JP7791763B2 - Suspension Control Device - Google Patents

Description

The present invention relates to a suspension control device.

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).

Such a suspension control device calculates a control command by multiplying the vehicle body's vertical speed by a skyhook gain (skyhook damping coefficient), and causes the suspension device to output the control force indicated by the control command. In this way, a suspension control device that performs skyhook control reduces the vehicle body's vertical speed using the damping force and control force generated by the suspension device, suppressing vehicle body vibration and improving ride comfort.

JP 2016-88358 A

Conventional suspension control devices can suppress vibrations in the vehicle body by isolating the transmission of vibrations from the road surface, but when driving at high speeds over uneven road surfaces or entering a slope, attempting to isolate the vibrations increases the gain, which increases the stroke of the suspension device, and vibrations caused by the suspension device fully expanding or compressing can be transmitted to the vehicle body, resulting in a worsening ride.

Therefore, the object of the present invention is to provide a suspension control device that can improve ride comfort.

To achieve the above object, the suspension control device of 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. It includes a road following control unit that generates a road following control command to make the body follow the road surface in the sprung 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 the road surface to be transmitted to the vehicle body in the unsprung resonance frequency band, a switching unit that determines the 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 determines a final control command for controlling the suspension device from the allocation, road following control command, and vibration isolation control command.

A suspension control device configured in this way calculates the final control command by calculating the allocation between road surface following control commands and vibration isolation control commands based on the road surface displacement detected by the preview sensor.This makes it possible to predict road surfaces where vibration isolation control alone would increase the stroke of the suspension device and worsen vehicle ride comfort, and switch between road surface following control commands and vibration isolation control commands to improve vehicle ride comfort.

The switching unit in the suspension control device may also calculate a road surface index by second-order differentiation of the road surface displacement on the road surface on which the wheels are traveling with respect to distance, and calculate the allocation of road surface following control commands and vibration isolation control commands based on the road surface index. A suspension control device configured in this way can easily and accurately predict the start of large bumps and slopes, and can predict road surfaces such as bumps and slopes that will increase the stroke amount of the suspension device in advance, optimizing the allocation of road surface following control commands and vibration isolation control commands, thereby further improving vehicle ride comfort.

Furthermore, the switching unit in the suspension control device may calculate a road surface index by low-pass filtering the moving average of road surface displacement on the road surface on which the wheels are traveling or the moving average of road surface displacement on the road surface on which the wheels are traveling, and then differentiating the moving average of 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 road surface displacement or road surface displacement can remove noise contained in the road surface displacement and mitigate sudden changes in 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 vehicle ride comfort.

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 where the stroke amount of the suspension device increases depending on the vehicle's traveling speed, optimizing the allocation of road surface following control commands and vibration isolation control commands, thereby further improving ride comfort in the vehicle.

The switching unit in the suspension control device may also determine the allocation based on the level, which is the magnitude of the amplitude of the suspension vibration estimated value. With a suspension control device configured in this way, the level of the suspension vibration estimated value is used, making it possible to accurately grasp the magnitude of the suspension device's stroke and optimize the allocation between the road following control command and the vibration isolation control command, thereby improving vehicle ride comfort regardless of the quality of the road surface on which the vehicle is traveling. Furthermore, even when the suspension vibration estimated value vibrates with a large amplitude, the level remains high, preventing hunting, which occurs when the allocation becomes oscillatory and frequently switches between road following control and vibration isolation control.

Furthermore, the switching unit in the suspension control device may determine 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 proportion of road-following control commands FC for each of the four wheels. With a suspension control device configured in this way, the distribution of road-following control commands and vibration isolation control commands in the suspension device is unified, thereby stabilizing the posture of the vehicle body.

The switching unit in the suspension control device may also process the distribution using a low-pass filter whose cutoff frequency changes depending on the vehicle's traveling speed, to determine the final distribution for each of the four wheels. A suspension control device configured in this way can execute control with optimal timing and optimal distribution, regardless of the vehicle's traveling speed.

Furthermore, the switching unit in the suspension control device may predict the road surface on which the wheels will travel based on the vehicle's steering angle, 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, optimizing the allocation of road surface following control commands and vibration isolation control commands, further improving vehicle ride comfort.

As a result, the suspension device of the present invention can improve the ride comfort of a vehicle.

1 is a diagram showing a vehicle equipped with a suspension control device according to an embodiment; 1 is a configuration diagram of a suspension control device according to an embodiment; 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. 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. 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. 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. FIG. 10 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. 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. FIG. 10 is a diagram showing detected road surface displacements and positions. FIG. 10 is a diagram showing the relationship between the level and distribution of estimated suspension vibration values. 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. 3 is a flowchart showing an example of a processing procedure in the suspension control device according to the embodiment.

The present invention will be described below based on the embodiment 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 for 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. When there is no need to particularly distinguish between the installation locations of the suspension device S and the wheel W, the subscripts will be omitted.

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). For example, they are adjustable damping force dampers that can adjust the damping force generated when they extend or retract. The suspension unit S may also be a telescopic cylinder or electric linear actuator that can adjust thrust using hydraulic or pneumatic pressure. The suspension unit S is equipped with a solenoid valve for adjusting the damping force and a driver for operating the solenoid valve, and is driven to extend or retract in response to control commands input from the suspension control unit C. Therefore, when the suspension units Sfl, Sfr, Srl, and Srr receive the final control command F_ref calculated by the suspension control unit C, they exert the damping force indicated by the final control command F_ref to suppress vibration of the vehicle body B.

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 directly above the four suspension units Sfl, Sfr, Srl, and Srr; a preview sensor P that detects road surface displacement ahead of the vehicle V; four stroke sensors H that detect the displacement X of each suspension unit Sfl, Sfr, Srl, and Srr; and a control and calculation unit U that calculates a final control command F_ref from the vertical acceleration α and displacement X. Each of the four suspension units Sfl, Sfr, Srl, and Srr on the vehicle V is paired with an acceleration sensor G directly above the suspension unit Sfl, Sfr, Srl, and Srr and a stroke sensor H corresponding to the suspension unit S. 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 units Sfl, Sfr, Srl, and Srr that make up 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, stroke sensor H, and 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 reference symbol for suspension unit S.

The acceleration sensors G are respectively installed 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 a rigid body, and three acceleration sensors G are installed on the vehicle body B so that they are not 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, only three acceleration sensors G may be installed 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, and Srr and information detected by the stroke sensors H corresponding to those suspension devices Sfl, Sfr, Srl, and Srr to determine the final control command F_ref and control those suspension devices Sfl, Sfr, Srl, and Srr.

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

As shown in Figure 2, the control calculation device U is composed of a road following control unit U1 that calculates a road following control command FC, a vibration isolation control unit U2 that calculates a vibration isolation control command FI, a switching unit U3 that calculates the distribution between the road following control command FC and the vibration isolation control command FI, and a final command calculation unit U4 that calculates a final control command F_ref from the road following control command FC, the vibration isolation control command FI, and the distribution calculated by the switching unit U3.

As shown in Figure 3, the road-following control unit U1 is specifically equipped with 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 the skyhook gain (skyhook damping coefficient), and an adder 15 that adds the values output by multipliers 12 and 14 to determine the road-following control command FC.

The differentiator 10 differentiates the displacement X detected by the stroke sensor H to determine the extension/retraction 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/retraction speed dX of the suspension unit S and the vertical velocity Bv of the vehicle body B. Since the extension/retraction 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 device C may obtain the extension/retraction 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 connected to the wheel W side of the suspension unit S that moves up and down 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/retraction speed dX. Furthermore, since the vertical velocity Bv of the vehicle body B can be obtained by adding the extension/contraction velocity dX of the suspension unit S to the vertical velocity of the wheel W, the suspension control unit C may eliminate the acceleration sensor G provided on the vehicle body B and provide an acceleration sensor on the wheel W to determine the vertical velocity Bv of the vehicle body B.

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, in this embodiment, the cutoff frequency fcut of the low-pass filter 11 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.

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

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 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. Furthermore, when the cycle of road surface displacement is long, the low-frequency control command Flow makes it more difficult for the suspension unit S to extend or contract, preventing fluctuations in the distance between the road surface and the vehicle body B and allowing the vehicle body B to follow the road surface displacement.

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.

The road surface 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 surface following control command FC, the suspension device S exerts a force that reduces vibration of the vehicle body B while causing the vehicle body B to follow the road surface displacement.

When the suspension control device C controls the suspension device S (road surface following control) by issuing 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, as shown in Figure 4, the gain is close to 0 dB in the sprung resonance frequency band, allowing the vehicle body B to follow road surface displacement, and the gain decreases in the unsprung resonance frequency band, isolating vibrations to the vehicle body B. This means that the vehicle body B follows the road surface in the sprung resonance frequency band, while vibrations in the unsprung resonance frequency band are isolated.

The proportion of low-frequency control and skyhook control can be adjusted by the ratio between the damping coefficient Clow used when calculating the low-frequency control command Flow and the skyhook gain Csky used when calculating the skyhook control command Fsky, and the damping coefficient Clow and skyhook gain Csky are set to suit the vehicle V. Furthermore, by obtaining a road surface following control command FC based on the low-frequency control command Flow and the skyhook control command Fsky and controlling the suspension device S using the road surface 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.

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, for example, as shown in Figure 5, the gain takes a negative value in the sprung resonance frequency band and then decreases even after exceeding the unsprung resonance frequency band, thereby isolating vibration from the road surface to the vehicle body B in the sprung resonance frequency band and unsprung resonance frequency band.

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 and unsprung resonant frequency bands. To achieve 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 the force that the suspension spring SP causes to vibrate the vehicle body B due to the displacement of the wheel W; and an adder 23 that adds the first and second commands to obtain the vibration isolation control command FI.

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 then second-order integration of this vertical acceleration. Since the first command calculation unit 21 calculates a first command to suppress vibration of the vehicle body B, which is a sprung member, it may process the vertical velocity Bv with a band-pass filter or low-pass filter to extract the vertical velocity Bv in the sprung resonance frequency band and then multiply it by a damping coefficient to obtain the first command. Furthermore, since the second command calculation unit 22 calculates the second command from the displacement of the wheel W, which is an unsprung member, it may process the displacement of the wheel W with a band-pass filter or low-pass filter to extract the displacement in the unsprung resonance frequency band and then obtain the second command.

As shown in FIG. 7 , the vibration isolation control unit U2 may include a third command calculation unit 24 that multiplies the vertical velocity Bv of the vehicle body B by a damping coefficient to calculate a third command; a fourth command calculation unit 25 that multiplies the vertical velocity of the wheel W by a damping coefficient to calculate a fourth command; and an adder 26 that adds the third and fourth commands to calculate a vibration isolation control command FI. Because the third command calculation unit 24 calculates the third command to suppress vibration of the vehicle body B, which is a sprung member, 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. Because the fourth command calculation unit 25 calculates the fourth command from the vertical velocity of the wheel W, which is an unsprung member, 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.

When the suspension control device C issues only the vibration isolation control command FI to the suspension device S, it attempts to easily expand and contract the suspension device S 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 favorable and has few irregularities, the suspension control device C performs vibration isolation control, which prevents the height of the vehicle body B from changing, improving ride comfort in the vehicle V. However, when the suspension control device C only performs vibration isolation control, the height of the vehicle body B tends to remain unchanged when the wheel W overcomes irregularities during high-speed driving or when entering a slope, resulting in an increased stroke of the suspension device S. 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 difficult for the suspension device S to expand and contract in response to input of high-frequency vibrations, while 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 device S performs road surface following control, when the wheel W goes over uneven surfaces during high-speed driving or when going up a slope, the suspension device S is less likely to expand or contract, preventing the stroke amount from increasing and reducing vibration. In this way, when the wheel W goes over uneven surfaces during high-speed driving or when going up a slope, the suspension control device C can improve the ride comfort of the vehicle V by performing road surface following control.

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 would fully extend or compress at full stroke, i.e., when the stroke of the suspension unit S is small and there is no risk of it reaching full stroke, isolating the transmission of vibrations from the road surface and suppressing vibrations in the vehicle body B can maintain a good ride comfort in the vehicle V. On the other hand, when the vehicle V is traveling at high speed over an uneven surface and approaches a slope, controlling the suspension unit S solely with the vibration isolation control command FI may gradually increase the stroke of the suspension unit S, causing the suspension unit S to fully extend or compress, thereby deteriorating the 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 the 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 calculating an index that estimates the stroke of the suspension unit S.

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 displacement with respect to distance, by second-order differentiation of the moving average of the road surface displacement Z that the prediction unit 31 predicts will 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 time units 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 traveling speed of the vehicle V to calculate a suspension vibration estimated value SV. The system is equipped with a level calculation unit 35 that calculates the magnitude of the suspension vibration estimated 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.

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. The preview sensor P may also be configured to detect road surface displacement Z only while 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. For example, as shown in FIG. 9, the road surface displacement Z at the position indicated by the 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 and lateral coordinates of the vehicle V and stored in the storage device. 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 it may also be a sensor with a detection range in all directions, centered on the predetermined distance L. Furthermore, since road surface displacement data becomes unnecessary after the vehicle V has traveled over the corresponding road surface, the unnecessary road surface displacement Z data can be updated with new road surface displacement Z data, and the storage device should have sufficient memory capacity to temporarily store the road surface displacement Z data as the vehicle V travels along these road surfaces. Road surface displacement data covering ranges in front of the vehicle V, front to back and left to right, is accumulated based on detection by the preview sensor P.

The prediction unit 31 predicts 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, based on the vehicle V, from the road surface displacement detected by the preview sensor P. Specifically, since the turning trajectory of the vehicle V changes depending on the traveling speed and steering angle while the vehicle V is turning, 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 this 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.

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 for each wheel Wfl, Wfr, Wrl, and Wrr. When calculating the road surface index RI for the road surface coordinates of the road surface on which the front left wheel Wfl is traveling, the index calculation unit 32 first calculates the moving average of a predetermined number N of road surface displacements Z at the road surface coordinates predicted by the prediction unit 31 for the wheel Wfl. Specifically, the index calculation unit 32 extracts a predetermined number N of road surface displacements Z from the road surface displacement Z at the road surface coordinates on the trajectory on which the wheel Wfl is traveling, starting from a road surface displacement Z a predetermined distance away from the vehicle V, and moving backward or forward toward the vehicle V, and then adds up these N road surface displacements Z and divides the sum by N to calculate the moving average. When calculating the moving average, the index calculation unit 32 may extract a predetermined number N of road surface displacements Z from the road surface coordinates on the trajectory of the wheel Wfl, starting with the most recent road surface displacement Z detected by the preview sensor P and working backward toward the vehicle V. The predetermined distance may be changed as desired and may vary depending on the traveling speed of the vehicle V. In this way, when the index calculation unit 32 calculates the moving average of 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 road surface properties. The value of the predetermined number N may be set to any value as long as it is equal to or less than the number of road surface coordinates of the road surface displacements Z predicted to be traveled by the wheel Wfl detected by the preview sensor P.

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 distance. Note that the road surface index RI is calculated for each wheel Wfl, Wfr, Wrl, and Wrr.

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 in the road surface displacement Z and noise. Therefore, by calculating the moving average of the road surface displacement Z, the index calculation unit 32 can accurately determine whether the road surface on which the vehicle V is about to travel contains large irregularities or the start of a slope that would increase the stroke amount of the suspension device S.

In addition, the index calculation unit 32 obtains the rate of change of the moving average rate of change of road surface displacement Z at a position a distance away from the current position of the wheels Wfl, Wfr, Wrl, and Wrr of the vehicle V by differentiating the value of the moving average twice with respect to distance, which is a predetermined distance L plus the distance from the front end of the vehicle V to each wheel Wfl, Wfr, Wrl, and Wrr. The rate of change of the moving average rate of change of this road surface displacement Z is then set as the road surface index RI.

Since the road surface index RI is the rate of change of the rate of change of road surface displacement Z, the absolute value of the road surface index RI tends to increase at the start of large unevenness or slopes where road surface displacement Z increases or decreases. In contrast, the value obtained by first-order differentiation of the moving average of 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 used to determine the allocation between the road surface following control command FC and the vibration isolation control command FI. Since it is desirable to adopt the road surface following control command FC in situations where the stroke amount of the suspension unit S is large, it is preferable for the index to be able to accurately determine the stroke amount of the suspension unit S. The value of the moving average or the value obtained by first-order differentiation of the moving average can be used as the road surface index RI, as it is possible to identify the start points of large irregularities and slopes, and so these can be used as the road surface index RI. However, the value obtained by second-order differentiation of the moving average tends to be larger at the start points of large irregularities and slopes, and is therefore optimal as the road surface index RI for determining the distribution. The number of samples required for the moving average, i.e., the number N, can be set arbitrarily, but if the resolution in the longitudinal direction of the vehicle V is coarse, the number N can be made extremely small.

In addition, 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 may also 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 a 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 the 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 is obtained in which the effects of sudden changes in the road surface displacement Z and noise are mitigated, making it possible to obtain a road surface index RI equivalent to that obtained by performing a moving average.

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 time units by dividing the road surface index RI by the vehicle V's traveling speed. 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 of the road surface displacement Z at a position a distance L from the current positions of the wheels Wfl, Wfr, Wrl, and Wrr of the vehicle V, plus the distances from the front end of the vehicle V to the four wheels Wfl, Wfr, Wrl, and Wrr. When the wheel W travels on a road surface for which the road surface index RI has been obtained during a certain control cycle, the allocation of the road surface following control command FC and the vibration isolation control command FI can be controlled based on the allocation calculated from the road surface index RI using 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.

The suspension vibration estimation unit 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 conversion unit 33, by the vehicle V's traveling speed, to calculate the suspension vibration estimate value 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 estimation unit 34 can be omitted and the road surface index RI used directly to calculate the distribution. However, the stroke amount 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 value SV calculated by multiplying the road surface index RI by the vehicle speed is a more optimal value for determining the magnitude of the suspension unit S stroke than the road surface index RI.

Unmodified, the suspension vibration estimated 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 suspension vibration estimated 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 amount of the suspension unit S will also become large. While the suspension vibration estimated value SV is fluctuating with a large amplitude, there are times when the suspension vibration estimated value SV becomes small, but even in such cases the stroke amount of the suspension unit S will become large. Therefore, to more accurately grasp the stroke amount of the suspension unit S, it is sufficient to determine the level, which is the magnitude of the amplitude of the suspension vibration estimated value SV. Therefore, the level calculation unit 35 determines the levels of the four suspension vibration estimated values SV obtained for each of the four wheels Wfl, Wfr, Wrl, and Wrr.

Specifically, the level calculation unit 35 takes the suspension vibration estimated value SV signal calculated by the suspension vibration estimation unit 34 as an original signal, generates multiple signals that differ only in phase from this original signal without changing the gain, and determines the maximum value of the multiple signals that differ in phase from the original signal as the level value of the suspension vibration estimated value SV. By generating multiple signals whose phases are shifted by a predetermined angle from the original signal and selecting the maximum value 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. The level calculation unit 35 may also calculate the envelope of the suspension vibration estimated value SV of the signal using processing such as peak hold or Hilbert transform to calculate the level, or may calculate the length of the resultant vector of the suspension vibration estimated value SV and the differential or integral value of the suspension vibration estimated value SV as the level.

The allocation calculation unit 36 calculates a pre-selection allocation, which is the allocation between 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 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 surface 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.

Therefore, the allocation calculation unit 36 calculates the pre-selection allocation using an upper threshold t1 and a lower threshold t2, which are set for the level of the estimated suspension vibration value SV. As shown in FIG. 10 , when the level of the estimated suspension vibration value SV exceeds the upper threshold t1, the allocation calculation unit 36 sets the allocation of the road surface 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 estimated suspension vibration value SV falls below the lower threshold t2, the allocation calculation unit 36 sets the allocation of the road surface 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 estimated suspension vibration 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 surface following control command FC in proportion to the level. Note that the upper threshold t1 and the lower threshold t2 may be determined based on the relationship between the level of the estimated suspension vibration value SV and the actual stroke amount of the suspension unit S, and the upper threshold t1 is set to a value smaller than the level at which the suspension unit S is considered to be at full stroke.

The pre-selection allocation can be considered as a gain by which the road following control command FC and the vibration isolation control command FI are multiplied. Specifically, the allocation calculation unit 36 determines the gain K1 by which the road following control command FC should be multiplied from the level of the suspension vibration estimated value SV. However, K1 is a value between 0 and 1.

Note that 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 magnitude of the amplitude of the road surface index RI.

The selection unit 37 selects the pre-selection allocation that maximizes the proportion of the road following control command FC from the pre-selection allocations for the four wheels Wfl, Wfr, Wrl, and Wrr calculated by the allocation calculation unit 36. In other words, the selection unit 37 selects the largest gain K1 from the gains K1 of the four pre-selection allocations as the allocation to be used for control. Because the selection unit 37 selects one allocation from the four pre-selection allocations in this way, it is possible to prevent inconsistent control of the four wheels Wfl, Wfr, Wrl, and Wrr with different allocations of the road following control command FC and the vibration isolation control command FI.

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 depending on the vehicle V's traveling speed. The allocation selected by the selection unit 37 is low-pass filtered to determine the final allocation for each of the four wheels Wfl, Wfr, Wrl, and Wrr. The faster the vehicle V's traveling speed, the shorter the time the wheels W travel on the road surface for which the road surface index RI is 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 low-pass filter's cutoff frequency fcut can be changed according to the traveling speed Vv by calculating f2cut = f2cut_low + m·Vv (m is an arbitrary coefficient). Note that the above-mentioned formula for calculating the cutoff frequency fcut from the vehicle speed Vv is just one example, and the formula can be modified to be optimal for the suspension control device C.

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. If there is no risk of sudden changes in the allocation, the final allocation calculation unit 38 may calculate the final allocation by delaying the time it takes for the wheels W to travel on the road surface for which the road surface index RI has been determined. 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 passed for the wheels W to travel on the road surface for which the road surface index RI has been determined according to the vehicle speed.

As a result of the above, the switching unit U3 increases the distribution of the road surface following control command FC when the index indicating the stroke amount of the suspension device S increases, and decreases the distribution of the road surface following control command FC when the index indicating the stroke amount of the suspension device S decreases.

As shown in FIG. 11, the final command calculation unit U4 includes a calculation unit 41 that calculates K2 = 1 - K1 to determine the gain K2 by which the vibration isolation control command FI should be multiplied from the gain K1 indicating the distribution of the road following control command FC determined by the switching unit U3; a multiplication unit 42 that multiplies the road following control command FC by the gain K1 indicating the distribution of the road following control command FC determined by the switching unit U3; 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.

Therefore, when the gain K1 is 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 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 gain K1 decreases. Furthermore, when the value of 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. On the other hand, when the value of 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 described 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 surface following control command FC. Furthermore, 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 surface following control command FC and calculates a final control command F_ref that prioritizes the road surface 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 to be output by the suspension unit S, and is input to the suspension unit S.

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 the driver (not shown) of the suspension device S. The suspension device S exerts a thrust force instructed by the final control command F_ref.

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 steps F1 to F6 to control the four suspension devices Sfl, Slr, Srl, and Srr.

The suspension control device C may be configured with the following hardware resources (not shown): an interface for capturing 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 the vertical acceleration α and displacement X to control the suspension device S; a calculation device 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 storage space for the CPU. Each component of the control and calculation device U can be implemented by the CPU executing the program. Alternatively, the control and calculation device U may be implemented using analog electronic circuits instead of the CPU executing the program.

The suspension control device C is configured as described above and operates as follows. When the vehicle V is traveling on a road surface (good road) that is smooth or has only minor irregularities, the wheels W (unsprung members) vibrate gently in the vertical direction, and the vehicle body B (sprung member) does not vibrate either. In this situation, the value of the road surface index RI is small, and the suspension vibration estimate SV also takes a small value, so gain K1, which indicates the distribution, takes a value of 0 or near 0, and gain K2 takes a value of 1 or near 1. When gain K1 takes a value of 0 or near 0, the proportion of the road surface 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 a final control command F_ref that has a high distribution of the vibration isolation control command FI. Therefore, when the vehicle V is traveling on a flat or relatively smooth road surface, 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, maintaining good ride comfort in the vehicle.

On the other hand, when the vehicle V moves from a good road onto a rough, uneven road (bad road), the wheels W begin to vibrate up and down with short periods and small amplitudes. Even in this situation, the road surface index RI decreases, and the suspension vibration estimate SV also decreases. Therefore, the gain K1, which indicates the distribution, assumes a value of 0 or near 0, and the gain K2 assumes a value of 1 or near 1. When the gain K1 assumes 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 a final control command F_ref that has a high distribution of the vibration isolation control command FI. Therefore, when the vehicle V travels on a rough, uneven road, 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, maintaining a comfortable ride.

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 using the final control command F_ref, in which the vibration isolation control command FI is dominant, and therefore if the suspension device S continues to be controlled using 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, causing the suspension device S to fully extend or compress, which may worsen 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 be traveling will increase, and the suspension control device C will be able to 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 near 1, and the gain K2 to a value of 0 or near 0, so that the proportion of the road surface 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 a final control command F_ref that has a high distribution of the road surface 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 surface 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 more difficult for the suspension unit S to expand or contract, preventing the suspension unit S from fully expanding or compressing, and maintaining good ride comfort in the vehicle.

Furthermore, the selected allocation, gain K1, changes proportionally to the level of the suspension vibration estimate SV. Therefore, the change in the allocation between the road following control command FC and the vibration isolation control command FI gradually changes according to the level of the suspension vibration estimate 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 fades out while the other fades in, generating the final control command F_ref. Therefore, the value of the final control command F_ref does not change suddenly, and the system switches seamlessly from road following control to vibration isolation control, or from road isolation control to road following control. Furthermore, the final allocation calculation unit 38 low-pass filters the selected allocation, gain K1, which alleviates sudden changes in gain K1, thereby further alleviating sudden changes in the value of the final control command F_ref.

As described above, the suspension control device C of the present invention is installed between the vehicle body B and wheels W of a vehicle V and controls a suspension device S that can apply vertical forces to the vehicle body B to suppress vibration of the vehicle body B. It includes 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, which 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.

The suspension control device C configured in this manner calculates the final control command F_ref by adjusting the distribution between 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 where vibration isolation control alone would increase the stroke amount of the suspension device S, thereby worsening the ride comfort of the vehicle V, and switch between the road surface following control command FC and the vibration isolation control command FI to improve ride comfort in the vehicle.

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 resonant frequency band, making it more difficult for the suspension device S to expand or contract. When the wheels W overcome unevenness in the road surface or enter 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 more difficult for vibrations from the road surface to be transmitted to the vehicle body B in the unsprung resonant frequency band, thereby controlling the height of the vehicle body B to not 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 and maintains a good ride comfort in the vehicle V.

Therefore, the suspension control device C of this embodiment selectively uses the road surface following control command FC and the vibration isolation control command FI depending on the road surface conditions, thereby improving the ride comfort of the vehicle V regardless of the characteristics of the road surface on which the vehicle V is traveling.

In addition, the suspension control device C of this embodiment calculates the road surface following control command FC based on the low-frequency control command Flow, which increases the force exerted by the suspension device S in response to vibrations of frequencies lower than the unsprung resonance frequency of the suspension device S, making it difficult for the suspension device S to expand or contract, and the skyhook control command Fsky, which suppresses vibration of the vehicle body B. This allows the suspension device S to exert a thrust that reduces the vibration of the vehicle body B while making the vehicle body B follow the road surface variations. Therefore, according to the suspension control device C of the present invention, when the distribution of the road surface following control command FC is increased, the suspension device S is controlled to make the vehicle body B follow the road surface and make it difficult for the suspension device S to expand or contract when going over uneven surfaces or entering a slope during high-speed driving. This 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, further improving the ride comfort of the vehicle V.

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. The cutoff frequency fcut of the low-pass filter 11 is set to be greater than the sprung resonance frequency fb and less 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 above 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 calculated 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-following ability of the vehicle body B while suppressing the transmission of vibrations in the unsprung resonance frequency band to the vehicle body B. Therefore, with the suspension control device C configured in this manner, it is possible to improve the road-following ability of the vehicle body B while suppressing vibrations in the unsprung resonance frequency band of the vehicle body B.

In addition, the switching unit U3 in the suspension control device C of this embodiment calculates the 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 calculates 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, increases at the start of large unevenness or slopes where the road surface displacement Z increases or decreases. By referencing the road surface index RI, it is easy to identify the start of unevenness or slopes where the stroke amount of the suspension device S increases. Therefore, the suspension control device C configured in this manner can easily and accurately predict the start of large unevenness or slopes, and can predict road surfaces such as the start of unevenness or slopes where the stroke amount of the suspension device S will increase in advance, thereby optimizing the allocation between the road surface following control command FC and the vibration isolation control command FI and further improving the ride comfort of the vehicle V.

In addition, the switching unit U3 in the suspension control device C of this embodiment calculates 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. Low-pass filtering the moving average of the road surface displacement Z or the road surface displacement Z removes noise contained in the road surface displacement Z and mitigates sudden changes in the road surface displacement Z. 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 referencing the road surface index RI calculated in this manner, it is possible to more accurately identify the starting 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 starting points of large unevenness or slopes. This allows for advance prediction of road surfaces such as the starting points of unevenness or slopes that will increase the stroke amount of the suspension device S, 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.

Furthermore, the switching unit U3 in the suspension control device C of this embodiment multiplies the road surface index RI by the vehicle V's traveling speed Vv to obtain the suspension vibration estimate SV, and then calculates the allocation based on the suspension vibration estimate SV. The stroke amount of the suspension device S tends to increase as the vehicle V's traveling speed Vv increases, and the suspension vibration estimate SV is calculated by multiplying the road surface index RI, which takes on large values at the start of large bumps or slopes, by the traveling speed Vv, making it an optimal index for determining the magnitude of the suspension device S's stroke amount. 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 depending on the vehicle V's traveling speed Vv, 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.

In addition, the switching unit U3 in the suspension control device C of this embodiment determines the allocation based on the level, which is the magnitude of the amplitude of the suspension vibration estimate SV. With a suspension control device C configured in this manner, the level of the suspension vibration estimate SV is used, so the stroke of the suspension device S can be accurately determined and the allocation between the road following control command FC and the vibration isolation control command FI can be optimized, improving ride comfort in the vehicle regardless of the quality of the road surface on which the vehicle V is traveling. Furthermore, even when the suspension vibration estimate SV vibrates with a large amplitude, the level remains high, preventing hunting, which occurs when the allocation becomes oscillatory and frequently switches between road following control and vibration isolation control.

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 from the pre-selection distributions calculated for each of the four wheels Wfl, Wfr, Wrl, and Wrr, so that the distribution of the road-following control command FC and the vibration isolation control command FI in the control of the suspension devices Sfl, Sfr, Srl, and Srr for each of the four wheels Wfl, Wfr, Wrl, and Wrr does not become inconsistent. Therefore, according to the suspension control device C of this embodiment, the distribution of the road surface following control command FC and the vibration isolation control command FI among the suspension devices Sfl, Sfr, Srl, and Srr is unified, making it possible to stabilize the posture of the vehicle body B.

In addition, 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 vehicle V's traveling speed Vv, 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 manner, a distribution of road surface following control command FC and 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 control can be executed with the optimal distribution at the optimal timing regardless of the traveling speed Vv.

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 calculates the allocation based on the road surface displacement Z of the predicted road surface. With the suspension control device C configured in this manner, the road surface on which the wheels W of the vehicle V will travel is predicted from the steering angle, making it possible to more accurately predict road surfaces on which the stroke amount of the suspension device S will increase depending on the path of the vehicle V, and optimize the allocation between the road surface following control command FC and the vibration isolation control command FI, thereby further improving the ride comfort of the vehicle V.

While the preferred embodiment of the present invention has been described in detail above, modifications, variations, and variations are possible without departing from the scope of the claims.

B: Vehicle body, C: Suspension control device, U1: Road surface 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 device, SV: Estimated suspension vibration value, V: Vehicle, W, Wfl, Wfr, Wrl, Wrr: Wheels, Z: Road surface displacement

Claims (8)

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 following control command, and the vibration isolation control command. The switching unit is
2. The suspension control device according to claim 1, wherein the road surface displacement on the road surface on which the wheels are traveling is differentiated twice with respect to distance to obtain a road surface index, and the distribution is calculated based on the road surface index. The switching unit is
3. The suspension control device according to claim 2, wherein the road surface index is determined 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. The switching unit is
4. The suspension control device according to claim 2, wherein an estimated suspension vibration value is calculated by multiplying the road surface index by a traveling speed of the vehicle, and the allocation is calculated based on the estimated suspension vibration value. The switching unit is
5. The suspension control device according to claim 4, wherein the allocation is calculated based on a level that is the magnitude of the amplitude of the estimated suspension vibration value. The switching unit is
6. The suspension control device according to claim 1, wherein a pre-selection distribution is calculated for each of four wheels on the front, rear, left, and right sides of the vehicle body, 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. The switching unit is
7. The suspension control device according to claim 6, wherein the distribution is processed by a low-pass filter having a cutoff frequency that changes in accordance with the traveling speed of the vehicle, and the final distribution for each of the four wheels is determined. 8. The suspension control device according to claim 1, wherein 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.