Damping force control method and vehicle suspension system

Abstract

To improve accuracy of grounding load control of an outer ring and an inner ring at the time of turning a vehicle.SOLUTION: A damping force control method comprises the steps of: detecting or estimating lateral acceleration of a vehicle (S3); and configuring, when the lateral acceleration is a prescribed value or more, a right and left distribution ratio that is a distribution ratio of damping force of a damping force variable damper between an outer ring and an inner ring based on a damping force ratio of damping force at expansion to damping force at compression when the damping force variable damper is compressed or expanded at the same stroke speed so that the damping force of the damping force variable damper of the outer ring that is a wheel at an outer side during turning is to be larger than the damping force of the damping force variable damper of the inner ring that is a wheel at an inner side during turning (S6).SELECTED DRAWING: Figure 12

Description

[Technical Field]

[0001] This invention relates to a damping force control method and a vehicle suspension system. [Background technology]

[0002] Patent Document 1 describes a damping force control device that controls the damping force of the outer wheel shock absorber to be high and the damping force of the inner wheel shock absorber to be low when a vehicle is turning. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 11-091327 [Overview of the project] [Problems that the invention aims to solve]

[0004] When a vehicle turns, the damping force of the variable damper on the outer wheel (the wheel on the outside of the turn) increases, and the damping force of the variable damper on the inner wheel (the wheel on the inside of the turn) decreases. By controlling these controls, changes in the ground contact load on the outer and inner wheels are suppressed, thereby suppressing the decrease in the overall lateral force of the vehicle caused by changes in ground contact load. However, since the damping coefficient of a damper fluctuates due to various factors, fluctuations in the damping coefficient may affect the control of the ground contact load on the outer and inner rings. The present invention aims to improve the accuracy of controlling the ground contact load of the outer and inner wheels when a vehicle is turning. [Means for solving the problem]

[0005] According to one aspect of the present invention, there is provided a damping force control method for controlling the damping force of a variable damping damper interposed between the vehicle body and the wheels of a vehicle and capable of variably controlling the damping force. In the damping force control method, the lateral acceleration of the vehicle is detected or estimated, and when the lateral acceleration is greater than or equal to a predetermined value, the damping force of the variable damping damper of the outer wheel, which is the wheel on the outside of the turn, is made greater than the damping force of the variable damping damper of the inner wheel, which is the wheel on the inside of the turn. The left-right distribution ratio, which is the distribution ratio of the damping forces of the variable damping dampers between the outer and inner wheels, is set based on the damping force ratio, which is the ratio of the damping force during extension to the damping force during compression that occurs when the variable damping dampers compress and extend at the same stroke speed.

Effects of the Invention

[0006] According to the present invention, it is possible to improve the accuracy of controlling the ground contact loads of the outer and inner wheels during vehicle turning.

Brief Description of the Drawings

[0007] [Figure 1] It is a schematic diagram of an example of a vehicle suspension device according to an embodiment. [Figure 2] It is a schematic diagram for explaining the problems of an embodiment. [Figure 3] It is a schematic diagram for explaining the effects of an embodiment. [Figure 4] (a) and (b) are schematic diagrams for explaining the damping coefficient of a damper. [Figure 5] It is a block diagram of a functional configuration example of a controller. [Figure 6] It is a schematic diagram for explaining a method of estimating the stroke speed of a variable damping damper. [Figure 7] It is a block diagram of a functional configuration example of a ground contact load control unit. [Figure 8] It is a block diagram of a functional configuration example of a roll rate envelope amplitude value estimation unit. [Figure 9] (a) and (b) are schematic diagrams of an example of the characteristics of the right front wheel distribution ratio. [Figure 10] It is a block diagram of a functional configuration example of a damping force control unit. [Figure 11] It is a schematic diagram for explaining the operation of the present invention. [Figure 12] It is a flowchart of the damping force control method of the embodiment.

Embodiments for Carrying Out the Invention

[0008] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that each drawing is schematic and may differ from the actual one. Also, the embodiments of the present invention shown below illustrate devices and methods for embodying the technical idea of the present invention, and the technical idea of the present invention does not specify the structure, arrangement, etc. of the components as follows. The technical idea of the present invention can be variously modified within the technical scope defined by the claims described in the claims.

[0009] (Configuration) FIG. 1 is a schematic diagram of an example of a vehicle suspension device according to an embodiment. The vehicle suspension device includes variable damping force dampers 4FL, 4FR, 4RL, and 4RR provided in suspensions respectively interposed between the vehicle body 2 of the vehicle 1 and the left front wheel 3FL, the right front wheel 3FR, the left rear wheel 3RL, and the right rear wheel 3RR, a controller 5, wheel speed sensors 6FL, 6FR, 6RL, and 6RR, a steering angle sensor 7, and a vehicle speed sensor 8.

[0010] In the following description, the left front wheel 3FL, the right front wheel 3FR, the left rear wheel 3RL, and the right rear wheel 3RR may be collectively referred to as "wheel 3" or "wheels 3FL, 3FR, 3RL, and 3RR". Also, the left front wheel 3FL and the right front wheel 3FR may be collectively referred to as "front wheel 3F", and the left rear wheel 3RL and the right rear wheel 3RR may be collectively referred to as "rear wheel 3R". Also, the variable damping force dampers 4FL, 4FR, 4RL, and 4RR may be collectively referred to as "variable damping force damper 4", and the wheel speed sensors 6FL, 6FR, 6RL, and 6RR may be collectively referred to as "wheel speed sensor 6".

[0011] The variable damping force damper 4 is a damping force generating device that dampens the elastic motion of the coil spring of the suspension installed between the unsprung mass and sprung mass of the vehicle 1, and the damping force can be changed by operating an actuator. For example, the variable damping damper 4 may be an electronically controlled damper. The electronically controlled damper has a cylinder filled with fluid, a piston that strokes within the cylinder, and orifices that control the fluid movement between fluid chambers formed above and below the piston.

[0012] The piston has orifices of multiple diameters, and when the actuator is operated, an orifice is selected from among the multiple orifices according to the control command. This makes it possible to generate a damping force corresponding to the orifice diameter. For example, if the orifice diameter is small, the movement of the piston is more easily restricted, so the damping force is high. Conversely, if the orifice diameter is large, the movement of the piston is less restricted, so the damping force is low.

[0013] Furthermore, the variable damping force damper 4 applicable to this embodiment is not limited to a configuration in which the damping force is changed by selecting the orifice diameter as described above, but various configurations of variable damping force dampers that can variably control the damping force can be employed. For example, the damping force may be controlled by placing an electromagnetic control valve on a passage connecting fluids formed above and below the piston and changing the amount of opening and closing of this electromagnetic control valve, or the damping force may be controlled by using magnetic fluid as the fluid and changing the fluidity of the fluid.

[0014] Wheel speed sensors 6FL, 6FR, 6RL, and 6RR detect the wheel speeds of the left front wheel 3FL, the right front wheel 3FR, the left rear wheel 3RL, and the right rear wheel 3RR, respectively. Such wheel speed sensors 6 are installed in many vehicle models for control systems such as ABS (Anti-lock Braking System), TCS (Traction Control System), and ESC (Electronic Stability Control). The wheel speed sensor 6 has a gear-shaped rotor mounted on a rotating part such as the drive shaft, axle hub, or brake drum, and a sensor consisting of a coil and magnetic poles is installed on its outer circumference with a gap of about 1 mm. When the rotor rotates, the magnetic flux passing through the coil changes, generating an alternating current, and thus the rotational speed of the wheel 3 is detected.

[0015] The steering angle sensor 7 detects the steering angle δ of the steering wheel. The vehicle speed sensor 8 detects the vehicle speed V of vehicle 1. Controller 5 is an electronic control unit (ECU) that independently controls the damping force of the variable damping dampers 4FL, 4FR, 4RL, and 4RR, which are mounted on wheels 3FL, 3FR, 3RL, and 3RR, respectively. The controller 5 includes, for example, a computer that includes a processor 5a and peripheral components such as a storage device 5b. The processor 5a may be, for example, a CPU (Central Processing Unit) or an MPU (Micro-Processing Unit).

[0016] The storage device 5b may include any of the following: a semiconductor storage device, a magnetic storage device, or an optical storage device. The storage device 5b may include memory such as ROM (Read Only Memory) and RAM (Random Access Memory) used as main memory, as well as registers and cache memory. The functions of the controller 5 described below are realized, for example, by the processor 5a executing a computer program stored in the storage device 5b.

[0017] The controller 5 may also be formed by dedicated hardware for performing the information processing described below. For example, the controller 5 may include functional logic circuits configured in a general-purpose semiconductor integrated circuit. For example, the controller 5 may have a programmable logic device (PLD) such as a field-programmable gate array (FPGA).

[0018] Next, the problems of the embodiment will be outlined with reference to Figure 2. In Figure 2, the vertical axis represents the cornering power, which is the force acting laterally on the vehicle body when the vehicle 1 turns, and the horizontal axis represents the ground contact load. During turns, lateral acceleration acts on the vehicle body, causing it to roll outwards. As a result, the ground contact load on the outer wheels (hereinafter sometimes referred to as "outer wheels") increases.

[0019] Conversely, the ground contact load on the inner wheel during a turn (hereinafter sometimes referred to as the "inner wheel") decreases. As a result, the average ground contact load of the outer and inner wheels decreases compared to the ground contact load during straight-line driving, reducing cornering power. When cornering power decreases, it becomes more difficult to turn even with steering input, causing the driver to input more steering input than necessary, requiring corrective steering during turns, and increasing the driver's workload.

[0020] Therefore, the vehicle suspension system of the embodiment detects or estimates the lateral acceleration Ax of the vehicle 1, determines whether the lateral acceleration Ax is greater than or equal to a predetermined value Ax1, and controls the variable damping damper 4 so that the damping force of the outer wheel variable damping damper 4 is greater than the damping force of the inner wheel variable damping damper A if the lateral acceleration Ax is greater than or equal to the predetermined value Ax1. This ensures the stability of the vehicle while turning, improves ride comfort, and ensures the vehicle's maneuverability at high speeds.

[0021] The effects of the embodiment will be explained in general terms with reference to Figure 3. Figure 3 is a schematic diagram comparing the case where damping force control according to the embodiment is performed (solid line) and the case where it is not performed (dashed line) for the steering amount on the same road surface. When damping force control according to the embodiment is not performed, the steering amount is large in parts A, B, and C in the figure. In part A, additional steering is performed because the vehicle's direction does not change despite steering at the beginning of the turn. In part B, the steering is corrected to compensate for being turned too far. Furthermore, in part C, the steering correction performed in part B is corrected to compensate for being turned too far. On the other hand, when damping force control is performed according to the embodiment, the amount of steering input is reduced compared to when damping force control is not performed. Thus, the present invention has the effect of improving the vehicle's responsiveness to steering input by controlling damping force.

[0022] However, since the damping coefficient of a damper fluctuates due to various factors, fluctuations in the damping coefficient may affect the control of the ground contact load on the outer and inner rings. For example, the damping coefficient when the damper extends may differ from the damping coefficient when it compresses. In the following explanation, the damping coefficient when the damper extends will be referred to as the "extension damping coefficient Ct," and the damping coefficient when the damper compresses will be referred to as the "compression damping coefficient Cc."

[0023] In the damper example in Figure 4(a), the extension damping coefficient Ct is greater than the compression damping coefficient Cc, while in the damper example in Figure 4(b), the compression damping coefficient Cc is greater than the extension damping coefficient Ct. For example, shock absorber type dampers have the characteristic that the extension damping coefficient Ct is greater than the compression damping coefficient Cc, while in strut suspension dampers, for example, the opposite characteristic is that the compression damping coefficient Cc is greater than the extension damping coefficient Ct. Furthermore, in the damper examples shown in Figures 4(a) and 4(b), the damping coefficient also changes with respect to the stroke speed. For both the extension damping coefficient Ct and the compression damping coefficient Cc, the damping coefficient is smaller in the region of high stroke speed (large absolute value of stroke speed) than in the region of low stroke speed (small absolute value of stroke speed).

[0024] Therefore, the vehicle suspension system of this embodiment is set based on the damping force ratio (Ft / Fc), which is the ratio of the damping force Ft during extension to the damping force (-Fc) generated when the variable damping force damper 4 compresses and extends at the same stroke speed (-Vs) and Vs, respectively. The damping force ratio (Ft / Fc) is equivalent to the damping coefficient ratio Ct / Cc = (Ft / Vs) / (Fc / Vs) = Ft / Fc when the variable damping force damper 4 compresses and extends at the same stroke speed.

[0025] By setting the distribution ratio of damping force between the outer and inner rings based on the damping force ratio (Ft / Fc), the damping force can be adjusted according to the damping coefficient characteristics of each individual variable damper 4. Therefore, the damping force of each variable damper 4 on the outer and inner rings can be controlled with greater precision. As a result, the precision of controlling the ground contact load of the outer and inner rings during cornering can be improved.

[0026] Figure 5 is a block diagram of an example of the functional configuration of the controller 5. The controller 5 comprises a vehicle behavior detection unit 10, a lateral acceleration estimation unit 11, a basic vibration damping control unit 12, a ground contact load control unit 13, and a damping force control unit 14. The vehicle behavior detection unit 10 detects the wheel speed ω of each of the wheels 3FL, 3FR, 3RL, and 3RR detected by the wheel speed sensor 6. s Based on the variations, the stroke speeds of the variable damping dampers 4FL, 4FR, 4RL, and 4RR for wheels 3FL, 3FR, 3RL, and 3RR (i.e., the stroke speeds of the suspensions for wheels 3FL, 3FR, 3RL, and 3RR) are estimated, respectively.

[0027] Figure 6 is a schematic diagram illustrating the method for estimating the stroke speed of a variable damping damper. When the unsprung mass vibrates due to road surface irregularities, wind-up occurs around the suspension rotation center C, as shown in Figure 6. θ represents the wind-up angle, L represents the distance from the wheel center to the suspension rotation center C, r0 represents the dynamic radius of the wheel 3, K1 represents the elastic modulus of the tire, K2 represents the elastic modulus of the suspension, and C srepresents the damping coefficient of the suspension, and θ φ represents the rotation angle of the wheel 3 due to wind-up, and y and z represent the longitudinal displacement and vertical displacement of the wheel center due to wind-up.

[0028] When wind-up occurs, the wheel speed sensor value ω detected by the wheel speed sensor 6 s includes a reference speed ω0 that is approximately the same as the running speed, a speed fluctuation ω caused by wind-up, θ a speed fluctuation ω based on the longitudinal movement generated by hitting bumps, φ and a disturbance ω such as sensor noise. d are included. ω s = ω0 + ω φ + ω θ + ω d …(1)

[0029] Since the longitudinal displacement y of the wheel center of the wheel 3 has a linear relationship with the wind-up angle θ, if the known characteristic coefficient between the longitudinal displacement y and the wind-up angle θ is K wuy it can be expressed as in the following equations (2) and (3). y = r0 × θ φ …(2) θ = K wuy × y …(3)

[0030] From the above equations (2) and (3), equation (4) is obtained, and by differentiating equation (4), equation (5) is obtained. θ = K wuy × r0 × θ φ …(4) ω θ = K wuy × r0 × ω φ …(5) Since the stroke amount λ of the suspension has a linear relationship with the longitudinal displacement characteristic y, if the known characteristic coefficient between the longitudinal displacement y and the stroke amount λ is K zy it can be expressed as in equation (6) below. By differentiating equation (6), the stroke speed dλ / dt in equation (7) is obtained.

[0031] λ = K zy×y …(6) dλ / dt=K zy ×r0×ω φ …(7) In the following explanation and drawings, the symbol for stroke velocity "dλ / dt" will be omitted and written as "dλ". Disturbance ω d If it can be ignored, dλ=K zy ×r0×(ω s -ω0) / (1+K wuy ×r0) …(8) Therefore, the stroke speed dλ is equal to the wheel speed sensor value ω s The difference between this and the reference speed ω0 (≒ driving speed) (i.e., the wheel speed sensor value ω) s It can be calculated from the fluctuations.

[0032] Refer to Figure 5. The vehicle behavior detection unit 10 estimates the sprung mass behavior (vertical displacement, roll, and pitch) from the calculated stroke velocities of each of the wheels 3FL, 3FR, 3RL, and 3RR. The vehicle behavior detection unit 10 outputs the sprung mass behavior information to the basic vibration damping control unit 12. It also outputs the stroke velocity dλ information to the damping force control unit 14. The lateral acceleration estimation unit 11 estimates the lateral acceleration Ax of the vehicle 1 based on the steering angle δ of the steering wheel and the vehicle speed V of the vehicle 1. In this embodiment, the sign of the lateral acceleration Ax in the left direction is defined as positive, and the sign of the lateral acceleration Ax in the right direction is defined as negative. For example, the lateral acceleration estimation unit 11 may estimate the lateral acceleration Ax based on the following equation (9). Ax=V 2 ×δ / (1+AV 2 ) …(9) In equation (9), A is the stability factor. This embodiment describes an example of estimating lateral acceleration Ax based on steering angle δ and vehicle speed V, but the present invention is not limited to such an example. Lateral acceleration may be estimated using a sensor capable of measuring it, or from other sensor values.

[0033] The basic vibration control unit 12 sets the basic required damping forces FbFL, FbFR, FbRL, and FbRR, which are the target values ​​for the damping force of the variable damping dampers 4FL, 4FR, 4RL, and 4RR for each wheel 3FL, 3FR, 3RL3, and RR, respectively, based on the vehicle behavior estimated by the vehicle behavior detection unit 10. The basic vibration control unit 12 sets the basic required damping forces FbFL, FbFR, FbRL, and FbRR based on skyhook control. The skyhook control theory envisions the vehicle body being suspended and fixed from the air, with the shock absorbers supported between the vehicle body and the air. Control command values ​​are generated according to this theory, and ride comfort is improved by inputting equivalent control command values ​​to the variable damping damper 4.

[0034] The ground contact load control unit 13 controls the ground contact load of each of the wheels 3FL, 3FR, 3RL, and 3RR by creating a difference in the damping force of the variable damping dampers 4FL, 4FR, 4RL, and 4RR when the vehicle 1 is turning. The ground contact load control unit 13 sets the ground contact load control damping forces FgFL, FgFR, FgRL, and FgRR, respectively, as target values ​​for the damping force of the variable damping dampers 4FL, 4FR, 4RL, and 4RR, which control the ground contact load of the wheels 3FL, 3FR, 3RL, and 3RR.

[0035] Figure 7 is a block diagram of an example of the functional configuration of the ground load control unit 13. The ground load control unit 13 comprises a roll rate envelope amplitude value estimation unit 20, gain multipliers 21f and 21r, a right front wheel distribution ratio setting unit 22f, a right rear wheel distribution ratio setting unit 22r, subtractors 23f and 23r, and multipliers 231 to 234. The roll rate envelope amplitude estimation unit 20 estimates the roll rate based on the lateral acceleration Ax estimated by the lateral acceleration estimation unit 11. The roll rate envelope amplitude estimation unit 20 estimates the roll rate envelope amplitude Ae, which is a combination of the lateral acceleration Ax, the roll rate, and the roll resonance component.

[0036] Figure 8 is a block diagram of an example of the functional configuration of the roll rate envelope amplitude value estimation unit 20. The roll rate envelope amplitude value estimation unit 20 comprises a phase-leaning component creation unit 20a, adders 20b and 20d, a phase-lag component creation unit 20c, and a Hilbert transform unit 20e. The phase-leaning component generation unit 20a outputs the derivative value of the lateral acceleration dAx by differentiating the estimated lateral acceleration Ax. The adder 20b adds the lateral acceleration Ax and the derivative value of the lateral acceleration dAx. The phase-delayed component generation unit 20c outputs a component F(Ax) obtained by delaying the phase of the estimated lateral acceleration Ax by 90°. The adder 20d adds F(Ax) to the value added in adder 20b. The Hilbert transform unit 20e calculates a scalar quantity based on the envelope waveform of the added value as the roll rate envelope amplitude value Ae.

[0037] Refer to Figure 7. Gain multiplier 21f calculates the target front wheel damping force value (Gf × Ae), which is the target value of the damping force generated in the variable damping dampers 4FL and 4FR of the front wheels 3F, by multiplying the roll rate envelope amplitude value Ae by the gain Gf, and outputs it to multipliers 231 and 232. Gain multiplier 21r calculates the target rear wheel damping force value (Gr × Ae), which is the target value of the damping force generated in the variable damping dampers 4RL and 4RR of the rear wheels 3RL and 3RR, by multiplying the roll rate envelope amplitude value Ae by the gain Gr, and outputs it to multipliers 233 and 234. By combining the roll motion component generated by the lateral acceleration Ax, the roll motion component as a vehicle body behavior, and the roll motion component due to the vehicle body's roll resonance, and setting the damping force accordingly, it is possible to reduce the roll behavior caused by steering and stabilize the vehicle's attitude.

[0038] Here, when vehicle 1 turns, a lateral acceleration acts on the vehicle body, causing the vehicle body to roll outwards during the turn. As a result, the variable damping damper 4 on the outer wheel compresses while the variable damping damper 4 on the inner wheel extends. Furthermore, as explained with reference to Figures 4(a) and 4(b), the extension damping coefficient Ct and the compression damping coefficient Cc of the variable damping force damper 4 are different.

[0039] Therefore, when the variable damping damper 4 generates damping force during vehicle 1's turn, if the extension damping coefficient Ct is greater than the compression damping coefficient Cc (Figure 4(a)), the damping force on the outer wheel side where the variable damping damper 4 compresses decreases, while the damping force on the inner wheel side where the variable damping damper 4 extends increases. As a result, the amount of compression on the outer wheel side becomes greater than the amount of extension on the inner wheel side. Conversely, when the compression damping coefficient Cc is greater than the extension damping coefficient Ct (Figure 4(b)), the damping force on the outer ring side where the variable damping damper 4 compresses increases, while the damping force on the inner ring side where the variable damping damper 4 extends decreases. As a result, the extension amount on the inner ring side becomes greater than the compression amount on the outer ring side.

[0040] Therefore, for example, if dampers with a characteristic where the extension damping coefficient Ct is greater than the compression damping coefficient Cc are used for the front wheel 3F variable dampers 4FL and 4FR, and dampers with a characteristic where the compression damping coefficient Cc is greater than the extension damping coefficient Ct are used for the rear wheel 3R variable dampers 4RL and 4RR, then by generating damping force at the same distribution ratio on the left front wheel 3FL and the right front wheel 3FR based on the target value (Gf × Ae), and generating damping force at the same distribution ratio on the left rear wheel 3RL and the right rear wheel 3RR based on the target value (Gr × Ae), the vehicle body can be formed in a posture where it sinks on the front wheel 3F side (diving pitch mode).

[0041] Furthermore, even if, for example, dampers with a characteristic where the extension damping coefficient Ct is greater than the compression damping coefficient Cc (Figure 4(a)) are used for all of the variable damping force dampers 4FL, 4FR, 4RL, and 4RR, or if dampers with a characteristic where the compression damping coefficient Cc is greater than the extension damping coefficient Ct (Figure 4(b)) are used, the vehicle body can be made to sink at the front 3F side by appropriately adjusting the distribution ratio of damping force between the front 3F side and the rear 3R side using the gains Gf and Gr.

[0042] Refer to Figure 7. The right front wheel distribution ratio setting unit 22f and the right rear wheel distribution ratio setting unit 22r set the right front wheel distribution ratio ODf, which is the distribution ratio of damping force for the right front wheel 3FR, and the right rear wheel distribution ratio ODr, which is the distribution ratio of damping force for the right rear wheel 3RR, respectively, based on the lateral acceleration Ax estimated by the lateral acceleration estimation unit 11. Figure 9(a) is a schematic diagram of the characteristics of the right front wheel distribution ratio ODf with respect to lateral acceleration Ax. The characteristics of the right rear wheel distribution ratio ODr are similar.

[0043] The front wheel left-right distribution ratio ODf has a value in the range of 0.5 ± ΔD, centered around the value "0.5". The range of change ΔD is set appropriately to a value greater than 0 and less than or equal to 0.5. In other words, the front wheel left-right distribution ratio ODf has a value in the range from an upper limit of 1 or less (0.5 + ΔD) to a lower limit of 0 or more (0.5 - ΔD). When the lateral acceleration Ax is between a predetermined value Ax1 and (-Ax1), the right front wheel distribution ratio ODf is set to "0.5". In this range, damping force is generated on both the left and right wheels with the same distribution ratio.

[0044] When the right front wheel 3FR is the outer wheel, within the range where the lateral acceleration Ax is between a predetermined value Ax1 and Ax2, the right front wheel distribution ratio ODf increases from "0.5" to the upper limit (0.5 + ΔD) as the lateral acceleration Ax increases, and is maintained at the upper limit (0.5 + ΔD) when the lateral acceleration Ax is greater than or equal to Ax2. When the right front wheel 3FR is the inner wheel, within the range where the lateral acceleration Ax is less than or equal to a predetermined value (-Ax1) and greater than or equal to (-Ax2), the right front wheel distribution ratio ODf decreases from "0.5" to the lower limit (0.5-ΔD) as the lateral acceleration Ax decreases, and is maintained at the lower limit (0.5-ΔD) when the lateral acceleration Ax is less than or equal to (-Ax2).

[0045] Refer to Figure 7. The right front wheel distribution ratio setting unit 22f outputs the right front wheel distribution ratio ODf to the subtractor 23f and the multiplier 232. The right rear wheel distribution ratio setting unit 22r outputs the right rear wheel distribution ratio ODr to the subtractor 23r and the multiplier 234. The subtractor 23f calculates the left front wheel distribution ratio (1-ODf), which is the damping force distribution ratio of the left front wheel 3FL, and outputs it to the multiplier 231. The subtractor 23r calculates the left rear wheel distribution ratio (1-ODr), which is the damping force distribution ratio of the left rear wheel 3RL, and outputs it to the multiplier 233.

[0046] Multiplier 231 calculates the ground contact load control damping force FgFL = Gf × Ae × (1 - ODf) for the left front wheel 3FL. Multiplier 232 calculates the ground contact load control damping force FgFR = Gf × Ae × ODf for the right front wheel 3FR. Multiplier 233 calculates the ground contact load control damping force FgRL = Gr × Ae × (1 - ODr) for the left rear wheel 3RL. Multiplier 234 calculates the ground contact load control damping force FgRR = Gr × Ae × ODr for the right rear wheel 3RR. In this way, by setting the ground load control damping forces FgFL, FgFR, FgRL, and FgRR, the ground load control damping force of the outer ring becomes greater than the ground load control damping force of the inner ring.

[0047] Furthermore, as explained with reference to Figures 4(a) and 4(b), the extension damping coefficient Ct and the compression damping coefficient Cc of the variable damping force damper 4 are different. Therefore, the damping force distribution ratio ODf:(1-ODf) between the right front wheel 3FR and the left front wheel 3FL, and the damping force distribution ratio ODr:(1-ODr) between the right rear wheel 3RR and the left rear wheel 3RL are set based on the damping force ratio (Ft / Fc). This improves the accuracy of the damping force distribution between the left and right wheels.

[0048] Figure 9(b) is a schematic diagram of an example setting of the damping force distribution ratio ODf:(1-ODf) between the right front wheel 3FR and the left front wheel 3FL based on the damping force ratio (Ft / Fc). The setting of the damping force distribution ratio ODr:(1-ODr) between the right rear wheel 3RR and the left rear wheel 3RL is similar. For example, as shown in Figure 9(b), the larger the damping force ratio (Ft / Fc), the larger the distribution ratio of the outer ring for the same lateral acceleration Ax (in other words, the smaller the distribution ratio of the inner ring).

[0049] In other words, within the range where the lateral acceleration Ax is less than or equal to a predetermined value (-Ax1), a larger damping force ratio (Ft / Fc) results in a smaller right front wheel distribution ratio ODf. As a result, when the right front wheel 3FR becomes the inner wheel and the variable damping damper 4FR extends, a larger extension damping coefficient Ct allows for a smaller right front wheel distribution ratio ODf to be set, thereby suppressing the effect of the increase in the damping coefficient of the variable damping damper 4FR during extension.

[0050] Furthermore, within the range where the lateral acceleration Ax is greater than or equal to a predetermined value Ax1, a larger damping force ratio (Ft / Fc) results in a larger right front wheel distribution ratio ODf being set. As a result, when the right front wheel 3FR becomes the outer wheel and the variable damping damper 4FR compresses, a larger compression damping coefficient Cc allows for a smaller right front wheel distribution ratio ODf to be set, thereby suppressing the effect of the increase in the damping coefficient of the variable damping damper 4FR during compression.

[0051] For example, if the damping force ratio (Ft / Fc) of the variable damping dampers 4FR and 4FL on the front wheel 3F is greater than the damping force ratio (Ft / Fc) of the variable damping dampers 4RR and 4RL on the rear wheel 3R, then the distribution ratio of the outer wheel of the front wheel 3F may be set to be greater than the distribution ratio of the outer wheel of the rear wheel 3R. Conversely, if the damping force ratio (Ft / Fc) of the rear wheel 3R variable dampers 4RR and 4RL is greater than the damping force ratio (Ft / Fc) of the front wheel 3F variable dampers 4FR and 4FL, then the distribution ratio of the outer wheel of the rear wheel 3R may be set to be greater than the distribution ratio of the outer wheel of the front wheel 3F.

[0052] Refer to Figure 5. The damping force control unit 14 controls the damping force of the variable dampers 4FL, 4FR, 4RL, and 4RR based on the basic required damping forces FbFL, FbFR, FbRL, and FbRR and the ground load control damping forces FgFL, FgFR, FgRL, and FgRR. Figure 10 is a block diagram of an example of the functional configuration of the damping force control unit 14. Although Figure 10 only shows the configuration of damping force control for the left front wheel 3FL variable damping damper 4FL, the damping force control for the other variable damping dampers 4FR, 4RL, and 4RR is performed by a similar configuration.

[0053] The damping force control unit 14 includes a saturation degree conversion unit 30, an arbitration unit 31, and a control signal conversion unit 32. The saturation conversion unit 30 converts the basic required damping force FbFL and the ground load control damping force FgFL into equivalent viscous damping coefficients Cb and Cg, respectively. Then, based on the maximum value Cmax and minimum value Cmin of the damping coefficient at the stroke speed dλ estimated by the vehicle behavior detection unit 10, the saturation degrees Kb and Kg[%] are calculated using the following formula. Kb=((Cb-Cmin) / (Cmax-Cmin))×100 Kg=((Cg-Cmin) / (Cmax-Cmin))×100

[0054] The arbitration unit 31 arbitrates which of the saturation degrees Kb converted in the saturation degree conversion unit 30 should be used for control, limits the arbitrated saturation degree using a preset saturation degree limit map based on the stroke speed dλ, and outputs the limited saturation degree as the final saturation degree. The control signal conversion unit 32 converts the control signal output by the arbitration unit 31 into a control signal corresponding to the saturation level and outputs it to the damping force variable damper 4FL.

[0055] Next, the operation of the present invention will be explained. When vehicle 1 enters a turning motion, a lateral acceleration Ax is generated due to the turning behavior. The generated lateral acceleration Ax is detected by the lateral acceleration estimation unit 11. When the lateral acceleration Ax is detected, the roll rate envelope amplitude value estimation unit 20 and gain multipliers 21f and 21r of the ground contact load control unit 13 set the damping force target values ​​(Gf × Ae) and (Gr × Ae) for the front wheel 3F and rear wheel 3R, respectively, and the vehicle body forms a posture in which it sinks on the front wheel 3F side (diving pitch mode).

[0056] As a result, the ground contact load on the front wheel 3F, which is the steering wheel, increases. As long as the absolute value of the lateral acceleration Ax is less than a predetermined value Ax1, the right front wheel distribution ratio setting unit 22f and the right rear wheel distribution ratio setting unit 22r distribute the damping force equally to the left and right wheels. As the turning motion progresses and the absolute value of the lateral acceleration Ax exceeds a predetermined value Ax1, the right front wheel distribution ratio setting unit 22f and the right rear wheel distribution ratio setting unit 22r set the distribution ratio of the damping force of the outer wheel to be greater than the distribution ratio of the damping force of the inner wheel, based on the characteristics explained with reference to Figures 9(a) and 9(b). This creates a difference in damping force between the outer and inner wheels, and as explained with reference to Figure 2, it is possible to suppress the decrease in the ground contact load of the turning inner wheel.

[0057] Refer to Figure 11. In the linear region where the vehicle's slip angle is relatively small, the lateral force during turning (cornering force) increases linearly, but it saturates once the slip angle increases to a certain extent. This invention utilizes this linear region for control, delaying the fluctuation of the ground contact load on the outer and inner wheels until the absolute value of the lateral acceleration Ax is equal to or greater than a predetermined value Ax1. This increases the slip angle from β1 to β2, and as a result increases the lateral tire force at the beginning of the turn from Fx1 to Fx2, enabling turning with a smaller steering angle.

[0058] Figure 12 is a flowchart of the damping force control method according to the embodiment. In step S1, the vehicle behavior detection unit 10 estimates the vehicle behavior on the spring (vertical displacement, roll, and pitch). In step S2, the basic vibration control unit 12 sets the basic required damping forces FbFL, FbFR, FbRL, and FbRR based on the vehicle behavior estimated by the vehicle behavior detection unit 10. In step S3, the lateral acceleration estimation unit 11 estimates the lateral acceleration Ax of the vehicle 1.

[0059] In step S4, the roll rate envelope amplitude value estimation unit 20 of the ground load control unit 13 estimates the roll rate envelope amplitude value Ae based on the lateral acceleration Ax. In step S5, the gain multipliers 21f and 21r calculate the target damping force values ​​for the front wheels (Gf × Ae) and the rear wheels (Gr × Ae). In step S6, the right front wheel distribution ratio setting unit 22f and the right rear wheel distribution ratio setting unit 22r, along with the subtractors 23f and 23r, set the left-right distribution ratio ODf:(1-ODf) of the damping force of the front wheel 3F and the left-right distribution ratio ODr:(1-ODr) of the damping force of the rear wheel 3R.

[0060] In step S7, multipliers 231 to 234 set the ground load control damping forces FgFL, FgFR, FgRL, and FgRR. In step S8, the damping force control unit 14 controls the damping force of the variable dampers 4FL, 4FR, 4RL, and 4RR based on the basic required damping forces FbFL, FbFR, FbRL, and FbRR and the ground load control damping forces FgFL, FgFR, FgRL, and FgRR. The process will then be completed.

[0061] (Effects of the embodiment) (1) In a damping force control method for controlling the damping force of a variable damping damper 4 interposed between the vehicle body 2 and the wheels 3 of a vehicle 1 and capable of variable damping force control, the lateral acceleration of the vehicle 3 is detected or estimated, and if the lateral acceleration is greater than or equal to a predetermined value, the left-right distribution ratio, which is the distribution ratio of the damping force of the variable damping dampers 4 between the outer and inner wheels, is set based on the damping force ratio, which is the ratio of the damping force during extension to the damping force during compression, when the variable damping damper is compressed and extended at the same stroke speed. For example, the left-right distribution ratio may be set such that the distribution ratio of the damping force of the outer ring's variable damper becomes larger when the damping force ratio is larger than when it is smaller.

[0062] This suppresses changes in the ground contact load of the outer and inner wheels, thereby reducing the decrease in the overall lateral force of the vehicle caused by changes in ground contact load. As a result, it is possible to ensure the stability of the vehicle during cornering, improve ride comfort, and ensure vehicle maneuverability at high speeds. In other words, it is possible to speed up the vehicle's response to steering input. Furthermore, by setting the left-right distribution ratio based on the damping force ratio, the accuracy of controlling the ground contact load of the outer and inner rings can be improved.

[0063] (2) The left-right distribution ratio may be set according to the amplitude of the lateral acceleration. This effectively suppresses the large fluctuation in the left and right ground loads in response to an increase in lateral acceleration. (3) When lateral acceleration occurs, the damping force of the variable damping damper will cause the vehicle to lower the front wheels, and then the left-right distribution ratio may be set so that the damping force of the outer wheel's variable damping damper is greater than the damping force of the inner wheel's variable damping damper. This delays the fluctuations in ground contact load between the outer and inner wheels, thereby increasing the slip angle. As a result, the lateral force of the tires in the initial stages of turning is increased, allowing the vehicle to turn with a smaller steering angle. [Explanation of Symbols]

[0064] 1...Vehicle, 2...Body, 3FL...Left front wheel, 3FR...Right front wheel, 3RL...Left rear wheel, 3RR...Right rear wheel, 4FL, 4FR, 4RL, 4RR...Variable damping force damper, 5...Controller, 5a...Processor, 5b...Memory device, 6FL, 6FR, 6RL, 6RR...Wheel speed sensor, 7...Steering angle sensor, 8...Vehicle speed sensor, 10...Vehicle behavior detection unit, 11...Lateral acceleration estimation unit, 12...Basic vibration damping control unit, 13...Ground load control unit, 14 ...damping force control unit, 20...roll rate envelope amplitude value estimation unit, 20a...phase lead component creation unit, 20b, 20d...adder, 20c...phase lag component creation unit, 20e...Hilbert transform unit, 21f, 21r...gain multiplier, 22f...right front wheel distribution ratio setting unit, 22r...right rear wheel distribution ratio setting unit, 23f, 23r...subtractor, 30...saturation degree conversion unit, 31...arbitration unit, 32...control signal conversion unit, 231, 232, 233, 234...multiplier

Claims

1. A damping force control method for controlling the damping force of a variable damping damper, which is interposed between the vehicle body and the wheels and whose damping force can be variedly controlled, The lateral acceleration of the vehicle is detected or estimated, When the absolute value of the lateral acceleration is greater than or equal to a predetermined value, the left-right distribution ratio, which is the distribution ratio of the damping force of the variable dampers between the outer and inner wheels, is set based on the damping force ratio, which is the ratio of the damping force during extension to the damping force during compression, when the variable damper is compressed and extended at the same stroke speed. A damping force control method characterized by the following:

2. The damping force control method according to claim 1, characterized in that the left-right distribution ratio is set such that the distribution ratio of the damping force of the variable damping damper on the outer ring becomes larger when the damping force ratio is larger than when the damping force ratio is smaller.

3. The damping force control method according to claim 1 or 2, characterized in that the left-right distribution ratio is set according to the amplitude of the lateral acceleration.

4. The damping force control method according to claim 1, characterized in that, when the aforementioned lateral acceleration occurs, the damping force of the variable damping damper forms a posture in which the front wheel side of the vehicle body is lowered, and then the left-right distribution ratio is set such that the damping force of the variable damping damper of the outer wheel becomes greater than the damping force of the variable damping damper of the inner wheel.

5. A variable damping damper, which is installed between the vehicle body and the wheels and allows for variable control of the damping force, A controller that detects or estimates the lateral acceleration of the vehicle, and if the absolute value of the lateral acceleration is greater than or equal to a predetermined value, sets the left-right distribution ratio, which is the distribution ratio of the damping force of the variable dampers between the outer and inner wheels, based on the damping force ratio, which is the ratio of the damping force during extension to the damping force during compression, when the variable dampers are compressed and extended at the same stroke speed, so that the damping force of the variable damper of the outer wheel (the wheel on the outside of the turn) is greater than the damping force of the variable damper of the inner wheel (the wheel on the inside of the turn), A vehicle suspension system characterized by comprising the following:

Images