is difficult for the occupants of the vehicle 900 to perceive it, so by intentionally stopping the phase compensation by the frequency response characteristic adjustment unit 9, an increase in gain occurring in the high-frequency band can be avoided.

[0059] (Modification 3) In the first embodiment described above, the frequency response characteristic adjustment unit 9 adjusted the phase so that the Nyquist trajectory would not enter the vibration degradation circle, as shown in Figures 4 to 7, and so that the Nyquist trajectory and the vibration degradation circle would be in contact at a fixed point. However, the function of the frequency response characteristic adjustment unit 9 is not limited to completely eliminating the entry of the Nyquist trajectory into the vibration degradation circle; it is sufficient if the entry of the Nyquist trajectory into the vibration degradation is reduced. The degree of vibration degradation can be reduced by moving the Nyquist trajectory away from (-1, 0) on the complex plane.

[0060] (Modification 4) In the first embodiment described above, the hardware configuration of the vehicle control system 10 was not particularly limited. However, the hardware configuration described below may be adopted.

[0061] Figure 9 shows the hardware configuration of the vehicle control system 10. The vehicle control system 10 is, for example, a computer and includes a CPU 41 which is a central processing unit, a ROM 42 which is a read-only storage device, a RAM 43 which is a read-write storage device, an input / output device 44 which is a user interface, and a communication device 45. The CPU 41 performs the various calculations mentioned above by loading the program stored in the ROM 42 into the RAM 43 and executing it.

[0062] The vehicle control system 10 may be implemented using a rewritable logic circuit such as an FPGA (Field Programmable Gate Array) or an application-specific integrated circuit such as an ASIC (Application Specific Integrated Circuit) instead of the combination of CPU 41, ROM 42, and RAM 43. Alternatively, the vehicle control system 10 may be implemented using a different configuration, such as a combination of CPU 41, ROM 42, RAM 43 and FPGA, instead of the combination of CPU 41, ROM 42, and RAM 43.

[0063] In Figure 9, for convenience, the vehicle control system 10 is shown as being composed of a single hardware device, but the vehicle control system 10 may be composed of multiple hardware devices. In this case, the hardware devices may be installed adjacent to each other, or they may be connected by a communication channel mounted on the vehicle 900, such as a local area network. Furthermore, some of the multiple hardware devices may be located outside the vehicle 900 and connected by vehicle-to-vehicle communication, communication via base stations or satellites, or even communication using the internet. Also, when the vehicle control system 10 is composed of a single hardware device, the vehicle control system 10 can also be called a "vehicle control device".

[0064] —Second Embodiment— A second embodiment of the vehicle control system will be described. In the following description, the same reference numerals are used for components that are the same as in the first embodiment, and the differences will be mainly explained. Points that are not specifically explained are the same as in the first embodiment. This embodiment differs from the first embodiment mainly in that it performs only gain adjustment. Also, in this embodiment the definition of the fixed point frequency band differs from that of the first embodiment.

[0065] In this embodiment, the frequency band near the fixed point where the gain of the pre-adjustment control force 71 exceeds 0 dB is defined as the "fixed point frequency band". For example, if the fixed point frequency is 10.0 Hz, the frequency band near the fixed point may be 9.5 Hz to 10.5 Hz or 8 Hz to 12 Hz.

[0066] In this embodiment, the frequency response characteristic adjustment unit 9 uses a filter that reduces the gain, such as a notch filter, targeting the fixed point frequency band. This suppresses the amplification of vibrations near the fixed point.

[0067] According to the second embodiment described above, the following effects can be obtained: (7) The adjustment of the frequency response characteristics in the frequency response characteristic adjustment unit 9 is gain adjustment, and a filter is applied to reduce the gain in the fixed point frequency band.

[0068] In the second embodiment described above, the condition regarding the gain of the pre-adjustment control force 71 may be removed from the definition of the fixed point frequency band, and the frequency near the fixed point may simply be defined as the fixed point frequency band.

[0069] In the embodiments and modifications described above, the configuration of the functional blocks is merely an example. Several functional configurations shown as separate functional blocks may be integrated, or a configuration represented in one functional block diagram may be divided into two or more functions. Furthermore, some of the functions of each functional block may be provided by other functional blocks.

[0070] In the embodiments and modifications described above, the program is stored in ROM 42, but the program may also be stored in a non-volatile storage device (not shown). Furthermore, the vehicle control system 10 may have an input / output interface (not shown), and the program may be read from another device via a medium available to the input / output interface and the vehicle control system 10 when needed. Here, the medium refers to, for example, a storage medium detachable from the input / output interface, or a communication medium, i.e., a wired, wireless, optical network, or a carrier wave or digital signal propagating through such a network. Also, some or all of the functions realized by the program may be realized by hardware circuits or FPGAs.

[0071] The embodiments and modifications described above may be combined in any way. Although various embodiments and modifications have been described above, the present invention is not limited to these. Other embodiments that can be conceivable within the scope of the technical idea of ​​the present invention are also included within the scope of the present invention.

[0072] 1: Vehicle model 2: Body 3: Tires 4: Suspension 5: Active suspension 6: Sprung mass acceleration sensor 7: Sensor noise processing unit 8: Control force calculation unit 9: Frequency response characteristic adjustment unit 10: Vehicle control system 71: Control force before adjustment 72: Control force after adjustment

Claims

1. A vehicle control system for controlling a vehicle, comprising: a control force calculation unit for calculating a control input; and a frequency response characteristic adjustment unit for adjusting the frequency response characteristics at the control input, wherein the frequency response characteristic adjustment unit adjusts the frequency response characteristics in a fixed point frequency band determined based on a fixed point where the ratio between the vibration of an external disturbance and the vibration of the vehicle body caused by the vibration remains constant regardless of the control input.

2. A vehicle control system according to claim 1, wherein the frequency response characteristic adjustment unit adjusts the frequency response characteristics such that the Nyquist trajectory indicating the control input and the vibration deterioration circle, which is a circle representing the vibration deterioration region, are tangent at the fixed point.

3. A vehicle control system according to claim 1, wherein the adjustment of the frequency response characteristics in the frequency response characteristic adjustment unit is gain adjustment, and a filter is applied to reduce the gain in the fixed point frequency band.

4. A vehicle control system according to claim 1, wherein the adjustment of the frequency response characteristics in the frequency response characteristic adjustment unit is phase adjustment, and the phase of the fixed point frequency band is advanced or delayed.

5. A vehicle control system according to claim 1, wherein the adjustment of the frequency response characteristics in the frequency response characteristic adjustment unit is phase compensation and gain adjustment, and the gain adjustment reduces the gain of the high-frequency band amplified by the phase compensation.

6. A vehicle control system according to claim 4, wherein the frequency response characteristic adjustment unit advances the phase when the Nyquist trajectory indicating the control input passes through the vibration deterioration circle, which is a circle indicating a vibration deterioration region, and then passes through the fixed point, and delays the phase when the Nyquist trajectory passes through the fixed point and then passes through the vibration deterioration circle.

7. A vehicle control system according to claim 1, wherein the fixed point frequency band is a frequency corresponding to a specific overlapping region which is part of the Nyquist trajectory indicating the control input, and the specific overlapping region overlaps with the vibration deterioration region circle, with one of its endpoints being the fixed point.

8. A vehicle control method executed by a vehicle control device, which is a computer that controls a vehicle, comprising: a control input calculation process for calculating a control input; and a frequency response characteristic adjustment process for adjusting the frequency response characteristics of the control input, wherein the frequency response characteristic adjustment process adjusts the frequency response characteristics in a fixed point frequency band determined based on a fixed point where the ratio between the vibration of an external disturbance and the vibration of the vehicle body caused by the vibration remains constant regardless of the control input.

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