Suspension control system

Abstract

To provide a suspension control system which can suppress occurrence of vibration at a boundary between presence and absence of a road surface displacement related value.SOLUTION: An actuator adjusts a suspension stroke of a control object wheel of a vehicle. A first acquisition part 80 repeatedly acquires a road surface displacement related value related to displacement in a vertical direction of a road surface at a prediction passage position of a control object wheel after a predetermined time from a current time, from a road surface data map in which the road surface displacement related value and a position are related with each other. A second acquisition part 82 acquires a change amount per unit time of the road surface displacement related value. A control part 88 controls the actuator, so that the control force generated by the actuator coincides with the target control force, when the control object wheel passes through the prediction passage position. When the change amount per unit time of the road surface displacement related value is equal to or more than a threshold, the calculation part 86 calculates the target control force so that the change amount per unit time of the target control force is decreased compared with a case in which the change amount is less than the threshold.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a suspension control system.

Background Art

[0002] Patent Document 1 discloses a vibration control device for a vehicle. The vibration control device acquires, as preview information, a road surface displacement-related value at a predicted passing position based on measurement data, and controls a control force generator based on a final target control force including a first target control force calculated using the preview information to perform preview vibration control. The measurement data includes data in which a road surface displacement-related value obtained when a measurement vehicle actually travels on a road surface is associated with position information indicating the position at which the road surface displacement-related value is obtained. When the vibration control device determines that there is a high probability that the road surface state has changed from a past time point, it sets the magnitude of the first target control force to be small.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] During preview vibration control, when the vehicle travels in a region where the presence or absence of road surface displacement-related values in the map of measurement data is mixed, at the boundary of the presence or absence of road surface displacement-related values, the road surface displacement-related value changes from a certain value to zero, or from zero to a certain value. Therefore, even when there is actually no step on the road surface at this boundary, vibration may occur. It is desirable to suppress such vibration generation.

[0005] An object of the present invention is to provide a suspension control system capable of suppressing vibration generation at the boundary of the presence or absence of road surface displacement-related values.

Means for Solving the Problems

[0006] To solve the above problems, a suspension control system according to one aspect of the present invention comprises an actuator for adjusting the suspension stroke of a wheel to be controlled by a vehicle, and a control device for controlling the actuator. The control device includes a first acquisition unit that repeatedly acquires road surface displacement-related values ​​at the predicted passing position of the wheel to be controlled after a predetermined time from the current time, from a road surface data map which associates road surface displacement-related values ​​related to vertical displacement of the road surface with position; a second acquisition unit that acquires the amount of change per unit time of the road surface displacement-related values ​​based on the acquired road surface displacement-related values; a calculation unit that calculates a target control force based on the acquired road surface displacement-related values; and a control unit that controls the actuator so that the control force generated by the actuator when the wheel to be controlled passes the predicted passing position matches the target control force. The calculation unit calculates the target control force such that, when the amount of change per unit time of the acquired road surface displacement-related values ​​is greater than or equal to a threshold, the amount of change per unit time of the target control force is smaller compared to when the amount of change is less than the threshold. [Effects of the Invention]

[0007] According to the present invention, a suspension control system can be provided that can suppress the generation of vibrations at the boundary between the presence and absence of road surface displacement-related values. [Brief explanation of the drawing]

[0008] [Figure 1] Figures 1(a) and 1(b) show an example of a map of road surface displacement-related values. [Figure 2] This diagram schematically shows the configuration of the vehicle according to the embodiment. [Figure 3] Figure 2 is a schematic diagram showing the configuration of the suspension. [Figure 4] This is a block diagram showing an example configuration of the suspension control system according to the embodiment. [Figure 5] This is a block diagram showing an example configuration of the map management device according to the embodiment. [Figure 6] This is a flowchart showing the suspension control process of the embodiment. [Modes for carrying out the invention]

[0009] Before describing the specific embodiments, let's explain the underlying knowledge. When performing preview control based on road surface displacement-related values, if there are consecutive areas with maps, control is possible, and if there are consecutive areas without maps, preview control is simply not possible. Having a map means that there are road surface displacement-related values. Not having a map means that there are no road surface displacement-related values, and that their value is zero. Road surface displacement-related values ​​include unsprung displacement, etc. However, as mentioned above, in situations where there is a mix of areas with and without maps, vibrations may occur in the vehicle's sprung mass structure even though there is no actual step at the boundary. Similar problems also arise in cases where the map is not generated properly, that is, when there is a mix of areas with and without maps, or when abnormal values ​​are stored in the map due to sensor value anomalies, etc.

[0010] Figures 1(a) and 1(b) show an example of a map of road surface displacement-related values. In this map, the intensity of the color represents the magnitude of the road surface displacement-related values. Region 302, where the intensity of the color is uniform, represents the absence of a map and the road surface displacement-related value being zero. In the state of the map shown in Figures 1(a) and 1(b), in the preview control of the comparative example, vibrations may occur depending on the driving path, even if there are no actual steps, because the road surface displacement-related values ​​change significantly.

[0011] Figure 1(a) shows an example of a map generated along a straight road. In Figure 1(a), within region 300, there is a map, and road surface displacement-related values ​​are set at each location. Within region 302, there is no map, and the road surface displacement-related values ​​are uniformly zero regardless of location. When a vehicle travels along path 304a, it travels along the boundary between the presence and absence of a map, causing alternating locations where the road surface displacement-related values ​​are zero and locations where they have values, resulting in vibrations in the sprung mass structure.

[0012] When a vehicle travels along route 304b, it crosses area 300 on the map, causing significant vibrations in the susprung mass when crossing from an area without a map to an area with a map, and vice versa. This situation is similar to, for example, crossing a road surface that has already been traveled on at an intersection.

[0013] Figure 1(b) shows an example of a sparsely and abnormally generated map. Such a map may be generated, for example, when the location information at the time of map creation was abnormal. When a vehicle travels along route 304c through a location where the map has been abnormally generated, vibrations occur in the sprung mass. If vibrations occur at the boundary between areas with and without a map, the vehicle user may experience an abnormal ride quality due to the execution of preview control.

[0014] To prevent oscillations at the boundary between map presence and absence, it is conceivable to continuously apply a rate limiter or low-pass filter to the target control force, etc., to suppress abrupt changes in the target control force. However, in this case, the continuous control performance will deteriorate.

[0015] Furthermore, if the check is performed after crossing the boundary, the control has already been implemented and the vibration has worsened, so the effect will be small, and it is necessary to take action when crossing the boundary.

[0016] Alternatively, it could be considered to embed boundary information into the map in advance so that boundaries can be detected beforehand. However, this would require boundary determination processing, increase the map size, and thus increase processing costs, storage costs, and communication costs.

[0017] Therefore, in this embodiment, if the rate of change per unit time of road surface displacement-related values ​​exceeds a threshold, it is determined that this is a map boundary, and a rate limiter or low-pass filter is applied to time-series data such as road surface displacement-related values ​​or target control force to reduce the rate of change per unit time of the target control force. This makes it possible to suppress the generation of vibrations of the sprung mass structure at the boundary without affecting the control performance outside the map boundary.

[0018] Hereinafter, embodiments for implementing the present disclosure will be described in detail with reference to the drawings. In the description, the same elements are denoted by the same reference numerals, and redundant descriptions are omitted as appropriate.

[0019] 1. Suspension and road surface displacement related values FIG. 2 schematically shows the configuration of the vehicle 1 of the embodiment. The vehicle 1 includes a left front wheel 2FL, a right front wheel 2FR, a left rear wheel 2RL, a right rear wheel 2RR, a suspension 3FL, a suspension 3FR, a suspension 3RL, a suspension 3RR, and a suspension control system 10. Corresponding ones of the suspensions 3FL, 3FR, 3RL, and 3RR are provided for each of the left front wheel 2FL, the right front wheel 2FR, the left rear wheel 2RL, and the right rear wheel 2RR. Hereinafter, when there is no particular need for distinction, each wheel is referred to as wheel 2, and each suspension is referred to as suspension 3.

[0020] FIG. 3 schematically shows the configuration of the suspension 3 in FIG. 2. The suspension 3 is provided to connect between the under-spring structure 4 and the above-spring structure 5 of the vehicle 1. The under-spring structure 4 includes the wheel 2. The suspension 3 includes a spring 3S, a damper 3D, and an actuator 3A. The damper 3D is also called a shock absorber. The spring 3S, the damper 3D, and the actuator 3A are provided in parallel between the under-spring structure 4 and the above-spring structure 5. The actuator 3A controls the stroke of the suspension 3. The spring constant of the spring 3S is K. The damping coefficient of the damper 3D is C. The actuator 3A applies a vertical control force Fc between the under-spring structure 4 and the above-spring structure 5, thereby adjusting the stroke of the suspension 3.

[0021] More specifically, actuator 3A is, for example, an electrically operated or hydraulically operated active actuator, and is an actuator that constitutes a so-called fully active suspension. Alternatively, actuator 3A may be, for example, an actuator that varies the damping force generated by damper 3D, or an actuator of an active stabilizer device. Furthermore, the “actuator” of this disclosure may be, for example, an actuator such as an electric motor that generates the longitudinal vehicle forces in a vehicle equipped with a suspension configured to convert the longitudinal vehicle forces acting on the wheels, namely driving force and braking force, into a control force Fc by utilizing the suspension geometry. The electric motor may be, for example, an in-wheel motor (IWM) provided on the wheel, or an electric motor capable of driving the wheel via the vehicle drive shaft.

[0022] Here, we define the terms. "Road surface displacement Zr" is the vertical displacement of the road surface RS. "Unsprung displacement Zu" is the vertical displacement of the unsprung structure 4. "Sprung displacement Zs" is the vertical displacement of the sprung structure 5. "Unsprung velocity Zu'" is the vertical velocity of the unsprung structure 4. "Sprung velocity Zs'" is the vertical velocity of the sprung structure 5. "Unsprung acceleration Zu''" is the vertical acceleration of the unsprung structure 4. "Sprung acceleration Zs''" is the vertical acceleration of the sprung structure 5. Note that the sign of each parameter is positive when it is upward and negative when it is downward.

[0023] Wheel 2 moves on the road surface RS. Hereinafter, values ​​related to the road surface displacement Zr will be referred to as "road surface displacement-related values". Examples of road surface displacement-related values ​​include road surface displacement Zr, road surface displacement velocity Zr' (which is the time derivative of road surface displacement Zr), unsprung displacement Zu, unsprung velocity Zu', unsprung acceleration Zu'', sprung displacement Zs, sprung velocity Zs', or sprung acceleration Zs''. Road surface displacement-related values ​​can also be said to be "vertical motion parameters" that relate to the vertical motion of wheel 2.

[0024] As an example, the following explanation will describe the case where the road surface displacement-related value is the unsprung displacement Zu. When generalizing, replace "unsprung displacement" with "road surface displacement-related value" in the following explanation.

[0025] Here, we will explain an example of the unsprung displacement calculation process. First, the unsprung acceleration Zs'' is detected by the unsprung acceleration sensor 22 installed on the sprung structure 5. Next, the unsprung displacement Zs is calculated by performing a second integral of the unsprung acceleration Zs''.

[0026] Next, the stroke ST, which is the relative displacement between the sprung mass structure 5 and the unsprung mass structure 4, is obtained. "Stroke ST" = "Sprung mass displacement Zs" - "Unsprung mass displacement Zu". For example, the stroke ST is detected by a stroke sensor installed on the suspension 3. As another example, the stroke ST may be estimated based on the sprung mass acceleration Zs'' by an observer configured based on a single-wheel two-degree-of-freedom model.

[0027] Next, filtering is performed on the time-series data of the sprung displacement Zs to suppress the effects of sensor drift and other factors. Similarly, filtering is performed on the time-series data of the stroke ST. For example, the filter is a bandpass filter that allows signal components in a specific frequency band to pass through. The specific frequency band may be set to include the sprung resonance frequency of vehicle 1. For example, the specific frequency band is 0.3 to 10 Hz.

[0028] Next, the difference between the sprung displacement Zs and the stroke ST is calculated as the unsprung displacement Zu.

[0029] Instead of filtering the time-series data of the sprung displacement Zs and stroke ST, filtering may be performed on the time-series data of the calculated unsprung displacement Zu.

[0030] As another example, the unsprung acceleration Zu'' may be detected by an unsprung acceleration sensor, and the unsprung displacement Zu may be calculated from the unsprung acceleration Zu''.

[0031] 2. Suspension control system Figure 4 is a block diagram showing an example configuration of the suspension control system 10 according to the embodiment. The suspension control system 10 is mounted on the vehicle 1. The suspension control system 10 includes a vehicle state sensor 20, a position sensor 40, a communication device 50, an actuator 3A, and an ECU 70. The ECU 70 is an electronic control unit.

[0032] The vehicle state sensor 20 detects the state of vehicle 1 and supplies the detection result to the ECU 70. The vehicle state sensor 20 includes a vehicle speed sensor 21 for detecting the vehicle speed V of vehicle 1, a sprung mass acceleration sensor 22 for detecting the sprung mass acceleration Zs'', and a stroke sensor 23 for detecting the stroke ST. The vehicle state sensor 20 may also include an unsprung mass acceleration sensor. The vehicle state sensor 20 may also include a lateral acceleration sensor, a yaw rate sensor, a steering angle sensor, etc.

[0033] The position sensor 40 detects the position and orientation of the vehicle 1 and supplies the detected position information to the ECU 70. For example, the position sensor 40 includes a GNSS (Global Navigation Satellite System) receiver.

[0034] The communication device 50 communicates with the outside of the vehicle 1.

[0035] The ECU 70 is a computer that controls vehicle 1. The ECU 70 includes a processor 71 and a storage device 72. The processor 71 performs various processes. For example, the processor 71 includes a CPU (Central Processing Unit). The storage device 72 stores various information necessary for processing by the processor 71. Examples of storage devices 72 include volatile memory, non-volatile memory, HDD (Hard Disk Drive), SSD (Solid State Drive), etc.

[0036] The processor 71 includes a first acquisition unit 80, a second acquisition unit 82, a determination unit 84, a calculation unit 86, and a control unit 88. The functions of the first acquisition unit 80, the second acquisition unit 82, the determination unit 84, the calculation unit 86, and the control unit 88 are realized when the processor 71 executes a suspension control program stored in the storage device 72. The suspension control program may be recorded on a computer-readable recording medium. The ECU 70 corresponds to an example of a "control device" in this disclosure.

[0037] The memory device 72 stores the unsprung displacement map 200. Details of the unsprung displacement map 200 will be described later.

[0038] The ECU 70 controls the suspension 3 by controlling the actuator 3A. Specifically, the ECU 70 performs vibration damping control to suppress vibrations of the vehicle 1 by controlling the suspension 3. The ECU 70 controls the actuator 3A to generate a vertical control force Fc between the unsprung mass structure 4 and the sprung mass structure 5, as shown in Figure 3. The vibration damping control includes "preview control," which will be described later. Details of the vibration damping control will be described later.

[0039] 3. Map Management Device 3-1. Example Configuration Figure 5 is a block diagram showing an example configuration of the map management device 100 according to the embodiment. The map management device 100 is a computer that manages various types of map information. The management of map information includes the generation, updating, provision, and distribution of map information. Typically, the map management device 100 is a management server on the cloud. The map management device 100 may also be a distributed system in which multiple servers perform distributed processing.

[0040] The map management device 100 includes a communication device 110. The communication device 110 is connected to a communication network N1. For example, the communication device 110 communicates with a number of vehicles 1 via the communication network N1.

[0041] The map management device 100 further includes a processor 120 and a storage device 130. The processor 120 performs various information processing. For example, the processor 120 includes a CPU. The storage device 130 stores various map information. The storage device 130 also stores various information necessary for processing by the processor 120. Examples of storage devices 130 include volatile memory, non-volatile memory, HDD, SSD, etc.

[0042] The map management program is a computer program for map management and is executed by the processor 120. The map management program is stored in the storage device 130. Alternatively, the map management program may be recorded on a computer-readable recording medium. The execution of the map management program by the processor 120 enables the functionality of the map management device 100.

[0043] The processor 120 communicates with the suspension control system 10 of the vehicle 1 via the communication device 110. The processor 120 collects various information from the suspension control system 10 and generates and updates map information based on the collected information. The processor 120 distributes the map information to the suspension control system 10. The processor 120 provides map information in response to requests from the suspension control system 10.

[0044] 3-2. Unsprung Displacement Map One of the map information managed by the map management device 100 is the unsprung displacement map 200. The unsprung displacement map 200 is a map relating to the unsprung displacement Zu, which is a road surface displacement-related value. The unsprung displacement map 200 is stored in the storage device 130. The unsprung displacement map 200 corresponds to an example of the "road surface data map in which road surface displacement-related values ​​related to the vertical displacement of the road surface are associated with position" as described in this disclosure.

[0045] The unsprung displacement map 200 represents the correspondence between position (X,Y) and unsprung displacement Zu in the XY plane. In other words, the unsprung displacement map expresses the unsprung displacement Zu as a function of position (X,Y). The XY plane represents the horizontal plane. For example, the absolute coordinate system in the horizontal plane is defined by the latitude and longitude directions, and position is defined by latitude and longitude.

[0046] The road area may be divided into a mesh-like structure on a horizontal plane. In other words, the road area may be divided into multiple unit areas (hereinafter referred to as "road surface sections") on a horizontal plane. A road surface section is, for example, a square. The length of one side of the square is, for example, 10 cm. The unsprung displacement map 200 represents the correspondence between the position of a road surface section and the unsprung displacement Zu. The position of a road surface section may be defined by a representative position of that section, for example, the center position, or by the latitude and longitude range of that section. The unsprung displacement Zu of a road surface section is, for example, the average value of the unsprung displacement Zu obtained within that road surface section. The smaller the road surface section, the higher the resolution of the unsprung displacement map 200.

[0047] 3-3. Map generation and update process The processor 120 collects information from multiple vehicles 1 via the communication device 110. Based on the information collected from the multiple vehicles 1, the processor 120 generates and updates the unsprung displacement map 200.

[0048] The position in the unsprung displacement map 200 represents the position that wheel 2 has passed through. The position of each wheel 2 is calculated based on the position information detected by the position sensor 40. Specifically, the relative positional relationship between the reference point of the vehicle position on vehicle 1 and each wheel 2 is known information. Based on this relative positional relationship and the vehicle position indicated by the positional information, the position of each wheel 2 can be calculated.

[0049] The unsprung displacement Zu is calculated by the method described above. Specifically, the sprung displacement Zs and stroke ST are obtained using the vehicle state sensor 20 mounted on the vehicle 1. For convenience, these sprung displacement Zs and stroke ST are referred to as "sensor-based information." The unsprung displacement Zu is calculated based on this sensor-based information.

[0050] For example, while vehicle 1 is in motion, the ECU 70 of the suspension control system 10 calculates the unsprung displacement Zu in real time based on sensor-based information. The ECU 70 also associates the wheel position with the unsprung displacement Zu at the same time. The ECU 70 then transmits a set of time-series data of wheel position and time-series data of unsprung displacement Zu to the map management device 100. The processor 120 of the map management device 100 generates and updates an unsprung displacement map based on the time-series data of wheel position and unsprung displacement Zu.

[0051] As another example, the ECU 70 of the suspension control system 10 associates the wheel position with sensor-based information at the same time. The ECU 70 then transmits a set of time-series data of wheel position and time-series data of sensor-based information to the map management device 100. The processor 120 of the map management device 100 calculates the unsprung displacement Zu based on the received sensor-based information. Furthermore, the processor 120 generates and updates an unsprung displacement map based on the time-series data of wheel position and time-series data of unsprung displacement Zu.

[0052] The processor 120 of the map management device 100 acquires map update information from the suspension control system 10 of the vehicle 1 via the communication device 110. The map update information includes time-series data of wheel positions, which are the positions of the vehicle 1. The map update information also includes time-series data of sensor-based information necessary for calculating the unsprung displacement Zu. Alternatively, the map update information may include time-series data of the unsprung displacement Zu calculated by the ECU 70 of the suspension control system 10.

[0053] The processor 120 of the map management device 100 generates and updates the unsprung displacement map 200 based on map update information.

[0054] Furthermore, the suspension control system 10 of vehicle 1 may maintain a database of unsprung displacement maps 200 and generate and update its own unsprung displacement maps 200. In other words, the map management device 100 may be included in the suspension control system 10.

[0055] 4. Preview control using unsprung displacement map The ECU 70 of the suspension control system 10 communicates with the map management device 100 via the communication device 50. The ECU 70 obtains an unsprung displacement map 200 of the area including the current position of the vehicle 1 from the map management device 100. The unsprung displacement map 200 is stored in the memory device 72. Then, based on the unsprung displacement map 200, the ECU 70 performs preview control, which is a type of vibration damping control. Preview control is performed to reduce vibrations of the sprung mass structure 5.

[0056] The first acquisition unit 80, the second acquisition unit 82, the determination unit 84, the calculation unit 86, and the control unit 88 repeatedly perform the following processing for each of the four controlled wheels at each time step.

[0057] The first acquisition unit 80 acquires the current position of each wheel 2. The relative positional relationship between the reference point of the vehicle position on the vehicle 1 and each wheel 2 is known information. Based on this relative positional relationship and the vehicle position indicated by the positional information, the position of each wheel 2 can be calculated.

[0058] The first acquisition unit 80 calculates the predicted passing position Pf of wheel 2 after a preview time tp from the current time. The preview time tp is a predetermined time, and is set in advance to be, for example, the time required from when the first acquisition unit 80 identifies the predicted passing position Pf until the actuator 3A of the suspension 3 outputs a control force Fc corresponding to the target control force Fc_t. The preview distance Lp is given by the product of the preview time tp and the vehicle speed V. The predicted passing position Pf is the position in the direction of vehicle travel that is forward from the current position by a preview distance Lp along the predicted path of movement in which wheel 2 is expected to move. The predicted path of movement can be determined, for example, based on the direction of travel of vehicle 1 and the current position P0 of wheel 2. The direction of travel can be determined, for example, by the following method. That is, the first acquisition unit 80 maps the current position P0 of the previous time step and the current position P0 of the current time step to map information, and then identifies the direction from the current position of the previous time step to the current position P0 of the current time step as the direction of travel. As a modified example, the first acquisition unit 80 may calculate a predicted driving route based on the vehicle speed V and the steering angle of the wheels 2, and calculate a predicted passing position Pf based on the predicted driving route.

[0059] The first acquisition unit 80 reads and acquires the unsprung displacement Zu at the calculated predicted passing position Pf from the unsprung displacement map 200.

[0060] The second acquisition unit 82 acquires the rate of change of unsprung displacement Zu per unit time based on the unsprung displacement Zu acquired by the first acquisition unit 80. The unit time is, for example, the length of one time step. If the main calculation period and the calculation period for reading the unsprung displacement map 200 are different, this time step refers to the calculation period for reading the map.

[0061] Specifically, the second acquisition unit 82 acquires the difference between the unsprung displacement Zu read by the first acquisition unit 80 from the unsprung displacement map 200 in the previous time step and the unsprung displacement Zu read by the first acquisition unit 80 from the unsprung displacement map 200 in the current time step, as the change in unsprung displacement Zu per unit time. The change in unsprung displacement Zu per unit time is assumed to represent an absolute value.

[0062] Next, the determination unit 84 determines whether the change in unsprung displacement Zu per unit time, acquired by the second acquisition unit 82, is greater than or equal to a threshold value. The threshold value can be appropriately determined by experiment or simulation. For example, if the time step for reading from the unsprung displacement map 200 is 10 [ms] and the difference in unsprung displacement Zu is 0.02 [m], the road surface input or unsprung input will be 2 [m / s]. Since this is considered a large input that is not likely to occur under normal circumstances, the threshold value is set so that such a value is greater than or equal to the threshold value.

[0063] If the rate of change per unit time of the unsprung displacement Zu acquired by the second acquisition unit 82 is less than the threshold, the predicted passing position Pf does not cross the boundary of the unsprung displacement map 200, or even if the predicted passing position Pf crosses the boundary, the rate of change in unsprung displacement Zu is small enough that it does not cause any problems regarding vibration generation. Therefore, the calculation unit 86 performs normal preview control. In other words, if the rate of change per unit time of the unsprung displacement Zu is less than the threshold, the calculation unit 86 calculates the target control force Fc_t of the actuator 3A of the suspension 3 based on the unsprung displacement Zu at the predicted passing position Pf acquired by the first acquisition unit 80. The target control force Fc_t is calculated, for example, as follows. This target control force Fc_t corresponds to the required value of the control force Fc needed for preview control.

[0064] The equation of motion for the spring structure 5 in Figure 3 is given by the following equation (1).

[0065] m·Zs''=C(Zu'-Zs')+K(Zu-Zs)-Fc ···(1) In equation (1), m is the mass of the sprung mass 5, C is the damping coefficient of the damper 3D, K is the spring constant of the spring 3S, and Fc is the vertical control force generated by the actuator 3A. If the vibration of the sprung mass 5 is completely canceled out by the control force Fc, then Zs''=0, Zs'=0, Zs=0, and the control force Fc is expressed by the following equation (2).

[0066] Fc = C·Zu' + K·Zu ···(2) The control force Fc that provides at least a vibration damping effect is expressed by the following equation (3).

[0067] Fc=α·C·Zu'+β·K·Zu ···(3) In equation (3), the control gain α is greater than 0 and less than or equal to 1, and the control gain β is also greater than 0 and less than or equal to 1. If the derivative term in equation (3) is omitted, the control force Fc that provides at least a vibration damping effect is expressed by the following equation (4).

[0068] Fc = β·K·Zu ···(4) The calculation unit 86 calculates the target control force Fc_t according to equation (3) or equation (4) above. That is, the calculation unit 86 calculates the target control force Fc_t by substituting the unsprung displacement Zu at the predicted passing position Pf into equation (3) or equation (4).

[0069] The control unit 88 transmits a control command to the actuator 3A, including the target control force Fc_t, so that the actuator 3A generates a control force Fc corresponding to the target control force Fc_t. The actuator 3A generates a control force Fc corresponding to the target control force Fc_t at a timing that is a preview time tp after the current time, i.e., at the timing when the wheel 2 passes the predicted passing position Pf. In other words, the control unit 88 controls the actuator 3A so that the control force Fc generated by the actuator 3A when the controlled wheel passes the predicted passing position Pf matches the target control force Fc_t.

[0070] Thus, with preview control using the unsprung displacement map 200, if the rate of change of the unsprung displacement Zu per unit time is less than a threshold, a control force Fc can be generated at an appropriate timing to suppress vibrations of the sprung structure 5 caused by the unsprung displacement Zu at the predicted passing position Pf of the wheel 2. This effectively suppresses vibrations of the sprung structure 5.

[0071] On the other hand, if the rate of change of unsprung displacement Zu per unit time exceeds a threshold, the predicted passing position Pf crosses the boundary of the unsprung displacement map 200, and it can be determined that the unsprung displacement Zu acquired in the current time step is abnormal. Therefore, assuming that the control described above based on the acquired unsprung displacement Zu is continued, there is a high concern that the control will increase vibrations beyond the original input, so a process to reduce vibrations is executed.

[0072] The calculation unit 86 calculates the target control force Fc_t such that, when the rate of change of the unsprung displacement Zu per unit time is greater than or equal to a threshold, the rate of change of the target control force Fc_t per unit time is smaller compared to when the rate of change is less than a threshold. The rate of change of the target control force Fc_t per unit time is the difference between the target control force Fc_t calculated in the previous time step and the target control force Fc_t calculated in the current time step. The rate of change of the target control force Fc_t per unit time is expressed as an absolute value.

[0073] For example, if the rate of change of unsprung displacement Zu per unit time is greater than or equal to a threshold, the calculation unit 86 applies a rate limiter to the time-series data of unsprung displacement Zu acquired in the current time step and past time steps to calculate the target control force Fc_t so that the rate of change of the target control force Fc_t per unit time is reduced. The rate limiter restricts the rate of change of unsprung displacement Zu per unit time to a predetermined limit value or less. It can also be said that the rate limiter suppresses the amount by which unsprung displacement Zu can change from the previous time step to the current time step.

[0074] In other words, the calculation unit 86 corrects the value of the unsprung displacement Zu acquired in the current time step using a rate limiter, thereby reducing the rate of change of the unsprung displacement Zu per unit time compared to before the correction. Then, the calculation unit 86 substitutes the corrected unsprung displacement Zu into equation (3) or equation (4) to calculate the target control force Fc_t.

[0075] The calculation unit 86 limits the rate of change of the target control force Fc_t per unit time by applying a rate limiter for a predetermined control time if the rate of change of the unsprung displacement Zu per unit time is greater than or equal to a threshold value. In other words, when the control time has elapsed, the limiting of the rate of change of the target control force Fc_t per unit time ends. The process of limiting the rate of change of the target control force Fc_t per unit time is called vibration reduction processing. The limit value and control time can be appropriately determined by experiment or simulation so as to reduce the vibration of the sprung structure 5.

[0076] This suppresses the abrupt change in the target control force Fc_t when the vehicle 1 passes the boundary between the presence and absence of unsprung displacement Zu in the unsprung displacement map 200, thereby suppressing the generation of vibration in the sprung structure 5. For example, when the vehicle 1 travels along paths 304a, 304b, or 304c in Figure 1(a), the vibration of the sprung structure 5 can be reduced compared to the comparative example where vibration reduction processing is not performed. The rate limiter is applied only when crossing the boundary between the presence and absence of unsprung displacement Zu and during the subsequent control time, so it does not affect normal vibration damping control at other times.

[0077] Furthermore, if the rate of change of the unsprung displacement Zu per unit time is greater than or equal to a threshold, the calculation unit 86 may apply a low-pass filter instead of a rate limiter to the time-series data of the unsprung displacement Zu acquired in the current time step and past time steps for the duration of the control time. By doing this, the calculation unit 86 can limit the rate of change of the target control force Fc_t per unit time. In other words, the calculation unit 86 corrects the value of the unsprung displacement Zu acquired in the current time step using a low-pass filter, thereby reducing the rate of change of the unsprung displacement Zu per unit time compared to before the correction, and suppressing sharp changes in the unsprung displacement Zu. The cutoff frequency of the low-pass filter can be appropriately determined by experiment or simulation so as to reduce the vibration of the sprung structure 5.

[0078] Furthermore, if the rate of change of the unsprung displacement Zu per unit time is greater than or equal to a threshold, the calculation unit 86 may apply a rate limiter or a low-pass filter to the time-series data of the target control force Fc_t calculated in the current time step and past time steps, instead of the unsprung displacement Zu. Through this process, the calculation unit 86 can calculate the target control force Fc_t in such a way that the rate of change of the target control force Fc_t per unit time is small.

[0079] In other words, the calculation unit 86 calculates the target control force Fc_t by substituting the unsprung displacement Zu acquired by the first acquisition unit 80 into equation (3) or equation (4) without correction. The calculation unit 86 applies a rate limiter or a low-pass filter to correct the value of the target control force Fc_t calculated in the current time step, thereby reducing the rate of change of the target control force Fc_t per unit time compared to before correction. The calculation unit 86 then supplies the corrected target control force Fc_t to the control unit 88.

[0080] Furthermore, the calculation unit 86 may calculate the target control force Fc_t such that, when the amount of change per unit time of the unsprung displacement Zu is greater than or equal to a threshold, the larger the amount of change, the greater the reduction in the amount of change per unit time of the target control force Fc_t. In this case, the calculation unit 86 may increase the strength of the rate limiter by decreasing the limit value of the rate limiter as the amount of change per unit time of the unsprung displacement Zu increases. Also, the calculation unit 86 may increase the strength of the low-pass filter by decreasing the cutoff frequency of the low-pass filter or increasing the order or number of stages of the low-pass filter as the amount of change per unit time of the unsprung displacement Zu increases. This process makes it possible to suppress vibration generation more effectively in accordance with the magnitude of the amount of change per unit time of the unsprung displacement Zu.

[0081] Figure 6 is a flowchart showing the suspension control process of the embodiment. The process in this flowchart is repeatedly executed at predetermined time steps for each of the controlled wheels while the vehicle 1 is in motion.

[0082] The first acquisition unit 80 acquires the current position of the wheel 2 (S10), acquires the predicted passing position Pf of the wheel 2 (S12), and acquires the unsprung displacement Zu of the predicted passing position Pf of the wheel 2 from the unsprung displacement map 200 (S14). The second acquisition unit 82 acquires the amount of change per unit time of the unsprung displacement Zu based on the unsprung displacement Zu acquired in the previous time step and the unsprung displacement Zu acquired in the current time step (S16).

[0083] If the rate of change of the unsprung displacement Zu per unit time is greater than or equal to a threshold (Y in S18), the calculation unit 86 performs vibration reduction processing to calculate the target control force Fc_t (S20), the control unit 88 controls the actuator 3A (S22), and the process ends.

[0084] On the other hand, if the rate of change of the unsprung displacement Zu per unit time is not greater than or equal to the threshold (N in S18), and if the time limit has elapsed since the last time the rate of change exceeded the threshold (Y in S24), the calculation unit 86 calculates the target control force Fc_t without performing vibration reduction processing (S26), and the process moves to S22. If the time limit has not elapsed since the last time the rate of change of the unsprung displacement Zu per unit time exceeded the threshold (N in S24), the process moves to S20.

[0085] According to the embodiment, when the amount of change per unit time of the road surface displacement-related value is greater than or equal to a threshold, the target control force Fc_t is calculated so that the amount of change per unit time of the target control force Fc_t is small. This makes it possible to suppress the occurrence of vibrations at the boundary between the presence and absence of road surface displacement-related values ​​without affecting control outside the boundary between the presence and absence of road surface displacement-related values. Therefore, it is possible to suppress the feeling of discomfort in ride comfort caused by the execution of preview control.

[0086] The present invention has been described above based on embodiments. The embodiments are merely illustrative, and it will be understood by those skilled in the art that various modifications are possible in combinations of each component and each processing process, and that such modifications also fall within the scope of the present invention.

[0087] (First variation) The control unit 88 may perform the following feedback control as vibration damping control in addition to the preview control described above by controlling the actuator 3A. That is, the feedback control is performed to reduce the vibration of the sprung mass structure 5. In an example in which preview control is performed with the feedback control, the control force Fc is expressed by, for example, the following equation (5). In this example, the calculation unit 86 calculates the target control force Fc_t according to equation (5).

[0088] Fc = β·K·Zu + γ·Zs ···(5) The first term on the right-hand side of equation (5) is the same as in equation (4) above, and is a feedforward term relating to preview control. The second term on the right-hand side is a feedback term relating to feedback control. This feedback term is the product of the feedback gain γ and the sprung displacement Zs when the target control force Fc_t is calculated. Note that instead of the sprung displacement Zs in the feedback term, any of the sprung velocity Zs', sprung acceleration Zs'', unsprung displacement Zu, unsprung velocity Zu', and unsprung acceleration Zu'' when the target control force Fc_t is calculated may be used.

[0089] The calculation unit 86 sets the basic gain γ0 as the feedback gain γ for feedback control when the amount of change per unit time of the sprung displacement Zs is less than a threshold.

[0090] The calculation unit 86 increases the feedback gain γ during the control time when the amount of change of the sprung displacement Zs per unit time is greater than or equal to a threshold, compared to when the amount of change is less than a threshold. In other words, in this case, the calculation unit 86 sets the feedback gain γ1 to be greater than the basic gain γ0. In this case, the target control force Fc_t calculated according to the above equation (5) is greater than when the feedback gain γ is the basic gain γ0. That is, when the amount of change of the sprung displacement Zs per unit time is greater than or equal to a threshold, feedback control is actively utilized compared to when the amount of change is less than a threshold.

[0091] The basic gains γ0 and γ1 can be determined as appropriate through experimentation or simulation. Gain γ1 may be a fixed value. Furthermore, if the rate limiter strength or the low-pass filter strength is increased as the rate of change of unsprung displacement Zu per unit time increases, gain γ1 may be set to increase as the rate of change of unsprung displacement Zu per unit time increases.

[0092] This allows for more aggressive vibration damping using feedback control during the execution of vibration reduction processing, when the damping effect of preview control is temporarily weakened, thereby suppressing the deterioration of vibration of the sprung mass structure 5.

[0093] (Second variation) If the amount of change per unit time of the sprung displacement Zs is greater than or equal to a threshold, the control unit 88 may, for the duration of the control time, perform preview control using the unsprung displacement Zu1 calculated for the position of the front wheel, in addition to the preview control using the unsprung displacement map 200 described above. Since the rear wheel is considered to follow the path of the front wheel, such control may be performed. In this case, the control force Fc is expressed by, for example, the following equation (6). In this example, the calculation unit 86 calculates the target control force Fc_t according to equation (6) while the vibration reduction process is being executed.

[0094] Fc=β·K·Zu+γa·Zu1 ···(6) The first term on the right-hand side of equation (6) is the same as in equation (4) above, and is a feedforward term relating to preview control using the unsprung displacement map 200. The second term on the right-hand side is a feedforward term relating to preview control using the unsprung displacement Zu1 calculated for the position of the front wheel. The second term on the right-hand side is the product of the gain γa and the unsprung displacement Zu1 at the position of the front wheel when the target control force Fc_t is calculated. The unsprung displacement Zu1 can be calculated using the detected value of the sprung acceleration sensor 22, as described above. The gain γa can be appropriately determined by experiment or simulation.

[0095] As a result, during the vibration reduction process, in which the damping effect by preview control using the unsprung displacement map 200 is temporarily weakened, the deterioration of vibration of the sprung structure 5 can be suppressed by damping the rear wheels using preview control based on the unsprung displacement Zu1 calculated for the position where the front wheels passed.

[0096] (Third variation) If the amount of change per unit time of the sprung displacement Zs is greater than or equal to a threshold, the control unit 88 may, during the control time, perform preview control using a known preview sensor in addition to the preview control using the unsprung displacement map 200 described above. The preview sensor (not shown) includes, for example, at least one of a camera sensor, LiDAR, and radar sensor. The preview sensor acquires the road surface displacement of the road surface in front of the vehicle 1. In this case, the control force Fc is expressed, for example, by the following equation (7). In this example, the calculation unit 86 calculates the target control force Fc_t according to equation (7) while the vibration reduction process is being executed.

[0097] Fc=β·K·Zu+γb·Z0 ···(7) The first term on the right-hand side of equation (7) is the same as in equation (4) above, and is a feedforward term relating to preview control using the unsprung displacement map 200. The second term on the right-hand side is a feedforward term relating to preview control using the preview sensor. The second term on the right-hand side is the product of the gain γb and the road surface displacement Z0 in front of vehicle 1, which is obtained by the preview sensor when calculating the target control force Fc_t. The gain γb can be appropriately determined by experiment or simulation. Preview control using the preview sensor is well known, so no further detailed explanation is provided.

[0098] As a result, while the vibration reduction process is being executed, during which the vibration damping effect by preview control using the unsprung displacement map 200 is temporarily weakened, vibration damping by preview control using the preview sensor can suppress the deterioration of vibration of the sprung structure 5.

[0099] Furthermore, at least two of the first, second, and third variations may be combined.

[0100] Furthermore, in this embodiment, the preview control is performed on all four wheels 2 of the vehicle 1. However, the wheels targeted for preview control are not limited to all wheels; for example, only the left and right front wheels, or only the left and right rear wheels, may be included. [Explanation of Symbols]

[0101] 1...Vehicle, 2...Wheel, 3...Suspension, 3A...Actuator, 5...Suspension structure, 10...Suspension control system, 70...ECU (Control Unit), 80...First acquisition unit, 82...Second acquisition unit, 84...Determination unit, 86...Calculation unit, 88...Control unit, 200...Unsprung displacement map (road surface data map).

Claims

1. An actuator that adjusts the suspension stroke of the controlled wheel of the vehicle, A control device for controlling the actuator, Equipped with, The control device is A first acquisition unit repeatedly acquires road surface displacement-related values ​​at the predicted passing position of the controlled wheel after a predetermined time from the current time, from a road surface data map in which road surface displacement-related values ​​related to the vertical displacement of the road surface are associated with position, A second acquisition unit acquires the amount of change per unit time of the road surface displacement-related values ​​based on the acquired road surface displacement-related values, A calculation unit that calculates the target control force based on the acquired road surface displacement-related values, A control unit controls the actuator so that the control force generated by the actuator matches the target control force when the controlled wheel passes the predicted passing position, It has, The calculation unit calculates the target control force such that, when the amount of change per unit time of the acquired road surface displacement-related value is greater than or equal to a threshold, the amount of change per unit time of the target control force is smaller compared to when the amount of change is less than the threshold. A suspension control system characterized by the following features.

2. If the amount of change per unit time of the acquired road surface displacement-related value is greater than or equal to the threshold, the calculation unit applies a rate limiter or a low-pass filter to the time-series data of the acquired road surface displacement-related value or the time-series data of the target control force to calculate the target control force so that the amount of change per unit time of the target control force becomes smaller. The suspension control system according to feature 1.

3. The calculation unit, if the amount of change per unit time of the acquired road surface displacement-related value is greater than or equal to the threshold, applies the rate limiter or the low-pass filter for a predetermined control time. The suspension control system according to claim 2, characterized in that it is the same as described in claim 2.

4. The calculation unit, when the amount of change per unit time of the acquired road surface displacement-related value is greater than or equal to the threshold, calculates the target control force such that the reduction in the amount of change per unit time of the target control force increases as the amount of change increases. The suspension control system according to any one of claims 1 to 3.

5. The control unit further performs feedback control to reduce vibration of the suprasprung structure by controlling the actuator. The calculation unit increases the feedback gain of the feedback control when the amount of change per unit time of the acquired road surface displacement-related value is greater than or equal to the threshold, compared to when the amount of change is less than the threshold. The suspension control system according to any one of claims 1 to 3.

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