Suspension Control Device

Abstract

To provide a suspension device which can improve ride comfort in a vehicle.SOLUTION: A suspension control device C includes: a road surface follow-up control section U1 which determines a road surface follow-up control command FC for making a vehicle body B follow up a road surface in a spring upper resonance frequency band; a vibration insulation control section U2 which determines a vibration insulation control command FI to be a control command for hardly transmitting vibration from the road surface to the vehicle body B in a spring lower resonance frequency band; a switching section U3 which determines allocation of the road surface follow-up control command FC and the vibration insulation control command FI on the basis of road surface displacement Z detected by a preview sensor P for detecting road surface displacement in the front of a traveling direction of a vehicle V; and a final command arithmetic section U4 which determines a final control command F_ref for controlling a suspension device S from the allocation, the road surface follow-up control command FC, and the vibration insulation control command FI.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a suspension control device. [Background technology]

[0002] Conventionally, suspension control devices that control a suspension device interposed between the sprung and unsprung members of a vehicle include those that perform skyhook control, which suppresses the transmission of vibrations input from the road surface to the vehicle body (sprung members) while driving (see, for example, Patent Document 1).

[0003] In such a suspension control device, a control command is calculated by multiplying the vertical speed of the vehicle body by a skyhook gain (skyhook damping coefficient), and the control force indicated by the control command is output to the suspension device. In this way, a suspension control device that performs skyhook control reduces the vertical speed of the vehicle body using the damping force and control force generated by the suspension device, thereby suppressing vibration of the vehicle body and improving ride comfort. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-88358 Summary of the Invention [Problem to be solved by the invention]

[0005] Conventional suspension control devices can suppress vibrations in the vehicle body by isolating the transmission of vibrations from the road surface, but when driving over uneven road surfaces at high speeds or when entering a slope, trying to isolate the vibrations increases the gain and the stroke amount of the suspension device, which can cause vibrations due to the suspension device being fully extended or compressed to be transmitted to the vehicle body, resulting in a worsening ride.

[0006] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a suspension control device that can improve ride comfort. [Means for solving the problem]

[0007] In order to achieve the above object, the suspension control device in the problem-solving means of the present invention controls a suspension device that is interposed between the body and wheels of a vehicle and can apply vertical forces to the body to suppress vibration of the body, and is equipped with a road following control unit that obtains a road following control command that causes the body to follow the road surface in a sprung resonance frequency band, a vibration isolation control unit that obtains a vibration isolation control command that is a control command that makes it difficult for vibrations from the road surface to be transmitted to the vehicle body in an unsprung resonance frequency band, a switching unit that obtains an allocation of the road following control command and the vibration isolation control command based on road surface displacement detected by a preview sensor that detects road surface displacement ahead in the direction of vehicle travel, and a final command calculation unit that obtains a final control command for controlling the suspension device from the allocation, the road following control command, and the vibration isolation control command.

[0008] In a suspension control device configured in this manner, the final control command is determined by calculating the distribution between the road surface following control command and the vibration isolation control command based on the road surface displacement detected by the preview sensor.Therefore, it is possible to predict road surfaces on which vibration isolation control alone would increase the stroke amount of the suspension device, thereby deteriorating the ride comfort of the vehicle, and switch between the road surface following control command and the vibration isolation control command, thereby improving the ride comfort of the vehicle.

[0009] Furthermore, the switching section in the suspension control device may obtain a road surface index by second-order differentiation of the road surface displacement of the road surface on which the wheels are traveling with respect to distance, and determine the distribution of the road surface following control command and the vibration isolation control command based on the road surface index. A suspension control device configured in this way makes it possible to easily and accurately predict the start points of large unevenness and slopes, and to foresee road surfaces such as unevenness or the start points of slopes that will increase the stroke amount of the suspension device in advance, thereby optimizing the distribution of the road surface following control command and the vibration isolation control command, and further improving the ride comfort of the vehicle.

[0010] Furthermore, the switching unit in the suspension control device may determine the road surface index by low-pass filtering the moving average of the road surface displacement on the road surface on which the wheels are traveling or the moving average of the road surface displacement on the road surface on which the wheels are traveling and then differentiating the moving average of the road surface displacement on the road surface on which the wheels are traveling by second order with respect to distance. Low-pass filtering the moving average of the road surface displacement or the road surface displacement can remove noise contained in the road surface displacement and mitigate sudden changes in the road surface displacement. This prevents the road surface index from taking large values ​​for small road surface changes that do not increase the stroke amount, making it possible to more accurately identify the start of bumps and slopes that increase the stroke amount of the suspension device. Therefore, a suspension control device configured in this manner can further improve the ride comfort of the vehicle.

[0011] Furthermore, the switching unit in the suspension control device may calculate a suspension vibration estimate by multiplying the road surface index by the vehicle's traveling speed, and calculate the allocation based on the suspension vibration estimate. A suspension control device configured in this way can more accurately predict road surfaces on which the stroke amount of the suspension device increases depending on the vehicle's traveling speed, and optimize the allocation of the road surface following control command and the vibration isolation control command, thereby further improving the ride comfort of the vehicle.

[0012] Furthermore, the switching unit in the suspension control device may determine the allocation based on a level, which is the magnitude of the amplitude of the suspension vibration estimated value. With a suspension control device configured in this manner, the level of the suspension vibration estimated value is used, so the stroke of the suspension device can be accurately determined and the allocation between the road following control command and the vibration isolation control command can be optimized, improving ride comfort in the vehicle regardless of the quality of the road surface on which the vehicle travels. Furthermore, even when the suspension vibration estimated value vibrates with a large amplitude, the level remains high, so the allocation becomes oscillatory, preventing hunting, which is the frequent switching between road following control and vibration isolation control.

[0013] Furthermore, the switching unit in the suspension control device may obtain a pre-selection distribution for each of the four wheels (front, rear, left, and right) of the vehicle body, and determine the distribution based on the pre-selection distribution that maximizes the ratio of the road following control command FC for each of the four wheels. With a suspension control device configured in this way, the distribution of the road following control command and the vibration isolation control command in the suspension device is unified, making it possible to stabilize the posture of the vehicle body.

[0014] Furthermore, the switching unit in the suspension control device may process the distribution using a low-pass filter whose cutoff frequency changes according to the vehicle's traveling speed to determine the final distribution for each of the four wheels. With a suspension control device configured in this way, control can be performed with optimal distribution at optimal timing regardless of the vehicle's traveling speed.

[0015] Furthermore, the switching unit in the suspension control device may predict the road surface on which the wheels will travel based on the steering angle of the vehicle, and determine the allocation based on the road surface displacement of the predicted road surface. A suspension control device configured in this way can more accurately predict road surfaces on which the stroke amount of the suspension device will increase depending on the vehicle's path, and optimize the allocation of the road surface following control command and the vibration isolation control command, thereby further improving the ride comfort of the vehicle. [Effects of the Invention]

[0016] As described above, the suspension device of the present invention can improve the ride comfort of a vehicle. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a diagram showing a vehicle equipped with a suspension control device according to an embodiment; [Figure 2] 1 is a configuration diagram of a suspension control device according to an embodiment; [Figure 3] FIG. 2 is a diagram illustrating a control block of a road surface following control unit of the suspension control device according to the embodiment. [Figure 4] 3 is a diagram showing a vibration transmission gain characteristic of vibration transmitted from a road surface input to a vehicle body in road surface following control of the suspension control device according to the embodiment; FIG. [Figure 5] 3 is a diagram showing a vibration transmission gain characteristic of vibration transmitted from a road surface input to a vehicle body in vibration isolation control of the suspension control device according to the embodiment; FIG. [Figure 6] FIG. 2 is a diagram showing a first example of a control block of a vibration isolation control unit in the suspension control device according to the embodiment. [Figure 7] FIG. 4 is a diagram showing a second example of a control block of a vibration isolation control unit in the suspension control device according to the embodiment. [Figure 8] 2 is a diagram showing a control block of a switching unit of a vibration isolation control unit in the suspension control device according to the embodiment; FIG. [Figure 9] FIG. 10 is a diagram showing detected road surface displacements and positions. [Figure 10] FIG. 10 is a diagram showing the relationship between the level and distribution of estimated suspension vibration values. [Figure 11] 3 is a diagram showing a control block of a switching unit of a final command calculation unit in the suspension control device according to the embodiment; FIG. [Figure 12] 3 is a flowchart showing an example of a processing procedure in the suspension control device according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0018] The present invention will be described below based on the embodiments shown in the drawings. As shown in Fig. 1, a suspension control device C in one embodiment controls a suspension device S that is interposed between a vehicle body B and a wheel W of a vehicle V and that applies a vertical force to the vehicle body B to suppress vibration of the vehicle body B, thereby suppressing vibration of the vehicle body B. In the following description, the subscripts of the suspension device S and the wheel W are as follows: fl indicates the front left side, fr indicates the front right side, rl indicates the rear left side, and rr indicates the rear right side, and the subscripts will be omitted when there is no need to particularly distinguish between the installation locations of the suspension device S and the wheel W.

[0019] The suspension units Sfl, Sfr, Srl, and Srr are arranged in parallel with the suspension springs SP and are interposed at four locations between the vehicle body B and the four wheels W (front, rear, left, and right), and are, for example, adjustable damping force dampers that can adjust the damping force generated when they extend or retract. Note that the suspension unit S may also be a telescopic cylinder or an electric linear actuator that can adjust thrust using hydraulic or pneumatic pressure. The suspension unit S includes a solenoid valve for adjusting the damping force and a driver for driving the solenoid valve, and is driven to extend or retract in response to a control command input from the suspension control device C. Thus, when the suspension units Sfl, Sfr, Srl, and Srr receive the final control command F_ref calculated by the suspension control device C, they exert the damping force indicated by the final control command F_ref to suppress vibration of the vehicle body B.

[0020] The suspension control device C includes four acceleration sensors G that detect the vertical acceleration α of the vehicle body B, which is the sprung member immediately above the four suspension devices Sfl, Sfr, Srl, and Srr, a preview sensor P that detects road surface displacement in front of the vehicle V, four stroke sensors H that detect the displacement X of each of the suspension devices Sfl, Sfr, Srl, and Srr, and a control calculation device U that calculates a final control command F_ref from the vertical acceleration α and the displacement X. Each of the four suspension devices Sfl, Sfr, Srl, and Srr on the vehicle V is paired with an acceleration sensor G immediately above the suspension device Sfl, Sfr, Srl, and Srr and a stroke sensor H corresponding to the suspension device S, and the suspension control device C processes the information detected by the acceleration sensors G and stroke sensors H to calculate the final control command F_ref, which is used to control the suspension devices Sfl, Sfr, Srl, and Srr that form the pair. Furthermore, when explaining the control of suspension units Sfl, Sfr, Srl, and Srr, only when it is necessary to distinguish between the acceleration sensor G, the stroke sensor H, and the control commands will it be clearly stated which of the suspension units Sfl, Sfr, Srl, and Srr it is controlling; in other cases, no subscript will be added to the symbol for suspension unit S.

[0021] The acceleration sensors G are respectively provided directly above the four suspension units Sfl, Sfr, Srl, and Srr, which are the control targets of the vehicle body B, and input the detected vertical acceleration α of the vehicle body B to the control and calculation unit U. The stroke sensor H detects the displacement X in the extension / contraction direction of each suspension unit Sfl, Sfr, Srl, and Srr, and inputs this to the control and calculation unit U. If the vehicle body B is considered to be a rigid body, and three acceleration sensors G are installed on the vehicle body B so as not to be aligned on the same line, the vertical acceleration of the units directly above the four suspension units Sfl, Sfr, Srl, and Srr of the vehicle body B can be calculated from the accelerations detected by the three acceleration sensors G. Therefore, it is also possible to provide only three acceleration sensors G on the vehicle body B to detect the vertical acceleration of the vehicle body B directly above the suspension units Sfl, Sfr, Srl, and Srr. In this case, the suspension control device C processes the vertical acceleration of the vehicle body B directly above the suspension devices Sfl, Sfr, Srl, Srr and information detected by the stroke sensors H corresponding to the suspension devices Sfl, Sfr, Srl, Srr to determine the final control command F_ref and control the suspension devices Sfl, Sfr, Srl, Srr.

[0022] As shown in FIG. 1, the preview sensor P is provided at the front end of the vehicle body B, and detects road surface displacement on the road surface at a position in front of the vehicle V and a predetermined distance L from the front end of the vehicle V in order to detect road surface displacement along which the vehicle V will travel. The preview sensor P is capable of detecting road surface displacement ahead of the vehicle V over a range extending in the width direction of the vehicle V so as to detect road surface displacement within a range through which the vehicle V may pass due to steering by the occupant. The preview sensor P may be any sensor that can detect road surface displacement ahead at a position distant from the vehicle V, and examples of sensors that can be used include millimeter-wave radar, microwave radar, laser radar, optical camera, ultrasonic sonar, and infrared sensor. The preview sensor P may be installed at a position on the vehicle body B other than the front end as long as it can detect road surface displacement.

[0023] As shown in FIG. 2, the control calculation device U is configured to include a road following control unit U1 that determines a road following control command FC, a vibration isolation control unit U2 that determines a vibration isolation control command FI, a switching unit U3 that determines the allocation between the road following control command FC and the vibration isolation control command FI, and a final command calculation unit U4 that determines a final control command F_ref from the road following control command FC, the vibration isolation control command FI, and the allocation determined by the switching unit U3.

[0024] In detail, as shown in FIG. 3, the road surface following control unit U1 includes a differentiator 10 that differentiates the displacement X detected by the stroke sensor H, a low-pass filter 11 that extracts the low-frequency component dX_low of the extension / retraction speed dX, a multiplier 12 that multiplies the low-frequency component dX_low of the extension / retraction speed by a damping coefficient, an integrator 13 that integrates the vertical acceleration α, a multiplier 14 that multiplies the vertical speed Bv by a skyhook gain (skyhook damping coefficient), and an adder 15 that adds the values ​​output by the multipliers 12 and 14 to obtain a road surface following control command FC.

[0025] The differentiator 10 differentiates the displacement X detected by the stroke sensor H to determine the extension / contraction speed dX of the suspension unit S. The integrator 13 integrates the vertical acceleration α to determine the vertical velocity Bv of the vehicle body B. The information required by the road-following control unit U1 to perform road-following control is the extension / contraction speed dX of the suspension unit S and the vertical velocity Bv of the vehicle body B. Since the extension / contraction speed dX of the suspension unit S is equal to the relative vertical velocity between the vehicle body B (the sprung member) and the wheel W (the unsprung member), the suspension control unit C may obtain the extension / contraction speed dX from the difference between the vertical velocity Bv of the vehicle body B and the vertical velocity of the wheel W. To obtain the vertical velocity of the wheel W, an acceleration sensor may be installed on the knuckle or suspension arm that supports the wheel W, or on a part of the suspension unit S that is connected to the wheel W side and moves up and down together with the wheel W. The vertical acceleration of the wheel W may then be obtained and integrated. In this way, an acceleration sensor may be installed instead of the stroke sensor H to obtain the extension / contraction speed dX. Furthermore, since the vertical velocity Bv of the vehicle body B can be obtained by adding the extension / retraction velocity dX of the suspension device S to the vertical velocity of the wheel W, the suspension control device C may eliminate the acceleration sensor G provided on the vehicle body B and provide an acceleration sensor on the wheel W to obtain the vertical velocity Bv of the vehicle body B.

[0026] The low-pass filter 11 filters the extension / contraction speed dX output by the differentiator 10 to extract the low-frequency component dX_low of the extension / contraction speed. The cutoff frequency fcut of the low-pass filter 11 is set so that fcut≦fw, where fw is the unsprung resonance frequency. Therefore, the low-pass filter 11 removes high-frequency components including the unsprung resonance frequency fw from the extension / contraction speed dX. More specifically, the cutoff frequency fcut of the low-pass filter 11 in this embodiment is set so that fb≦fcut≦fw, where fb is the sprung resonance frequency. Therefore, in this embodiment, the low-frequency component dX_low of the extension / contraction speed dX extracted by the low-pass filter 11 is a signal in which the high-frequency side above the sprung resonance frequency fb has been removed from the extension / contraction speed dX.

[0027] Multiplier 12 multiplies the low-frequency component dX_low extracted by low-pass filter 11 by damping coefficient Clow to obtain low-frequency control command Flow. Meanwhile, multiplier 14 multiplies vertical velocity Bv by skyhook gain Csky to obtain skyhook control command Fsky. Note that integrating vertical acceleration α with integrator 13 removes some high-frequency components, so vertical velocity Bv is not filtered. However, since the vertical velocity Bv in the sprung resonance frequency band is the preferred information for obtaining skyhook control command Fsky, vertical velocity Bv may be processed with a bandpass filter or low-pass filter to extract the vertical velocity Bv in the sprung resonance frequency band, and then multiplied by skyhook gain Csky to obtain skyhook control command Fsky. Adder 15 then adds the obtained low-frequency control command Flow and skyhook control command Fsky to obtain road-following control command FC.

[0028] The low-frequency control command Flow is a command obtained by multiplying the low-frequency component dX_low of the extension / contraction speed of the suspension unit S by the damping coefficient Clow, and therefore is a command that reduces the damping force generated when the suspension unit S extends or contracts at high frequencies, but increases the damping force generated when the suspension unit S extends or contracts at low frequencies. In other words, when the cycle of road surface displacement is short, the low-frequency control command Flow makes it easier for the suspension unit S to extend or contract, making it less likely that vibrations input from the road surface will be transmitted to the vehicle body B. On the other hand, when the cycle of road surface displacement is long, the low-frequency control command Flow makes it harder for the suspension unit S to extend or contract, preventing fluctuations in the distance between the road surface and the vehicle body B, and causing the vehicle body B to follow the road surface displacement.

[0029] On the other hand, the skyhook control command Fsky is a command obtained by multiplying the vertical velocity Bv by the skyhook gain Csky, and is therefore a command to increase the damping force generated by the suspension device S in proportion to the vertical velocity Bv of the vehicle body B. In other words, the skyhook control command Fsky causes the suspension device S to exert a damping force proportional to the magnitude of the vibration of the vehicle body B, thereby suppressing the vibration of the vehicle body B.

[0030] The road following control command FC is a control command obtained by adding the low-frequency control command Flow and the skyhook control command Fsky. When the suspension control device C controls the suspension device S using the road following control command FC, the suspension device S exerts a force that reduces vibration of the vehicle body B while making the vehicle body B follow the displacement of the road surface.

[0031] When the suspension control device C controls the suspension device S (road surface following control) by giving only the road surface following control command FC to the suspension device S, the vibration transmission gain from the road surface input to the vehicle body B has a characteristic such that the gain is close to 0 dB in the sprung resonance frequency band, so that the vehicle body B follows the road surface displacement, and the gain decreases in the unsprung resonance frequency band, so that the vibration to the vehicle body B is insulated, as shown in Figure 4. In other words, the vehicle body B follows the road surface in the sprung resonance frequency band, but vibrations in the unsprung resonance frequency band are insulated.

[0032] The proportion of low-frequency control and skyhook control can be adjusted by the ratio between the damping coefficient Clow when calculating the low-frequency control command Flow and the skyhook gain Csky when calculating the skyhook control command Fsky, and the damping coefficient Clow and the skyhook gain Csky are set to suit the vehicle V. Furthermore, if a road following control command FC is obtained based on the low-frequency control command Flow and the skyhook control command Fsky and the suspension device S is controlled by the road following control command FC, the vehicle body B can follow the road surface in the sprung resonance frequency band while suppressing the transmission of vibrations in the unsprung resonance frequency band to the vehicle body B.

[0033] The vibration isolation control unit U2 calculates a vibration isolation control command FI. When the suspension control device C controls the suspension device S by providing only the vibration isolation control command FI to the suspension device S (vibration isolation control), the vibration transmission gain from the road surface input to the vehicle body B has a characteristic such that the gain takes a negative value in the sprung resonance frequency band and then decreases even after the unsprung resonance frequency band is exceeded, as shown in Fig. 5, so that vibration from the road surface to the vehicle body B is isolated in the sprung resonance frequency band and the unsprung resonance frequency band.

[0034] The vibration isolation control command FI only needs to be a control command that can isolate vibrations from the vehicle body B in the sprung resonant frequency band and the unsprung resonant frequency band. To obtain such characteristics, for example, as shown in Fig. 6, the vibration isolation control unit U2 may include a first command calculation unit 21 that multiplies the vertical velocity Bv of the vehicle body B by a damping coefficient to obtain a first command, a second command calculation unit 22 that calculates a second command from the displacement of the wheel W to cancel out the force of the suspension spring SP that vibrates the vehicle body B due to the displacement of the wheel W, and an adder 23 that adds together the first command and the second command to obtain the vibration isolation control command FI.

[0035] The displacement of the wheel W may be obtained by adding the displacement X of the suspension device S detected by the stroke sensor H to the vertical displacement of the vehicle body B obtained by second-order integration of the vertical velocity Bv of the vehicle body B detected by the acceleration sensor G, or by detecting the vertical acceleration of the wheel W with an acceleration sensor and second-order integration of this vertical acceleration. Note that the first command calculation unit 21 calculates a first command to suppress vibration of the vehicle body B, which is a sprung member, so the first command may be obtained by processing the vertical velocity Bv with a band-pass filter or a low-pass filter to extract the vertical velocity Bv in the sprung resonance frequency band and then multiplying it by a damping coefficient. Note that the second command calculation unit 22 calculates the second command from the displacement of the wheel W, which is an unsprung member, so the second command may be obtained by processing the displacement of the wheel W with a band-pass filter or a low-pass filter to extract the displacement in the unsprung resonance frequency band.

[0036] 7, the vibration isolation control unit U2 may include a third command calculation unit 24 that calculates a third command by multiplying the vertical velocity Bv of the vehicle body B by a damping coefficient, a fourth command calculation unit 25 that calculates a fourth command by multiplying the vertical velocity of the wheel W by a damping coefficient, and an adder 26 that adds the third command and the fourth command to calculate a vibration isolation control command FI. Note that the third command calculation unit 24 calculates the third command to suppress vibration of the vehicle body B, which is a sprung member, so it may process the vertical velocity Bv with a band-pass filter or a low-pass filter to extract the vertical velocity Bv in the sprung resonance frequency band and then multiply it by the damping coefficient to obtain the third command. Note that the fourth command calculation unit 25 calculates the fourth command from the vertical velocity of the wheel W, which is an unsprung member, so it may process the vertical velocity of the wheel W with a band-pass filter or a low-pass filter to extract the vertical velocity in the unsprung resonance frequency band and then multiply it by the damping coefficient to obtain the fourth command.

[0037] When the suspension control device C issues only the vibration isolation control command FI to the suspension device S, it makes it easier for the suspension device S to expand and contract in response to vibrations from the wheel W side, suppressing vertical fluctuations of the vehicle body B and maintaining the vehicle body B at a constant height regardless of road surface displacement. Therefore, when the road surface is good and has few irregularities, if the suspension control device C performs vibration isolation control, control is executed to prevent the height of the vehicle body B from changing, improving the ride comfort of the vehicle V. However, when the suspension control device C only performs vibration isolation control, when the wheel W goes over an irregularity during high-speed driving or when entering a slope, the height of the vehicle body B tends to not change, and the stroke amount of the suspension device S tends to increase. In contrast, when the suspension control device C issues only the road surface following control command FC to the suspension device S, it makes it harder for the suspension device S to expand and contract in response to input of high-frequency vibrations, while making it harder for the vibrations to be transmitted to the vehicle body B, preventing fluctuations in the distance between the road surface and the vehicle body B and allowing the vehicle body B to follow road surface displacement. Therefore, when the suspension unit S performs road surface following control, when the wheel W goes over an uneven surface during high-speed travel or when going up a slope, the suspension unit S is made less likely to expand or contract, preventing the stroke amount from increasing and reducing vibration. In this way, when the wheel W goes over an uneven surface during high-speed travel or when going up a slope, the suspension control unit C can improve the ride comfort of the vehicle V by performing road surface following control.

[0038] Next, the switching unit U3 determines the allocation of the road surface following control command FC and the vibration isolation control command FI. When the suspension unit S is not in a situation where it will fully extend or compress after full stroke, that is, when the stroke amount of the suspension unit S is small and there is no risk of it reaching its full stroke, it is possible to maintain good ride comfort in the vehicle V by isolating the transmission of vibration from the road surface and suppressing the vibration of the vehicle body B. On the other hand, when the vehicle V is traveling at high speed over an uneven surface and approaches a slope, if the suspension unit S is controlled only by the vibration isolation control command FI, the stroke amount of the suspension unit S will gradually increase, causing the suspension unit S to fully extend or compress, which could result in a deterioration in ride comfort in the vehicle V. Therefore, it is better to increase the allocation of the road surface following control command FC to prevent the suspension unit S from fully extending or compressing, thereby suppressing a deterioration in ride comfort in the vehicle V. Therefore, in the suspension control device C of this embodiment, the switching unit U3 determines the allocation of the road surface following control command FC and the vibration isolation control command FI by obtaining an index for estimating the stroke amount of the suspension unit S.

[0039] Specifically, as shown in FIG. 8, the switching unit U3 includes a prediction unit 31 that predicts the road surface on which the four wheels Wfl, Wfr, Wrl, and Wrr will travel, an index calculation unit 32 that calculates a road surface index RI, which is the rate of change of the rate of change of the road surface index with respect to the distance, by second-order differentiation of a moving average of road surface displacements Z that are predicted by the prediction unit 31 to be traveled by each wheel Wfl, Wfr, Wrl, and Wrr from among the road surface displacements detected by the preview sensor P, a conversion unit 33 that converts the road surface index RI into a time unit by dividing the road surface index RI by the traveling speed of the vehicle V, and a suspension vibration estimation unit 34 that multiplies the road surface index RI converted into time units by the conversion unit 33 by the traveling speed of the vehicle V to calculate an estimated suspension vibration value SV. a distribution calculation unit 36 ​​that calculates a pre-selection distribution, which is a distribution of the road surface following control command FC and the vibration isolation control command FI for each of the four wheels Wfl, Wfr, Wrl, and Wrr, based on the magnitude of the suspension vibration estimated value SV calculated by the level calculation unit 35; a selection unit 37 that selects the pre-selection distribution that maximizes the proportion of the road surface following control command FC from the four pre-selection distributions calculated by the distribution calculation unit 36; and a final distribution calculation unit 38 that processes the distribution selected by the selection unit 37 using a low-pass filter whose cutoff frequency changes according to the traveling speed of the vehicle V, and calculates a final distribution for each of the four wheels Wfl, Wfr, Wrl, and Wrr.

[0040] When the ignition key of the vehicle V is turned on, the preview sensor P constantly detects road surface displacement Z at a position a predetermined distance L away from the vehicle V at a predetermined sampling rate. Note that the preview sensor P may be configured to detect the road surface displacement Z only when the vehicle V is traveling. The road surface displacement detected by the preview sensor P is associated with the longitudinal and lateral positions of the vehicle V relative to the vehicle V and temporarily stored and updated in a storage device in the hardware constituting the suspension control device C. Therefore, for example, as shown in FIG. 9, the road surface displacement Z at a position indicated by a black dot in FIG. 9 between the distance L ahead of the vehicle V and the vehicle V is detected by the preview sensor P and is known. The road surface displacement Z is then paired with the longitudinal coordinate and the lateral coordinate of the vehicle V and stored in the storage device. Note that the preview sensor P is also capable of detecting road surface displacement Z in the lateral direction of the vehicle V at a position a predetermined distance L away from the front of the vehicle V, but the preview sensor P may also be a sensor having a detection range in all directions, front to back, left to right, with the predetermined distance L as its center. Since the road surface displacement data becomes unnecessary after the vehicle V has traveled over the road surface, the unnecessary road surface displacement Z data is updated with new road surface displacement Z data, and the storage device should have a sufficient storage capacity to temporarily store the road surface displacement Z data along which the vehicle V travels. Based on the detection by the preview sensor P, data on road surface displacements in the ranges ahead of the vehicle V and in the front, rear, left and right directions is stored.

[0041] The prediction unit 31 predicts, from the road surface displacement detected by the preview sensor P, the longitudinal and lateral coordinates of the road surface on which each of the wheels Wfl, Wfr, Wrl, and Wrr of the vehicle V will travel, with the vehicle V as the reference. Specifically, while the vehicle V is turning, the turning trajectory of the vehicle V changes depending on the traveling speed and steering angle, so the prediction unit 31 obtains information on the traveling speed and steering angle from the vehicle V and predicts the longitudinal and lateral coordinates of the road surface on which the vehicle V will travel. Since there is a correlation between the traveling speed, the steering angle, and the traveling trajectory of each of the wheels Wfl, Wfr, Wrl, and Wrr of the vehicle V, for example, the prediction unit 31 may extract the road surface coordinates on the traveling trajectory from the traveling speed and the steering angle based on the correlation that has been determined in advance. In addition, since the vehicle V has sensors installed therein that detect the vehicle V's traveling speed and steering angle and transmit the information to the vehicle V's ECU via the CAN bus, the suspension control device C of this embodiment is configured to obtain the information required by the prediction unit 31 from the CAN bus, but may also be provided with a separate vehicle speed sensor that detects the vehicle speed and a steering angle sensor that detects the steering angle. Furthermore, the prediction unit 31 may predict the road surface coordinates using the yaw rate of the vehicle V instead of the steering angle. The prediction unit 31 predicts the road surface coordinates on which each wheel Wfl, Wfr, Wrl, and Wrr travels in sequence for each control cycle of the suspension control device C, depending on the traveling conditions of the vehicle V. Since the vehicle V moves forward while traveling, the prediction unit 31 predicts road surface coordinates slightly ahead of the road surface coordinates predicted by the prediction unit 31 in the previous control cycle.

[0042] Next, the index calculation unit 32 calculates a road surface index RI, which is the rate of change of the rate of change of the road surface displacement Z with respect to distance, by second-order differentiation of the moving average of the road surface displacement Z predicted by the prediction unit 31 to be traveled by each wheel Wfl, Wfr, Wrl, and Wrr. When calculating the road surface index RI for the road surface coordinate of the road surface on which the front left wheel Wfl is travelling, the index calculation unit 32 first calculates the moving average of a predetermined number N of road surface displacements Z at the road surface coordinate on which the prediction unit 31 predicted that the wheel Wfl will travel. Specifically, the index calculation unit 32 extracts a predetermined number N of road surface displacements Z from the road surface displacement Z at a predetermined distance away from the vehicle V as the starting point, moving backwards or forwards toward the vehicle V, among the road surface displacements Z at the road surface coordinate on the trajectory on which the wheel Wfl is travelling, adds up these N road surface displacements Z, and divides the sum by N to calculate the moving average. When calculating the value of the moving average, the index calculation unit 32 may extract a predetermined number N of road surface displacements Z from among the road surface displacements Z of the road surface coordinates on the trajectory along which the wheels Wfl are traveling, starting with the most recent road surface displacement Z detected by the preview sensor P and going back toward the vehicle V, or the predetermined distance may be changed as desired and may be variable according to the traveling speed of the vehicle V. In this way, when the index calculation unit 32 calculates the moving average of the road surface displacements Z, as the vehicle V moves forward while traveling, the road surfaces belonging to the predetermined number N are updated and replaced, and the value changes depending on the properties of the road surface. The value of the predetermined number N may be set as desired, provided it is equal to or less than the number of road surface coordinates of the road surface displacements Z along which the wheels Wfl are predicted to travel as detected by the preview sensor P.

[0043] The index calculation unit 32 then calculates the road surface index RI of the road surface on which the wheel Wfl is traveling by second-order differentiating the moving average value calculated as described above with respect to the distance. The road surface index RI is calculated for each of the wheels Wfl, Wfr, Wrl, and Wrr.

[0044] When the index calculation unit 32 calculates the moving average of the road surface displacement Z, the value of the moving average is an averaged value that reduces the effects of sudden changes and noise in the road surface displacement Z. Therefore, by the index calculation unit 32 calculating the moving average of the road surface displacement Z, it becomes possible to accurately determine whether the road surface on which the vehicle V is about to travel has large irregularities or the start of a slope that will increase the stroke amount of the suspension device S.

[0045] Furthermore, the index calculation unit 32 obtains the rate of change of the moving average rate of change of the road surface displacement Z at a position that is a distance obtained by adding the distance from the front end of the vehicle V to each wheel Wfl, Wfr, Wrl, Wrr to a predetermined distance L from the current positions of the wheels Wfl, Wfr, Wrl, Wrr of the vehicle V. Then, the rate of change of the rate of change of the moving average of the road surface displacement Z is set as the road surface index RI.

[0046] Because the road surface index RI is the rate of change of the rate of change of the road surface displacement Z, the absolute value of the road surface index RI tends to increase at the start of a large unevenness or slope where the road surface displacement Z increases or decreases. In contrast, the value obtained by first-order differentiation of the moving average of the road surface displacement Z always becomes large when the vehicle V is continuously traveling up a slope. The stroke amount of the suspension unit S does not become very large when the vehicle V is continuously traveling up a slope, but becomes large when the vehicle V enters a slope. The road surface index RI is an index for determining the allocation of the road following control command FC and the vibration isolation control command FI, and since it is desirable to adopt the road following control command FC in situations where the stroke amount of the suspension unit S is large, it is preferable that the road surface index RI be an index that can accurately determine the stroke amount of the suspension unit S. Even if the value of the moving average or the value obtained by first-order differentiation of the moving average is used as the road surface index RI, it is possible to grasp the starting points of large unevenness or slopes, so these may be used as the road surface index RI, but the value obtained by second-order differentiation of the moving average tends to be larger at the starting points of large unevenness or slopes, so it is optimal as the road surface index RI for determining the distribution. Note that the number of samples required for the moving average, that is, the number N, can be set arbitrarily, but if the resolution in the longitudinal direction of the vehicle V is coarse, the number N may be made extremely small.

[0047] Furthermore, in this embodiment, the index calculation unit 32 obtains the road surface index RI by second-order differentiation of the moving average value of the road surface displacement Z with respect to distance, but it is also possible to obtain a moving average value of the second-order differentiation of the road surface displacement Z with respect to distance, and use this moving average value as the road surface index RI. Furthermore, instead of obtaining the moving average of the road surface displacement Z, the index calculation unit 32 may obtain the road surface index RI by second-order differentiation of a value obtained by processing the road surface index Z with a low-pass filter, or may obtain the road surface index RI by second-order differentiation of the road surface index Z and then processing it with a low-pass filter. By processing the road surface displacement Z with a low-pass filter, a value in which the effects of sudden changes in the road surface displacement Z and noise are mitigated is obtained, so it is possible to obtain a road surface index RI that is equivalent to the case in which the road surface index RI is obtained by performing a moving average.

[0048] Once the road surface index RI is calculated by the index calculation unit 32, the conversion unit 33 converts the road surface index RI into a value in time units by dividing the road surface index RI by the traveling speed of the vehicle V. The road surface index RI is a value obtained by differentiating the road surface displacement Z with respect to distance, and is therefore the rate of change of the moving average rate of change of the road surface displacement Z at positions that are a distance away from the current positions of the wheels Wfl, Wfr, Wrl, and Wrr of the vehicle V that is the sum of a predetermined distance L from the current positions of the wheels Wfl, Wfr, Wrl, and Wrr of the vehicle V and the distances from the front end of the vehicle V to the four wheels Wfl, Wfr, Wrl, and Wrr. When the time comes for the wheel W to travel on a road surface for which the road surface index RI has been obtained in a certain control cycle, the allocation of the road following control command FC and the vibration isolation control command FI can be controlled as an allocation calculated from the road surface index RI by processing described below. However, the timing at which the road surface index RI is calculated occurs before the wheel W travels on the road surface coordinates corresponding to the road surface index RI. Since it is easier to treat the road surface index RI based on time rather than distance, in the suspension control device C of this embodiment, the conversion unit 33 divides the road surface index RI by the driving speed and converts the units of the road surface index RI obtained for each of the four wheels Wfl, Wfr, Wrl, and Wrr into time units.

[0049] The suspension vibration estimator 34 multiplies the road surface index RI calculated for each of the four wheels Wfl, Wfr, Wrl, and Wrr, converted into time units by the converter 33, by the traveling speed of the vehicle V, to calculate the suspension vibration estimate SV for each of the four wheels Wfl, Wfr, Wrl, and Wrr. Because the road surface index RI is the rate of change of the rate of change of the road surface displacement Z, the suspension vibration estimator 34 can be omitted and the road surface index RI can be used directly to calculate the distribution, but the stroke of the suspension unit S tends to increase due to input from the road surface the higher the traveling speed of the vehicle V. Therefore, the suspension vibration estimate SV calculated by multiplying the road surface index RI by the vehicle speed is a more optimal value for determining the magnitude of the stroke of the suspension unit S than the road surface index RI.

[0050] If left as is, the estimated suspension vibration value SV will exhibit a negative value when the road surface displacement Z decreases, that is, when the road surface height decreases. Furthermore, when the crest value of the estimated suspension vibration value SV becomes high, it is highly likely that the vehicle is going over an uneven road surface while traveling at high speed or that the vehicle is at the start of a slope, and the stroke of the suspension unit S will also become large. While the estimated suspension vibration value SV is fluctuating with a large amplitude, there are times when the estimated suspension vibration value SV becomes small, but even in such cases the stroke of the suspension unit S will become large. Therefore, to more accurately grasp the stroke of the suspension unit S, it is sufficient to determine the level, which is the magnitude of the amplitude of the estimated suspension vibration value SV. Therefore, the level calculation unit 35 calculates the level of each of the four estimated suspension vibration values ​​SV calculated for each of the four wheels Wfl, Wfr, Wrl, and Wrr.

[0051] Specifically, the level calculation unit 35 uses the signal of the estimated suspension vibration value SV calculated by the suspension vibration estimator 34 as an original signal, generates a plurality of signals that differ only in phase from the original signal without changing the gain, and sets the maximum value of the plurality of signals that differ in phase from the original signal as the level value of the estimated suspension vibration value SV. If a plurality of signals whose phases are shifted by a predetermined angle from the original signal are generated and the maximum value is selected from these signals, this maximum value will be a value that approximates the peak value of the original signal, making it possible to calculate the level value in a timely manner. Note that the level calculation unit 35 may also calculate the envelope of the estimated suspension vibration value SV of the signal by processing such as peak hold or Hilbert transform to calculate the level, or may calculate the length of a composite vector of the estimated suspension vibration value SV and its derivative or integral value as the level.

[0052] The allocation calculation unit 36 ​​calculates a pre-selection allocation, which is an allocation between the road following control command FC and the vibration isolation control command FI for each of the four wheels Wfl, Wfr, Wrl, and Wrr, based on the level of the suspension vibration estimated value SV calculated by the level calculation unit 35. The level of the suspension vibration estimated value SV is an index that indicates the magnitude of the stroke amount of the suspension unit S, and as described above, when the stroke amount of the suspension unit S is large, increasing the proportion of the road following control command FC improves the ride comfort of the vehicle V, and when the stroke amount of the suspension unit S is small, increasing the proportion of the vibration isolation control command FI improves the ride comfort of the vehicle V.

[0053] Therefore, the allocation calculation unit 36 ​​determines the pre-selection allocation using an upper threshold t1 and a lower threshold t2 that are set for the level of the suspension vibration estimated value SV. As shown in Fig. 10 , when the level of the suspension vibration estimated value SV exceeds the upper threshold t1, the allocation calculation unit 36 ​​sets the allocation of the road following control command FC to 100% and the pre-selection allocation of the vibration isolation control command FI to 0%. When the level of the suspension vibration estimated value SV falls below the lower threshold t2, the allocation calculation unit 36 ​​sets the allocation of the road following control command FC to 0% and the pre-selection allocation of the vibration isolation control command FI to 100%. When the level of the suspension vibration estimated value SV is equal to or greater than the lower threshold t2 and equal to or less than the upper threshold t1, the allocation calculation unit 36 ​​increases the pre-selection allocation of the road following control command FC in proportion to the level. The upper threshold t1 and the lower threshold t2 may be determined based on the relationship between the level of the suspension vibration estimated value SV and the actual stroke amount of the suspension unit S, and the upper threshold t1 is set to a value that is at least smaller than the level at which the suspension unit S is considered to be at full stroke.

[0054] The pre-selection allocation can be regarded as a gain by which the road following control command FC and the vibration isolation control command FI are multiplied, and therefore, specifically, the allocation calculation unit 36 ​​determines the gain K1 by which the road following control command FC should be multiplied from the value of the level of the suspension vibration estimated value SV, where K1 is a value between 0 and 1.

[0055] The allocation calculation unit 36 ​​calculates the pre-selection allocation based on the level of the suspension vibration estimated value SV calculated by the level calculation unit 35, but the pre-selection allocation may also be calculated based on the level, which is the road surface index RI or the amplitude of the road surface index RI.

[0056] The selection unit 37 selects a pre-selection distribution that maximizes the ratio of the road following control command FC from the pre-selection distributions of the four wheels Wfl, Wfr, Wrl, and Wrr calculated by the distribution calculation unit 36. That is, the selection unit 37 selects the largest gain K1 from the gains K1 of the four pre-selection distributions as the distribution to be used for control. Since the selection unit 37 selects one distribution from the four pre-selection distributions in this way, it is possible to prevent inconsistent control of the four wheels Wfl, Wfr, Wrl, and Wrr with different distributions of the road following control command FC and the vibration isolation control command FI.

[0057] In the suspension control device C of this embodiment, the final allocation calculation unit 38 is configured with a low-pass filter whose cutoff frequency changes according to the traveling speed of the vehicle V. The final allocation calculation unit 38 low-pass filters the allocation selected by the selection unit 37 to determine the final allocation for each of the four wheels Wfl, Wfr, Wrl, and Wrr. The faster the traveling speed of the vehicle V, the shorter the time that the wheel W travels on the road surface for which the road surface index RI has been determined. Since the delay caused by the low-pass filter occurs in the stop band, the higher the traveling speed, the shorter the delay time of the allocation processed by the low-pass filter. Therefore, for example, if the cutoff frequency is f2cut, the minimum cutoff frequency is f2cut_low, and the traveling speed is Vv, the cutoff frequency fcut of the low-pass filter can be changed according to the traveling speed Vv by calculating f2cut=f2cut_low+m·Vv (m is an arbitrary coefficient). The above-mentioned formula for calculating the cutoff frequency fcut from the traveling speed Vv is only an example, and the formula can be changed to be optimal for the suspension control device C.

[0058] Furthermore, the final allocation calculation unit 38 performs low-pass filtering on the allocation selected by the selection unit 37, thereby mitigating sudden changes in the allocation. Note that if there is no risk of a sudden change in the allocation, the final allocation calculation unit 38 may calculate the final allocation with a delay equivalent to the time it takes for the wheels W to travel on the road surface for which the road surface index RI has been calculated. The switching unit U3 calculates the final allocation for each predetermined control cycle, but the calculated final allocation may be temporarily stored in a storage device, and the temporarily stored final allocation may be adopted as the final allocation to be used in the current control once the time has elapsed for the wheels W to travel on the road surface for which the road surface index RI has been calculated according to the vehicle speed.

[0059] As described above, the switching unit U3 increases the allocation of the road surface following control command FC when the index indicating the stroke amount of the suspension device S increases, and decreases the allocation of the road surface following control command FC when the index indicating the stroke amount of the suspension device S decreases.

[0060] As shown in FIG. 11, the final command calculation unit U4 includes a calculation unit 41 that calculates K2=1-K1 to determine a gain K2 to be multiplied by the vibration isolation control command FI from a gain K1 indicating the distribution of the road surface following control command FC determined by the switching unit U3, a multiplication unit 42 that multiplies the gain K1 indicating the distribution of the road surface following control command FC determined by the switching unit U3 by the road surface following control command FC, a multiplication unit 43 that multiplies the gain K2 determined by the calculation unit 41 by the vibration isolation control command FI, and an addition unit 44 that adds the values ​​output by the multiplication unit 42 and the multiplication unit 43 to determine the final control command F_ref.

[0061] Therefore, when the gain K1 is a value greater than 0 and less than 1, the final command calculation unit U4 increases the allocation of the road surface following control command FC relative to the vibration isolation control command FI as the value of the gain K1 increases, and increases the allocation of the vibration isolation control command FI relative to the road surface following control command FC as the value of the gain K1 decreases. Also, when the value of the gain K1 is 1, the final command calculation unit U4 sets the allocation of the vibration isolation control command FI to 0, and uses the road surface following control command FC as the final control command F_ref as is. On the other hand, when the value of the gain K1 is 0, the final command calculation unit U4 sets the allocation of the road surface following control command FC to 0, and uses the vibration isolation control command FI as the final control command F_ref as is.

[0062] From the above, when the stroke amount of the suspension unit S is estimated to be small, the final command calculation unit U4 increases the allocation of the vibration isolation control command FI and calculates a final control command F_ref that prioritizes the vibration isolation control command FI over the road following control command FC. On the other hand, when the stroke amount of the suspension unit S is estimated to be large, the final command calculation unit U4 increases the proportion of the road following control command FC and calculates a final control command F_ref that prioritizes the road following control command FC over the vibration isolation control command FI. This final control command F_ref is a command that indicates the magnitude and direction of the thrust that the suspension unit S should output, and is input to the suspension unit S.

[0063] In this way, the suspension control device C in this embodiment calculates the final control command F_ref based on the vertical acceleration α of the vehicle body B and the displacement X of the suspension device S, and inputs the final control command F_ref to a driver (not shown) of the suspension device S. The suspension device S exerts a thrust force instructed by the final control command F_ref.

[0064] As shown in FIG. 12, while the vehicle V is traveling, the suspension control device C detects the vertical acceleration α of the vehicle body B using the acceleration sensor G and detects the displacement X of the suspension device S using the stroke sensor H (step F1). Next, the suspension control device C calculates a road-following control command FC based on the vertical acceleration α and the displacement X (step F2), and further calculates a vibration isolation control command FI based on the vertical acceleration α and the displacement X (step F3). The suspension control device C also calculates a distribution (gains K1, K2) based on the road displacement Z detected by the preview sensor P (step F4), and calculates a final control command F_ref based on the road-following control command FC, the vibration isolation control command FI, and the distribution (gain K1) (step F5). The suspension control device C then provides the final control command F_ref to the suspension device S to control the suspension device S (step F6). The suspension control device C repeatedly performs the processes from step F1 to step F6 to control the four suspension devices Sfl, Slr, Srl, and Srr.

[0065] Although not shown, the suspension control device C may be configured with the following hardware resources: an interface for receiving signals output by the acceleration sensor G, stroke sensor H, and preview sensor P; a storage device such as a ROM (Read Only Memory) that stores a program used for processing required to control the suspension device S by receiving the vertical acceleration α and displacement X; an arithmetic unit such as a CPU (Central Processing Unit) that executes processing based on the program; and a storage device such as a RAM (Random Access Memory) that provides a storage area for the CPU. Each component of the control and arithmetic unit U can be realized by the CPU executing the program. Alternatively, the control and arithmetic unit U may be realized by analog electronic circuits instead of by the CPU executing the program.

[0066] The suspension control device C is configured as described above and operates as follows. When the vehicle V travels on a road surface (good road) that is smooth or has only small irregularities, the wheels W, which are unsprung members, vibrate gently in the vertical direction, and the vehicle body B, which is a sprung member, does not vibrate either. In this situation, the value of the road surface index RI becomes small, and the suspension vibration estimate value SV also takes a small value, so the gain K1, which indicates the distribution, takes a value of 0 or near 0, and the gain K2 takes a value of 1 or near 1. When the gain K1 takes a value of 0 or near 0, the proportion of the road following control command FC in the final control command F_ref becomes 0% or close to 0%, so the suspension control device C controls the suspension device S with the final control command F_ref in which the distribution of the vibration isolation control command FI is high. Therefore, when the vehicle V is traveling on a flat or road with few irregularities, the vibration isolation control command FI becomes dominant in the final control command F_ref, and the suspension device S exerts a damping force to isolate vibrations from the road surface, thereby maintaining a good ride comfort in the vehicle.

[0067] On the other hand, when the vehicle V enters a rough road surface (bad road) from a good road, the wheels W begin to vibrate up and down with short periods and small amplitudes. In this situation, the road surface index RI also becomes small, and the estimated suspension vibration value SV also becomes small, so the gain K1, which indicates the distribution, becomes 0 or a value close to 0, and the gain K2 becomes 1 or a value close to 1. When the gain K1 becomes 0 or a value close to 0, the proportion of the road following control command FC in the final control command F_ref becomes 0% or close to 0%, so the suspension control device C controls the suspension device S with the final control command F_ref, which has a high distribution of the vibration isolation control command FI. Therefore, when the vehicle V travels on a rough road surface with bumps and bumps, the vibration isolation control command FI becomes dominant in the final control command F_ref, and the suspension device S exerts a damping force to isolate vibrations from the road surface, thereby maintaining a good ride comfort in the vehicle.

[0068] Furthermore, when the vehicle V goes over an uneven surface or enters a slope while traveling at high speed, the suspension control device C has been controlling the suspension device S based on the final control command F_ref in which the vibration isolation control command FI is dominant up until that point, and therefore if the suspension control device C continues to control the suspension device S based on the final control command F_ref in which the vibration isolation control command FI is dominant, the stroke amount of the suspension device S will increase, which may cause the suspension device S to fully extend or compress, thereby deteriorating the ride comfort of the vehicle V. In such a case, the level of the suspension vibration estimated value SV for the road surface over which the wheels Wfl, Wfr, Wrl, and Wrr of the vehicle V will travel will increase, and the suspension control device C can therefore know in advance that the stroke amount of the suspension device S will increase. When the wheels Wfl, Wfr, Wrl, and Wrr of the vehicle V travel on a road surface that increases the stroke amount of the suspension unit S, the suspension control device C sets the gain K1, which indicates the distribution, to a value of 1 or close to 1, and the gain K2 to a value of 0 or close to 0, so that the proportion of the road following control command FC in the final control command F_ref is 100% or close to 100%. Therefore, in such a situation, the suspension control device C controls the suspension unit S with the final control command F_ref having a high distribution of the road following control command FC. Therefore, when the vehicle V goes over an uneven surface or enters a slope while traveling at high speed, the road following control command FC becomes dominant in the final control command F_ref, increasing the damping force of the suspension unit S and making it difficult for the suspension unit S to expand or contract, thereby preventing the suspension unit S from expanding or contracting to its full extent, and maintaining a good ride comfort in the vehicle.

[0069] Furthermore, since the gain K1, which is the selected allocation, changes in proportion to the level of the suspension vibration estimated value SV, the change in the allocation between the road following control command FC and the vibration isolation control command FI changes gradually according to the level of the suspension vibration estimated value SV. Therefore, when switching between control based on the road following control command FC and control based on the vibration isolation control command FI, one of them fades out while the other fades in, and the final control command F_ref is generated. Therefore, the value of the final control command F_ref does not change suddenly, and the control is seamlessly switched from road following control to vibration isolation control, or from road isolation control to road following control. Furthermore, since the final allocation calculation unit 38 low-pass filters the gain K1, which is the selected allocation, sudden changes in the gain K1 are alleviated, and sudden changes in the value of the final control command F_ref are further alleviated.

[0070] As described above, the suspension control device C of the present invention controls a suspension device S that is interposed between a vehicle body B and a wheel W of a vehicle V and is capable of applying a vertical force to the vehicle body B to suppress vibration of the vehicle body B, and is equipped with a road following control unit U1 that determines a road following control command FC that causes the vehicle body B to follow the road surface in the sprung resonance frequency band, a vibration isolation control unit U2 that determines a vibration isolation control command FI that is a control command that makes it difficult for vibrations from the road surface to be transmitted to the vehicle body B in the unsprung resonance frequency band, a switching unit U3 that determines the allocation of the road following control command FC and the vibration isolation control command FI based on the road surface displacement Z detected by a preview sensor P that detects road surface displacement ahead in the direction of travel of the vehicle V, and a final command calculation unit U4 that determines a final control command F_ref for controlling the suspension device S from the allocation, the road following control command FC, and the vibration isolation control command FI.

[0071] The suspension control device C configured in this manner calculates the final control command F_ref by adjusting the distribution of the road surface following control command FC and the vibration isolation control command FI based on the road surface displacement Z detected by the preview sensor P. Therefore, it is possible to predict road surfaces on which the stroke amount of the suspension device S would increase and the ride comfort of the vehicle V would deteriorate if vibration isolation control alone were used, and to switch between the road surface following control command FC and the vibration isolation control command FI, thereby improving the ride comfort of the vehicle.

[0072] In the suspension control device C of this embodiment, increasing the allocation of the road surface following control command FC increases the force exerted by the suspension device S to cause the vehicle body B to follow the displacement of the road surface in the sprung resonance frequency band, making it difficult for the suspension device S to expand or contract. When the wheels W overcome unevenness in the road surface or when entering a slope while the vehicle V is traveling at high speed, the suspension control device C performs road surface following control to suppress the suspension device S from expanding or contracting to the full extent, thereby maintaining a good ride comfort in the vehicle V. On the other hand, in the suspension control device C of this embodiment, increasing the allocation of the vibration isolation control command FI makes it difficult for vibrations from the road surface to be transmitted to the vehicle body B in the unsprung resonance frequency band, thereby controlling the height of the vehicle body B not to change. Therefore, when the vehicle V is traveling on a good road surface, the suspension control device C suppresses vibrations of the vehicle body B to maintain a good ride comfort in the vehicle V.

[0073] Therefore, according to the suspension control device C of this embodiment, the road surface following control command FC and the vibration isolation control command FI can be used depending on the road surface conditions, thereby improving the ride comfort of the vehicle regardless of the road surface characteristics on which the vehicle V is traveling.

[0074] Furthermore, in the suspension control device C of this embodiment, when calculating the road surface following control command FC, the road surface following control command FC is calculated based on a low-frequency control command Flow that increases the force exerted by the suspension device S in response to vibrations of a frequency lower than the unsprung resonance frequency of the suspension device S, making it difficult for the suspension device S to expand or contract, and a skyhook control command Fsky that suppresses vibration of the vehicle body B, so that the suspension device S exerts a thrust that reduces the vibration of the vehicle body B while making the vehicle body B follow the road surface displacement. Thus, according to the suspension control device C of the present invention, when the distribution of the road surface following control command FC is increased, when going over uneven surfaces during high-speed driving or when entering a slope, the suspension device S is controlled to make the vehicle body B follow the road surface, making it difficult for the suspension device S to expand or contract, which not only prevents the actuator A from reaching full stroke but also prevents the transmission of vibrations of the wheels W to the vehicle body B, thereby further improving the ride comfort of the vehicle V.

[0075] The suspension control device C also has a low-pass filter 11 that processes the extension / contraction speed dX of the suspension device S to obtain low-frequency components, and the cutoff frequency fcut of the low-pass filter 11 is set to be equal to or higher than the sprung resonance frequency fb and equal to or lower than the unsprung resonance frequency fw. Therefore, the low-frequency component dX_low of the extension / contraction speed dX processed by the low-pass filter 11 is a signal in which the high-frequency side higher than the sprung resonance frequency fb has been removed from the extension / contraction speed dX. According to the suspension control device C configured in this manner, the low-frequency control command Flow is determined based on the extension / contraction speed dX processed by the low-pass filter 11 set as described above. Therefore, the thrust force of the suspension device S can be increased for vibrations in the sprung resonance frequency band of the suspension device S, while the thrust force of the suspension device S can be reduced for vibrations in the unsprung resonance frequency band, thereby improving the road surface tracking ability of the vehicle body B and suppressing the transmission of vibrations in the unsprung resonance frequency band to the vehicle body B. Therefore, the suspension control device C configured in this manner can improve the road surface following ability of the vehicle body B while suppressing vibrations in the unsprung resonance frequency band of the vehicle body B.

[0076] Furthermore, the switching unit U3 in the suspension control device C of this embodiment obtains a road surface index RI by second-order differentiation of the road surface displacement Z of the road surface on which the wheels W travel with respect to distance, and determines the allocation between the road surface following control command FC and the vibration isolation control command FI based on the road surface index RI. The road surface index RI, which is the rate of change of the rate of change of the road surface displacement Z, becomes large at the start of large unevenness or a slope where the road surface displacement Z rises or falls, and by referring to the road surface index RI, it is easy to grasp the start of unevenness or a slope where the stroke amount of the suspension device S will be large. Therefore, the suspension control device C configured in this manner can easily and accurately predict the start of large unevenness or a slope, and can optimize the allocation between the road surface following control command FC and the vibration isolation control command FI by foreseeing road surfaces such as the start of unevenness or a slope where the stroke amount of the suspension device S will be large, thereby further improving the ride comfort of the vehicle V.

[0077] Furthermore, the switching unit U3 in the suspension control device C of this embodiment is configured to calculate the road surface index RI by low-pass filtering the moving average of the road surface displacement Z on the road surface on which the wheel W travels or the road surface displacement Z on the road surface on which the wheel W travels. By low-pass filtering the moving average of the road surface displacement Z or the road surface displacement Z, noise contained in the road surface displacement Z can be removed and sudden changes in the road surface displacement Z can be mitigated. This prevents the road surface index RI from taking large values ​​for small road surface changes that do not increase the stroke amount. Therefore, by referring to the road surface index RI calculated in this manner, it is possible to more accurately identify the start points of unevenness or slopes that will increase the stroke amount of the suspension device S. Therefore, the suspension control device C configured in this manner can easily and accurately predict the start points of large unevenness or slopes, and can predict road surfaces such as the start points of unevenness or slopes that will increase the stroke amount of the suspension device S in advance, thereby optimizing the distribution of the road surface following control command FC and the vibration isolation control command FI, thereby further improving the ride comfort of the vehicle V.

[0078] Furthermore, the switching unit U3 in the suspension control device C of this embodiment multiplies the road surface index RI by the traveling speed Vv of the vehicle V to obtain the estimated suspension vibration value SV, and then determines the allocation based on the estimated suspension vibration value SV. The stroke amount of the suspension device S tends to increase as the traveling speed Vv of the vehicle V increases, and the estimated suspension vibration value SV is obtained by multiplying the road surface index RI, which takes a large value at the start of a large unevenness or slope, by the traveling speed Vv, and is therefore an optimal index for determining the magnitude of the stroke amount of the suspension device S. Therefore, the suspension control device C configured in this manner can more accurately predict road surfaces on which the stroke amount of the suspension device S will increase in accordance with the traveling speed Vv of the vehicle V, thereby optimizing the allocation of the road surface following control command FC and the vibration isolation control command FI, thereby further improving the ride comfort of the vehicle V.

[0079] Furthermore, the switching unit U3 in the suspension control device C of this embodiment is configured to determine the allocation based on the level, which is the magnitude of the amplitude of the suspension vibration estimate SV. With the suspension control device C configured in this manner, the level of the suspension vibration estimate SV is used, so it is possible to accurately grasp the magnitude of the stroke of the suspension device S and optimize the allocation between the road following control command FC and the vibration isolation control command FI, thereby improving the ride comfort of the vehicle regardless of the quality of the road surface on which the vehicle V travels. Furthermore, even when the suspension vibration estimate SV vibrates with a large amplitude, the level remains high, so it is possible to prevent hunting, in which the allocation becomes oscillatory and frequently switches between road following control and vibration isolation control.

[0080] Furthermore, the switching unit U3 in the suspension control device C of this embodiment calculates a pre-selection distribution for each of the four wheels Wfl, Wfr, Wrl, and Wrr on the front, rear, left, and right sides of the vehicle body B, and calculates the distribution based on the pre-selection distribution that maximizes the proportion of the road-following control command FC for each of the four wheels Wfl, Wfr, Wrl, and Wrr. The suspension control device C configured in this manner calculates the distribution based on the pre-selection distribution that maximizes the proportion of the road-following control command FC among the pre-selection distributions calculated for each of the four wheels Wfl, Wfr, Wrl, and Wrr. Therefore, the distribution of the road-following control command FC and the vibration isolation control command FI in the control of the suspension units Sfl, Sfr, Srl, and Srr for each of the four wheels Wfl, Wfr, Wrl, and Wrr is consistent. Therefore, the suspension control device C of this embodiment standardizes the distribution of the road-following control command FC and the vibration isolation control command FI for the suspension units Sfl, Sfr, Srl, and Srr, thereby stabilizing the posture of the vehicle body B.

[0081] Furthermore, the switching unit U3 in the suspension control device C of this embodiment processes the distribution using a low-pass filter whose cutoff frequency changes according to the traveling speed Vv of the vehicle V, and determines the final distribution for each of the four wheels Wfl, Wfr, Wrl, and Wrr. With the suspension control device C configured in this way, a distribution of the road following control command FC and the vibration isolation control command FI suitable for traveling on a certain road surface can be applied according to the traveling speed Vv when each of the four wheels Wfl, Wfr, Wrl, and Wrr actually travels on that road surface, so that control can be executed with an optimal distribution at an optimal timing regardless of the traveling speed Vv.

[0082] Furthermore, the switching unit U3 in the suspension control device C of this embodiment predicts the road surface on which the wheels W will travel based on the steering angle of the vehicle V, and determines the allocation based on the road surface displacement Z of the predicted road surface. With the suspension control device C configured in this way, the road surface on which the wheels W of the vehicle V will travel is predicted from the steering angle, so it is possible to more accurately predict road surfaces on which the stroke amount of the suspension device S will increase depending on the course of the vehicle V, and optimize the allocation of the road surface following control command FC and the vibration isolation control command FI, thereby further improving the ride comfort of the vehicle V.

[0083] Although the preferred embodiment of the present invention has been described in detail, modifications, variations and changes can be made thereto without departing from the scope of the appended claims. [Explanation of symbols]

[0084] B···Vehicle body, C···Suspension control device, U1···Road following control unit, U2···Vibration isolation control unit, U3···Switching unit, U4···Final command calculation unit, P···Preview sensor, RI···Road surface index, S, Sfl, Sfr, Srl, Srr···Suspension unit, SV···Suspension vibration estimation value, V···Vehicle, W, Wfl, Wfr, Wrl, Wrr···Wheels, Z···Road displacement

Claims

1. 1. A suspension control device that controls a suspension device that is interposed between a vehicle body and a wheel of a vehicle and that is capable of applying a force in a vertical direction to the vehicle body to suppress vibration of the vehicle body, a road surface following control unit that generates a road surface following control command for causing the vehicle body to follow a road surface in a sprung mass resonance frequency band; a vibration isolation control unit that generates a vibration isolation control command that is a control command that makes it difficult for vibrations from a road surface to be transmitted to the vehicle body in an unsprung resonance frequency band; a switching unit that determines a distribution of the road surface following control command and the vibration isolation control command based on a road surface displacement detected by a preview sensor that detects a road surface displacement ahead in a traveling direction of the vehicle; a final command calculation unit that calculates a final control command for controlling the suspension device from the distribution, the road surface following control command, and the vibration isolation control command; A suspension control device characterized by:

2. The switching unit is The road surface displacement on the road surface on which the wheels are traveling is second-order differentiated with respect to distance to obtain a road surface index, and the allocation is obtained based on the road surface index.

2. The suspension control device according to claim 1.

3. The switching unit is The road surface index is obtained by performing a moving average of the road surface displacement on the road surface on which the wheels are traveling or by performing a low-pass filter process on the road surface displacement on the road surface on which the wheels are traveling.

3. The suspension control device according to claim 2.

4. The switching unit is The road surface index is multiplied by the vehicle running speed to obtain a suspension vibration estimate, and the allocation is obtained based on the suspension vibration estimate.

4. The suspension control device according to claim 2 or 3.

5. The switching unit is The allocation is calculated based on a level that is the magnitude of the amplitude of the estimated suspension vibration value.

5. The suspension control device according to claim 4.

6. The switching unit is A distribution for each of the four wheels on the front, rear, left and right sides of the vehicle body is calculated as a pre-selection distribution, and the distribution is calculated based on the pre-selection distribution that maximizes the ratio of the road following control command for each of the four wheels.

6. The suspension control device according to claim 1, wherein the suspension control device is a suspension control device.

7. The switching unit is The distribution is processed by a low-pass filter whose cutoff frequency changes according to the traveling speed of the vehicle, and the final distribution for each of the four wheels is obtained.

7. The suspension control device according to claim 6.

8. The switching unit predicts a road surface on which the wheels will travel based on a steering angle of the vehicle, and determines the distribution based on a road surface displacement on the predicted road surface.

8. The suspension control device according to claim 1, wherein the suspension control device is a suspension control device.

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