Suspension control device, suspension control method, and suspension control program

Abstract

To suppress understeer by preventing a ground load applied to an outer-wheel side front wheel from being relatively small when slip is detected during turning of a vehicle.SOLUTION: A suspension control device that outputs a control command value to a suspension device of a vehicle to control an attenuation force of an attenuation force variable damper, comprises a turning state detection unit 211 that detects a turning state of the vehicle, a slip state detection unit 212 that detects a slip state of the vehicle, a road surface friction coefficient estimation calculation unit 213 that estimates a road surface friction coefficient μ of a road surface on which the vehicle is grounded, and a control unit 214 that, when the turning state detection unit detects that the vehicle is turning and the slip state detection unit detects that the vehicle is in a slip state, acquires a control command value corresponding to the road surface friction coefficient estimated by the road surface friction coefficient estimation calculation unit and inputs the control command value to the suspension.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a suspension control device that inputs a control command value to a suspension device of a vehicle to control the damping force of a variable damping force damper. [Background technology]

[0002] Conventionally, electronically controlled dampers using variable damping force dampers have been known for vehicle suspension systems, which calculate the damper stroke speed based on CAN (Control Area Network) information from vehicle speed sensors, etc., and provide optimal damping force according to road conditions. Variable damping force dampers are actuators installed between the vehicle body and each of the four wheels, and vary the force that suppresses relative displacement between the body and the wheels. The force generated between the body and wheels can be varied, making it possible to adjust between a "soft" and a "hard" state.

[0003] For example, when the vehicle speed is below a certain level, the damping force of the variable damping damper is set to a "soft state," and when the speed is above that level, the damping force is switched from the "soft state" to a "medium state" or "hard state" to improve vehicle stability. Also, when the driver turns the steering wheel to make a sudden turn in cornering, the damping force of the variable damping damper is controlled to switch between the "medium state" and the "hard state" depending on the steering angular velocity and vehicle speed at that time.

[0004] The electronically controlled dampers described above use various methods to detect road conditions. For example, there are models that use dedicated detection devices to detect road conditions ahead and control the suspension and steering. There is also a model known as IECAS (registered trademark) that does not use dedicated detection devices but quickly estimates vehicle behavior from CAN information from existing sensors, such as wheel speed, and changes damping force characteristics and variable characteristics to create suspension settings that respond comfortably to driver operation. The registered trademark IECAS stands for Intelligent Electronic Control Adaptive Suspension.

[0005] According to IECAS (registered trademark), the state of the vehicle can be determined and the next behavior can be estimated by utilizing data detected by wheel speed sensors, which changes tire radius due to loads on the tires and external disturbances. By using not only wheel speed but also data such as longitudinal and lateral G, yaw rate, steering angle, and engine torque acquired via the CAN, the handling and behavior desired by the driver can be created. For convenience, this model will be referred to as the prior art in the following explanation.

[0006] Furthermore, for example, Patent Document 1 describes a technology for a vehicle suspension device that improves handling stability when cornering while traveling on a low-friction road surface (low μ road surface), and further improves vehicle body stability when cornering while traveling on a high-friction road surface. According to the technology described in Patent Document 1, as shown in a flowchart of "total roll control processing" in Figure 3 of the document, for example, in a vehicle having an anti-roll function, a control unit executes a "low μ road surface traveling determination routine," and then determines whether the vehicle is traveling on a low μ road surface with a low friction coefficient, and if it determines that the vehicle is traveling on a low μ road surface, executes a "low μ road surface roll control routine," and if it determines that the vehicle is not traveling on a low μ road surface with a low friction coefficient, executes a "normal anti-roll control routine." [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 7-101219 (see paragraph

[0024] and Figure 3) Summary of the Invention [Problem to be solved by the invention]

[0008] Incidentally, during a transitional state of turning, such as when entering a corner, the load acts most heavily on the outer front wheel while maintaining an appropriate damping ratio (damping force), and the tire lateral force (the force acting perpendicular to the direction of tire rotation that occurs in the tire due to skidding, etc.) becomes less than the grip force (the force with which the tire grips the road surface), making cornering possible.

[0009] However, as shown in Figure 10, which shows the relationship between grip force F and damping force DF (damping ratio), in region a, while a higher damping force DF has the effect of suppressing the vehicle's roll rate, the trade-off is that the vertical load N does not act on the outer front wheel, increasing the tire lateral force and exceeding grip force F (horizontal axis), resulting in understeer. Also, as shown in region b, for example, when the road surface friction coefficient (low μ) is low, the friction circle (see Figure 9, described below) becomes relatively smaller (because of the relationship grip force F = μN, low μ results in low grip force F), which reduces grip force F and narrows the appropriate range X of tire lateral force (narrowed appropriate range Y). As a result, the damping force DF, which was appropriate on dry road surfaces, becomes over-damped, expanding the region in which understeer occurs.

[0010] In this case, for example, if grip force F decreases on a low-μ road, as indicated by the thick downward arrow in area c surrounded by solid and dashed lines, it is necessary to increase the vertical load (ground load N) on the outer front wheel by adjusting the damping force DF to restore grip force F by setting the tire lateral force within the appropriate range X, as indicated by the thick upward arrow. As a result, the friction circle can be increased even on low-μ roads. However, when slip is detected, conventional technologies that quickly estimate vehicle behavior based on wheel speed and adjust the damping force characteristics and variable characteristics make it difficult to estimate appropriate vehicle behavior. Therefore, the estimation for changing the damping force characteristics is canceled and the system switches to fixed current value mode, which tends to provide a fixed current value and set a high damping force as a fail-safe. In fixed current value mode, the current value output to the variable damping damper (actuator) for damping force control cannot be precisely controlled. Therefore, when slip is detected during a vehicle turn, an increase in damping force relatively reduces the ground load on the outer front wheel, resulting in understeer.

[0011] Patent Document 1 does not mention such a problem, nor does it mention any countermeasures for it. Furthermore, as described above, the prior art is configured to perform anti-roll control in two stages: when driving on a low μ road surface and when driving on a high μ road surface. This may result in the damping force being released (weakened) too much, which could lead to control of the tendency to oversteer. In this case, the roll may increase excessively, which could worsen the ride comfort more than necessary.

[0012] Therefore, an object of the present invention is to provide a suspension control device that, for example, when slip is detected while the vehicle is turning, outputs an appropriate current according to the road surface conditions to control the damping force of a variable damping damper, thereby preventing the ground load on the outer front wheel from becoming relatively small, which in turn increases roll and the ground load on the outer front wheel, thereby suppressing understeer.Another object of the present invention is to provide a suspension control device that, for example, estimates the road surface friction coefficient and controls the damping force so that the ground load on the outer front wheel is appropriate in accordance with the estimated road surface friction coefficient, thereby suppressing the tendency toward oversteer due to excessive control, ensuring steerability near the target steering characteristic and minimizing deterioration of ride comfort.

[0013] Other objects of the present invention will become apparent to those skilled in the art by referring to the following exemplary aspects and best modes, as well as the accompanying drawings. [Means for solving the problem]

[0014] In the following, embodiments of the present invention will be illustrated to facilitate an understanding of the outline of the present invention.

[0015] One aspect of the present invention is a suspension control device that inputs a control command value to a suspension device of a vehicle to control the damping force of a variable damping force damper, and includes: a turning state detection unit that detects the turning state of the vehicle; a slip state detection unit that detects the slip state of the vehicle; a friction coefficient estimation calculation unit that estimates the road surface friction coefficient of the road surface on which the vehicle is in contact with the ground; and a control unit that performs turning slip control by, when the turning state detection unit detects that the vehicle is turning and the slip state detection unit detects that the vehicle is in a slip state, acquiring the control command value corresponding to the road surface friction coefficient estimated by the friction coefficient estimation calculation unit and inputting the control command value to the suspension device.

[0016] In one aspect of the present invention, when the slip state detection unit detects that the vehicle is in a slip state, the control unit performs cornering slip control by acquiring a control command value corresponding to the road friction coefficient estimated by the friction coefficient estimation calculation unit and inputting the control command value to the suspension device. Since F = μN, if the road friction coefficient μ is low for the same ground load N, the grip force F also decreases. To obtain the grip force F required to control the vehicle when traveling on a road surface with a low road friction coefficient μ, the ground load N must be increased. Therefore, for example, when slip is detected while the vehicle is turning, a suspension control device can be provided that outputs an appropriate current according to the road conditions to control the damping force of the variable damping damper, thereby preventing the ground load N applied to the outer front wheel from becoming relatively small, thereby increasing roll and increasing the ground load N applied to the outer front wheel, thereby suppressing understeer. Furthermore, for example, by estimating the road surface friction coefficient μ and controlling the damping force DF so that the ground load N applied to the outer front wheel is appropriate in accordance with the estimated road surface friction coefficient μ, it is possible to suppress the tendency toward oversteer due to excessive control, ensure steerability near the target steering characteristics, and minimize deterioration in ride comfort.

[0017] For example, as shown in the friction circle in FIG. 9, as the road friction coefficient μ decreases, the friction circle also becomes smaller in proportion (friction circle A in low μ roll control according to Patent Document 1, shown by the dashed line in FIG. 9, → friction circle B in fixed current value mode according to the conventional technology, shown by the dashed line). In contrast, in an embodiment of the present invention, the control unit estimates the magnitude of the road friction coefficient μ, that is, the size of the friction circle, and performs cornering slip control by increasing the ground contact load N on the outer front wheel so that the friction circle becomes large enough that the force applied to the tire does not cause slip (friction circle C, shown by the solid line in FIG. 9). In other words, by adjusting the ground contact load N, the size of the friction circle can be compensated for until the tire grips, and desired steering characteristics and ride comfort can be maintained even in the event of slip.

[0018] Those skilled in the art will readily appreciate that the exemplified embodiments according to the present invention can be further modified without departing from the spirit of the present invention. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a diagram showing a schematic configuration of a main part of a vehicle to which a suspension control device and a suspension control method according to an embodiment of the present invention are applied. [Figure 2] FIG. 2 is a block diagram showing the configuration of a control system of the suspension control device according to the embodiment of the present invention. [Figure 3] FIG. 3 is a flowchart showing an example of a basic processing operation of the suspension control device according to the embodiment of the present invention. [Figure 4] FIG. 4 is a flowchart showing an example of the turning slip processing operation of the suspension control device according to the embodiment of the present invention. [Figure 5] FIG. 5 is a flowchart showing another example of the turning slip processing operation of the suspension control device according to the embodiment of the present invention. [Figure 6] FIG. 6 is a flowchart showing yet another example of the turning slip processing operation of the suspension control device according to the embodiment of the present invention. [Figure 7] FIG. 7 is a diagram used to explain the time required for transition from turning slip control to normal control by the suspension control device according to the embodiment of the present invention. [Figure 8] FIG. 8 is a diagram used to explain the relationship between the road surface friction coefficient μ and the slip gain of the suspension control device according to the embodiment of the present invention. [Figure 9] FIG. 9 is a diagram showing, for comparison and contrast, friction circles obtained by a suspension control device according to an embodiment of the present invention and a conventional suspension control device. [Figure 10] FIG. 10 is a diagram cited to explain the relationship between the grip force and the damping force (damping ratio) of a conventional suspension control device. DETAILED DESCRIPTION OF THE INVENTION

[0020] The best mode described below is used to facilitate understanding of the present invention, and therefore, those skilled in the art should be aware that the present invention is not unduly limited by the mode described below (hereinafter referred to as the present mode).

[0021] [Configuration of the embodiment] (Vehicle configuration) Please refer to Figure 1. Figure 1 is a diagram that shows a schematic configuration of the main parts of a vehicle 1 to which a suspension control device and a suspension control method of this embodiment are applied. In Figure 1, a total of four wheels 3, 4, for example, left and right front wheels 3 and left and right rear wheels 4 (only one is shown), are provided on the underside of a vehicle body that constitutes the body of the vehicle 1. Front wheel suspensions 5, 5 (hereinafter referred to as front wheel suspensions 5) are provided between the left and right front wheels 3 and the vehicle body, respectively. The front wheel suspensions 5 include suspension springs 6 (hereinafter simply referred to as springs 6) and adjustable damping shock absorbers (hereinafter referred to as variable damping dampers 7) that are provided in parallel with the springs 6.

[0022] Rear-wheel suspensions 5, 5, 8, 8 (hereinafter referred to as rear-wheel suspensions 8) are provided between the left and right rear wheels 4 and the vehicle body. The rear-wheel suspensions 8 include suspension springs 9 (hereinafter simply referred to as springs 9) and adjustable damping shock absorbers (hereinafter referred to as variable damping dampers 10) provided in parallel with the springs 9. The variable damping dampers 7, 10 are configured, for example, by semi-active dampers that are hydraulic cylinder devices (variable damping shock absorbers) that allow for adjustable damping force. In other words, the vehicle 1 is equipped with a semi-active suspension system that uses variable damping shock absorbers.

[0023] Here, the variable damping force dampers 7, 10 are variable damping force generating devices (variable damping force shock absorbers) provided between the body and wheels 3, 4 of the vehicle 1. The characteristics of the generated damping force (damping force characteristics) of the variable damping force dampers 7, 10 are variably controlled by the suspension ECU 21 described above. For this purpose, the variable damping force dampers 7, 10 are provided with a variable damping force actuator (not shown) including a damping force adjustment valve and a solenoid, etc., to adjust the damping force characteristics continuously (or in multiple stages) from hard characteristics (hard characteristics) to soft characteristics (soft characteristics). The variable damping force dampers 7, 10 variably adjust their damping force characteristics in accordance with a control command value (current value) supplied from the suspension ECU 21 to the variable damping force actuator.

[0024] The damping force adjustment valve may employ a conventionally known structure, such as a pressure control system that controls the pilot pressure of a damping force generating valve or a flow control system that controls the passage area. The variable damping force dampers 7 and 10 may be any type capable of continuously (or multi-stagely) adjusting the damping force, such as a pneumatic damper, an electromagnetic damper, an electrorheological fluid damper, or a magnetic fluid damper. The variable damping force dampers 7 and 10 may also be air dampers (air suspensions) using air springs, hydraulic dampers (height adjustment devices) with front, rear, left, and right hydraulic cylinders connected by piping, or stabilizers that apply force to the left and right wheels 3 and 4. The variable damping force dampers 7 and 10 may also be fully active dampers composed of hydraulic, electric, or pneumatic actuators capable of generating thrust. That is, the vehicle 1 may be equipped with a fully active suspension system using a fully active damper, in which case the stroke length of the suspensions 5 and 8 can be controlled by thrust.

[0025] Next, a description will be given of various sensors 11, 12, 13, 14, 15, and 16 that detect the state of the vehicle 1. As shown in Fig. 1, the vehicle 1 is provided with a vehicle speed sensor 11, a wheel speed sensor 12, a longitudinal acceleration sensor 13, a lateral acceleration sensor 14, a steering angle sensor 15, and a roll angle sensor 16. These sensors 11, 12, 13, 14, 15, and 16 are sensors that are generally mounted on the vehicle 1 as behavior sensors shown in Fig. 1. More specifically, they are sensors that are mainly used to control the braking, driving, and steering of the vehicle 1.

[0026] The vehicle speed sensor 11 is provided, for example, on an output shaft (not shown) of a transmission mounted on the vehicle 1. The vehicle speed sensor 11 detects the vehicle body speed, which is the speed of the vehicle 1 (vehicle body). The detection information (a signal corresponding to the vehicle body speed) of the vehicle speed sensor 11 is output to a vehicle control ECU 30 mounted on the vehicle 1 (vehicle body), for example, via a CAN (Control Area Network) (not shown), which is an in-vehicle LAN communication. Although not shown, the information (vehicle body speed) of the vehicle speed sensor 11 is also output via the CAN and the vehicle control ECU 30 to a suspension ECU 21, which is a suspension control device of this embodiment, or an accelerator ECU, a brake ECU, etc., which are not shown.

[0027] The wheel speed sensor 12 is provided, for example, on a wheel support hub unit (not shown) that supports the wheels 3, 4. The wheel speed sensor 12 is provided corresponding to each of the wheels 3, 4. The wheel speed sensor 12 detects the rotational speed of the wheels 3, 4. Information (wheel speed) from the wheel speed sensor 12 is transmitted via the CAN 39 and the vehicle control ECU 30. Note that the vehicle speed sensor 11 may be omitted, and the vehicle speed may be obtained from the wheel speed of the wheel speed sensor 12.

[0028] The longitudinal acceleration sensor 13 and the lateral acceleration sensor 14 are provided, for example, on the vehicle body on the sprung side of the vehicle 1. The longitudinal acceleration sensor 13 detects the acceleration (deceleration, acceleration) of the vehicle 1 (vehicle body) in the longitudinal direction. The lateral acceleration sensor 14 detects the acceleration (lateral acceleration) of the vehicle 1 (vehicle body) in the left-right direction. The steering angle sensor 15 is provided, for example, on a steering wheel (not shown) of the vehicle 1. The steering angle sensor 15 detects the steering angle (rotation angle) generated by the steering operation of the driver who drives the vehicle 1 or the steering angle of the wheels (front wheels 3). The roll angle sensor 16 detects an actual roll state value, which is the value of the roll state of the vehicle 1 that actually occurs in the vehicle 1 (the angle of rotation about the longitudinal axis of the vehicle 1).

[0029] The detection data from the vehicle speed sensor 11, wheel speed sensor 12, longitudinal acceleration sensor 13, lateral acceleration sensor 14, steering angle sensor 15, and roll angle sensor 16 described above are output to, for example, the suspension ECU 21, which is the suspension control device of this embodiment, via the CAN 39 and the vehicle control ECU 30, or to an accelerator ECU, brake ECU, steering ECU, etc., which are not shown.

[0030] These behavior sensors (vehicle speed sensor 11, wheel speed sensor 12, longitudinal acceleration sensor 13, lateral acceleration sensor 14, steering angle sensor 15, and roll angle sensor 16) are not sensors provided exclusively for the suspension system (variable damping force dampers 7, 10). In other words, they may be sensors mounted on vehicle 1 for purposes other than controlling variable damping force dampers 7, 10, in other words, sensors mounted on vehicle 1 to primarily control on-board devices other than variable damping force dampers 7, 10. In this case, specifically, the behavior sensors are mounted on vehicle 1 as sensors primarily for controlling the engine that drives and / or brakes vehicle 1, the driving motor, vehicle braking / driving devices (accelerator, brake) such as hydraulic brakes and electric brakes, and steering devices such as an electric power steering device that steers vehicle 1. Note that the behavior sensors may also include torque sensors that detect torque acting on drive wheels, pressure sensors that detect brake pressure, etc.

[0031] Please refer to Fig. 2. Fig. 2 is a block diagram showing the configuration of a control system of the suspension control device (suspension ECU 21) according to this embodiment. As shown in Fig. 2, the suspension ECU 21 includes a turning state detection unit 211, a slip state detection unit 212, a road surface friction coefficient estimation calculation unit 213, a control unit 214, and a control command value output unit 215.

[0032] The turning state detection unit 211 receives as input, for example, the lateral acceleration detected by the lateral acceleration sensor 14, the rate of change of rotational motion around the vertical axis of the vehicle body (roll rate), the rate of change of lateral rotational motion around the roll axis (yaw rate), the steering angle detected by the steering angle sensor 15, or data such as brake pressure, and can detect the turning state of the vehicle 1 when entering a corner or while cornering (for example, a turning transient state when entering a corner, while cornering, a state after exiting a corner, etc.). Whether the vehicle 1 is performing the above-mentioned cornering operation can be determined, for example, based on a change in the steering angle acquired from the input steering angle sensor 15, or based on the road curvature of a driving route ahead of the vehicle set from the driving route, or the road curvature set from the road shape ahead of the vehicle photographed by a camera.

[0033] Furthermore, the slip state detection unit 212 receives as input, for example, a VSA flag indicating that a VSA (Vehicle Stability Assist) that suppresses a sudden change in behavior of the vehicle 1 due to skidding of the vehicle 1 has operated, and can detect the slip state of the vehicle 1 including the presence or absence of slip (for example, slip on a low μ road, slip on a high μ road, etc.). The turning state of the vehicle 1 detected by the turning state detection unit 211 and the slip state of the vehicle 1 detected by the slip state detection unit 212 are output to the control unit 214.

[0034] The road surface friction coefficient estimation calculation unit 213 receives, for example, torque acting on the drive wheels as an input, and calculates the sum P of the driving forces acting on the drive wheels of the vehicle 1 by calculating the following calculation formula (1), and further calculates the sum of the grip forces F acting on the drive wheels by calculating the following calculation formula (2). Note that the calculation method of the road surface friction coefficient μ by the road surface friction coefficient estimation calculation unit 213 may follow any known method and is not limited to the following calculation formula (2).

[0035]

number

[0036] Next, the road surface friction coefficient estimation calculation unit 213 determines the slip ratio using the following calculation formula (3), and if the following conditional formula (3) is satisfied, it estimates that the minimum value on the left side is the road surface friction coefficient μ, selects parameters suitable for the road surface friction coefficient μ, and outputs them to the control unit 214.

[0037]

number

[0038] In the above-mentioned formulas (1) to (3), P is the sum of the driving forces acting on the drive shaft of the vehicle 1, T e is the engine torque, P n is the transmission gear ratio, P F is the final reduction ratio, η n is the transmission efficiency of the transmission, η F is the final drive transmission efficiency, Rt is the effective tire radius, F is the total grip force acting on the drive wheels, μ is the coefficient of friction between the road surface and the tire, and W is the total weight of the wheels 3 and 4.

[0039] When the turning state detection unit 211 detects the turning state of the vehicle 1 and the slip state detection unit 212 detects a slip state of the outer front wheel of the vehicle 1, the road surface friction coefficient estimation calculation unit 213 can estimate the road surface friction coefficient μ of the road surface on which the outer front wheel is in contact with the ground. When the turning state detection unit 211 detects the turning state of the vehicle 1 and the slip state detection unit 212 further detects a slip state of the other wheels 3 and 4, the road surface friction coefficient estimation calculation unit 213 can estimate the road surface friction coefficient μ of the road surface on which the other wheels 3 and 4 are in contact with the ground. The road surface friction coefficient estimation calculation unit 213 continues to calculate and estimate the road surface friction coefficient μ at least while performing turning slip control, and can perform control to reduce the change range of the slip gain, which is a dimensionless quantity that references the road surface friction coefficient μ, when the road surface friction coefficient μ increases more than when it decreases, given the same amount of increase or decrease in the road surface friction coefficient μ. Details will be described later.

[0040] When the turning state detection unit 211 detects that the vehicle 1 is turning and the slip state detection unit 212 detects that the vehicle 1 is in a slip state, the control unit 214 acquires a control command value that directly or indirectly corresponds to the road surface friction coefficient μ estimated by the road surface friction coefficient estimation calculation unit 213, and performs turning slip control by supplying the control command value (current I) to the variable damping force dampers 7, 10 of the suspension device (front wheel suspension 5, rear wheel suspension 8) via the control command value output unit 215.

[0041] Furthermore, except for specific states including a slip state, the control unit 214 can also perform normal control in which a control command value is calculated by estimating the stroke of the variable damping force dampers 7, 10 from the rotational speeds of the wheels 3, 4 of the vehicle 1. The control unit 214 can also perform control in which a slip gain, which is a dimensionless quantity that references the road surface friction coefficient, is calculated, and the slip gain is multiplied by the control command value to relatively increase the ground contact load N of the outer front wheel of the vehicle 1.

[0042] Furthermore, when it is determined that the vehicle 1 has an oversteer tendency relative to the target steering condition during a turning transient state from when the vehicle 1 starts turning until the turning attitude is determined, the control unit 214 can correct the control command value to increase and induce the vehicle 1 to have an understeer tendency, and on the other hand, when it is determined that the vehicle 1 has an understeer tendency relative to the target steering condition during the turning transient state, the control unit 214 can correct the control command value to decrease and induce the vehicle 1 to have an oversteer tendency. Furthermore, when it is determined that the vehicle 1 has an oversteer tendency relative to the target steering condition during a turning transient state from when the vehicle 1 starts turning until the turning attitude is determined, the control unit 214 can correct the slip gain and induce the vehicle 1 to have an understeer tendency, and on the other hand, when it is determined that the vehicle 1 has an understeer tendency relative to the target steering condition during the turning transient state, the control unit 214 can correct the slip gain and induce the vehicle 1 to have an oversteer tendency.

[0043] In addition, the control unit 214 can perform control to set the time required to transition from turning slip control to normal control, which estimates the stroke of the variable damping force dampers 7, 10 from the rotational speed of the wheels 3, 4 of the vehicle 1 and calculates a control command value, to a length equal to or longer than the minimum time required to transition from normal control to turning slip control.

[0044] For this reason, the control unit 214 includes a main control unit 40, a turning slip control unit 41, a slip gain calculation unit 42, a normal control unit 43, and an ESC (Electronic Stability Control) priority control unit 44.

[0045] When the turning state detection unit 211 detects that the vehicle 1 is turning and the slip state detection unit 212 detects that the vehicle 1 is in a slip state, the turning slip control unit 41 has a function of acquiring a control command value that directly or indirectly corresponds to the road friction coefficient μ estimated by the road friction coefficient estimation calculation unit 213 and supplying the control command value (current I) to the variable damping force dampers 7, 10 of the suspension devices (front wheel suspension 5, rear wheel suspension 8) via a control command value output unit 215. The turning slip control unit 41 has a damping force map that shows the relationship between the road friction coefficient μ and the control command value (current I) to be output to the variable damping force dampers 7, 10 (variable damping force actuators), and can input a control command value for controlling the variable damping force dampers 7, 10 according to the input road friction coefficient μ to the control command value output unit 215 (described later).

[0046] The slip gain calculation unit 42 acquires the road surface friction coefficient μ estimated by the road surface friction coefficient estimation calculation unit 213 and can correct the control command value acquired from the turning slip control unit 51. Here, in making the correction, for example, the turning slip control unit 41 calculates the driving force P and grip force F acting on the drive wheels using the above-mentioned calculation formulas (1) and (2), determines the slip ratio by assuming that the vehicle 1 will slip when the driving force P exceeds the grip force F, and estimates the minimum value of the left-hand side of the above-mentioned calculation formula (3) as the road surface friction coefficient μ. Then, it selects parameters appropriate for the road surface friction coefficient μ and inputs them to the turning slip control unit 41, which then inputs a final control command value to the control command value output unit 215.

[0047] The normal operation control unit 43 can estimate the stroke of the variable damping force dampers 7, 10 from the rotational speeds of the wheels 3, 4 of the vehicle 1, calculate a control command value (current I), and input the calculated value to the control command value output unit 215. The normal operation control unit 43 performs steering stability control and ride comfort control, selects control command values ​​output from each of them, and supplies a drive current I based on the final control command value to the variable damping force actuator that drives the variable damping force dampers 7, 10, thereby controlling the damping force of the variable damping force dampers 7, 10. The normal operation control unit 43 has, for example, a damping force map in which damping force characteristics indicating the relationship between the target damping force and relative velocity and the control command value output to the variable damping force dampers 7, 10 are stored, and can generate a control command value for controlling the variable damping force dampers 7, 10 based on the input target damping force and relative velocity. This control command value is an anti-roll control command value, and is, for example, a control command value for the current I supplied to the variable damping force actuator.

[0048] The ESC priority control unit 44 receives as input an ESC flag indicating that an ESC system (side slip prevention system) is operating, which prevents the vehicle 1 (vehicle body) from becoming unstable in posture when slip occurs during cornering or the like by separately controlling the tires 3, 4 of the vehicle 1, and maintains running stability.If the ESC flag is ON, priority is given to control by an ESC control system (not shown), and the ESC priority control unit 44 inputs a control command value generated by the ESC system to the control command value output unit 215. Note that if the ESC flag is OFF, the control command value generated by the turning slip control unit 41 is valid, and the control command value is input to the control command value output unit 215.

[0049] In this embodiment, the suspension control device will be described as using only an ESC system as an example of a cooperative control system, with priority control given to operating the ESC system over cornering slip control. However, the same applies when other cooperative control systems such as a TCS (Traction Control System) or ABS (Anti-lock Brake System) are used. In this case, the TCS system refers to a TCS flag indicating that it is operating, and the ABS system refers to an ABS flag indicating that it is operating. If either one is enabled, a control command value generated by the enabled (operating) TCS or ABS system is input to control command value output unit 215, which controls variable damping force dampers 7, 10 of the suspension device (front wheel suspension 5, rear wheel suspension 8). Furthermore, priority control giving priority to operating the cooperative control system over cornering slip control is not required.

[0050] When the control unit 141 detects that the vehicle 1 is turning by the turning state detection unit 211 and that the vehicle 1 is in a slip state by the slip state detection unit 212, the main control unit 40 becomes the control center for performing turning slip control, acquiring a control command value that directly or indirectly corresponds to the road surface friction coefficient μ estimated by the road surface friction coefficient estimation calculation unit 213, and supplying the control command value (current I) to the variable damping force dampers 7, 10 of the suspension devices (front wheel suspension 5, rear wheel suspension 8) via a control command value output unit 215, and in addition to acting as an interface with the turning state detection unit 211, slip state detection unit 212, and road surface friction coefficient estimation calculation unit 213, it also controls the sequence control of the turning slip control unit 41, slip gain control unit 42, normal state control unit 43, and ESC priority control unit 44 described above.

[0051] In order to perform the above-described control, the control unit 214 of the suspension ECU 21, which is the suspension control device of this embodiment, includes, for example, a built-in memory (ROM / RAM) or an external processor, and the processor executes a program (suspension control program) recorded in the ROM to perform the functions of the main control unit 40, turning slip control unit 41, slip gain calculation unit 42, normal control unit 43, and ESC priority control unit 44. Furthermore, at least some of the above-described functions can also be realized by hardware such as an FPGA (Field Programmable Gate Array) or logic circuit, rather than by a processor.

[0052] Finally, the control command value output unit 215 obtains the control command value output from the turning slip control unit 41, the normal control unit 43, or the ESC priority control unit 44, and supplies a drive current I based on the final control command value to the damping force variable dampers 7, 10 (damping force variable actuators), thereby controlling the damping force of the damping force variable dampers 7, 10.

[0053] [Operation of the embodiment] Please refer to Fig. 3. Fig. 3 is a flowchart showing an example of the basic processing operation of the suspension control device (suspension ECU 21) of this embodiment. Below, the basic processing operation of the suspension control device (suspension ECU 21) of this embodiment will be described with reference to Fig. 3.

[0054] 3, in the suspension ECU 21, the control unit 214 (main control unit 40) first determines whether the vehicle 1 is currently traveling (step ST11). For example, if an ignition switch (not shown) is turned on, the main control unit 40 can determine that the vehicle 1 is currently traveling (step ST11 "YES"). Next, if the main control unit 40 determines that the vehicle 1 is not traveling in a straight line but is entering a corner or the like based on the steering angle detected by the steering angle sensor 15 (see FIG. 1) (step ST12 "YES"), the main control unit 40 acquires the estimated result of the road surface friction coefficient μ estimated and calculated by the road surface friction coefficient estimation calculation unit 213 and transfers it to the turning slip control unit 41 (step ST13). Next, when the turning state detection unit 211 detects the turning state during cornering (entering a corner, exiting a corner, etc.) based on lateral acceleration, roll rate, steering angle, brake pressure, etc., the main control unit 40 takes in this information and hands it over to the turning slip control unit 41.

[0055] When the turning state detection unit 211 detects the entry into a turn while cornering (turning transient state) (step ST14 "YES"), the main control unit 40 determines whether or not ESC intervention is required (step ST15). The presence or absence of ESC intervention can be determined by the ESC priority control unit 44 under sequence control by the main control unit 40 by referring to an ESC flag indicating that an ESC system (not shown) is operating. Here, if it is determined that ESC has not intervened (step ST15 "YES"), the main control unit 40 activates turning slip control by the turning slip control unit 41, and if the turning state detection unit 211 detects that the vehicle 1 is turning and the slip state detection unit 212 detects that the vehicle 1 is in a slip state, the turning slip control unit 41 obtains a control command value that directly or indirectly corresponds to the road surface friction coefficient μ estimated by the road surface friction coefficient estimation calculation unit 213, and supplies the control command value (current I) to the variable damping force dampers 7, 10 of the suspension devices (front wheel suspension 5, rear wheel suspension 8) via the control command value output unit 215, thereby executing turning slip control (step ST16).

[0056] On the other hand, if it is determined in step ST15 that ESC intervention is required (step ST15 "NO"), the main control unit 40 activates ESC priority control by the ESC priority control unit 44, and executes ESC priority control in which the ESC priority control unit 44 inputs the control command value generated by the TCS system to the control command value output unit 215 (step ST17). Note that, as described above, it is not necessary to determine whether ESC intervention is required and to perform priority control.

[0057] In step ST14, if the turning state detection unit 211 does not detect a turning initiation (turning transient state) during cornering (step ST14 "NO"), the main control unit 40 activates normal control by the normal control unit 43. As a result, the normal control unit 43 estimates the stroke of the variable damping force dampers 7, 10 from the rotational speeds (wheel speed sensors 12) of the wheels 3, 4 of the vehicle 1, calculates a control command value (current I), and inputs the control command value to the control command value output unit 215. The normal control unit 43, for example, refers to a damping force map in which damping force characteristics indicating the relationship between the target damping force, relative speed, and the control command value to be output to the variable damping force dampers 7, 10 are stored, and outputs a control command value for controlling the variable damping force dampers 7, 10 according to the input target damping force and relative speed. This control command value is an anti-roll control command value, and is, for example, a control command value that becomes a command signal for the current I to be supplied to the variable damping force dampers 7, 10 (variable damping force actuators).

[0058] After the turning slip control is performed by the turning slip control unit 41 in step ST16, or after the ESC priority control unit 44 is performed in step ST17, if the turning state detection unit 211 detects that the vehicle 1 is in a cornering state (step ST18 "YES"), the main control unit 40 returns to the processing of step ST12. On the other hand, if the turning state detection unit 211 detects that the vehicle 1 has exited the corner (step ST18 "NO"), the normal control unit 43 performs handling stability control and ride comfort control under sequence control by the main control unit 40 (step ST19). In this way, the control unit 214 selects appropriate control command values ​​output from the turning slip control unit 41, the normal control unit 43, and the ESC priority control unit 44, and inputs a current I based on the final control command value to the damping force variable dampers 7 and 10 (damping force variable actuators) to the control command value output unit 215, so that the damping force DF of the damping force variable dampers 7 and 10 can be controlled by the control command value output unit 215.

[0059] As described above, according to the suspension control device (suspension ECU 21) of this embodiment, when the slip state detection unit 212 detects that the vehicle 1 is in a slip state, the control unit 214 (turning slip control unit 41) acquires a control command value that directly or indirectly corresponds to the road friction coefficient μ estimated by the road friction coefficient estimation calculation unit 213, and supplies the control command value to the variable damping force dampers 7, 10 of the suspension device (front wheel suspension 5, rear wheel suspension 8), thereby performing turning slip control. FIG. 9 shows a friction circle. The friction circle is a conceptual diagram that represents the limit of tire grip force F as a circle. The friction circle represents the force acting in the acceleration / deceleration (braking force) direction, which is vertical grip, and the force acting in the cornering direction, which is lateral grip, (left turning force, right turning force), as vectors, and the resultant force cannot exceed the friction circle.

[0060] That is, as the road surface friction coefficient μ decreases, the friction circle also decreases proportionally (friction circle A in low μ roll control according to Patent Document 1, shown by the dashed line in FIG. 9, → friction circle B in fixed current value mode according to the conventional technology, shown by the dashed line). In contrast, the suspension control device (suspension ECU 21) of this embodiment estimates the magnitude of the road surface friction coefficient μ, that is, the size of the friction circle, and performs control to increase the ground contact load N on the outer front wheel so that the friction circle becomes large enough that the force applied to the tire does not cause slip (friction circle C, shown by the solid line in FIG. 9). In other words, by adjusting the ground contact load N, the size of the friction circle can be compensated for until the tire grips, making it possible to maintain desired steering characteristics and ride comfort even during slippage.

[0061] The details of the turning slip control by the control unit 214 will be described below with reference to the flowcharts shown in FIGS.

[0062] Please refer to Fig. 4. Fig. 4 is a flowchart showing an example of a turning slip processing operation by the suspension control device (suspension ECU 21) of this embodiment. According to Fig. 4, first, under sequence control by the main control unit 40, the control unit 214 causes the turning state detection unit 211 to acquire sensor data indicating the behavior of the vehicle 1 (step ST21). The behavior of the vehicle 1 here refers to lateral acceleration, roll rate, yaw rate, steering angle, brake pressure, etc. The turning state detection unit 211 detects whether the vehicle 1 is turning or not from the behavior of the vehicle 1, and passes the detection result to the control unit 214 (main control unit 40) (step ST22). Here, turning refers to the period from when the vehicle enters a corner to when it exits the corner.

[0063] When the turning state detection unit 211 detects that the vehicle 1 is turning (step ST22 "YES"), the main control unit 40 determines the turning state (entering cornering (turning transient state), cornering, exiting cornering, etc.) from, for example, the yaw rate acquired by the yaw rate sensor, and passes the turning state data to the turning slip control unit 41 via the main control unit 40 (step ST23). On the other hand, the slip state detection unit 212 detects the slip state including the presence or absence of slip (for example, slip on a low μ road, slip on a high μ road, etc.) from the VSA flag, etc., and passes the slip state data to the turning slip control unit 41 via the main control unit 40 (step ST24).

[0064] The main control unit 40 further obtains the road surface friction coefficient μ estimated during cornering by calculating the above-mentioned equation (1) from the road surface friction coefficient estimation calculation unit 213, and passes it on to the turning slip control unit 41 (step ST25). Note that the road surface friction coefficient estimation calculation unit 213 receives, for example, torque acting on the drive wheels as an input, and can obtain the sum P of the driving forces acting on the drive wheels of the vehicle 1 by calculating the above-mentioned equation (1), and can further obtain the sum F of the grip forces acting on the drive wheels by calculating the above-mentioned equation (2).

[0065] Under sequence control by the main control unit 40, the turning slip control unit 41 acquires turning state data of the vehicle 1 from the turning state detection unit 211, slip state data of the vehicle 1 from the slip state detection unit 212, and road surface friction coefficient data from the road surface friction coefficient estimation calculation unit 213, and compares the driving force P and grip force F obtained by calculating the above-mentioned calculation formula (1) (step ST26). Here, if the driving force P is equal to or greater than the grip force F (step ST26 "YES"), the turning slip control unit 41 generates a control command value (current I) adjusted to an appropriate damping force corresponding to the road surface friction coefficient μ, and inputs the control command value output unit 215 (step ST27). On the other hand, if the driving force P is less than the grip force F (step ST26 "NO"), under sequence control by the main control unit 40, the normal control unit 43 estimates the stroke of the damping force variable dampers 7, 10, generates a control command value (current I), and inputs it to the control command value output unit 215 (step ST28).

[0066] The normal control unit 43 has, for example, a damping force map in which damping force characteristics indicating the relationship between the target damping force and relative velocity and the control command value to be output to the damping force variable dampers 7, 10 are stored, and based on the input target damping force and relative velocity, it can output a control command value for controlling the damping force variable dampers 7, 10 in accordance with these. This control command value is an anti-roll control command value, and is, for example, a control command value that becomes a command signal for the current I to be supplied to the damping force variable actuator.

[0067] Incidentally, when transitioning to turning slip control, it is preferable to immediately shift the steering characteristics to an oversteer tendency in order to stabilize vehicle behavior, and when returning from turning slip control to normal control, it is preferable to gradually return to normal control in order to suppress the feeling of shock. Figure 7 shows a diagram cited for explaining the time it takes for the suspension control device (suspension ECU 21) of this embodiment to transition from turning slip control to normal control.

[0068] As shown in Fig. 7, the control unit 214 (main control unit 40) controls the transition time (ON-to-OFF transition time C) from turning slip control A to normal control B, which calculates a control command value by estimating the stroke of the variable damping force dampers 7, 10 from the rotational speeds (wheel speed sensors 12) of the wheels 3, 4 of the vehicle 1, to be equal to or longer than the minimum required time (C1>C2) for transitioning from normal control B to turning slip control A. For example, the main control unit 40 holds the current value at the moment when slip is no longer detected, instructs the normal control unit 43 to resume calculation of the current value during normal control, and gradually (for example, over about 300 milliseconds) brings the current difference closer to the current value during normal control, thereby reducing the sense of shock.

[0069] Next, reference is made to FIG. 5. FIG. 5 is a flowchart showing another example of the turning slip processing operation by the suspension control device (suspension ECU 21) of this embodiment. According to FIG. 5, first, the turning state detection unit 211 detects the turning state of the vehicle 1 from the lateral acceleration, roll rate, yaw rate, steering angle, brake pressure, etc., which indicate the behavior of the vehicle 1 (ST31). Here, the turning state of the vehicle 1 refers to a turning transient state when entering a corner, during cornering, a state after exiting the corner, etc. Note that during cornering refers to the period from when entering a corner to when exiting the corner.

[0070] Here, if the turning state of the vehicle 1 detected by the turning state detection unit 211 is a "turning transient state" from when the vehicle 1 starts turning until the turning posture is determined (step ST32 "YES"), under sequence control of the main control unit 40, the turning slip control unit 41 determines whether the vehicle 1 has a tendency to oversteer with respect to the target steering condition (step ST33). If it is determined that the vehicle 1 has a tendency to oversteer (step ST33 "YES"), the turning slip control unit 41 corrects the control command value to increase, thereby guiding the vehicle 1 toward a tendency to understeer (step ST34). On the other hand, if it is determined that the vehicle 1 has a tendency to understeer with respect to the target steering condition during the turning transient state (step ST35 "YES"), the turning slip control unit 41 corrects the control command value to decrease, thereby performing control to guide the vehicle 1 toward a tendency to oversteer (step ST36).

[0071] Furthermore, as described above, in the turning transient state from when the vehicle 1 starts turning until the turning posture is determined, if it is determined that the vehicle 1 has a tendency to oversteer with respect to the target steering condition (step ST33 "YES"), the turning slip control unit 41 may correct the slip gain (PID gain when PID control is applied) to induce the vehicle 1 to have a tendency to understeer, and on the other hand, if it is determined that the vehicle 1 has a tendency to understeer with respect to the target steering condition in the turning transient state (step ST35 "YES"), the turning slip control unit 41 may correct the slip gain to induce the vehicle 1 to have a tendency to oversteer (step ST36).

[0072] Here, the slip gain is corrected by the slip gain calculation unit 42. The slip gain calculation unit 42 acquires the road surface friction coefficient μ estimated by the road surface friction coefficient estimation calculation unit 213 and corrects the control command value acquired from the turning slip control unit 41. In making the correction, for example, the turning slip control unit 41 calculates the driving force P and the grip force F acting on the drive wheels using the above-mentioned calculation formulas (1) and (2), determines the slip ratio according to calculation formula (3) assuming that the vehicle 1 will slip when the driving force P exceeds the grip force F, sets the minimum value on the left side of calculation formula (3) as the road surface friction coefficient μ, selects parameters appropriate for this μ, and passes them to the turning slip control unit 41, which then inputs the corrected control command value to the control command value output unit 215.

[0073] This allows handling during slip turns to be closer to standard steering. For example, by applying PID control, the slip gain (PID gain) can be set in a direction that leads to standard steering.

[0074] Next, reference is made to FIG. 6. FIG. 6 is a flowchart showing yet another example of the turning slip processing operation by the suspension control device (suspension ECU 21) of this embodiment. According to FIG. 6, first, the turning state detection unit 211 detects the turning state of the vehicle 1 (step ST41). If it detects that the vehicle 1 is turning (step ST42 "YES"), the road surface friction coefficient estimation calculation unit 213 estimates the road surface friction coefficient μ of the road surface on which the wheels 3, 4 are in contact with the ground, and transfers this to the main control unit 40 (step ST43). Next, the slip state detection unit 212 detects the slip state of the vehicle 1. The slip state detection unit 212 receives as input the value of the VSA flag, which indicates that the VS, which suppresses sudden changes in the behavior of the vehicle 1 due to skidding of the vehicle 1, has operated, and transfers the slip state of the vehicle 1, including the presence or absence of slip, to the main control unit 40.

[0075] Under sequence control by the main control unit 40, the turning slip control unit 41 determines the slip state, including the presence or absence of slip, detected by the slip state detection unit 212 (step ST44). If it is determined that slip is present (step ST44 "YES"), the turning slip control unit 41 further determines whether or not the outer front wheel is slipping (step ST45). If it is determined that the outer front wheel is slipping (step ST45 "YES"), the turning slip control unit 41 further determines whether or not multiple wheels are slipping (step ST46). If it is determined that multiple wheels are not slipping (step ST46 "NO"), the turning slip control unit 41 performs turning slip control by acquiring a control command value that directly or indirectly corresponds to the road surface friction coefficient μ estimated by the road surface friction coefficient estimation calculation unit 213 and inputting the acquired control command value to the control command value output unit 215 (step ST47). On the other hand, if it is determined in step ST46 that multiple wheels are slipping (step ST46 "YES"), the turning slip control unit 41 performs a stronger turning slip control that can increase the ground contact load N of the outer front wheel more when the outer front wheel and other wheels are slipping than when only the outer front wheel is slipping (step ST48).

[0076] In this way, when turning state detection unit 211 detects a turning state, road surface friction coefficient estimation calculation unit 213 estimates the road surface friction coefficient μ of the road surface on which wheels 3 and 4 are in contact with the ground, and turning slip control unit 41 is configured to perform turning slip control to increase the ground contact load N of the outer front wheel more when the outer front wheel is slipping with the other wheels than when only the outer front wheel is slipping. In other words, when vehicle 1 is in a turning state, turning slip control unit 41 determines whether the grip of not only the outer front wheel but also the other wheels can be relied upon, and if it is determined that it can be relied upon, it maintains ride comfort with weak turning slip control, but if it is determined that it cannot be relied upon, it increases the ground contact load N applied to the outer front wheel, thereby restoring the grip force F of the outer front wheel and improving turning ability, thereby suppressing understeer.

[0077] On the other hand, if it is determined in step ST46 that the outer front wheel is not slipping (step ST46 "NO"), in other words, if a wheel other than the outer front wheel is slipping, the outer wheel on which the load acts is gripping, so the turning slip control unit 41 performs fixed current control by inputting a fixed current value to the control command value output unit 215 to control the damping force DF of the damping force variable dampers 7, 10 (step ST49). Note that normal control may be used instead of fixed current control. Furthermore, if it is determined in step ST42 that the vehicle 1 is not turning (step ST42 "NO"), and if it is determined in step ST44 that the vehicle is not slipping (step ST44 "NO"), under sequence control by the main control unit 40, the normal control unit 43 performs normal control in which it estimates the stroke of the damping force variable dampers 7, 10 from the rotational speeds (wheel speed sensors 12) of the wheels 3, 4 of the vehicle 1, calculates a control command value (current I), and inputs it to the control command value output unit 215 (step ST50).

[0078] In this way, when the turning state detection unit 211 detects a turning state, the road surface friction coefficient estimation calculation unit 213 estimates the road surface friction coefficient μ of the road surface on which the outer front wheel is in contact with the ground, and the turning slip control unit 41 performs turning slip control when only the outer front wheel is in a slipping state, and when wheels other than the outer front wheel are in a slipping state, the outer wheel on which the ground load N acts is gripping, so by performing fixed current control or normal control, it is possible to perform appropriate turning slip control on split μ roads that have become slippery due to snow, rain, etc.

[0079] Incidentally, when slippage increases, it is preferable to immediately shift the steering characteristics toward an oversteer tendency, and when the slippage decreases, it is preferable to gradually return the steering characteristics to the original position in order to suppress the sense of shock. For this reason, as shown in Figure 8, for example, which shows the relationship between the road friction coefficient μ and the slip gain, when the road friction coefficient μ (shown by a dashed line) is decreasing, in other words, when slippage is increasing, the turning slip control unit 41 greatly changes the slip gain (shown by a chain line), and when the road friction coefficient μ is increasing, in other words, when slippage is decreasing, the turning slip control unit 41 performs control to gradually change (gradually return) the slip gain.

[0080] That is, road surface friction coefficient estimation calculation unit 213 continues to estimate and calculate the road surface friction coefficient μ while turning slip control is being performed, and turning slip control unit 41 performs control to gradually change (gradually return) the slip gain input from slip gain calculation unit 42. That is, when the amount of change in road surface friction coefficient μ is the same, turning slip control unit 41 performs control to reduce the amount of change in slip gain, which is a dimensionless quantity that references the road surface friction coefficient μ, when the road surface friction coefficient μ increases more than when it decreases. In this way, when the tendency for slippage increases, the steering characteristics can be quickly shifted to an oversteer tendency, improving vehicle stability, and when the tendency for slippage decreases, the gradual return can reduce the sense of shock.

[0081] [Effects of the embodiment] As described above, the suspension control device (suspension ECU 21) of this embodiment is a suspension control device (suspension ECU 21) that outputs control command values ​​to suspension devices (front wheel suspensions 5, rear wheel suspensions 8) of the vehicle 1 to control the damping forces of the variable damping dampers 7, 10, as shown in Fig. 1. The suspension control device (suspension ECU 21) includes, as shown in Fig. 2, a turning state detection unit 211 that detects the turning state of the vehicle 1, a slip state detection unit 212 that detects the slip state of the vehicle 1, a road surface friction coefficient estimation calculation unit 213 that estimates the road surface friction coefficient μ of the road surface on which the vehicle 1 is in contact, and a control unit 214 that performs turning slip control by acquiring a control command value corresponding to the road surface friction coefficient estimated by the road surface friction coefficient estimation calculation unit 213 and inputting the control command value to the suspensions (variable damping force damper actuators).

[0082] According to the suspension control device (suspension ECU 21) of this embodiment, when the slip state detection unit 212 detects that the vehicle 1 is in a slip state, the control unit 214 performs cornering slip control by acquiring a control command value corresponding to the road friction coefficient μ estimated by the road friction coefficient estimation calculation unit 213 and inputting the control command value to the variable damping force dampers 7, 10 of the suspension device (front wheel suspension 5, rear wheel suspension 8). Since F=μN, if the road load N is the same, the grip force F also decreases when the road friction coefficient μ is low. Since the ground load N must be increased to obtain the grip force F required to control the vehicle 1 when traveling on a road surface with a low road friction coefficient μ, for example, if slip is detected while the vehicle 1 is turning, a suspension control device can be provided that prevents the ground load N on the outer front wheel from becoming relatively small by outputting an appropriate current according to the road surface conditions and controlling the damping force of the variable damping dampers 7, 10, thereby increasing roll and increasing the ground load N on the outer front wheel, thereby suppressing understeer. Also, for example, by estimating the road friction coefficient μ and controlling the damping force DF so that the ground load N on the outer front wheel is appropriate in accordance with the estimated road friction coefficient μ, it is possible to suppress the tendency toward oversteer due to excessive control, ensure steerability near the target steering characteristic, and minimize deterioration of ride comfort.

[0083] For example, as shown in the friction circle in FIG. 9, as the road friction coefficient μ decreases, the friction circle also becomes smaller in proportion (friction circle A in low μ roll control according to Patent Document 1, shown by the dashed line in FIG. 9, → friction circle B in fixed current value mode according to the conventional technology, shown by the dashed line). In contrast, in an embodiment of the present invention, the control unit estimates the magnitude of the road friction coefficient μ, that is, the size of the friction circle, and performs cornering slip control by increasing the ground contact load N on the outer front wheel so that the friction circle becomes large enough that the force applied to the tire does not cause slip (friction circle C, shown by the solid line in FIG. 9). In other words, by adjusting the ground contact load N, the size of the friction circle can be compensated for until the tire grips, and desired steering characteristics and ride comfort can be maintained even in the event of slip.

[0084] Furthermore, in the suspension control device of this embodiment, the suspension device may be, for example, a semi-active type suspension device (front wheel suspension 5, rear wheel suspension 8) having variable damping force dampers 7, 10 and suspension springs (springs 9) as shown in Fig. 1, and, for example, as shown in Fig. 2, the control unit 214 (normal state control unit 43) may perform normal state control in which, except for specific states including a slip state, the control unit 214 estimates the stroke of the variable damping force dampers 7, 10 from the rotational speed of the wheels 3, 4 of the vehicle 1 and calculates a control command value. The normal state control unit 43 can estimate the stroke of the variable damping force dampers 7, 10 from the rotational speed of the wheels 3, 4 of the vehicle 1, calculate a control command value (current I), and input it to the control command value output unit 215. In this way, by estimating the stroke from the wheel speed, a stroke sensor is not required. Also, if slippage occurs in the vehicle 1, the behavior of the vehicle 1 is estimated based on the wheel speed and the damping force characteristics and variable characteristics are changed. However, since it becomes difficult to estimate the behavior of the vehicle 1, by switching to normal control, a sensorless suspension control device that is not dependent on the wheel speed can be provided.

[0085] Furthermore, in the suspension control device of this embodiment, the control unit 214 (slip gain calculation unit 42) may calculate a slip gain, which is a dimensionless quantity that references the road surface friction coefficient μ, and multiply the control command value generated by the turning slip control unit 41 by this slip gain to perform control that relatively increases the ground contact load N of the outer front wheel of the vehicle 1. In this way, by calculating the slip gain and reflecting it in the determination of the final control command value, the current value can be made nonlinear with respect to the magnitude of the friction coefficient μ.

[0086] Furthermore, in the suspension control device of this embodiment, when a flag (ESC flag) indicating that a cooperative control system (an ESC system not shown here) is operating is enabled, the control unit 214 (ESC priority control unit 44) may prioritize control by the cooperative control system, obtain control command values ​​calculated by the cooperative control system, and input the control command values ​​to the variable damping force dampers 7, 10 of the suspension devices (front wheel suspension 5, rear wheel suspension 8). According to the suspension control device of this embodiment, for example, by prioritizing control by the ESC system, advanced posture stabilization control is possible, and also, by networking other systems such as TCS and ABS using CAN, optimal convenience can be achieved between them.

[0087] Furthermore, in the suspension control device of this embodiment, if the control unit 214 (turning slip control unit 41) determines that the vehicle 1 has a tendency to oversteer with respect to the target steering condition during a turning transition state from when the vehicle 1 starts turning until the turning posture is determined, it may correct the control command value to increase, thereby inducing a tendency for the vehicle 1 to understeer, and if it determines that the vehicle 1 has a tendency to understeer with respect to the target steering condition during the turning transition state, it may correct the control command value to decrease, thereby inducing a tendency for the vehicle 1 to oversteer. For example, by applying PID control or the like to set the slip gain (PID gain) in a direction that induces standard steering, it is possible to bring the handling during slip turning closer to standard steering.

[0088] Furthermore, in the suspension control device of this embodiment, if the control unit 214 (turning slip control unit 41) determines that the vehicle 1 has a tendency to oversteer with respect to the target steering condition during a turning transition state from when the vehicle 1 starts turning until the turning posture is determined, the control unit 214 may correct the slip gain using the slip gain calculation unit 42 to induce the vehicle 1 to have a tendency to understeer, and if the control unit 214 determines that the vehicle 1 has a tendency to understeer with respect to the target steering condition during the turning transition state, the control unit 214 may correct the slip gain using the slip gain calculation unit 42 to induce the vehicle 1 to have a tendency to oversteer. For example, by applying PID control or the like to set the slip gain (PID gain) in a direction that induces the vehicle 1 to have a standard steering, the handling during slip turning can be made to approach the standard steering more closely.

[0089] Furthermore, in the suspension control device of this embodiment, the control unit 214 (main control unit 40) may perform control to set the time required for transition from turning slip control to normal control, which estimates the stroke of the variable damping force dampers 7, 10 from the rotational speeds of the wheels 3, 4 of the vehicle 1 and calculates a control command value, to be equal to or longer than the minimum time required for transition from normal control to turning slip control. For example, as shown in Fig. 7, the control unit 214 (main control unit 40) performs control to set the time (ON-to-OFF transition time C) required for transition from turning slip control A to normal control B, which estimates the stroke of the variable damping force dampers 7, 10 from the rotational speeds (wheel speed sensors 12) of the wheels 3, 4 of the vehicle 1 and calculates a control command value, to be equal to or longer than the minimum time required for transition from normal control B to turning slip control A (C1>C2). For this reason, the main control unit 40, for example, holds the current value at the moment when slippage is no longer detected, instructs the normal control unit 43 to resume calculation of the current value during normal control, and gradually (for example, over about 300 milliseconds) brings the current difference closer to the current value during normal control, thereby reducing the sense of shock.

[0090] Furthermore, in the suspension control device of this embodiment, slip state detection unit 212 detects the slip state of the outer front wheel when turning state detection unit 211 detects a turning state, road surface friction coefficient estimation calculation unit 213 estimates the road surface friction coefficient μ of the road surface on which the outer front wheel is in contact with the ground when turning state detection unit 211 detects a turning state, and control unit 214 (turning slip control unit 41) performs turning slip control when the outer front wheel is in a slip state, and control unit 214 (normal control unit 43) performs fixed current control or normal control when a wheel other than the outer front wheel is in a slip state. In this way, by independently detecting the slip state of the outer front wheel, which is subjected to the greatest ground load N, it is possible to appropriately control the ON / OFF of turning slip control on, for example, a split μ road that is slippery due to snow, rain, etc.

[0091] Furthermore, in the suspension control device of this embodiment, when the turning state detection unit 211 detects a turning state, the slip state detection unit 212 further detects the slip state of the other wheels, and when the turning state detection unit 211 detects a turning state, the road surface friction coefficient estimation calculation unit 213 estimates the road surface friction coefficient μ of the road surface on which the other wheels are in contact with the ground, and at this time the control unit 214 (turning slip control unit 41) may perform turning slip control to increase the ground contact load N of the outer front wheel more when the outer front wheel and the other wheels are slipping than when only the outer front wheel is slipping. In this way, when turning state detection unit 211 detects a turning state, road surface friction coefficient estimation calculation unit 213 estimates the road surface friction coefficient μ of the road surface on which wheels 3 and 4 are in contact with the ground, and control unit 214 (turning slip control unit 41) is configured to perform turning slip control to increase the ground contact load N of the outer front wheel more when the outer front wheel is slipping with the other wheels than when only the outer front wheel is slipping. In other words, when vehicle 1 is in a turning state, control unit 214 (turning slip control unit 41) determines whether the grip of not only the outer front wheel but also the other wheels can be relied upon, and if it is determined that it can be relied upon, it maintains ride comfort with weak turning slip control, but if it is determined that it cannot be relied upon, it applies a larger load to the outer front wheel to reduce the grip force F of the outer front wheel and improve turning ability, thereby suppressing understeer.

[0092] Furthermore, in the suspension control device of this embodiment, the road surface friction coefficient estimation calculation unit 213 may continue to estimate and calculate the road surface friction coefficient μ at least while cornering slip control is being performed, and may perform control to reduce the amount of change in the slip gain, which is a dimensionless quantity that references the road surface friction coefficient, when the road surface friction coefficient μ increases more than when it decreases, provided that the amount of increase or decrease in the road surface friction coefficient μ is the same. For example, as shown in Figure 8, which shows the relationship between the road surface friction coefficient μ and the slip gain, the slip gain (represented by a chain line) is greatly changed when the road surface friction coefficient μ (represented by a dashed line) is on a decreasing trend, in other words, when the slip is tending to increase, and the slip gain is gradually changed (gradually returned) when the road surface friction coefficient μ is on an increasing trend, in other words, when the slip is tending to decrease. That is, road surface friction coefficient estimation calculation unit 213 continues to estimate and calculate road surface friction coefficient μ while cornering slip control is being performed, and control unit 214 performs control to reduce the range of change in slip gain, which is a dimensionless quantity that references road surface friction coefficient μ, when the road surface friction coefficient μ increases more than when it decreases, assuming that the amount of change in road surface friction coefficient μ is the same. In this way, when the tendency for slippage increases, the steering characteristics can be quickly shifted to an oversteer tendency, improving vehicle stability, and when the tendency for slippage decreases, the steering characteristics can be gradually shifted back, reducing the sense of shock.

[0093] 1, the suspension control method of this embodiment is a suspension control method that outputs control command values ​​to suspension devices (front wheel suspensions 5, rear wheel suspensions 8) of a vehicle 1 to control the damping forces of dampers 7, 10. The suspension control method includes, for example, as shown in FIG. 4, a turning state detection step (ST21 to ST23) that detects a turning state of the vehicle 1, a slip state detection step (ST24) that detects a slip state of the vehicle 1, a friction coefficient estimation calculation step (ST25) that estimates a road surface friction coefficient of the road surface on which the vehicle 1 is in contact, and a turning slip control step (ST26 to ST28) that, when it is detected that the vehicle 1 is turning and that the vehicle 1 is in a slip state, acquires a control command value corresponding to the estimated road surface friction coefficient and inputs the control command value to the suspension devices.

[0094] According to the suspension control method of this embodiment, when the control unit 214 (turning slip control unit 41) detects that the vehicle 1 is in a slip state, the control unit 214 (turning slip control unit 41) performs turning slip control by acquiring a control command value that directly or indirectly corresponds to the estimated road friction coefficient and inputting the control command value to the suspension device. Since F = μN, if the road friction coefficient μ is low for the same ground load N, the grip force F also decreases. To obtain the grip force F required to control the vehicle 1 when traveling on a road surface with a low road friction coefficient μ, the ground load N must be increased. Therefore, for example, when slip is detected while the vehicle is turning, a suspension control device can be provided that outputs an appropriate current according to the road conditions to control the damping force of the damping-force variable damper, thereby preventing the ground load N applied to the outer front wheel from becoming relatively small. This increases roll, which increases the ground load N applied to the outer front wheel, thereby suppressing understeer. Furthermore, for example, by estimating the road surface friction coefficient μ and controlling the damping force DF so that the ground load N applied to the outer front wheel is appropriate in accordance with the estimated road surface friction coefficient μ, it is possible to suppress the tendency toward oversteer due to excessive control, ensure steerability near the target steering characteristics, and minimize deterioration in ride comfort.

[0095] For example, as shown in the friction circle in FIG. 9, as the road friction coefficient μ decreases, the friction circle also becomes smaller in proportion (friction circle A in low μ roll control according to Patent Document 1, shown by the dashed line in FIG. 9, → friction circle B in fixed current value mode according to the conventional technology, shown by the dashed line). In contrast, in this embodiment of the present invention, the control unit 214 (turning slip control unit 41) estimates the magnitude of the road friction coefficient μ, that is, the size of the friction circle, and performs turning slip control by increasing the ground load N on the outer front wheel so that the friction circle becomes large enough that the force applied to the tire does not cause slip (friction circle C, shown by the solid line in FIG. 9). In other words, by adjusting the ground load N, the size of the friction circle can be compensated for until the tire grips, and desired steering characteristics and ride comfort can be maintained even when slip occurs.

[0096] 1, the suspension control program of this embodiment is a suspension control program that outputs control command values ​​to suspension devices (front wheel suspensions 5, rear wheel suspensions 8) of vehicle 1 to control the damping forces of variable damping force dampers 7, 10. The suspension control program causes a processor included in a suspension control device (suspension ECU 21) to execute the following processes, as shown in FIG. 4, for example: a process of detecting a turning state of vehicle 1 (steps ST21 to ST23), a process of detecting a slip state of vehicle 1 (step ST24), a process of estimating a road surface friction coefficient of the road surface on which vehicle 1 is in contact (step ST25), and a process of acquiring a control command value corresponding to the road surface friction coefficient and inputting the control command value to the suspension devices when it is detected that vehicle 1 is turning and that vehicle 1 is in a slip state (steps ST26 to ST28).

[0097] According to the suspension control program of this embodiment, a processor in the suspension control device (suspension ECU 21) reads and sequentially executes the suspension control program stored in memory. When a slip state of the vehicle 1 is detected, the processor acquires a control command value corresponding directly or indirectly to the estimated road friction coefficient and inputs the control command value to the suspension device (front wheel suspension 5, rear wheel suspension 8), thereby performing cornering slip control. Since F = μN, if the road friction coefficient μ is low for the same ground load N, the grip force F also decreases. To obtain the grip force F required to control the vehicle 1 when traveling on a road surface with a low road friction coefficient μ, the ground load N must be increased. Therefore, for example, when slip is detected while the vehicle is cornering, the suspension control device can output an appropriate current according to the road surface conditions to control the damping force of the variable damping dampers 7, 10, thereby preventing the ground load N applied to the outer front wheel from becoming relatively small. This increases roll, thereby increasing the ground load N applied to the outer front wheel and suppressing understeer. Furthermore, for example, by estimating the road surface friction coefficient μ and controlling the damping force DF so that the ground load N applied to the outer front wheel is appropriate in accordance with the estimated road surface friction coefficient μ, it is possible to suppress the tendency toward oversteer due to excessive control, ensure steerability near the target steering characteristics, and minimize deterioration in ride comfort.

[0098] For example, as shown in the friction circle in FIG. 9, as the road friction coefficient μ decreases, the friction circle also becomes smaller in proportion (friction circle A in low μ roll control according to Patent Document 1, shown by the dashed line in FIG. 9, → friction circle B in fixed current value mode according to the conventional technology, shown by the dashed line). In contrast, in this embodiment of the present invention, the control unit 214 (turning slip control unit 41) estimates the magnitude of the road friction coefficient μ, that is, the size of the friction circle, and performs turning slip control by increasing the ground load N on the outer front wheel so that the friction circle becomes large enough that the force applied to the tire does not cause slip (friction circle C, shown by the solid line in FIG. 9). In other words, by adjusting the ground load N, the size of the friction circle can be compensated for until the tire grips, and desired steering characteristics and ride comfort can be maintained even when slip occurs.

[0099] The present invention is not limited to the above-described exemplary embodiments, and those skilled in the art will be able to easily modify the above-described exemplary embodiments to the extent that they fall within the scope of the claims. [Explanation of symbols]

[0100] 1 Vehicle, 3, 4 Wheel, 5, 8 Suspension, 6, 9 Suspension spring, 7, 10 Variable damping force damper, 11 Vehicle speed sensor, 12 Wheel speed sensor, 13 Longitudinal acceleration sensor, 14 Lateral acceleration sensor, 15 Steering angle sensor, 16 Roll angle sensor, 21 Suspension ECU (suspension control device), 30 Vehicle control ECU, 40 Main control unit, 41 Turning slip control unit, 42 Slip gain calculation unit, 43 Normal control unit, 44 ESC priority control unit, 211 Turning state detection unit, 212 Slip state detection unit, 213 Road surface friction coefficient estimation calculation unit, 214 Control unit, 215 Control command value output unit

Claims

1. A suspension control device that outputs a control command value to a suspension device of a vehicle to control a damping force of a variable damping force damper, a turning state detection unit that detects a turning state of the vehicle; a slip state detection unit that detects a slip state of the vehicle; a road surface friction coefficient estimation calculation unit that estimates a road surface friction coefficient of a road surface on which the vehicle is in contact; a control unit that performs turning slip control, when the turning state detection unit detects that the vehicle is turning and the slip state detection unit detects that the vehicle is in a slip state, by acquiring the control command value corresponding to the road surface friction coefficient estimated by the road surface friction coefficient estimation calculation unit and inputting the control command value to the suspension device; A suspension control device having:

2. The suspension device comprises: A semi-active type suspension device having the variable damping force damper and a suspension spring, The control unit 2. The suspension control device according to claim 1, wherein, except for specific conditions including the slip state, normal control is performed in which the stroke of the variable damping force damper is estimated from the rotational speed of a wheel of the vehicle to calculate the control command value.

3. The control unit 2. The suspension control device according to claim 1, wherein a slip gain, which is a dimensionless quantity that references the road surface friction coefficient, is calculated, and the slip gain is multiplied by the control command value to perform control that relatively increases the ground contact load of the outer front wheel of the vehicle.

4. The control unit 2. The suspension control device according to claim 1, wherein, when a cooperative control system is operating, control by the cooperative control system is given priority, a control command value calculated by the cooperative control system is acquired, and the control command value is input to the suspension device.

5. The control unit When it is determined that the vehicle has an oversteer tendency relative to a target steering condition during a turning transition state from when the vehicle starts turning until the turning attitude is determined, the control command value is corrected to be larger to induce the vehicle to have an understeer tendency, 2. The suspension control device according to claim 1, wherein, when it is determined that the vehicle has an understeer tendency with respect to the target steering condition during the turning transient state, the control command value is corrected to be smaller to induce the vehicle to have an oversteer tendency.

6. The control unit 2. A suspension control device according to claim 1, wherein, if it is determined that the vehicle has an oversteer tendency with respect to a target steering condition during a turning transition state from when the vehicle starts turning until the turning attitude is determined, the slip gain is corrected to induce the vehicle to have an understeer tendency, and if it is determined that the vehicle has an understeer tendency with respect to the target steering condition during the turning transition state, the slip gain is corrected to induce the vehicle to have an oversteer tendency.

7. The control unit 2. The suspension control device according to claim 1, wherein the control device performs control such that a time required for transitioning from the turning slip control to a normal control in which a stroke of the damping force variable damper is estimated from the rotational speed of a wheel of the vehicle and the control command value is calculated is set to a length equal to or longer than a minimum time required for transitioning from the normal control to the turning slip control.

8. The slip state detection unit detecting a slip state of the outer front wheel when the turning state detection unit detects the turning state; The road surface friction coefficient estimation calculation unit When the turning state detection unit detects the turning state, it estimates a road surface friction coefficient of a road surface on which the outer front wheel is in contact with the ground; The control unit 2. The suspension control device according to claim 1, wherein the turning slip control is performed when the outer front wheel is in a slipping state, and the fixed current control or normal control is performed when a wheel other than the outer front wheel is in a slipping state.

9. The slip state detection unit When the turning state detection unit detects the turning state, it further detects a slip state of another wheel, The road surface friction coefficient estimation calculation unit When the turning state detection unit detects the turning state, it estimates a road surface friction coefficient of a road surface on which the other wheel is in contact with the ground; The control unit 2. The suspension control device according to claim 1, wherein the cornering slip control is performed to increase the ground contact load of the outer front wheel more when the outer front wheel and the other wheels are slipping than when only the outer front wheel is slipping.

10. The road surface friction coefficient estimation calculation unit 2. A suspension control device according to claim 1, wherein the road friction coefficient estimation calculation is continued at least while the cornering slip control is being performed, and when the amount of change in the road friction coefficient is the same, the slip gain, which is a dimensionless quantity that references the road friction coefficient, is controlled to be smaller when the road friction coefficient increases than when it decreases.

11. A suspension control method for controlling a damping force of a variable damping force damper by inputting a control command value to a suspension device of a vehicle, comprising: a turning state detection step of detecting a turning state of the vehicle; a slip state detection step of detecting a slip state of the vehicle; a road surface friction coefficient estimation calculation step of estimating a friction coefficient of a road surface on which the vehicle is in contact; a turning slip control step of acquiring the control command value that directly or indirectly corresponds to the estimated road surface friction coefficient and inputting the control command value to the suspension device when it is detected that the vehicle is turning and that the vehicle is in a slip state; A suspension control method comprising:

12. A suspension control program for outputting a control command value to a suspension device of a vehicle to control a damping force of a variable damping force damper, A processor included in the suspension control device A process of detecting a turning state of the vehicle; A process for detecting a slip state of the vehicle; A process of estimating a road friction coefficient of a road surface on which the vehicle is in contact; a process of acquiring the control command value corresponding to the estimated road surface friction coefficient and inputting the control command value to the suspension device when it is detected that the vehicle is turning and that the vehicle is in a slipping state; A suspension control program that executes the above.

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