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 technology]

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

[0003] [Patent Document 1] Patent Publication No. 2022-064361 Summary of the Invention [Problem to be solved by the invention]

[0004] During preview vibration suppression control, when the vehicle travels through an area in the map of measurement data where the road surface displacement-related values ​​are mixed, the road surface displacement-related values ​​change from a certain value to zero, or from zero to a certain value, at the boundary between the presence and absence of the road surface displacement-related values. Therefore, even if there is no actual difference in the road surface at this boundary, vibrations may occur. It is desirable to suppress the occurrence of such vibrations.

[0005] An object of the present invention is to provide a suspension control system capable of suppressing the occurrence of vibration at the boundary between the presence and absence of a road surface displacement-related value. [Means for solving the problem]

[0006] In order to solve the above problem, a suspension control system according to an embodiment of the present invention includes an actuator that adjusts a suspension stroke of a controlled wheel of a vehicle, and a control device that controls the actuator. The control device includes a first acquisition unit that repeatedly acquires a road surface displacement-related value at a predicted passing position of the controlled wheel a predetermined time after a current time from a road surface data map in which a road surface displacement-related value related to a vertical displacement of a road surface is associated with a position, a second acquisition unit that acquires a change amount per unit time of the road surface displacement-related value based on the acquired road surface displacement-related value, a calculation unit that calculates a target control force based on the acquired road surface displacement-related value, and a control unit that controls the actuator so that the control force generated by the actuator when the controlled wheel passes the predicted passing position coincides with the target control force. When the change amount per unit time of the acquired road surface displacement-related value is equal to or greater than a threshold value, the calculation unit calculates the target control force so that the change amount per unit time of the target control force is smaller than when the change amount is less than the threshold value. Effect of the Invention

[0007] According to the present invention, it is possible to provide a suspension control system that can suppress the occurrence of vibrations at the boundary between the presence and absence of a road surface displacement-related value. [Brief description of the drawings]

[0008] [Figure 1] 1(a) and 1(b) are diagrams showing an example of a map of road surface displacement-related values. [Diagram 2] 1 is a diagram illustrating a schematic configuration of a vehicle according to an embodiment. [Diagram 3] FIG. 3 is a diagram illustrating a schematic configuration of the suspension in FIG. 2. [Figure 4] 1 is a block diagram showing a configuration example of a suspension control system according to an embodiment; [Diagram 5] 1 is a block diagram showing an example of a configuration of a map management device according to an embodiment; [Figure 6] 4 is a flowchart showing a suspension control process according to the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Before describing the embodiment in detail, the knowledge on which the invention is based will be described. When performing preview control based on a road surface displacement-related value, if there are consecutive locations with a map, the control can be performed well, and if there are consecutive locations without a map, the preview control cannot be performed. The presence of a map indicates that there is a road surface displacement-related value. The absence of a map indicates that there is no road surface displacement-related value, and that the value is zero. The road surface displacement-related value is an unsprung displacement, etc. However, as described above, in a situation where there is a mixture of the presence and absence of a map, vibrations may occur in the sprung structure of the vehicle even though there is no actual step at the boundary. In addition, similar problems occur in cases where the map is not generated well, that is, in cases where there is a mixture of the presence and absence of a map, or where an abnormal value is stored in the map due to an abnormal sensor value, etc.

[0010] 1(a) and (b) show an example of a map of road surface displacement-related values. In this map, the magnitude of the road surface displacement-related value is represented by a shade of color. A uniformly shaded area 302 indicates that there is no map and the road surface displacement-related value is zero. In the case of the map shown in FIG. 1(a) and (b), in the preview control of the comparative example, depending on the driving route, the road surface displacement-related value may change significantly even if there is no actual step, which may cause vibration.

[0011] Fig. 1(a) shows an example where a map is generated along a straight road. In Fig. 1(a), a map is present in an area 300, and road surface displacement-related values ​​are set at each position. In an area 302, there is no map, and the road surface displacement-related values ​​are uniformly zero regardless of position. When a vehicle travels along a route 304a, the vehicle travels on the boundary between the presence and absence of a map, and therefore places where the road surface displacement-related value is zero and places where a value is present alternately occur, causing vibrations in the sprung structure.

[0012] When the vehicle travels along route 304b, it crosses an area 300 with a map, and large vibrations are generated in the sprung structure when it crosses from an area without a map to an area with a map, and vice versa. This situation corresponds to, for example, when the vehicle crosses a road surface that has been traveled once before at an intersection.

[0013] FIG. 1(b) shows an example of a map that is sparsely generated abnormally. Such a map may be generated, for example, when the position information at the time of map generation is abnormal. When the vehicle travels along the route 304c through a location where the map is abnormally generated, vibrations occur in the sprung structure. When vibrations occur at the boundary between the presence and absence of a map, the user of the vehicle may feel an uncomfortable ride caused by the execution of preview control.

[0014] In order to prevent the oscillation at the boundary between the presence and absence of the map, it is conceivable to apply a constant rate limiter or a low-pass filter to the target control force, etc., to suppress the sudden change in the target control force. However, in this case, the constant control performance is degraded.

[0015] Furthermore, even if the determination is made after the boundary is crossed, the control has already been implemented and the vibration has worsened, so the effect is small and it is necessary to take action when crossing the boundary.

[0016] It is also possible to embed boundary information in the map in advance so that the boundaries can be detected in advance, but this requires boundary determination processing and increases the map capacity, resulting in higher processing costs, storage costs, and communication costs.

[0017] Therefore, in the embodiment, when the amount of change per unit time of the road surface displacement-related value is equal to or greater than a threshold value, it is determined that the boundary of the map is present, and the amount of change per unit time of the target control force is reduced by applying a rate limiter or a low-pass filter to time-series data such as the road surface displacement-related value or the target control force, etc. This makes it possible to suppress the occurrence of vibration of the sprung structure at the boundary of the map without affecting the control performance outside the boundary.

[0018] Hereinafter, embodiments of 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 duplicated description will be omitted as appropriate.

[0019] 1. Suspension and road surface displacement related values 2 shows a schematic configuration of a vehicle 1 according to an 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. The left front wheel 2FL, the right front wheel 2FR, the left rear wheel 2RL, and the right rear wheel 2RR are provided with corresponding suspensions 3FL, 3FR, 3RL, and 3RR, respectively. Hereinafter, unless otherwise required, each wheel will be referred to as a wheel 2, and each suspension will be referred to as a suspension 3.

[0020] FIG. 3 shows a schematic configuration of the suspension 3 in FIG. 2. The suspension 3 is provided to connect between the unsprung structure 4 and the sprung structure 5 of the vehicle 1. The unsprung structure 4 includes the wheels 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 unsprung structure 4 and the sprung structure 5. The actuator 3A controls the stroke of the suspension 3. The spring 3S has a spring constant K. The damper 3D has a damping coefficient C. The actuator 3A applies a vertical control force Fc between the unsprung structure 4 and the sprung structure 5, thereby adjusting the stroke of the suspension 3.

[0021] More specifically, the actuator 3A is, for example, an electric or hydraulic active actuator, and is an actuator constituting a so-called full active suspension. Alternatively, the actuator 3A may be, for example, an actuator that varies the damping force generated by the damper 3D, or an actuator of an active stabilizer device. Furthermore, the "actuator" of the present disclosure may be, for example, an actuator such as an electric motor that generates a vehicle longitudinal force in a vehicle equipped with a suspension configured to be able to convert the driving force and braking force acting on the wheels, which are the vehicle longitudinal forces, 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 may be an electric motor capable of driving the wheel via a vehicle drive shaft.

[0022] Here, the terms are defined. "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. The sign of each parameter is positive when pointing upward and negative when pointing downward.

[0023] The 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 the road surface displacement-related values ​​include the road surface displacement Zr, the road surface displacement velocity Zr' which is the time derivative value of the road surface displacement Zr, the unsprung displacement Zu, the unsprung velocity Zu', the unsprung acceleration Zu'', the sprung displacement Zs, the sprung velocity Zs', and the sprung acceleration Zs'', etc. The road surface displacement-related values ​​can also be said to be "vertical movement parameters" which are parameters related to the vertical movement of the wheel 2.

[0024] As an example, the case where the road surface displacement-related value is the unsprung displacement Zu will be described below. When generalizing, the "unsprung displacement" in the following description should be read as the "road surface displacement-related value".

[0025] Here, an example of the unsprung displacement calculation process will be described. First, the sprung acceleration Zs'' is detected by the sprung acceleration sensor 22 installed in the sprung structure 5. Next, the sprung displacement Zs is calculated by integrating the sprung acceleration Zs'' twice.

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

[0027] Next, in order to suppress the influence of sensor drift and the like, a filtering process is performed on the time series data of the sprung displacement Zs. Similarly, a filtering process is performed on the time series data of the stroke ST. For example, the filter is a band-pass filter that passes signal components in a specific frequency band. The specific frequency band may be set so as to include the sprung resonance frequency of the 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 performing filtering processing on the time series data of the sprung displacement Zs and the stroke ST, filtering processing may be performed on the time series data of the calculated unsprung displacement Zu.

[0030] As yet 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 4 is a block diagram showing an example of the configuration of a suspension control system 10 according to an embodiment. The suspension control system 10 is mounted on a 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 the vehicle 1 and supplies the detection result to the ECU 70. The vehicle state sensor 20 includes a vehicle speed sensor 21 that detects the vehicle speed V of the vehicle 1, a sprung acceleration sensor 22 that detects the sprung acceleration Zs'', and a stroke sensor 23 that detects the stroke ST. The vehicle state sensor 20 may include an unsprung acceleration sensor. The vehicle state sensor 20 may 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 Global Navigation Satellite System (GNSS) receiver.

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

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

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

[0037] The storage device 72 stores an unsprung displacement map 200. The unsprung displacement map 200 will be described in detail later.

[0038] The ECU 70 controls the actuator 3A to control the suspension 3. Specifically, the ECU 70 performs vibration suppression control to suppress vibration 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 structure 4 and the sprung structure 5 as shown in FIG. 3. The vibration suppression control includes a "preview control" to be described later. The vibration suppression control will be described in detail later.

[0039] 3.Map management device 3-1. Configuration example 5 is a block diagram showing an example of a configuration of a map management device 100 according to an embodiment. The map management device 100 is a computer that manages various types of map information. The management of map information includes the generation, update, provision, and distribution of the map information. Typically, the map management device 100 is a management server on a cloud. The map management device 100 may 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 large 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 executes 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 required for processing by the processor 120. Examples of the storage device 130 include a volatile memory, a non-volatile memory, a HDD, and an SSD.

[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 in a computer-readable recording medium. The functions of the map management device 100 are realized by the processor 120 executing the map management program.

[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 the map information in response to a request 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 an unsprung displacement map 200. The unsprung displacement map 200 is a map relating to 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 a "road surface data map in which a road surface displacement-related value related to the vertical displacement of the road surface is associated with a position" in the present disclosure.

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

[0046] The road area may be divided into a mesh shape on a horizontal plane. That is, the road area may be divided into a plurality of unit areas (hereinafter referred to as "road surface sections") on a horizontal plane. The 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 the road surface section and the unsprung displacement Zu. The position of the road surface section may be defined by a representative position of the road surface section, for example, a central position, or may be defined by a latitude range and a longitude range of the road surface section. The unsprung displacement Zu of the road surface section is, for example, an average value of the unsprung displacement Zu acquired within the road surface section. The smaller the road surface section is, the higher the resolution of the unsprung displacement map 200 is.

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

[0048] The positions in the unsprung displacement map 200 are positions through which the wheels 2 have passed. The position of each wheel 2 is calculated based on position information detected by the position sensor 40. Specifically, the relative positional relationship between a reference point of the vehicle position on the vehicle 1 and each wheel 2 is known information. The position of each wheel 2 can be calculated based on the relative positional relationship and the vehicle position indicated by the position information.

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

[0050] For example, while the vehicle 1 is traveling, the ECU 70 of the suspension control system 10 calculates the unsprung displacement Zu in real time based on the sensor-based information. The ECU 70 also associates the wheel position and the unsprung displacement Zu at the same timing. The ECU 70 then transmits a set of time series data of the wheel position and time series data of the 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 the wheel position and the time series data of the unsprung displacement Zu.

[0051] As another example, the ECU 70 of the suspension control system 10 associates the wheel positions with the sensor-based information at the same timing. Then, the ECU 70 transmits a set of time-series data of the wheel positions and time-series data of the 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 the wheel positions and the time-series data of the 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 the wheel positions, which are the positions of the vehicle 1. The map update information also includes time series data of sensor-based information required to calculate 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 the map update information.

[0054] The suspension control system 10 of the vehicle 1 may hold a database of the unsprung displacement map 200 and generate and update its own unsprung displacement map 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 acquires an unsprung displacement map 200 of an area including the current position of the vehicle 1 from the map management device 100. The unsprung displacement map 200 is stored in the storage device 72. Then, the ECU 70 executes preview control, which is a type of vibration suppression control, based on the unsprung displacement map 200. The preview control is executed to reduce vibration of the sprung 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 execute the following process for each time step for each of the four control target wheels.

[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. The position of each wheel 2 can be calculated based on the relative positional relationship and the vehicle position indicated by the position information.

[0058] The first acquisition unit 80 calculates a predicted passing position Pf of the 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, a time required from when the first acquisition unit 80 specifies 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 a position forward in the vehicle traveling direction from the current position by the preview distance Lp along the predicted moving path along which the wheel 2 is predicted to move. The predicted moving path can be specified, for example, based on the traveling direction of the vehicle 1 and the current position P0 of the wheel 2. The traveling direction can be specified, 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 specifies the direction from the current position of the previous time step to the current position P0 of the current time step as the traveling direction. As a modified example, the first acquisition unit 80 may calculate a predicted travel route based on the vehicle speed V and the steering angle of the wheels 2, and calculate the predicted passing position Pf based on the predicted travel route.

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

[0060] The second acquisition unit 82 acquires the amount of change in the 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. When 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 amount of change per unit time of the unsprung displacement Zu. The amount of change per unit time of the unsprung displacement Zu is represented by an absolute value.

[0062] Next, the determination unit 84 determines whether the amount of change per unit time of the unsprung displacement Zu acquired by the second acquisition unit 82 is equal to or greater than a threshold value. The threshold value can be appropriately determined by experiment or simulation. For example, if the time step of reading from the unsprung displacement map 200 is 10 [ms] and the difference in the unsprung displacement Zu is 0.02 [m], the road input or unsprung input is 2 [m / s]. This is considered to be a large input that is unlikely to occur normally, so the threshold value is determined so that such a value is equal to or greater than the threshold value.

[0063] When the amount of change per unit time of the unsprung displacement Zu acquired by the second acquisition unit 82 is less than the threshold value, the predicted passing position Pf does not cross the boundary of the unsprung displacement map 200, or the amount of change in the unsprung displacement Zu is such that there is no problem with vibration generation even if the predicted passing position Pf crosses the boundary. Therefore, the calculation unit 86 executes normal preview control. That is, when the amount of change per unit time of the unsprung displacement Zu is less than the threshold value, 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 a required value of the control force Fc required for the preview control.

[0064] The equation of motion for the sprung structure 5 in FIG. 3 is expressed 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 structure 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 structure 5 is completely cancelled 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 the vibration damping effect is expressed by the following formula (3).

[0067] Fc=α·C·Zu'+β·K·Zu ···(3) In formula (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. When the differential term in formula (3) is omitted, a control force Fc that provides at least a vibration damping effect is expressed by the following formula (4).

[0068] Fc = β K Zu (4) The calculation unit 86 calculates the target control force Fc_t according to the above formula (3) or formula (4). 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 formula (3) or formula (4).

[0069] The control unit 88 transmits a control command including the target control force Fc_t to the actuator 3A 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 after the preview time tp from the current time, that is, 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 control target wheel passes the predicted passing position Pf coincides with the target control force Fc_t.

[0070] In this way, according to the preview control using the unsprung displacement map 200, when the amount of change per unit time of the unsprung displacement Zu is less than the threshold value, it is possible to generate, at an appropriate timing, the control force Fc for suppressing the vibration of the sprung structure 5 caused by the unsprung displacement Zu at the predicted passing position Pf of the wheel 2. This makes it possible to effectively suppress the vibration of the sprung structure 5.

[0071] On the other hand, if the amount of change per unit time of the unsprung displacement Zu is equal to or greater than the threshold value, 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 at the current time step is abnormal. Therefore, assuming that the above-described control based on the acquired unsprung displacement Zu is continued, there is a high concern that the control will increase vibration more than the original input, so a process for reducing vibration is executed.

[0072] When the amount of change per unit time of the unsprung displacement Zu is equal to or greater than a threshold value, the calculation unit 86 calculates the target control force Fc_t so that the amount of change per unit time of the target control force Fc_t is smaller than when the amount of change is less than the threshold value. The amount of change per unit time of the target control force Fc_t 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 amount of change per unit time of the target control force Fc_t is expressed as an absolute value.

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

[0074] That is, the calculation unit 86 corrects the value of the unsprung displacement Zu acquired at the current time step using a rate limiter, thereby making the amount of change in the unsprung displacement Zu per unit time smaller than 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] When the amount of change per unit time of the unsprung displacement Zu is equal to or greater than a threshold value, the calculation unit 86 applies a rate limiter for a predetermined control time to limit the amount of change per unit time of the target control force Fc_t. In other words, when the control time has elapsed, the limiting of the amount of change per unit time of the target control force Fc_t ends. The process of limiting the amount of change per unit time of the target control force Fc_t is called a vibration reduction process. The limiting value and the control time can be appropriately determined by experiment or simulation so that the vibration of the sprung structure 5 is reduced.

[0076] This makes it possible to suppress abrupt changes in the target control force Fc_t when the vehicle 1 passes over the boundary between the presence and absence of unsprung displacement Zu in the unsprung displacement map 200, thereby suppressing the occurrence of vibration in the sprung structure 5. For example, when the vehicle 1 travels along the path 304a, path 304b in Fig. 1(a), or path 304c in Fig. 1(b), the vibration of the sprung structure 5 can be reduced compared to the comparative example in which the vibration reduction process is not executed. The rate limiter is applied only when crossing the boundary between the presence and absence of unsprung displacement Zu and during the control time thereafter, so there is no effect on normal vibration suppression control other than this.

[0077] In addition, when the amount of change per unit time of the unsprung displacement Zu is equal to or greater than a threshold value, 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 the past time steps during the control time. Through this process, the calculation unit 86 can limit the amount of change per unit time of the target control force Fc_t. That is, the calculation unit 86 corrects the value of the unsprung displacement Zu acquired in the current time step using a low-pass filter, thereby making the amount of change per unit time of the unsprung displacement Zu smaller than before the correction, thereby suppressing abrupt changes in the unsprung displacement Zu. The cutoff frequency of the low-pass filter can be appropriately determined by experiment or simulation so that the vibration of the sprung structure 5 is reduced.

[0078] Furthermore, when the amount of change per unit time of the unsprung displacement Zu is equal to or greater than a threshold value, 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 at the current time step and the past time step, instead of the unsprung displacement Zu. Through this process, the calculation unit 86 can calculate the target control force Fc_t so that the amount of change per unit time of the target control force Fc_t is small.

[0079] That is, the calculation unit 86 substitutes the unsprung displacement Zu acquired by the first acquisition unit 80 into equation (3) or equation (4) without correction to calculate the target control force Fc_t. 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 at the current time step, thereby making the amount of change in the target control force Fc_t per unit time smaller than before correction. Then, the calculation unit 86 supplies the corrected target control force Fc_t to the control unit 88.

[0080] Furthermore, when the amount of change per unit time of the unsprung displacement Zu is equal to or greater than a threshold value, the calculation unit 86 may calculate the target control force Fc_t such that the greater 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. Furthermore, 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 more effectively suppress the occurrence of vibration in accordance with the magnitude of the amount of change per unit time of the unsprung displacement Zu.

[0081] 6 is a flowchart showing the suspension control process according to the embodiment. The process of this flowchart is repeatedly executed for each of the control target wheels at predetermined time steps while the vehicle 1 is traveling.

[0082] The first acquisition unit 80 acquires the current position of the wheel 2 (S10), acquires a 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 change in the unsprung displacement Zu per unit time is greater than or equal to the threshold value (Y in S18), the calculation unit 86 executes vibration reduction processing to calculate the target control force Fc_t (S20), and the control unit 88 controls the actuator 3A (S22), and the processing ends.

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

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

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

[0087] (First Modification) The control unit 88 may execute the following feedback control as vibration damping control in addition to the above-mentioned preview control by controlling the actuator 3A. That is, the feedback control is executed to reduce vibration of the sprung structure 5. The control force Fc in the example in which the preview control is performed together with the feedback control 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 side of equation (5) is the same as equation (4) above, and is a feedforward term related to preview control. The second term on the right side is a feedback term related to feedback control. This feedback term is the product of the feedback gain γ and the sprung displacement Zs at the time of calculating the target control force Fc_t. Note that instead of the sprung displacement Zs in the feedback term, any one of the sprung velocity Zs', sprung acceleration Zs'', unsprung displacement Zu, unsprung velocity Zu', and unsprung acceleration Zu'' at the time of calculating the target control force Fc_t may be used.

[0089] When the amount of change in the sprung displacement Zs per unit time is less than the threshold value, the calculation unit 86 sets the basic gain γ0 as the feedback gain γ of the feedback control.

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

[0091] The basic gain γ0 and the gain γ1 can be appropriately determined by experiments or simulations. The gain γ1 may be a fixed value. In addition, when the strength of the rate limiter is increased as the amount of change in the unsprung displacement Zu per unit time increases, or when the strength of the low-pass filter is increased, the gain γ1 may be set to be larger as the amount of change in the unsprung displacement Zu per unit time increases.

[0092] As a result, during execution of the vibration reduction process in which the vibration damping effect of the preview control is temporarily weakened, the vibration can be more actively damped using feedback control, thereby suppressing deterioration of the vibration of the sprung structure 5.

[0093] (Second Modification) When the amount of change in the sprung displacement Zs per unit time is equal to or greater than a threshold value, the control unit 88 may execute, for the rear wheels during the control time, preview control using the unsprung displacement Zu1 calculated for the passing position of the front wheels, in addition to the preview control using the unsprung displacement map 200 described above. Since the rear wheels are considered to follow the path of the front wheels, such control may be executed. 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) during the execution of the vibration reduction process.

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

[0095] As a result, during execution of the vibration reduction process in which the vibration damping effect of the preview control using the unsprung displacement map 200 is temporarily weakened, the rear wheels are damped by preview control using the unsprung displacement Zu1 calculated for the passing position of the front wheels, thereby suppressing the deterioration of vibration of the sprung structure 5.

[0096] (Third Modification) When the amount of change in the sprung displacement Zs per unit time is equal to or greater than a threshold value, the control unit 88 may execute preview control using a known preview sensor during the control time 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, a LiDAR, and a radar sensor. The preview sensor acquires the road surface displacement of the road surface ahead of the vehicle 1. The control force Fc in this case is expressed, for example, by the following formula (7). In this example, the calculation unit 86 calculates the target control force Fc_t according to formula (7) during the execution of the vibration reduction process.

[0097] Fc=β·K·Zu+γb·Z0 ···(7) The first term on the right side of equation (7) is the same as equation (4) above, and is a feedforward term related to preview control using the unsprung displacement map 200. The second term on the right side is a feedforward term related to preview control using a preview sensor. The second term on the right side is the product of gain γb and the road surface displacement Z0 ahead of the vehicle 1 acquired by the preview sensor when calculating the target control force Fc_t. Gain γb can be appropriately determined by experiment or simulation. Preview control using a preview sensor is well known, so further detailed explanation will be omitted.

[0098] As a result, during execution of the vibration reduction process in which the vibration damping effect by the preview control using the unsprung displacement map 200 is temporarily weakened, the vibration deterioration of the sprung structure 5 can be suppressed by damping through preview control using the preview sensor.

[0099] At least two of the first, second and third modified examples may be combined.

[0100] In the embodiment, the preview control is performed on all four wheels 2 of the vehicle 1. However, the wheels that are the subject of the preview control are not limited to all wheels, and may be, for example, only the left and right front wheels or only the left and right rear wheels. [Explanation of symbols]

[0101] 1...vehicle, 2...wheel, 3...suspension, 3A...actuator, 5...sprung structure, 10...suspension control system, 70...ECU (control device), 80...first acquisition unit, 82...second acquisition unit, 84...judgment unit, 86...calculation unit, 88...control unit, 200...unsprung displacement map (road surface data map).

Claims

1. An actuator for adjusting a suspension stroke of a controlled wheel of the vehicle; A control device for controlling the actuator; Equipped with The control device includes: a first acquisition unit that repeatedly acquires a road surface displacement-related value at a predicted passing position of the control target wheel a predetermined time after a current time from a road surface data map in which a road surface displacement-related value related to a vertical displacement of the road surface is associated with a position; a second acquisition unit that acquires an amount of change in the road surface displacement-related value per unit time based on the acquired road surface displacement-related value; A calculation unit that calculates a target control force based on the acquired road surface displacement related value; a control unit that controls the actuator so that a control force generated by the actuator when the control target wheel passes through the predicted passing position coincides with the target control force; having the calculation unit calculates the target control force such that, when a change amount per unit time of the acquired road surface displacement-related value is equal to or greater than a threshold value, a change amount per unit time of the target control force is smaller than a change amount per unit time of the target control force when the change amount is less than the threshold value. A suspension control system comprising:

2. when the amount of change per unit time of the acquired road surface displacement-related value is equal to or greater than the threshold value, the calculation unit calculates the target control force so as to reduce the amount of change per unit time of the target control force by applying 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; 2. The suspension control system of claim 1.

3. the calculation unit applies the rate limiter or the low-pass filter for a predetermined control time when the amount of change per unit time of the acquired road surface displacement-related value is equal to or greater than the threshold value.

3. The suspension control system of claim 2.

4. 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 equal to or greater than the threshold value, the amount of reduction in the amount of change per unit time of the target control force increases as the amount of change increases.

4. A suspension control system according to claim 1.

5. The control unit further performs feedback control to reduce vibration of the sprung structure by controlling the actuator, the calculation unit increases a feedback gain of the feedback control when an amount of change per unit time of the acquired road surface displacement-related value is equal to or greater than the threshold value, compared with a case where the amount of change is less than the threshold value; 4. A suspension control system according to claim 1.

Images