Vehicle

Abstract

One embodiment of this vehicle has: a turning device that varies the ratio of the operation amount of a steering operation member to the turning amount of a turning wheel of the vehicle; and a force generation device that is provided between the body of the vehicle and the turning wheel and can change generated force by the relative movement of a cylinder and a rod. The force generation device comprises a first force generation mechanism and a second force generation mechanism. When the movement speed of the rod relative to the cylinder is in a first speed range, the second force generation mechanism operates during turning without the first force generation mechanism operating, but when the movement speed is in a second speed range that is higher-speed than the first speed range, the second force generation mechanism operates with the first force generation mechanism. The present invention thereby makes it possible to achieve not only a sense of quick steering but also a sense of safety and stability.

Description

vehicle

[0001] The present invention relates to a vehicle.

[0002] The steer-by-wire steering device of Patent Document 1 has a steering gear ratio variable unit that varies the steering gear ratio in accordance with the vehicle speed, and a steering gear ratio change unit that changes the steering gear ratio based on the vehicle behavior in relation to the traveling direction of the vehicle.

[0003] JP 2022-040481 A

[0004] Vehicles equipped with steering devices such as steer-by-wire, which change the steering gear ratio (the ratio of the amount of steering of the vehicle's steered wheels to the amount of operation of the steering operation member), can achieve quick handling by changing the steering gear ratio.However, quick steering can worsen roll behavior, which can reduce the vehicle's sense of stability and the driver's sense of security.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a vehicle that can provide both a quick steering feel and a sense of stability and security.

[0006] Therefore, in one aspect, the vehicle of the present invention has a steering device that varies the ratio of the operation amount of a steering operation member to the steered amount of the steered wheels of the vehicle, and a force generating device that is provided between the body of the vehicle and the steered wheels and is capable of changing the generated force through relative movement between a cylinder and a rod, the force generating device comprising a first force generating mechanism and a second force generating mechanism, the second force generating mechanism operating during steering when the movement speed of the rod relative to the cylinder is in a first speed range and the first force generating mechanism is not operating, and operating together with the first force generating mechanism when the movement speed is in a second speed range that is faster than the first speed range.

[0007] According to the present invention, it is possible to achieve both a quick steering feel and a sense of stability and security.

[0008] 1 is a schematic diagram showing a vehicle equipped with a steer-by-wire steering system. FIG. 2 is a conceptual diagram showing one aspect of a hydraulic circuit of a shock absorber. FIG. 3 is a conceptual diagram showing another aspect of a hydraulic circuit of a shock absorber. FIG. 4 is a diagram showing damping force characteristics of a shock absorber. FIG. 5 is a functional block diagram of a steering control device. FIG. 6 is a diagram showing the correlation between vehicle speed and steady-state yaw rate gain k. FIG. 7 is a diagram showing the correlation between vehicle speed and target yaw rate differential value gain K3. FIG. 8 is a diagram showing the correlation between vehicle speed and damping ratio ζ. FIG. 9 is a diagram showing the correlation between vehicle speed and natural angular frequency ωn. FIG. 10 is a diagram showing the correlation between steering operation frequency and yaw rate gain. FIG. 11 is a diagram showing the correlation between steering operation frequency and yaw rate phase. FIG. 12 is a diagram showing the step response of yaw rate when damping ratio ζ and natural angular frequency ωn are variable while maintaining the same steering capacity ζωn. FIG. 13 is a time chart showing the difference in operation angle due to differences in steering device and shock absorber. FIG. 14 is a time chart showing the difference in steering angle due to differences in steering device and shock absorber. 1 is a time chart showing a difference in yaw rate due to differences in steering devices and shock absorbers. FIG. 1 is a time chart showing a difference in roll angle due to differences in steering devices and shock absorbers. FIG. 1 is a cross-sectional view of a shock absorber of a first embodiment. FIG. 2 is a partial cross-sectional view of a shock absorber of a first embodiment. FIG. 3 is a partial cross-sectional view of a shock absorber of a second embodiment. FIG. 4 is a partial cross-sectional view of a shock absorber of a second embodiment. FIG. 5 is a conceptual diagram showing a hydraulic circuit of a shock absorber of a second embodiment. FIG. 6 is a cross-sectional view of a shock absorber of a third embodiment. FIG. 7 is a conceptual diagram showing a hydraulic circuit of a shock absorber of a third embodiment. FIG. 8 is a diagram showing a damping force characteristic of a shock absorber of a third embodiment. FIG. 9 is a cross-sectional view of a shock absorber of a fourth embodiment. FIG. 10 is a partial cross-sectional view of a shock absorber of a fourth embodiment. FIG. 11 is a partial cross-sectional view of a shock absorber of a fourth embodiment. FIG. 12 is a partial cross-sectional view of a shock absorber of a fourth embodiment. FIG. 13 is a schematic diagram showing an aspect of a vehicle to which longitudinal G control is applied. FIG. 14 is a graph showing a difference in cornering force depending on whether longitudinal G control is performed. FIG. 15 is a diagram showing a difference in driving trajectory depending on whether longitudinal G control is performed.

[0009] Hereinafter, an embodiment of a vehicle according to the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing one aspect of a vehicle 500. The vehicle 500 is a four-wheeled automobile equipped with a pair of left and right front wheels 501, 502 and a pair of left and right rear wheels 503, 504. The vehicle 500 includes a steering device 600 that changes the amount of steering of the steered front wheels 501, 502 (in other words, the direction of the front wheels 501, 502) in accordance with the amount of operation of a steering operation member 611, and shock absorbers 700 that are force generating devices provided between the vehicle body and each of the wheels 501-504 and whose generated force can be changed by the relative movement of a cylinder and a rod. The shock absorbers 700, together with springs, are provided between the vehicle body and suspension arms and form suspensions that support the wheels 501-504.

[0010] Steering device 600 is a steer-by-wire type steering device in which steering operation member 611 and front wheels 501, 502, which are steered wheels, are mechanically separated, and the steering gear ratio (steering gear ratio = operation amount / steered amount), which is the ratio of the operation amount of steering operation member 611 to the steering amount of front wheels 501, 502, is variable. Steering device 600 will be described in detail below.

[0011] The steering device 600 has a steering input device 610, a steering mechanism 620, and a steering control device 630. A steering operation by the driver of the vehicle 500 is input to the steering input device 610 via a steering operation member 611 such as a steering wheel.

[0012] Steering mechanism 620 includes steering motor 621 as a road wheel actuator that applies a steering force to front wheels 501, 502. Steering control device 630 controls steering input device 610 and steering mechanism 620. Steering control device 630 controls steering motor 621 based on an electrical signal of the driver's steering operation, thereby changing the steering angle, which is the amount of steering of front wheels 501, 502, in accordance with the amount of operation of steering operation member 611.

[0013] The steering input device 610 includes a steering operation member 611, a steering reaction force imparting device 612, and an operation angle sensor 613. The steering operation member 611 is an operator that accepts steering operations by the driver, and in this embodiment, a steering wheel is used, but it may also be a dial-type or stick-type steering input member.

[0014] The steering reaction force imparting device 612 is a means for biasing the steering operation member 611 toward the neutral position (in other words, the straight-ahead position of the vehicle 500), and applies a pseudo steering reaction force to the steering operation member 611 by means of a motor or the like. The operation angle sensor 613 detects the operation angle θ, which is the steering operation amount of the steering operation member 611, that is, the rotation angle of the steering shaft 611A, as a first physical quantity related to the operation amount of the steering operation member 611.

[0015] Steering mechanism 620 includes steering motor 621 and conversion mechanism 622 that converts the rotational motion of the output shaft of steering motor 621 into linear motion. Conversion mechanism 622 converts the rotational motion of steering motor 621 into linear motion of rack shaft 623, for example by a rack and pinion system, thereby changing the steering angle (amount of steering) of front wheels 501, 502, which are steerable wheels connected to rack shaft 623.

[0016] Furthermore, steering mechanism 620 has a steering angle sensor 624 that detects steering angle δ of front wheels 501, 502, and a motor control device 625 that drives and controls steering motor 621. Motor control device 625 acquires a signal of steering angle command δtg (target steering angle) output by steering control device 630, and controls steering motor 621 so that actual steering angle δ detected by steering angle sensor 624 approaches steering angle command δtg.

[0017] Note that the target control amount of steering motor 621 is not limited to steering angle command δtg, and may be any command for a state quantity correlated with the steering angle of front wheels 501, 502, such as a target stroke amount of rack shaft 623. Furthermore, steering angle sensor 624 can detect the stroke amount of rack shaft 623, the rotation angle of steering motor 621 (in other words, the rotation angle of the pinion shaft), and the like, as physical quantities correlated with steering angle δ. Furthermore, a system can be configured in which steering control device 630 acquires a signal of steering angle δ output by steering angle sensor 624, and outputs a control signal for steering motor 621.

[0018] The steering control device 630 is an electronic control device equipped with an MCU (Micro Controller Unit) 630A having one or more processors that execute steering control. The steering control device 630 controls the operation of the steer-by-wire steering device 600 by controlling the steering input device 610 and the steering motor 621.

[0019] In detail, MCU 630A calculates and processes various signals acquired from the outside to determine the target steering reaction force and the turning angle command δtg, outputs a signal of the target steering reaction force to steering input device 610, and outputs a signal of the turning angle command δtg to motor control device 625. Note that MCU 630A can also be referred to as a microcomputer, a processor, a processing device, an arithmetic device, etc.

[0020] For use in steering control, the MCU 630A acquires signals output by sensors that detect the running state of the vehicle 500, information indicating the driving characteristics of the driver of the vehicle 500, and the like. The vehicle 500 is equipped with sensors that detect the running state of the vehicle 500, such as wheel speed sensors 501a-504a that detect wheel speeds WS1-WS4, which are the rotational speeds of the wheels 501-504, an acceleration sensor 560 that detects the acceleration αx in the longitudinal direction of the vehicle 500, and a yaw rate sensor 540 that detects the yaw rate γac generated in the vehicle 500, and the MCU 630A acquires the detection signals of these sensors. Here, the MCU 630A calculates the vehicle speed v of the vehicle 500, which represents the running state of the vehicle 500, based on the wheel speeds WS1-WS4 (second physical quantities related to the vehicle speed of the vehicle 500) detected by the wheel speed sensors 501a-504a.

[0021] Vehicle 500 also includes a drive mode selection switch 550 that allows the driver to specify the driving characteristics of vehicle 500, and MCU 630A acquires a signal indicating the state of the drive mode specified by drive mode selection switch 550. The drive mode is associated with the output characteristics of the drive source of vehicle 500, and includes multiple modes such as sport mode, comfort mode, racing mode, and normal mode, and is configured so that the driver can arbitrarily select one of them by operating drive mode selection switch 550.

[0022] Here, MCU 630A has a function of variably controlling the steering gear ratio in accordance with the traveling state of vehicle 500 and the amount of operation of steering operation member 611. For example, MCU 630A reduces the steering gear ratio (set as a quick ratio) as vehicle speed v decreases, and determines steering angle command δtg from the amount of steering operation of steering operation member 611 based on the steering gear ratio corresponding to vehicle speed v.

[0023] Although quick handling can be achieved by such variable control of the steering gear ratio, quick steering can also worsen roll behavior, potentially damaging the vehicle's sense of stability and the driver's sense of security. Therefore, by combining shock absorber 700, which can suppress roll at the start of movement, with steering device 600, which has a variable steering gear ratio, quick steering can be achieved while also providing a sense of stability and security.

[0024] It should be noted that the steering device with a variable steering gear ratio is not limited to steer-by-wire steering device 600. For example, it may be a steering device that converts the rotation of a steering shaft mechanically connected to steering operation member 611 into lateral displacement of a tie rod via a gear device such as a rack and pinion, and that is equipped with a transmission ratio variable mechanism that changes the rotation transmission ratio (gear ratio) of the gear device in accordance with vehicle speed, etc.

[0025] Shock absorber 700 to be combined with steering device 600 with a variable steering gear ratio has, for example, two valves arranged in parallel or in series that open in the same stroke, and is configured so that in a region (first speed region) where the moving speed of the piston rod relative to the cylinder (hereinafter referred to as the piston speed) is low, only one of the two valves is opened, and in a region (second speed region) where the moving speed is higher than that, both valves are opened. Shock absorbers 700 of this type are disclosed in, for example, Japanese Patent Nos. 7168782, 711836, and 7402017.

[0026] FIG. 2 shows one example of a hydraulic circuit for shock absorber 700A, which has two valves arranged in parallel that open during the same stroke. As shown in FIG. 2, shock absorber 700A has a first damping force generating mechanism 700d and a second damping force generating mechanism 700e arranged in parallel in a passage 700c connecting an upper chamber 700a and a lower chamber 700b, which are formed by dividing the interior of a cylinder with a piston. The first damping force generating mechanism 700d includes a first damping force generating mechanism 700d1 on the extension side and a first damping force generating mechanism 700d2 on the compression side, which are arranged in parallel. An orifice 700x is provided in the common passage between the first damping force generating mechanism 700d1 on the extension side and the first damping force generating mechanism 700d2 on the compression side, allowing constant communication between the upper chamber 700a and the lower chamber 700b. The orifice 700x may have a much smaller area than the other orifices, such as the orifice 700f. If it is not required during the assembly process, it need not be provided. Similarly, the second damping force generating mechanism 700e is configured by arranging a second damping force generating mechanism 700e1 on the extension side and a second damping force generating mechanism 700e2 on the compression side in parallel. The orifice 700f is provided closer to the upper chamber 700a than the second damping force generating mechanism 700e.

[0027] Here, the main valve of the first damping force generating mechanism 700d (first damping force generating mechanism 700d1 on the extension side and first damping force generating mechanism 700d2 on the compression side) has higher rigidity and a higher valve opening pressure than the sub-valves of the second damping force generating mechanism 700e (second damping force generating mechanism 700e1 on the extension side and second damping force generating mechanism 700e2 on the compression side). Therefore, during the same stroke, in the extremely low speed range (first speed range) where the piston speed is lower than a predetermined value, the main valve of the first damping force generating mechanism 700d is closed and the sub-valve of the second damping force generating mechanism 700e is open. Then, in the normal speed range (second speed range) where the piston speed is equal to or higher than this predetermined value, both the main valve of the first damping force generating mechanism 700d and the sub-valve of the second damping force generating mechanism 700e are open.

[0028] Figure 3 shows one embodiment of the hydraulic circuit of a shock absorber 700B, which is another embodiment of the shock absorber 700, in which two valves that open during the same stroke are arranged in series. Note that in Figure 3, the same elements as in Figure 2 are assigned the same reference numerals. As shown in Figure 3, in shock absorber 700B, a first damping force generating mechanism 700d is arranged on the upper chamber 700a side of a passage 700c that connects an upper chamber 700a and a lower chamber 700b, which are formed by dividing the interior of a cylinder with a piston, and a second damping force generating mechanism 700e is arranged on the lower chamber 700b side in series with the first damping force generating mechanism 700d. The first damping force generating mechanism 700d is composed of a first damping force generating mechanism 700d1 on the extension side and a first damping force generating mechanism 700d2 on the compression side that are arranged in parallel. An orifice 700f1 is provided in parallel with the first extension-side damping force generating mechanism 700d1, and an orifice 700f2 is provided in parallel with the first compression-side damping force generating mechanism 700d2. The second damping force generating mechanism 700e is composed of a second extension-side damping force generating mechanism 700e1 and a second compression-side damping force generating mechanism 700e2 arranged in parallel. In addition, an orifice 700y is provided in parallel with the second extension-side damping force generating mechanism 700e1 and the second compression-side damping force generating mechanism 700e2. The area of ​​this orifice 700y can be much smaller than that of other orifices, such as orifice 700f1.

[0029] Here again, the main valves of the first damping force generating mechanism 700d (first damping force generating mechanism 700d1 on the extension side and first damping force generating mechanism 700d2 on the compression side) are set to have higher rigidity and a higher valve opening pressure than the sub-valves of the second damping force generating mechanism 700e (second damping force generating mechanism 700e1 on the extension side and second damping force generating mechanism 700e2 on the compression side). Thus, in the same stroke, in the extremely low speed range (first speed range) where the piston speed is lower than a predetermined value, the main valve of the first damping force generating mechanism 700d is closed and the sub-valve of the second damping force generating mechanism 700e is open. Then, in the normal speed range (second speed range) where the piston speed is equal to or higher than this predetermined value, both the main valve of the first damping force generating mechanism 700d and the sub-valve of the second damping force generating mechanism 700e are open.

[0030] Figure 4 is a diagram showing the correlation between piston speed and damping force in shock absorbers 700A, 700B equipped with the hydraulic circuit shown in Figure 2 or 3. As described above, in shock absorbers 700A, 700B, in the low-speed region (first speed region) where the piston speed is below a predetermined speed, the first damping force generating mechanism 700d is not operating and the second damping force generating mechanism 700e is operating, and in the high-speed region (second speed region) where the piston speed is equal to or higher than the predetermined speed, both the first damping force generating mechanism 700d and the second damping force generating mechanism 700e are operating.

[0031] Therefore, the slope of the increase in damping force relative to an increase in piston speed in the low-speed region is steeper than the slope in the high-speed region. In other words, the change in damping force (the rate of change in generated force) relative to a unit change in piston speed in the low-speed region where the piston speed is less than the predetermined speed S1 is greater than that in the high-speed region where the piston speed is equal to or greater than the predetermined speed S1.

[0032] In this way, shock absorbers 700A, 700B quickly generate damping force in response to an increase in piston speed when the piston speed is low. Therefore, even if the steering gear ratio in steering device 600 is changed to a small value to set quick steering characteristics and the turning speed of front wheels 501, 502, which are the steered wheels, increases, the roll at the start of movement that accompanies such quick steering can be effectively suppressed by the damping force generated by shock absorbers 700A, 700B.

[0033] In other words, in the low-speed region where the piston speed is below a predetermined speed, the second damping force generating mechanism 700e operates when steering is performed while the first damping force generating mechanism 700d is not operating, and by quickly building up the damping force, the roll behavior of the vehicle 500 when steering can be suppressed from worsening due to quick steering. Therefore, the roll behavior of the vehicle 500 when steering can be smoothed while obtaining a quick steering feel by changing the steering gear ratio, thereby improving the stability of the vehicle body and the driver's sense of security.

[0034] 4 indicates the damping force characteristics in which the damping force changes at a constant slope over the entire piston speed range in shock absorber 700 that does not include second damping force generating mechanism 700e (sub-valve, low-speed valve) and is equipped only with first damping force generating mechanism 700d (main valve). When a shock absorber with such damping force characteristics is used, it is not possible to generate a large damping force in the low-speed range of piston speed, and therefore it is not possible to effectively suppress roll at the start of movement that occurs due to quick steering, resulting in a deterioration in roll behavior and possibly a loss of vehicle stability and a loss of driver security.

[0035] In contrast to this, when shock absorbers 700A, 700B are used in which the slope of the damping force relative to the piston speed switches between the low-speed region and the high-speed region of the piston speed, as shown by the solid line in Figure 4, the damping force can be quickly raised from the low-speed region. Therefore, when shock absorber 700 including first damping force generating mechanism 700d (main valve) and second damping force generating mechanism 700e (sub-valve, low-speed valve) is used, the roll at the start of movement caused by quick steering can be reduced compared to when a shock absorber is used in which the damping force changes at a constant slope over the entire piston speed range.

[0036] Below, a detailed description will be given of control in which the target dynamic characteristics of vehicle 500 are found from the amount of operation of steering operation member 611 and the target steering angle of front wheels 501, 502 is determined based on the target dynamic characteristics, which is a preferred mode of variable control of the steering gear ratio performed by steering control device 630. Here, MCU 630A has a function to control steering angle δ as steering control based on the target dynamic characteristics, so that the gain and phase of yaw rate γ, which is the vehicle behavior of vehicle 500 in response to the steering operation of steering operation member 611 by the driver, become the target gain and target phase.

[0037] In detail, MCU 630A sets damping ratio ζ and natural angular frequency ωn [rad / s] (dynamic characteristic information indicating target dynamic characteristic) to achieve the target gain and target phase (target dynamic characteristic), and finds a target yaw rate to be generated in vehicle 500 from the steering operation amount (operation angle θ) of steering operation member 611, the steady-state yaw rate gain of vehicle 500 based on vehicle speed v of vehicle 500, the damping ratio ζ and natural angular frequency ωn, and a pre-given vehicle model. MCU 630A then obtains a steering angle command δtg (target control amount) which is the control amount of steering motor 621 that will result in the target yaw rate, and outputs a signal equivalent to steering angle command δtg to steering motor 621 (motor control device 625).

[0038] 5 is a block diagram showing steering angle control by MCU 630 A. MCU 630 A includes functional units such as a steady-state yaw rate gain calculation unit 631, a vehicle response characteristic setting unit 632 (dynamic characteristic information generation unit), a target yaw rate calculation unit 633, a target yaw rate differential value calculation unit 634, a comparison unit 635, a virtual vehicle model 636, an addition unit 637, and an integration unit 638.

[0039] The steady-state yaw rate gain calculation unit 631 acquires a signal of the vehicle speed v [km / h] obtained from the output of the wheel speed sensors 501a-504a, and calculates the steady-state yaw rate gain k based on the acquired signal of the vehicle speed v. FIG. 6 shows one aspect of the correlation between the vehicle speed v and the steady-state yaw rate gain k in the steady-state yaw rate gain calculation unit 631. In the example of the characteristics shown in FIG. 6, in the region where the vehicle speed v is equal to or less than a predetermined speed v1, the steady-state yaw rate gain k gradually increases as the vehicle speed v increases. In the region where the vehicle speed v exceeds the predetermined speed v1, the steady-state yaw rate gain k gradually decreases as the vehicle speed v increases. When the vehicle speed v is near the predetermined speed v1, the steady-state yaw rate gain k reaches a local maximum value (maximum value). Note that the predetermined speed v1 is set to a high value, for example, about 90 km / h.

[0040] The vehicle response characteristic setting unit 632 (dynamic characteristic information generating unit) sets the damping ratio ζ and the natural angular frequency ωn, which represent the response characteristics (dynamic characteristics) of the vehicle 500, to arbitrary constant values ​​regardless of the vehicle speed v. For example, the vehicle response characteristic setting unit 632 sets the damping ratio ζ to 1.0 and the natural angular frequency ωn to arbitrary constant values ​​according to the vehicle characteristics. As will be described later, the damping ratio ζ and the natural angular frequency ωn are constants for setting the gain and phase of the yaw rate, which is the vehicle behavior of the vehicle 500 in response to the steering operation of the driver of the vehicle 500, to target gain and target phase, and the damping ratio ζ and the natural angular frequency ωn are arbitrarily determined based on the required yaw rate response characteristics.

[0041] Note that the damping ratio ζ is over-damped when ζ > 1 and under-damped when 1 > ζ > 0, so the damping ratio ζ is basically set to 1.0, which is the critical damping state, but is not limited to 1.0. Furthermore, since the natural angular frequency ωn [rad / s] is expressed as ωn = 2π fn when the natural frequency is fn [Hz], the vehicle response characteristic setting unit 632 can set the natural frequency fn instead of the natural angular frequency ωn.

[0042] The target yaw rate calculation unit 633 acquires signals of the operation angle θ, the vehicle speed v, the steady-state yaw rate gain k, the damping ratio ζ, and the natural angular frequency ωn, and calculates the target yaw rate γ based on these signals. In detail, the target yaw rate calculation unit 633 is a conversion processing unit that receives the steering angle δ calculated from the operation angle θ and the steering gear ratio N, and the vehicle speed v, and converts the transfer function G1(s) when outputting the target yaw rate γ into a second-order delay system expressed by Equation 1. As shown in Equation 1, the transfer function G1(s) is determined using the steady-state yaw rate gain k, the damping ratio ζ, and the natural angular frequency ωn.

[0043] In this embodiment, the steering gear ratio N is the ratio of the steering operation amount (operation angle θ) of the steering operation member 611 to the steering angle δ of the steered wheels, and is defined as "steering gear ratio N = operation angle θ / steering angle δ". Therefore, the steering angle δ is calculated as "steering angle δ = operation angle θ / steering gear ratio N". Note that the steering gear ratio is set to a smaller value (quick ratio) as the vehicle speed v is lower, for example.

[0044] The target yaw rate differential value calculation unit 634 acquires signals of the operation angle θ, vehicle speed v, steady-state yaw rate gain k, damping ratio ζ, and natural angular frequency ωn, and calculates the target yaw rate differential value γ (dot) based on these signals. In detail, the target yaw rate differential value calculation unit 634 is a conversion processing unit that receives the steering angle δ calculated from the operation angle θ and the steering gear ratio N, and the vehicle speed v, and converts the transfer function G2(s) when outputting the target yaw rate differential value γ (dot) into a second-order delay system represented by Equation 2. As shown in Equation 2, the transfer function G2(s) is determined using the steady-state yaw rate gain k, the damping ratio ζ, and the natural angular frequency ωn.

[0045] A comparison unit 635 determines the deviation between the target yaw rate γ calculated by the target yaw rate calculation unit 633 and the yaw rate estimated value γest output by the virtual vehicle model 636 as a control deviation e (e = γ - γest). An addition unit 637 is a functional unit for calculating a steering angle command δtg (target steering angle), and determines the steering angle command δtg by summing up the following various signals.

[0046] The control deviation e calculated by the comparison unit 635 is integrated by an integration unit 638 (integral operator), and the integral of the control deviation e is multiplied by an integral gain K5, and "the integral of the control deviation e × K5" is output to an addition unit 637. Also, the target yaw rate differential value γ (dots) calculated by the target yaw rate differential value calculation unit 634 is multiplied by a target yaw rate differential value gain K3, and "the target yaw rate differential value γ (dots) × K3" is output to the addition unit 637. FIG. 7 is a diagram illustrating an example of the correlation between the target yaw rate differential value gain K3 and the vehicle speed v. The target yaw rate differential value gain K3 rapidly decreases to a predetermined value as the vehicle speed v increases in a low vehicle speed range where the vehicle speed v is lower than a predetermined speed, and maintains the predetermined value in a medium to high vehicle speed range where the vehicle speed v exceeds the predetermined speed.

[0047] The target yaw rate γ calculated by the target yaw rate calculation unit 633 is multiplied by a target yaw rate gain K4, and "target yaw rate γ×K4" is output to the adder 637. Furthermore, the adder 637 receives a value obtained by multiplying the yaw rate estimated value γest output by the virtual vehicle model 636 by a yaw rate estimated value gain K1 (yaw rate estimated value γest×K1), and a value obtained by multiplying the vehicle body sideslip angle estimated value βest output by the virtual vehicle model 636 by a vehicle body sideslip angle estimated value gain K2 (vehicle body sideslip angle estimated value βest×K2).

[0048] Then, adder 637 outputs the sum (see Equation 3) of the “yaw rate estimated value γest×K1,” “vehicle body sideslip angle estimated value βest×K2,” “target yaw rate differential value γ (dot)×K3,” “target yaw rate γ×K4,” and “integral value of control deviation e×K5” as a steering angle command δtg to steering mechanism 620 and virtual vehicle model 636.

[0049] Steering mechanism 620 drives and controls steering motor 621 so that actual steering angle δ becomes steering angle command δtg. Virtual vehicle model 636 uses a vehicle model such as a two-wheel model that is given in advance to determine yaw rate estimate γest and vehicle body sideslip angle estimate βest, which represent the behavior of vehicle 500 when vehicle speed v and steering angle command δtg are given.

[0050] The equation of motion of the two-wheel model is generally expressed by Equation 4. From the equation of motion of Equation 4, the differential value of the yaw rate γ and the differential value of the vehicle body sideslip angle β have a relationship as shown in Equation 5.

[0051] The yaw rate estimated value γest and vehicle body sideslip angle estimated value βest output by the virtual vehicle model 636 are used for the turning angle command δtg, and the turning angle command δtg is corrected in accordance with the deviation between the yaw rate estimated value γest and the target yaw rate γ. In this way, in the turning angle control by the MCU 630A, model following control (MFC) is used, which causes the output of the virtual vehicle model 636 to follow.

[0052] If a two-wheel model is used for the virtual vehicle model 636 for model following control and the target yaw rate responds with a second-order delay, when the steady-state yaw rate gain k that varies according to the vehicle speed v, and the damping ratio ζ and natural angular frequency ωn for achieving the target gain and phase are arbitrarily set, a state equation such as that shown in Equation 6 can be established. The asterisk in Equation 6 indicates a target value.

[0053] For each variable in the state equation of Equation 6, weights Q and R are set using the evaluation function shown in Equation 7, and the gain for each variable is calculated using linear quadratic regulator design (LQR design). The sum of the calculated gain for each variable and each variable becomes the turning angle command δtg, and the turning angle command δtg is determined according to the above-mentioned equation 3.

[0054] The settings of the damping ratio ζ and the natural angular frequency ωn will be described in detail below. Fig. 8 is a diagram illustrating an example of the correlation between the damping ratio ζ and the vehicle speed v. Here, the characteristic shown by the solid line in Fig. 8 indicates the setting characteristic of the damping ratio ζ in the vehicle response characteristic setting unit 632, which sets the damping ratio ζ to a constant value (for example, ζ = 1.0) regardless of the vehicle speed v.

[0055] 8 indicates the correlation between vehicle speed v and damping ratio ζ in a two-wheel steering vehicle equipped with electric power steering (EPS) in which steering operation member 611 is mechanically connected to steered front wheels 501, 502. In the case of a two-wheel steering vehicle equipped with electric power steering, the vehicle characteristic is that damping ratio ζ decreases as vehicle speed v increases, but vehicle response characteristic setting unit 632 sets damping ratio ζ to 1.0 regardless of vehicle speed v so that damping ratio ζ does not decrease as vehicle speed v increases.

[0056] 9 is a diagram illustrating an example of the correlation between the natural angular frequency ωn and the vehicle speed v. Here, the characteristic shown by the solid line in FIG. 9 indicates the setting characteristic of the natural angular frequency ωn in the vehicle response characteristic setting unit 632, which sets the natural angular frequency ωn to a constant value regardless of the vehicle speed v. Note that the characteristic shown by the dotted line in FIG. 9 indicates the correlation between the vehicle speed v and the natural angular frequency ωn in a two-wheel steering vehicle equipped with electric power steering. In the case of a vehicle equipped with electric power steering, the natural angular frequency ωn decreases as the vehicle speed v increases, as a vehicle characteristic.

[0057] 9 shows the correlation between vehicle speed v and stable handling capacity ζωn in a two-wheel steering vehicle equipped with electric power steering. Stable handling capacity ζωn is the product of damping ratio ζ and natural angular frequency ωn (ζωn = ζ × ωn). In the case of a vehicle equipped with electric power steering, the damping ratio ζ and natural angular frequency ωn decrease as the vehicle speed v increases, and therefore the stable handling capacity ζωn also decreases as the vehicle speed v increases.

[0058] Fig. 10 is a diagram showing the correlation between the steering operation frequency and the yaw rate gain for each vehicle speed in a two-wheel steering vehicle equipped with electric power steering (EPS), and Fig. 11 is a diagram showing the correlation between the steering operation frequency and the phase for each vehicle speed. As shown in Fig. 10 and Fig. 11, in the case of a two-wheel steering vehicle equipped with electric power steering (EPS), the damping ratio ζ and the natural angular frequency ωn become smaller as the vehicle speed v increases, so that the yaw rate gain becomes excessive for fast steering at high vehicle speeds, as shown in Fig. 10, and the phase lag becomes excessive for fast steering at high vehicle speeds, as shown in Fig. 11.

[0059] For this reason, in the case of a two-wheel steering vehicle equipped with electric power steering, the resonance peak of the yaw rate increases at high speeds, and the driver is required to operate the steering within a small operating angle range so as not to turn the steering operation member 611 too much. Also, in the case of a two-wheel steering vehicle equipped with electric power steering, the phase lag of the yaw rate increases at high speeds, and the driver is required to predict the behavior of the vehicle 500 and perform a steering operation that artificially compensates for the phase lag. Therefore, in two-wheel steering vehicles equipped with electric power steering, the maneuverability and stability at high speeds tend to deteriorate.

[0060] In contrast to this, the steering control of the present application utilizes the characteristics of steer-by-wire, which can arbitrarily control the tire angle of front wheels 501, 502 in response to the steering operation of steering operation member 611, and controls the damping ratio ζ and natural angular frequency ωn to be constant regardless of vehicle speed v, for setting the gain and phase of the yaw rate in response to the steering operation of the driver of vehicle 500 to target gain and target phase, by model following control using a virtual vehicle model. This makes it possible to suppress the occurrence of resonance peaks in the high-speed range, as shown in Fig. 10, and also makes it possible to reduce the phase delay, as shown in Fig. 11.

[0061] Therefore, the operability of the driver at high speeds is improved and the burden of driving operations can be reduced. In particular, in an emergency avoidance driving situation, when avoiding an obstacle and when returning to the original lane, the yaw rate actually generated in the vehicle 500 converges and follows the yaw rate expected by the driver without overshooting, so that unnecessary steering operations such as corrective steering are not required and obstacle avoidance can be performed with ease.

[0062] Incidentally, by arbitrarily setting the damping ratio ζ and the natural angular frequency ωn to constant values ​​regardless of the vehicle speed, it is possible to variably control the yaw rate response characteristics, and the system is not limited to a configuration in which the damping ratio ζ and the natural angular frequency ωn are fixed values, but can make the damping ratio ζ and the natural angular frequency ωn variable depending on conditions such as the running state of vehicle 500 and the driving characteristics of the driver. In other words, steering control device 630 (vehicle response characteristic setting unit 632) can set the damping ratio ζ and the natural angular frequency ωn to achieve yaw rate convergence characteristics that are suitable for the running state of vehicle 500 or the driver, in order to set the yaw rate gain and phase, which are the vehicle behavior of the vehicle in response to the steering operation of the driver, to the target yaw rate gain and target phase.

[0063] Furthermore, by making the damping ratio ζ and the natural angular frequency ωn variable according to conditions such as the driving state of the vehicle 500 and the driving characteristics of the driver, it is possible to set response and convergence characteristics that are more appropriate for the driving state of the vehicle 500 and the driving characteristics of the driver. Note that the driving state of the vehicle 500 includes the setting state of the steering gear ratio N according to the vehicle speed v, the steering operation state such as primary steering and secondary steering, and the driving characteristics of the driver include the driver's skill level and preferences for the response of the vehicle behavior to driving operations.

[0064] Here, when the damping ratio ζ and the natural angular frequency ωn are variable, the turning control device 630 (vehicle response characteristic setting section 632) can vary the damping ratio ζ and the natural angular frequency ωn so that the stable handling capacity ζωn, which is the value obtained by multiplying the damping ratio ζ and the natural angular frequency ωn, remains constant. If the stable handling capacity ζωn is constant, the convergence follows an envelope, and the convergence time remains the same even if the damping ratio ζ and the natural angular frequency ωn are variable.

[0065] Therefore, after adapting the natural angular frequency ωn based on the damping ratio ζ = 1.0, if it is desired to improve the responsiveness relative to the base specifications, the damping ratio ζ is set to a value within the range of ζ < 1.0 that provides the required responsiveness, and the natural angular frequency ωn is adapted so that the value of the stable handling capacity ζωn is the same as that of the base specifications even when the damping ratio ζ is set to ζ < 1.0. This makes it possible to obtain a higher responsiveness than that of the base specifications that is suited to the driving state or driver of the vehicle 500, while maintaining the same convergence time as that of the base specifications.

[0066] Figure 12 illustrates the transient response to a step input when the damping ratio ζ is gradually reduced from 1.0 while the natural angular frequency ωn is gradually increased so that the stable handling capacity ζωn is the same as in the case of a base specification where the damping ratio ζ = 1.0. As shown in Figure 12, when the damping ratio ζ is reduced to improve responsiveness, if the natural angular frequency ωn is increased so that the stable handling capacity ζωn is the same, the convergence time will be the same even if the responsiveness is changed by varying the damping ratio ζ. Furthermore, if the damping ratio ζ and the natural angular frequency ωn are varied within a range where the convergence time is the same, it is easy to determine whether the response and convergence characteristics are within appropriate ranges, and this is expected to reduce the man-hours required for adjusting the damping ratio ζ and the natural angular frequency ωn during the design and development stage of steering control device 630 (vehicle response characteristic setting unit 632).

[0067] Steering control device 630 (vehicle response characteristic setting section 632) can vary damping ratio ζ and natural angular frequency ωn, for example, in accordance with the drive mode designated by the driver using drive mode selection switch 550. In other words, the drive mode designated by the driver represents the driver's level of skill and their preference for the response of vehicle behavior to driving operations, and for example, if sport mode or racing mode is selected, it can be estimated that the driver is more skilled or that the driver prefers quicker response of vehicle behavior to driving operations than if comfort mode or normal mode is selected.

[0068] Therefore, when the sport mode or racing mode is selected, the steering control device 630 (vehicle response characteristic setting section 632) can make the damping ratio ζ smaller to increase the response compared to when the comfort mode or normal mode is selected. By changing the damping ratio ζ in this way, the response characteristic can be set to be more suited to the driving characteristics of the driver, improving the steering operability of the driver.

[0069] In changing the damping ratio ζ and the natural angular frequency ωn in accordance with the driving characteristics of the driver, if the natural angular frequency ωn is changed in accordance with the change in the damping ratio ζ so that the stable handling capacity ζωn does not change, it is possible to change the responsiveness while maintaining the same convergence time. Furthermore, the determination of the driver's driving characteristics is not limited to determination based on the specified drive mode, and steering control device 630 (vehicle response characteristic setting section 632) can estimate the driver's skill level and the driver's preferred reaction speed from, for example, a history of accelerator operation speed and accelerator operation amount.

[0070] Furthermore, steering control device 630 (vehicle response characteristic setting unit 632) can vary damping ratio ζ so as to lower the yaw rate gain (responsiveness) from secondary steering onwards compared to primary steering. If the responsiveness during vehicle behavior correction from secondary steering onwards is made the same as when turning the primary steering further, the difficulty of steering increases, and secondary steering, which is steering to the opposite side while the primary behavior is occurring, is performed, making it difficult to return to the original lane in emergency avoidance, etc. Therefore, by lowering the responsiveness from secondary steering onwards compared to primary steering and relatively lowering the responsiveness during steering back (secondary steering) to a level that allows the driver to handle the behavior correction, it is possible to achieve both emergency avoidance and behavior convergence.

[0071] In particular, experienced drivers tend to understand and predict vehicle characteristics and turn back (secondary steering) faster than turning further (primary steering) when correcting behavior through secondary steering. Therefore, if the base response is increased based on the driver's expertise, making the response after secondary steering the same as when turning further in primary steering would likely cause significant disruption in vehicle behavior, making it difficult to correct behavior after secondary steering.

[0072] Therefore, the process of lowering the responsiveness at secondary steering and onward compared to that at primary steering can be performed on the condition that the damping ratio ζ is set to less than 1.0 as a base specification based on the driving characteristics of the driver. In other words, when the damping ratio ζ is set to less than 1.0 as a base specification, for example, the process of returning the damping ratio ζ to 1.0 at secondary steering and onward can be performed. Also, even when the damping ratio ζ and the natural angular frequency ωn are changed due to the primary steering and secondary steering, the natural angular frequency ωn can be changed in accordance with the change in the damping ratio ζ so that the steering stability capacity ζωn does not change.

[0073] Furthermore, when the steering gear ratio N is set to a smaller value as the vehicle speed v decreases, if the steering gear ratio is set to a quick ratio at low vehicle speeds, the yaw rate gain is likely to become large, and steering operability deteriorates. Therefore, when the steering gear ratio N is set to a small value at low vehicle speeds, the steering control device 630 (vehicle response characteristic setting section 632) can change the damping ratio ζ and the natural angular frequency ωn in accordance with the vehicle speed v so that the phase is more delayed than when the steering gear ratio N is set to a large value at high vehicle speeds. Even in such variable settings of the damping ratio ζ and the natural angular frequency ωn in accordance with the vehicle speed v, the natural angular frequency ωn can be changed in accordance with the change in the damping ratio ζ so that the stable handling capacity ζωn does not change.

[0074] Here, the effects of combining shock absorber 700 with steering angle control (variable control of the steering gear ratio using an MFC) according to the block diagram of FIG. 5 will be described. FIGS. 13-16 are time charts illustrating changes in the operation angle, steering angle, yaw rate, and roll angle at the start of a steering operation during a lane change of vehicle 500. The characteristics shown by the solid lines in FIGS. 13-16 represent a combination of steering angle control according to the block diagram of FIG. 5 and shock absorber 700 (hereinafter referred to as "the present invention"). The characteristics shown by the dashed dotted lines in FIGS. 13-16 represent a combination of electric power steering (EPS) and a shock absorber in which the damping force increases at a constant rate with an increase in piston speed (hereinafter referred to as "original"). The characteristics shown by the dotted lines in Figures 13-16 represent the case where a steer-by-wire type steering device in which the steering gear ratio is variable depending on the vehicle speed is combined with shock absorber 700 which has a fast damping force rise response in the low speed range (hereinafter referred to as "variable ratio").

[0075] 13 to 16, in a scene where a low-frequency steering operation such as a lane change is performed, in the case of the present invention, the change in the steering angle is not as rapid as in the case of a variable ratio (see FIG. 14), but the phase of the yaw rate can be advanced from the original phase and made equivalent to that of a variable ratio (see FIG. 15), and the amount of operation of steering operation member 611 by the driver is minimized (see FIG. 13). Furthermore, in the case of the present invention, the phase of the yaw rate can be advanced equivalent to that of a variable ratio while the roll angle can be made smaller than that of a variable ratio (see FIG. 16). In other words, by combining the steering angle control according to the block diagram of FIG. 5 with shock absorber 700, the gain and phase of the yaw rate in the low-frequency range can be made closer to the target characteristics than in the case of a shock absorber in which the damping force increases at a constant rate with an increase in piston speed.

[0076] The structure of the shock absorber 700 will be described in detail below. Figures 17 to 19 show a shock absorber 700A1, which is one embodiment of the shock absorber 700A that includes the hydraulic circuit shown in Figure 2. As shown in Figure 17, the shock absorber 700A1 is a so-called monotube hydraulic shock absorber, and includes a cylinder 2 that is filled with oil (not shown) as a working fluid. The cylinder 2 has a cylindrical shape with a bottom. The cylinder 2 is an integrally molded product that includes a cylindrical body 11 and a bottom 12 that is formed on the lower side of the body 11 and closes the lower part of the body 11.

[0077] The shock absorber 700A1 has a partition 15 and a piston 18, both of which are slidably provided inside the cylinder 2. The partition 15 is provided between the piston 18 and the bottom 12 of the cylinder 2. The piston 18 defines two chambers, an upper chamber 19 and a lower chamber 20, inside the cylinder 2, and the partition 15 defines the lower chamber 20 and a gas chamber 16 inside the cylinder 2. Oil is sealed in the upper chamber 19 and the lower chamber 20 inside the cylinder 2 as a working fluid, and gas is sealed in the gas chamber 16 inside the cylinder 2.

[0078] The shock absorber 700A1 is equipped with a piston rod 21, one axial end of which is disposed inside the cylinder 2 and fixedly connected to the piston 18, and the other axial end of which extends outside the cylinder 2. A rod guide 22 is fitted and fixed to the upper open end of the cylinder 2, and a seal member 23 is fitted above the rod guide 22, which is closer to the outside of the cylinder 2. The upper end of the cylinder 2 is crimped radially inward to form a locking portion 26, and the locking portion 26 and the rod guide 22 hold the seal member 23 in place. A friction member 24 is provided between the rod guide 22 and the seal member 23.

[0079] The rod guide 22, friction member 24, and seal member 23 are all annular, and the piston rod 21 is slidably inserted through the rod guide 22, friction member 24, and seal member 23, respectively, and extends from the inside to the outside of the cylinder 2. The piston rod 21 has a main shaft portion 27 and a mounting shaft portion 28 having a smaller diameter. The main shaft portion 27 of the piston rod 21 is slidably fitted into the rod guide 22, friction member 24, and seal member 23, and the mounting shaft portion 28 is disposed within the cylinder 2 and connected to the piston 18 and the like. The end of the main shaft portion 27 on the mounting shaft portion 28 side forms a shaft step portion 29 that widens in a direction perpendicular to the axis.

[0080] An axially extending passage notch 30 is formed in the outer periphery of the mounting shaft portion 28 at an axially intermediate position, and a male thread 31 is formed at the tip position on the axially opposite side from the main shaft portion 27. The passage notch 30 is formed, for example, by cutting out a flat surface in the outer periphery of the mounting shaft portion 28 in a plane parallel to the central axis of the mounting shaft portion 28. The piston rod 21 is provided with an annular stopper member 32, a pair of supports 33, a coil spring 34, and a buffer body 35 in a portion of the main shaft portion 27 between the piston 18 and the rod guide 22. The piston rod 21 is inserted into the inner periphery of the stopper member 32, and the stopper member 32 is fixed to the main shaft portion 27 by crimping.

[0081] The pair of supports 33 and coil springs 34 have the piston rod 21 inserted therethrough and are disposed between the stopper member 32 and the rod guide 22. The cushioning body 35 has the piston rod 21 inserted therethrough and is disposed between the supports 33 and the rod guide 22. As shown in Figure 18, the piston 18 is composed of a metal piston body 36 connected to the piston rod 21, and an annular sliding member 37 made of synthetic resin that is attached integrally to the outer circumferential surface of the piston body 36 and slides inside the cylinder 2.

[0082] The piston body 36 is provided with a plurality of passage holes 38 (only one of which is shown in FIG. 18 because it is a cross section) that allow communication between the upper chamber 19 and the lower chamber 20, and a plurality of passage holes 39 (only one of which is shown in FIG. 18 because it is a cross section) that allow communication between the upper chamber 19 and the lower chamber 20. The plurality of passage holes 38 open radially outward on one axial side of the piston 18 (upper side in FIG. 18 ) and radially inward on the other axial side of the piston 18 (lower side in FIG. 18 ). The piston body 36 is formed with an annular groove 55 on the axial side toward the lower chamber 20, which connects the plurality of passage holes 38.

[0083] A first damping force generating mechanism 41 is provided on the lower chamber 20 side of the annular groove 55, and generates a damping force by opening and closing the passages in the annular groove 55 and the plurality of passage holes 38. By disposing the first damping force generating mechanism 41 on the lower chamber 20 side, the passages in the plurality of passage holes 38 and the annular groove 55 serve as extension-side passages through which oil flows from the upper chamber 19, which is upstream, to the lower chamber 20, which is downstream, when the piston 18 moves toward the upper chamber 19, i.e., during the extension stroke. The first damping force generating mechanism 41 provided for the passages in the plurality of passage holes 38 and the annular groove 55 serves as an extension-side damping force generating mechanism (first extension-side damping force generating mechanism 700d1 in FIG. 2 ) that generates a damping force by suppressing the flow of oil from the passages in the extension-side plurality of passage holes 38 and the annular groove 55 to the lower chamber 20. The multiple passage holes 39 open radially outward on the other axial side of the piston 18 (lower side in FIG. 18 ) and radially inward on one axial side of the piston 18 (upper side in FIG. 18 ) of the piston 18. An annular groove 56 is formed in the piston body 36 to connect the multiple passage holes 39 to the upper chamber 19 in the axial direction.

[0084] A first damping force generating mechanism 42 is provided on the upper chamber 19 side of the annular groove 56, and generates a damping force by opening and closing the passages in the plurality of passage holes 39 and the annular groove 56. By disposing the first damping force generating mechanism 42 on the upper chamber 19 side, the passages in the plurality of passage holes 39 and the annular groove 56 become compression-side passages through which oil flows from the lower chamber 20, which is upstream, to the upper chamber 19, which is downstream, when the piston 18 moves toward the lower chamber 20, i.e., during the compression stroke. The first damping force generating mechanism 42 provided for the passages in the plurality of passage holes 39 and the annular groove 56 serves as a compression-side damping force generating mechanism (compression-side first damping force generating mechanism 700d2 in FIG. 2 ) that generates a damping force by suppressing the flow of oil from the compression-side passage holes 39 and the passages in the annular groove 56 to the upper chamber 19.

[0085] The piston body 36 has a generally circular disk shape, and an insertion hole 44 is formed axially through its radial center, into which the mounting shaft portion 28 of the piston rod 21 is inserted. The insertion hole 44 has a small-diameter hole portion 45 on one axial side into which the mounting shaft portion 28 of the piston rod 21 is fitted, and a large-diameter hole portion 46 on the other axial side, which has a larger diameter than the small-diameter hole portion 45. The small-diameter hole portion 45 is provided on the axial side of the upper chamber 19, and the large-diameter hole portion 46 is provided on the axial side of the lower chamber 20. An annular inner seat portion 47 is formed at the end of the piston body 36 on the axial side facing the lower chamber 20, radially inward of the opening of the annular groove 55 on the lower chamber 20 side.

[0086] Furthermore, an annular valve seat portion 48 constituting part of the first damping force generating mechanism 41 is formed at the end of the piston body 36 facing the lower chamber 20 in the axial direction, radially outward of the opening of the annular groove 55 on the lower chamber 20 side. An annular inner seat portion 49 is formed at the end of the piston body 36 facing the upper chamber 19 in the axial direction, radially inward of the opening of the annular groove 56 on the upper chamber 19 side. Further, an annular valve seat portion 50 constituting part of the first damping force generating mechanism 42 is formed at the end of the piston body 36 facing the upper chamber 19 in the axial direction, radially outward of the opening of the annular groove 56 on the upper chamber 19 side.

[0087] The insertion hole 44 of the piston body 36 has a large-diameter hole portion 46 that is located closer to the inner seat portion 47 in the axial direction than the small-diameter hole portion 45. The passage within the large-diameter hole portion 46 of the piston body 36 is always in communication with a piston rod passage portion 51 within the passage cutout 30 of the piston rod 21, overlapping in the axial direction. The piston body 36 has a stepped portion radially outward from the valve seat portion 48 that is lower in axial height than the valve seat portion 48, and the opening of the compression-side passage hole 39 on the lower chamber 20 side is located in this stepped portion. Similarly, the piston body 36 has a stepped portion radially outward from the valve seat portion 50 that is lower in axial height than the valve seat portion 50, and the opening of the extension-side passage hole 38 on the upper chamber 19 side is located in this stepped portion.

[0088] The first damping force generating mechanism 42 on the compression side includes a valve seat portion 50 of the piston 18, and has, in order from the piston 18 side in the axial direction, a plurality of (specifically, two) discs 62 of the same inner diameter and the same outer diameter, a single disc 63, a plurality of (specifically, four) discs 64 of the same inner diameter and the same outer diameter, a plurality of (specifically, two) discs 65 of the same inner diameter and the same outer diameter, a plurality of (specifically, four) discs 66 of the same inner diameter but with outer diameters that decrease the further away from the piston 18 in the axial direction, a single disc 67, a single disc 68, and a single annular member 69.

[0089] A plurality of discs 64, a plurality of discs 65, and a plurality of discs 66 constitute a compression-side main valve 71 that is releasable from the valve seat portion 50. When the main valve 71 is releasable from the valve seat portion 50, it connects the passages in the plurality of passage holes 39 and the annular groove 56 with the upper chamber 19, and generates a damping force by suppressing the flow of oil between the valve seat portion 50 and the main valve 71. The annular member 69, together with the disc 68, abuts against the main valve 71 to restrict deformation of the main valve 71 in the opening direction beyond a specified limit.

[0090] The passages within the multiple passage holes 39 and the annular groove 56, and the passage between the main valve 71 and the valve seat 50 that appears when the valve is open, form a first compression passage 72 through which oil flows from the lower chamber 20, which is the upstream side within the cylinder 2, to the upper chamber 19, which is the downstream side, as the piston 18 moves toward the lower chamber 20. The first compression damping force generating mechanism 42 that generates a damping force includes the main valve 71 and the valve seat 50, and is therefore provided in this first passage 72. The first passage 72 is formed in the piston 18 including the valve seat 50, and oil passes through it when the piston rod 21 and piston 18 move toward the compression side.

[0091] The extension-side first damping force generating mechanism 41 includes the valve seat portion 48 of the piston 18 and has, in order from the piston 18 side in the axial direction, a disk 82, a disk 83, a disk 84, a plurality of (specifically, four) disks 85 having the same inner and outer diameters, a disk 86, a plurality of (specifically, two) disks 87 having the same inner and outer diameters, a plurality of (specifically, two) disks 88 having the same inner diameter but with outer diameters that decrease with increasing distance from the piston 18 in the axial direction, and a disk 89. The disks 82 to 89 are made of metal and are all plain disks in the shape of perforated circular flat plates of a constant thickness into which the mounting shaft portion 28 of the piston rod 21 can be fitted.

[0092] The disc 82 has a notch 90 formed from a midpoint radially outward of the inner seat portion 47 to the inner circumferential edge thereof, which constantly connects the passages in the annular groove 55 and the passage holes 38 with the passages in the large diameter hole portion 46 of the piston 18 and the piston rod passage portion 51 in the passage cutout portion 30 of the piston rod 21. The discs 85, one disc 86, the discs 87, and the discs 88 constitute an extension-side main valve 91 that can be seated on and removed from the valve seat portion 48. When the main valve 91 is released from the valve seat portion 48, it connects the passages in the annular groove 55 and the passage holes 38 with the lower chamber 20 and suppresses the flow of oil between the main valve 91 and the valve seat portion 48, thereby generating a damping force.

[0093] The passages within the multiple passage holes 38 and the annular groove 55, and the passage between the main valve 91 and the valve seat 48 that appears when the valve is open, form a first extension passage 92 through which hydraulic fluid flows from the upper chamber 19, which is the upstream side of the cylinder 2, to the lower chamber 20, which is the downstream side, as the piston 18 moves toward the upper chamber 19. The first extension damping force generating mechanism 41 that generates damping force includes the main valve 91 and the valve seat 48, and is therefore provided in this first passage 92. The first passage 92 is formed in the piston 18, including the valve seat 48, and hydraulic fluid passes through the first passage 92 when the piston rod 21 and piston 18 move toward the extension side. Note that the compression first damping force generating mechanism 42 or the extension first damping force generating mechanism 41 is provided with an orifice (not shown) corresponding to the orifice 700x in FIG. 2 at the position of either the main valve 71, 91 or the valve seat 48, 50.

[0094] In the extension side first damping force generating mechanism 41, no fixed orifice is formed in either the valve seat portion 48 or the main valve 91 abutting thereon, which would allow communication between the upper chamber 19 and the lower chamber 20, even when these are in contact with each other. In other words, when the valve seat portion 48 and the main valve 91 are in contact with each other over the entire circumference, the extension side first damping force generating mechanism 41 does not allow communication between the upper chamber 19 and the lower chamber 20.

[0095] As shown in Figure 19, on the opposite side of the piston 18 of the first damping force generating mechanism 41 on the extension side, there are provided, in order from the first damping force generating mechanism 41 side, one cap member 101, one flexible disc 100 (flexible member, movable member), multiple (specifically, two) discs 102, one sub-valve 107 (second sub-valve), one valve seat member 109 with an O-ring 108 provided on the outer periphery, one sub-valve 110 (first sub-valve), one disc 111, one disc 113, and multiple (specifically, two) annular members 114, with the mounting shaft portion 28 of the piston rod 21 fitted inside each of them.

[0096] A male thread 31 is formed on the mounting shaft portion 28 of the piston rod 21 in a portion that protrudes beyond the annular member 114, and a nut 115 is threaded onto this male thread 31. The nut 115 abuts against the annular member 114. As shown in Figure 19, the cap member 101 has a perforated, disc-shaped bottom portion 122 of a constant thickness, an intermediate tapered portion 123 that extends from the outer peripheral edge of the bottom portion 122 toward one axial direction of the bottom portion 122 while expanding in diameter, and a cylindrical portion 124 that extends in the opposite direction from the bottom portion 122 from the edge of the intermediate tapered portion 123 opposite the bottom portion 122.

[0097] The bottom portion 122 is a perforated disk-like member into whose inner periphery the mounting shaft portion 28 of the piston rod 21 is fitted. By fitting the mounting shaft portion 28 into the inner periphery of the bottom portion 122, the cap member 101 is positioned radially relative to the piston rod 21 and arranged coaxially. A plurality of passage holes 126 are formed in the bottom portion 122 between the inner periphery and the outer periphery, penetrating the bottom portion 122 in the axial direction of the bottom portion 122. The plurality of passage holes 126 are arranged at equal intervals in the circumferential direction of the bottom portion 122 at positions equidistant from the center of the bottom portion 122, and are formed closer to the outer periphery than the center between the inner periphery and the outer periphery of the bottom portion 122.

[0098] The cap member 101 is oriented such that the bottom portion 122 is closer to the piston 18 than the cylindrical portion 124 and abuts against the disk 89, and the inner periphery of the bottom portion 122 is fitted onto the mounting shaft portion 28. The cap member 101 is thicker than the disks 85 to 88, and, together with its cylindrical shape with a bottom, has higher rigidity than the disks 85 to 88. Therefore, the cap member 101 abuts against the main valve 91, which is made up of multiple disks 85 to 88, and restricts deformation of the main valve 91 in the opening direction beyond a specified level.

[0099] The flexible disk 100 has a main body portion 301 and a disk protrusion portion 302 (flexible member-side protrusion portion) protruding from the main body portion 301. In its natural state before being assembled to the shock absorber 700A1, the main body portion 301 is a perforated circular flat plate with a constant thickness, and its inner and outer peripheral surfaces are coaxial. The disk protrusion portion 302 protrudes from the main body portion 301 to one side in the axial direction of the main body portion 301. The disk protrusion portion 302 is annular and coaxial with the main body portion 301, and is formed closer to the outer peripheral surface than the center position between the inner and outer peripheral surfaces of the main body portion 301. The main body portion 301 is configured so that the mounting shaft portion 28 of the piston rod 21 can be fitted inside. By fitting the mounting shaft portion 28 to the inner peripheral portion of the main body portion 301, the flexible disk 100 is positioned radially and coaxially with the piston rod 21.

[0100] The disk protrusion 302 extends from the outer periphery of the main body 301 to one axial direction while tapering in diameter, then turns back radially inward toward the other axial direction, and extends to the other axial direction while tapering in diameter until it joins the main body 301. The disk protrusion 302 has an axisymmetric shape. The apex of the disk protrusion 302 on the opposite side of the main body 301 in the axial direction of the flexible disk 100 is circular and concentric with the inner and outer peripheries of the flexible disk 100, and its height from the main body 301 is constant around the entire circumference.

[0101] The flexible disk 100 is housed within the cap member 101, with the disk protrusion 302 oriented to protrude from the main body portion 301 toward the bottom portion 122 in the axial direction, and the disk protrusion 302 abuts against the bottom portion 122. The disk 102 has an outer diameter smaller than the minimum inner diameter of the disk protrusion 302. When the flexible disk 100 is incorporated into the shock absorber 700A1, the inner peripheral side of the main body portion 301 is sandwiched between the disk 102 and the bottom portion 122. As a result, the main body portion 301 elastically deforms in a tapered shape so that the radially outer portion moves away from the bottom portion 122 in the axial direction.

[0102] When the flexible disk 100 is incorporated into the shock absorber 700A1, the inner diameter of the tip surface of the disk protrusion 302 that abuts against the bottom portion 122 is larger than twice the maximum distance from the center of the bottom portion 122 to the plurality of passage holes 126. As a result, the flexible disk 100 is arranged so that the annular disk protrusion 302 surrounds all of the plurality of passage holes 126 radially outward from the bottom portion 122 and abuts against the bottom portion 122 over the entire circumference.

[0103] The flexible disk 100 has an inner peripheral abutment portion 303 at a portion of the main body portion 301 that overlaps with the disk 102 and that always abuts against the disk 102 and the bottom portion 122 of the cap member 101 over the entire circumference. The outer diameter of the inner peripheral abutment portion 303 is smaller than twice the smallest distance from the center of the bottom portion 122 to the plurality of passage holes 126. As a result, the flexible disk 100 has an inner peripheral abutment portion 303 that is disposed so as to surround the entire plurality of passage holes 126 radially inward of the bottom portion 122 and abuts against the bottom portion 122 over the entire circumference.

[0104] When the flexible disk 100 is incorporated into the shock absorber 700A1, the main body portion 301 comprises an inner circumferential contact portion 303, a flexible portion 305 between the inner circumferential contact portion 303 and the disk protruding portion 302, and an outer circumferential edge portion 306 radially outward of the disk protruding portion 302. The outer diameter of the outer circumferential edge portion 306 is smaller than the minimum inner diameter of the intermediate tapered portion 123 of the cap member 101, so that the flexible disk 100 does not come into contact with the intermediate tapered portion 123 or the cylindrical portion 124. The flexible disk 100 has a tapered shape such that the flexible portion 305 and the outer circumferential edge portion 306 move axially away from the bottom portion 122 as they extend radially outward. The flexible disk 100 is flexible so that the flexible portion 305 approaches the bottom portion 122 and returns to its original state.

[0105] The valve seat member 109 is a perforated disk-like member with a through hole 131 formed at its radial center, extending axially and penetrating its thickness, for inserting the mounting shaft portion 28. The through hole 131 has a small-diameter hole portion 132 on one axial side into which the mounting shaft portion 28 of the piston rod 21 is fitted, and a large-diameter hole portion 133 on the other axial side, the large-diameter hole portion 133 having a larger diameter than the small-diameter hole portion 132. The valve seat member 109 has an annular inner seat portion 134 at its axial end on the large-diameter hole portion 133 side so as to surround the large-diameter hole portion 133, and a valve seat portion 135 extending radially outward from the inner seat portion 134. The valve seat portion 135 has a connecting portion 203.

[0106] The valve seat member 109 has an annular inner seat portion 138 at its end on the axially opposite side of the small-diameter hole portion 132, surrounding the small-diameter hole portion 132, and a valve seat portion 139 extending radially outward from the inner seat portion 138. The inner seat portion 138 is annular and centered on the central axis of the valve seat member 109, and has a connecting portion 213. The valve seat member 109 is formed with a passage recess 215 recessed in the axial direction of the valve seat member 109 from its tip end surface on the protruding side. The bottom surface of the passage recess 215 is formed by the main body portion 140. A passage hole 216 is formed in the center of the passage recess 215, penetrating the valve seat member 109 in the axial direction. The passage hole 216 and the passage recess 215 into which the passage hole 216 opens form a first passage portion 151 provided in the valve seat member 109.

[0107] 18 , the passage hole 206 and the passage recess 205 into which this passage hole 206 opens form a second passage portion 152 provided in the valve seat member 109. The valve seat member 109 is provided with a plurality of second passage portions 152, specifically four second passage portions 152, which are aligned in the radial direction of the valve seat member 109 and equally spaced apart in the circumferential direction of the valve seat member 109. The plurality of first passage portions 151 and the plurality of second passage portions 152 are provided in the valve seat member 109 and constitute a valve seat member passage portion 150 through which oil flows.

[0108] As shown in FIG. 19 , the valve seat member 109 has an annular seal groove 145 recessed radially inward at the axially central position of its outer periphery. An O-ring 108 is disposed within this seal groove 145. The valve seat member 109 is fitted to the cylindrical portion 124 of the cap member 101 at its outer periphery with its inner seat portion 138 and valve seat portion 139 facing away from the bottom portion 122, and is disposed within the cap member 101. In this state, the O-ring 108 seals the gap between the cylindrical portion 124 of the cap member 101 and the valve seat member 109. The cap member 101, the O-ring 108, and the valve seat member 109 form a cap chamber 146 inside the cap member 101. The cap chamber 146 is disposed between the bottom portion 122 of the cap member 101 and the valve seat member 109. The flexible disk 100 , the plurality of disks 102 and the sub-valve 107 are provided in the cap chamber 146 .

[0109] The flexible disk 100 is provided in the cap chamber 146 between the sub-valve 107 and the bottom 122 of the cap member 101. The flexible disk 100 is constantly in contact with the bottom 122 of the cap member 101 over its entire circumference, with the disk protrusion 302 surrounding the entire plurality of passage holes 126 radially outward from the bottom 122. The flexible disk 100 is also constantly in contact with the bottom 122 of the cap member 101 over its entire circumference, with the inner contact portion 303 surrounding the entire plurality of passage holes 126 radially inward from the bottom 122. Therefore, the flexible disk 100 divides the cap chamber 146 into an intermediate chamber 147 located closer to the sub-valve 107 than the flexible disk 100, and a communication chamber 149 (volume chamber) located closer to the passage holes 126 than the flexible disk 100. The communication chamber 149 is always in communication with the communication passages 148 in the plurality of passage holes 126. The communication between the intermediate chamber 147 and the communication passages 148 is blocked by the flexible disk 100.

[0110] The volume of the intermediate chamber 147 changes as the flexible disk 100 bends. That is, the bending of the flexible disk 100 causes the intermediate chamber 147 to function as an accumulator. The communication chamber 149 decreases in volume to absorb the increase in the volume of the intermediate chamber 147, thereby discharging oil, or increases in volume to absorb the decrease in the volume of the intermediate chamber 147, thereby allowing oil to flow in. This prevents the deformation of the flexible disk 100 from being hindered by the oil in the communication chamber 149.

[0111] As shown in FIG. 18 , the annular valve seat member 109 and the bottomed, cylindrical cap member 101 are disposed in the lower chamber 20, which is one of the upper chamber 19 and the lower chamber 20. The valve seat portion 135 of the valve seat member 109 is disposed on the cap chamber 146 side, and the valve seat portion 139 is disposed on the lower chamber 20 side. The valve seat member 109 separates the lower chamber 20 from an intermediate chamber 147 of the cap chamber 146, and is provided facing both the intermediate chamber 147 and the lower chamber 20. A plurality of passage grooves 225 are provided facing the lower chamber 20, and a plurality of second passage portions 152 are constantly in communication with the lower chamber 20 via the passages in the plurality of passage grooves 225. A communication passage 148 formed in the bottom portion 122 of the cap member 101 is constantly in communication with the lower chamber 20, which is one of the upper chamber 19 and the lower chamber 20.

[0112] The radial passage 222 in the passage groove 221 that opens into the first passage portion 151 of the valve seat member 109 is constantly in communication with the intermediate chamber 147, and constantly connects the intermediate chamber 147 with the passage in the large-diameter hole 133 of the valve seat member 109 and the piston rod passage 51 in the passage cutout 30 of the piston rod 21. Thus, the intermediate chamber 147 is constantly in communication with the upper chamber 19 via the radial passage 222 in the passage groove 221 of the valve seat member 109, the passage in the large-diameter hole 133 of the valve seat member 109, the piston rod passage 51 in the passage cutout 30 of the piston rod 21 and the passage in the large-diameter hole 46 of the piston 18, the passage in the cutout 90 of the disc 82, and the passages in the annular groove 55 and the plurality of passage holes 38 of the piston 18.

[0113] As shown in Fig. 19 , the disk 102 has an outer diameter equal to that of the inner seat portion 47. The sub-valve 107 is disk-shaped and, as shown in Fig. 18 , has an outer diameter equal to that of the valve seat portion 135 of the valve seat member 109. The sub-valve 107 is constantly in contact with the inner seat portion 134 and is able to be seated on and removed from the valve seat portion 135. The sub-valve 107 seats on the entire valve seat portion 135 to close all of the second passage portions 152. The sub-valve 107 also seats on the entirety of one of the valve seat forming portions of the valve seat portion 135 to close the second passage portion 152 inside that valve seat forming portion.

[0114] 18 , the sub-valve 107, which is releasable from the valve seat portion 135, is provided in the cap chamber 146. When the sub-valve 107 is releasable from the valve seat portion 135 within the cap chamber 146, it connects the multiple second passage portions 152 with an intermediate chamber 147 of the cap chamber 146 and connects the lower chamber 20 with the upper chamber 19. At this time, the sub-valve 107 generates a damping force by suppressing the flow of hydraulic fluid between the valve seat portion 135 and the sub-valve 107. The sub-valve 107 is an inflow valve that opens when hydraulic fluid flows from the lower chamber 20 into the intermediate chamber 147 via the multiple second passage portions 152, and is a check valve that restricts the outflow of hydraulic fluid from the intermediate chamber 147 to the lower chamber 20 via the second passage portions 152. Here, the passage hole 216 constituting the first passage portion 151 opens outside the range of the valve seat portion 135 of the valve seat member 109, and therefore is constantly in communication with the intermediate chamber 147 regardless of the sub-valve 107 shown in FIG. 18 seated on the valve seat portion 135.

[0115] The passages in the multiple passage grooves 225, the multiple second passage portions 152, the passage between the sub-valve 107 and the valve seat portion 135 that appears when the valve is opened, the intermediate chamber 147, the radial passage 222 in the passage groove 221 of the valve seat member 109, the passage in the large diameter hole portion 133 of the valve seat member 109, the piston rod passage portion 51 in the passage cutout portion 30 of the piston rod 21 and the passage in the large diameter hole portion 46 of the piston 18, the passage in the cutout portion 90 of the disc 82, and the passages in the annular groove 55 of the piston 18 and the multiple passage holes 38 constitute a second passage 172 through which oil flows from the lower chamber 20, which is upstream within the cylinder 2, to the upper chamber 19, which is downstream, as the piston 18 moves toward the lower chamber 20. The second passage 172 serves as a compression-side passage through which oil flows from the lower chamber 20, which is the upstream side, to the upper chamber 19, which is the downstream side, during the movement of the piston 18 toward the lower chamber 20, i.e., the compression stroke.

[0116] The second passage 172 includes a piston rod passage portion 51 within a passage cutout portion 30 formed by cutting out the piston rod 21. A sub-valve 107, a valve seat portion 135, a plurality of discs 102, a flexible disc 100, and a cap member 101 are provided in the compression-side second passage 172 and constitute a compression-side second damping force generating mechanism 173 that opens and closes the second passage 172 and suppresses the flow of hydraulic fluid from the second passage 172 to the upper chamber 19, thereby generating a damping force. The sub-valve 107 that constitutes the compression-side second damping force generating mechanism 173 (corresponding to the compression-side second damping force generating mechanism 700e2 in FIG. 2) is the compression-side sub-valve.

[0117] In the second passage 172, when the second damping force generating mechanism 173 is in an open state, the passage within the cutout portion 90 of the disk 82 is the narrowest among the portions with fixed flow path cross-sectional area, and the flow path cross-sectional area is narrower than the upstream and downstream sides thereof, forming an orifice 175 in the second passage 172. The orifice 175, which corresponds to the orifice 700f in Fig. 2, is located downstream of the sub-valve 107 in the flow of oil when the sub-valve 107 is open and oil flows in the second passage 172. The orifice 175 is formed by cutting out the disk 82 that abuts against the piston 18 of the first damping force generating mechanism 41.

[0118] In the compression-side second damping force generating mechanism 173, no fixed orifice is formed in either the valve seat portion 135 or the sub-valve 107 abutting thereon, which would communicate between the upper chamber 19 and the lower chamber 20, even when these are in contact. In other words, the compression-side second damping force generating mechanism 173 does not communicate between the upper chamber 19 and the lower chamber 20 when the valve seat portion 135 and the sub-valve 107 are in contact around the entire circumference. The compression-side second passage 172, which can communicate between the upper chamber 19 and the lower chamber 20, is parallel to the compression-side passage, the first passage 72, which can also communicate between the upper chamber 19 and the lower chamber 20. The first passage 72 is provided with the first damping force generating mechanism 42, and the second passage 172 is provided with the second damping force generating mechanism 173. Thus, the compression-side first damping force generating mechanism 42 and second damping force generating mechanism 173 are arranged in parallel.

[0119] 19 , the sub-valve 110 is disk-shaped and has an outer diameter equal to that of the valve seat portion 139 of the valve seat member 109. The sub-valve 110 is constantly in contact with the inner seat portion 138 and is capable of being seated on and removed from the valve seat portion 139. The sub-valve 110 seats on the entire valve seat portion 139 to close all of the first passage portions 151. The sub-valve 110 also seats on the entirety of any one of the valve seat components of the valve seat portion 139 to close the first passage portion 151.

[0120] The sub-valve 110 is provided in the lower chamber 20, and when it leaves the valve seat 139, it connects the intermediate chamber 147 to the lower chamber 20. At this time, the sub-valve 110 suppresses the flow of hydraulic fluid between the sub-valve 110 and the valve seat 139, generating a damping force. The sub-valve 110 is a discharge valve that opens when hydraulic fluid is discharged from the intermediate chamber 147 to the lower chamber 20 through the multiple first passage portions 151 of the valve seat member 109, and is also a check valve that restricts the inflow of hydraulic fluid from the lower chamber 20 into the intermediate chamber 147 through the first passage portion 151. Here, the passage hole 206 that constitutes the second passage portion 152 opens outside the range of the valve seat 139 of the valve seat member 109, and therefore is always in communication with the lower chamber 20 regardless of whether the sub-valve 110 is seated on the valve seat portion 139 shown in FIG. 18 .

[0121] The passages in the multiple passage holes 38 and the annular groove 55 of the piston 18, the passage in the cutout 90 of the disk 82, the piston rod passage portion 51 in the passage cutout 30 of the piston rod 21, the passage in the large diameter hole portion 46 of the piston 18 and the passage in the large diameter hole portion 133 of the valve seat member 109, the radial passage 222 in the passage groove 221 of the valve seat member 109, the intermediate chamber 147, the multiple first passage portions 151 of the valve seat member 109, and the passage between the sub-valve 110 and the valve seat portion 139 that appears when the valve is opened constitute a second passage 182 through which oil flows from the upper chamber 19, which is the upstream side within the cylinder 2, to the lower chamber 20, which is the downstream side, when the piston 18 moves toward the upper chamber 19.

[0122] The second passage 182 serves as an extension-side passage through which hydraulic fluid flows from the upper chamber 19 (upstream) to the lower chamber 20 (downstream) when the piston 18 moves toward the upper chamber 19, i.e., during the extension stroke. The second passage 182 includes a piston rod passage portion 51 within a passage cutout 30 formed by cutting out the piston rod 21. The cap member 101, the sub-valve 110, the valve seat portion 139, the discs 111 and 113, and the annular member 114 are provided in the extension-side second passage 182. The cap member 101, the sub-valve 110, the valve seat portion 139, the discs 111 and 113, and the annular member 114 constitute an extension-side second damping force generating mechanism 183 (corresponding to the extension-side second damping force generating mechanism 700e1 in FIG. 2 ) that opens and closes the second passage 182 to suppress the flow of hydraulic fluid from the second passage 182 to the lower chamber 20 and generates a damping force. The sub-valve 110 that constitutes the extension-side second damping force generating mechanism 183 is the extension-side sub-valve.

[0123] As shown in Figure 19, the communication chamber 149 communicating with the lower chamber 20 is arranged in parallel with the second passage 172 shown in Figure 18 and the second passage 182 shown in Figures 18 and 19. The second damping force generating mechanisms 173, 183 have a volume variable mechanism 185 that can change the volume of the communication chamber 149. The volume variable mechanism 185 is composed of the flexible disk 100, the bottom 122 of the cap member 101, the communication chamber 149, and the communication passage 148. The flexible disk 100 changes the volume of the communication chamber 149 so as to decrease the volume by deforming and moving toward the bottom 122, and changes the volume of the communication chamber 149 so as to increase the volume by deforming and moving away from the bottom 122.

[0124] In the second passage 182, when the second damping force generating mechanism 183 is in an open state, the passage within the cutout portion 90 of the disk 82 shown in FIG. 18 has the narrowest flow path cross-sectional area among the portions with fixed flow path cross-sectional area, and the flow path cross-sectional area is narrower than that on the upstream side and downstream side, forming an orifice 175 in the second passage 182 as well. The orifice 175 is common to the second passages 172, 182. The orifice 175 is located upstream of the sub-valve 110 in the flow of oil when the sub-valve 110 is open and oil flows in the second passage 182. The sub-valve 110 and the above-described sub-valve 107 open and close independently of each other.

[0125] In the extension-side second damping force generating mechanism 183, no fixed orifice is formed in either the valve seat portion 139 or the sub-valve 110 abutting thereon, which would allow communication between the upper chamber 19 and the lower chamber 20, even when these are in contact with each other. In other words, when the valve seat portion 139 and the sub-valve 110 are in contact with each other over the entire circumference, the extension-side second damping force generating mechanism 183 does not allow communication between the upper chamber 19 and the lower chamber 20. The annular member 114, together with the disk 113, abuts against the sub-valve 110 to restrict deformation of the sub-valve 110 in the opening direction beyond a specified level.

[0126] 2, shock absorber 700A1 may be configured so that the upper chamber 19 and the lower chamber 20 can communicate with each other only via the first damping force generating mechanisms 41, 42 and the second damping force generating mechanisms 173, 183. The extension-side second passage 182, which can communicate between the upper chamber 19 and the lower chamber 20, is parallel to the extension-side first passage 92, which can also communicate between the upper chamber 19 and the lower chamber 20, except for the passages in the annular groove 55 on the upper chamber 19 side and the multiple passage holes 38. In the parallel portion, the first damping force generating mechanism 41 is provided in the first passage 92, and the second damping force generating mechanism 183 is provided in the second passage 182. Therefore, the extension-side first damping force generating mechanism 41 and the second damping force generating mechanism 183 are arranged in parallel.

[0127] The second damping force generating mechanism 173, 183 includes a valve seat member 109, a sub-valve 110 provided on one side of a valve seat member passage portion 150, which is a portion of the second passage 172, 182 provided in the valve seat member 109, a sub-valve 107 provided on the other side of the valve seat member passage portion 150, and a bottomed, cylindrical cap member 101 provided between the piston 18 and the valve seat member 109 in the second passage 172, 182. The valve seat member 109 is provided within the cap member 101, the sub-valve 110 is provided on the lower chamber 20 side of the valve seat member 109, and the sub-valve 107 is provided within a cap chamber 146 between the bottom 122 of the cap member 101 and the valve seat member 109. The valve seat member 109 is provided with a radial passage 222 that communicates with the piston rod passage portion 51 and extends radially toward the extension-side first passage portion 151.

[0128] 19, the flexible disk 100 abuts against the bottom 122 at the disk protrusion 302, and when the inner abutment portion 303 is clamped between the bottom 122 of the cap member 101 and the disk 102, the disk protrusion 302 abuts against the bottom 122 of the cap member 101 over the entire circumference with a preload equal to its height. Note that the sub-valve 107 bends toward the flexible disk 100 when it is open, but a sufficient gap is provided between the sub-valve 107 and the flexible disk 100 so that the sub-valve 107 does not come into contact with the flexible disk 100 even at its maximum lift.

[0129] As described above, the shock absorber 700A1 has the first passage 92 and the second passage 182 arranged in parallel to each other as a flow path for flowing hydraulic fluid from the upper chamber 19 to the lower chamber 20 during the extension stroke, and the main valve 91 and the sub-valve 110 arranged in parallel. The orifice 175 is also connected in series with the sub-valve 110. Of the first extension-side damping force generating mechanism 41 and the second extension-side damping force generating mechanism 183, the main valve 91 of the first damping force generating mechanism 41 has higher rigidity and a higher valve opening pressure than the sub-valve 110 of the second damping force generating mechanism 183. Therefore, during the extension stroke, in the extremely low speed range where the piston speed is lower than a predetermined value, the first damping force generating mechanism 41 is closed, while the second damping force generating mechanism 183 is open. In the normal speed range where the piston speed is equal to or higher than this predetermined value, both the first damping force generating mechanism 41 and the second damping force generating mechanism 183 are open. The sub-valve 110 is an extremely low speed valve that opens when the piston speed is in an extremely low speed range to generate a damping force.

[0130] Furthermore, shock absorber 700A1 has first passage 72 and second passage 172 arranged in parallel as a flow path for flowing oil from lower chamber 20 to upper chamber 19 during the compression stroke, and has main valve 71 and sub-valve 107 arranged in parallel. Furthermore, orifice 175 is connected in series with sub-valve 107 in second passage 172. Here, of compression-side first damping force generating mechanism 42 and compression-side second damping force generating mechanism 173, main valve 71 of first damping force generating mechanism 42 has higher rigidity and a higher valve-opening pressure than sub-valve 107 of second damping force generating mechanism 173.

[0131] Therefore, during the compression stroke, when the piston speed is in the extremely low speed region where it is slower than a predetermined value, the first damping force generating mechanism 42 is closed and the second damping force generating mechanism 173 is open, and when the piston speed is in the normal speed region where it is equal to or higher than the predetermined value, both the first damping force generating mechanism 42 and the second damping force generating mechanism 173 are open. The sub-valve 107 is an extremely low speed valve that opens when the piston speed is in the extremely low speed region and generates a damping force.

[0132] As a result, the damping force characteristics of shock absorber 700A1 relative to piston speed are as shown in Figure 4. That is, the rate of increase in the extension-side damping force relative to an increase in piston speed in the normal speed region is lower than the rate of increase in the extension-side damping force relative to an increase in piston speed in the extremely low speed region. In other words, the slope of the rate of increase in the extension-side damping force relative to an increase in piston speed in the normal speed region can be made flatter than in the extremely low speed region. Note that in shock absorber 700A1, first damping force generating mechanisms 41, 42 and second damping force generating mechanisms 173, 183 all operate without power from external actuators.

[0133] Next, a shock absorber 700A2, which is a more preferred embodiment of the shock absorber 700A having the hydraulic circuit shown in Figure 2, will be described with reference to Figures 20 to 22. Note that parts common to the shock absorber 700A1 shown in Figures 17 to 19 are designated by the same names and reference numerals. The shock absorber 700A2 shown in Figures 20 to 22 does not have the stopper member 32, pair of supports 33, coil spring 34, and shock absorber 35 that are provided in the shock absorber 700A1. Furthermore, in the shock absorber 700A2, the compression-side first damping force generating mechanism 42D (corresponding to the compression-side first damping force generating mechanism 700d2 in Figure 2) is partially different from the first damping force generating mechanism 42.

[0134] The first damping force generating mechanism 42D includes a valve seat portion 50 of the piston 18, and has, in order from the axial piston 18 side, one disc 62, a plurality of discs 64 (specifically, two) of the same inner diameter and outer diameter, a plurality of discs 65 (specifically, three) of the same inner diameter and outer diameter, a plurality of discs 66D (specifically, two) of the same inner diameter and outer diameter, one disc 67, one disc 68D, and one annular member 69D.

[0135] The mounting shaft portion 28 can be fitted into the base plate portion 501. The base plate portion 501 is a perforated circular flat plate of a constant thickness. The stepped plate portion 502 is located radially outward of the base plate portion 501. The stepped plate portion 502 is offset from the base plate portion 501 in the axial direction of the base plate portion 501. The annular member 69D abuts against the shaft step portion 29 at the base plate portion 501, with the stepped plate portion 502 protruding from the base plate portion 501 on the side opposite the piston 18.

[0136] The shock absorber 700A2 has an annular shock absorber 35D. The main shaft portion 27 of the piston rod 21 is fitted inside the shock absorber 35D. The shock absorber 35D is provided on the opposite side of the annular member 69D from the piston 18. In the shock absorber 700A2, when the piston rod 21 is fully extended, the shock absorber 35D abuts against the rod guide 22 (see FIG. 17 ).

[0137] A plurality of discs 64, a plurality of discs 65, and a plurality of discs 66D constitute a compression-side main valve 71D that can be seated on and removed from the valve seat 50. When the main valve 71D is released from the valve seat 50, the passages in the plurality of passage holes 39 and the annular groove 56 communicate with the upper chamber 19 and suppress the flow of hydraulic fluid between the valve seat 50, thereby generating a damping force. The annular member 69D and the disc 68D abut against the main valve 71D to restrict deformation of the main valve 71D in the opening direction beyond a specified level. The passages in the plurality of passage holes 39 and the annular groove 56, and the passage between the main valve 71D and the valve seat 50 that appears when the valve is open, constitute a compression-side first passage 72 similar to that of the shock absorber 700A1.

[0138] As shown in FIG. 20, the first extension side damping force generating mechanism 41D (corresponding to the first extension side damping force generating mechanism 700d1 in FIG. 2) includes the valve seat portion 48 of the piston 18, and has, in axial order from the piston 18 side, one disc 82, one disc 83, a plurality of discs 85 (specifically, four discs) having the same inner and outer diameters, one disc 86, a plurality of discs 87 (specifically, three discs) having the same inner and outer diameters, and one disc 88D.

[0139] The plurality of discs 85, one disc 86, and the plurality of discs 87 constitute an extension-side main valve 91D that can be seated on and removed from the valve seat 48. When the main valve 91D is lifted from the valve seat 48, the main valve 91D connects the passages in the annular groove 55 and the plurality of passage holes 38 to the lower chamber 20, and generates a damping force by suppressing the flow of oil between the valve seat 48 and the annular groove 55. The passages in the plurality of passage holes 38 and the annular groove 55, and the passage between the main valve 91D and the valve seat 48 that appears when the valve is open, constitute a first extension-side passage 92 similar to that of the shock absorber 700A1.

[0140] On the side of the extension-side first damping force generating mechanism 41D opposite the piston 18, there are provided, in order from the first damping force generating mechanism 41D side, a cap member 101D that is partially different from that of the shock absorber 700A1, one disk 511, one disk 512, one disk 513, one disk 514, and one flexible disk 515 (flexible member, moving member), with the mounting shaft portion 28 of the piston rod 21 fitted inside each of them. Furthermore, on the side of the flexible disk 515 opposite the piston 18, there are provided, in order from the flexible disk 515 side, one disk 516, one disk 517, one disk 518, one disk 519, one stopper member 521, one spring disk 522, and one disk 523, with the mounting shaft portion 28 of the piston rod 21 fitted inside each of them.

[0141] In addition, on the side of the disc 523 opposite the piston 18, there are provided, in order from the disc 523 side, a sub-valve 107 (one-side sub-valve) similar to that of the shock absorber 700A1, a valve seat member 109 similar to that of the shock absorber 700A1, a sub-valve 110 (other-side sub-valve) similar to that of the shock absorber 700A1, one disc 524, one spring disc 525, one disc 526, and an annular member 114 similar to that of the shock absorber 700A1, with the mounting shaft portion 28 of the piston rod 21 fitted inside each of them.

[0142] As shown in FIG. 20 , the cap member 101D is a bottomed, cylindrical, one-piece molded product formed integrally by plastic processing of a metal plate. The cap member 101D has a perforated, disc-shaped bottom portion 122D of a constant thickness and a cylindrical tubular portion 124D extending from the outer peripheral edge of the bottom portion 122D in the opposite direction from the bottom portion 122D. The bottom portion 122D has a shape similar to the bottom portion 122 of the shock absorber 700A1 but is thinner than the bottom portion 122. The bottom portion 122D has a plurality of passage holes 126D similar to the passage holes 126 of the shock absorber 700A1. The passage holes 126D form a communication passage 148. The tubular portion 124D has a shape similar to the tubular portion 124 of the shock absorber 700A1 but is thinner than the tubular portion 124. The cap member 101D is attached to the attachment shaft portion 28 of the piston rod 21 in such a direction that the cylindrical portion 124D protrudes from the bottom portion 122D to the side opposite to the piston 18.

[0143] The disks 511-514, 516-519, 523, 524, 526, flexible disk 515, stopper member 521, and spring disks 522 and 525 are all housed within the cap member 101D. The valve seat member 109 is also housed within the cap member 101D. The spring disks 522 and 525 are each annular, with the mounting shaft portion 28 of the piston rod 21 fitted therein. A passage hole 530 is formed in the stopper member 521, penetrating it in the axial direction, with the radial position of the stopper member 521 coinciding with the passage hole 126D of the cap member 101D. The interior of the passage hole 530 forms a communicating passage 531.

[0144] The spring disc 522 has a base plate portion 535 in the shape of a circular plate with holes that fits onto the mounting shaft portion 28, and a plurality of spring plate portions 536 that extend radially outward from equally spaced positions around the circumferential direction of the base plate portion 535. The outer diameter of the base plate portion 535 is smaller than twice the shortest distance from the center of the stopper member 521 to the passage hole 530. The spring plate portions 536 are inclined relative to the base plate portion 535 so that the extending tip ends are spaced apart from the base plate portion 535 in the axial direction of the base plate portion 535.

[0145] The spring disc 522 is attached to the mounting shaft 28 so that the spring plate portions 536 extend from the base plate portion 535 toward the sub-valve 107 in the axial direction of the base plate portion 535. The outer diameter of the disc 523 is smaller than the outer diameter of the base plate portion 535 of the spring disc 522. The spring disc 522 has multiple spring plate portions 536 that abut against the sub-valve 107. The disc 524 is a common part with the disc 523.

[0146] The spring disk 525 has a perforated circular flat base plate 541 that fits onto the mounting shaft 28, and multiple spring leaf portions 542 that extend radially outward from the base plate 541 at equally spaced positions around the circumferential direction of the base plate 541. The outer diameter of the base plate 541 is larger than that of the disk 524. The spring leaf portions 542 are inclined relative to the base plate 541 so that their distal ends are spaced farther from the base plate 541 in the axial direction of the base plate 541. The spring disk 525 is attached to the mounting shaft 28 so that the spring leaf portions 542 extend from the base plate 541 toward the sub-valve 110 in the axial direction of the base plate 541. The multiple spring leaf portions 542 of the spring disk 525 abut against the sub-valve 110. The disk 526 has an outer diameter equal to that of the sub-valve 110.

[0147] An O-ring 551 is provided between the bottom portion 122D of the cap member 101D and the flexible disk 515. The O-ring 551 is provided radially outward of the flexible disk 515 relative to the communicating passage 148. At this position, the O-ring 551 abuts against the flexible disk 515 and the bottom portion 122D with an interference. At this position, the O-ring 551 seals the gap between the flexible disk 515 and the bottom portion 122D over the entire circumference. The O-ring 551 supports, at one axial side, the outer circumferential side of the flexible disk 515, whose inner circumferential side is clamped in the axial direction so as to be integral with the piston rod 21.

[0148] An O-ring 552 is provided between the flexible disk 515 and the stopper member 521. The O-ring 552 is a common part with the O-ring 551. The O-ring 552 is provided radially outward of the flexible disk 515 relative to the communicating passage 531. At this position, the O-ring 552 abuts against the flexible disk 515 and the stopper member 521 with an interference, thereby sealing the gap between the flexible disk 515 and the stopper member 521 over the entire circumference. The O-ring 552 is provided between the flexible disk 515 and the sub-valve 107. The O-ring 552 supports the outer circumferential side of the flexible disk 515 on the other axial side opposite the O-ring 551.

[0149] The flexible disk 515 is flexible such that the portion radially inward of the O-ring 551 approaches the bottom 122D and returns to its original state. The flexible disk 515 is flexible such that the portions between the O-ring 551 and the disks 514 and 516 approach the bottom 122D and return to their original state. The O-ring 551 has a circular cross section along a plane including the central axis. Therefore, when the amount of bending of the flexible disk 515 toward the bottom 122D increases, the O-ring 551 moves the fulcrum supporting the flexible disk 515 inward in the radial direction of the flexible disk 515. When the amount of bending of the flexible disk 515 decreases from this state, the O-ring 551 moves the fulcrum supporting the flexible disk 515 outward in the radial direction of the flexible disk 515.

[0150] The flexible disk 515 is flexible such that a portion radially inward of the O-ring 552 approaches the stopper member 521 and returns to its original state. The flexible disk 515 is flexible such that portions between the O-ring 551 and the disks 514 and 516 approach the stopper member 521 and return to their original state. The O-ring 552 has a circular cross section along a plane including the central axis. Therefore, when the amount of bending of the flexible disk 515 toward the stopper member 521 increases, the O-ring 552 moves the fulcrum supporting the flexible disk 515 inward in the radial direction of the flexible disk 515. When the amount of bending of the flexible disk 515 decreases from this state, the O-ring 552 moves the fulcrum supporting the flexible disk 515 outward in the radial direction of the flexible disk 515.

[0151] The cap member 101D, O-ring 108, and valve seat member 109 form a cap chamber 146 between the bottom portion 122D of the cap member 101D and the valve seat member 109. The sub-valve 107 is provided within this cap chamber 146. The flexible disk 515 and O-rings 551 and 552 are provided within the cap chamber 146. The flexible disk 515 is provided between the bottom portion 122D of the cap member 101D and the sub-valve 107. The flexible disk 515 and the O-rings 551 and 552 divide the cap chamber 146 into an intermediate chamber 147 located closer to the sub-valve 107 than the flexible disk 515, and a communication chamber 149 located closer to the multiple passage holes 126D than the flexible disk 515. The intermediate chamber 147 is provided between the flexible disk 515 and the stopper member 521. The intermediate chamber 147 is blocked from communication with the communication chamber 149 and the communication passage 148 by the flexible disk 515 and O-rings 551 and 552 .

[0152] The deflection of the flexible disk 515 changes the volumes of the intermediate chamber 147 and the communicating chamber 149. That is, the deflection of the flexible disk 515 allows the intermediate chamber 147 and the communicating chamber 149 to function as accumulators. The communicating chamber 149 decreases in volume to absorb the increase in the volume of the intermediate chamber 147, thereby discharging oil to the lower chamber 20, and increases in volume to absorb the decrease in the volume of the intermediate chamber 147, thereby allowing oil to flow in from the lower chamber 20. Conversely, the intermediate chamber 147 decreases in volume to absorb the increase in the volume of the communicating chamber 149, thereby discharging oil to the upper chamber 19, and increases in volume to absorb the decrease in the volume of the communicating chamber 149, thereby allowing oil to flow in from the upper chamber 19.

[0153] The sub-valve 107 is seated on the valve seat 135 by the biasing force of the spring disc 522, closing the second passage 152. The sub-valve 107, the valve seat 135, the disc 523, the spring disc 522, and the stopper member 521 are provided in the compression-side second passage 172 and constitute a compression-side second damping force generating mechanism 173D (corresponding to the compression-side second damping force generating mechanism 700e2 in FIG. 2 ) that opens and closes the second passage 172 and suppresses the flow of hydraulic fluid from the second passage 172 to the upper chamber 19, thereby generating a damping force.

[0154] The intermediate chamber 147, which communicates with the upper chamber 19, constitutes the second passage 172. The second damping force generating mechanisms 173D, 183D have a volume variable mechanism 185D that can change the volume of the intermediate chamber 147. The volume variable mechanism 185D is composed of a flexible disk 515, O-rings 551, 552, the cylindrical portion 124D of the cap member 101D, disks 516-519, a stopper member 521, the intermediate chamber 147, and a communication passage 531. The intermediate chamber 147 is provided in the flow path between the flexible disk 515 and the sub-valve 107. The volume variable mechanism 185D changes the volume of the intermediate chamber 147 so that it increases when the flexible disk 515 deforms and moves toward the bottom 122D, and changes the volume of the intermediate chamber 147 so that it decreases when the flexible disk 515 deforms and moves away from the bottom 122D.

[0155] The sub-valve 110 is seated on the valve seat 139 by the biasing force of the spring disc 525, closing the first passage 151. The sub-valve 110, the valve seat 139, the disc 524, the spring disc 525, and the disc 526 are provided in the extension-side second passage 182 and constitute an extension-side second damping force generating mechanism 183D (corresponding to the extension-side second damping force generating mechanism 700e1 in FIG. 2 ) that opens and closes the second passage 182 and suppresses the flow of hydraulic fluid from the second passage 182 to the lower chamber 20, thereby generating a damping force.

[0156] The communication chamber 149, which is always in communication with the lower chamber 20 via the communication passage 148, is disposed in parallel with the second passage 182. The second damping force generating mechanisms 173D, 183D have a volume variable mechanism 561 that can change the volume of the communication chamber 149. The volume variable mechanism 561 is composed of a flexible disk 515, O-rings 551, 552, the bottom portion 122D of the cap member 101D, disks 511-514, the communication chamber 149, and the communication passage 148. The communication chamber 149 is provided in the flow path between the flexible disk 515 and the sub-valve 110 via the lower chamber 20 and the communication passage 148.

[0157] The flexible disk 515 is modified to decrease the volume of the communication chamber 149 by deforming and moving toward the bottom 122D, and is modified to increase the volume of the communication chamber 149 by deforming and moving away from the bottom 122D. The flexible disk 515 and O-rings 551, 552 are shared by the volume variable mechanism 185D and the volume variable mechanism 561. The volume variable mechanism 185D and the volume variable mechanism 561 constitute an accumulator 565.

[0158] There is a gap between the stopper member 521 and the cylindrical portion 124D of the cap member 101D. Therefore, no radial pressure difference occurs across the O-ring 552. The O-ring 551 is subjected to the pressure difference between the intermediate chamber 147 and the communication chamber 149. This pressure difference is equivalent to the pressure difference occurring across the second damping force generating mechanisms 173D and 183D. This pressure difference causes the O-ring 551 to seal between the bottom portion 122D of the cap member 101D and the flexible disc 515.

[0159] 22 shows the hydraulic circuit of shock absorber 700A2. Specifically, first damping force generating mechanisms 41D, 42D and second damping force generating mechanisms 173D, 183D are provided in parallel between upper chamber 19 and lower chamber 20. An orifice 175 and a piston rod passage 51 are provided between upper chamber 19 and second damping force generating mechanisms 173D, 183D. An intermediate chamber 147 of a volume variable mechanism 185D of accumulator 565 is connected to piston rod passage 51. In addition, a communication chamber 149 of a volume variable mechanism 561 of accumulator 565 is connected to the lower chamber 20 via a communication passage 148 serving as an orifice.

[0160] Of the first damping force generating mechanism 41D and the second damping force generating mechanism 183D, both of which are on the extension side, the main valve 91D of the first damping force generating mechanism 41D has higher rigidity and a higher valve opening pressure than the sub-valve 110 of the second damping force generating mechanism 183D. Therefore, during the extension stroke, in the extremely low speed region where the piston speed is slower than a predetermined value, the first damping force generating mechanism 41D remains closed while the second damping force generating mechanism 183D opens. Furthermore, in the normal speed region where the piston speed is equal to or higher than this predetermined value, both the first damping force generating mechanism 41D and the second damping force generating mechanism 183D open.

[0161] That is, during the extension stroke, the pressure in the upper chamber 19 increases, and the pressure in the lower chamber 20 decreases. Then, the oil in the upper chamber 19 flows into the intermediate chamber 147 via the passages in the plurality of passage holes 38 of the piston 18 and the annular groove 55, the orifice 175, the passage in the large diameter hole portion 46 of the piston 18, the piston rod passage portion 51 in the passage cutout 30 of the piston rod 21 and the passage in the large diameter hole portion 133 of the valve seat member 109, the radial passage 222 in the passage groove 221 of the valve seat member 109, and the communication passage 531 of the stopper member 521.

[0162] This causes the pressure in the intermediate chamber 147 to increase. As a result, the portion of the volume variable mechanism 185D that is radially inward from the position where the flexible disk 515 abuts against the O-ring 551 bends toward the bottom 122D, increasing the capacity of the intermediate chamber 147. As a result, the volume variable mechanism 185D suppresses an increase in the pressure in the intermediate chamber 147. At this time, because the flexible disk 515 bends and moves toward the bottom 122D, the volume variable mechanism 561 reduces the volume of the communication chamber 149.

[0163] During the extension stroke of shock absorber 700A2 when a low-frequency input (large-amplitude vibration) is applied, the amount of oil flowing from upper chamber 19 to intermediate chamber 147 increases, causing large deformation of flexible disk 515. As the amount of deformation of flexible disk 515 increases, the reaction force due to the support rigidity of the clamped inner periphery increases, limiting the amount of deformation. This causes pressure to build up in intermediate chamber 147. As a result, pressure in second passage 182 increases to the point where second damping force generating mechanism 183D opens.

[0164] As a result, the damping force rises sharply during the extension stroke until the second damping force generating mechanism 183D, where the piston speed is low, opens. Furthermore, during the extension stroke, as the piston speed increases and enters the extremely low speed region, the second damping force generating mechanism 183D opens while the first damping force generating mechanism 41D remains closed. This causes hydraulic fluid in the upper chamber 19 to flow to the lower chamber 20 via the second extension passage 182. Furthermore, as the piston speed increases further during the extension stroke and enters the normal speed region, the first damping force generating mechanism 41D opens while the second damping force generating mechanism 183D remains open, causing hydraulic fluid in the upper chamber 19 to flow to the lower chamber 20 via the second extension passage 182 and the first extension passage 92.

[0165] During the extension stroke when a high-frequency input (small-amplitude vibration) occurs in which a higher frequency than the low-frequency input described above is input to the shock absorber 700A2, the amount of hydraulic fluid flowing from the upper chamber 19 to the intermediate chamber 147 is small. Therefore, the deformation of the flexible disk 515 is also small. Therefore, the volume variable mechanism 185D can absorb the volume of hydraulic fluid flowing into the intermediate chamber 147 by the amount of deflection of the flexible disk 515. This reduces the pressure increase in the intermediate chamber 147. Therefore, during the buildup of the extremely low-speed damping force, it is possible to achieve a state as if the flexible disk 515 were not present and the intermediate chamber 147 were constantly connected to the lower chamber 20 via the communication passage 148 of the cap member 101D, i.e., a state identical to that without the second damping force generating mechanism 183D. Therefore, during the extension stroke, the buildup of the extremely low-speed damping force is gentler than the damping force characteristics during the low-frequency input.

[0166] Furthermore, in the extremely low speed region, the flexible disc 515 bends, increasing the volume of oil flowing into the intermediate chamber 147 while the second damping force generating mechanism 183D opens, so the extremely low speed damping force for the same piston speed has a lower characteristic than during low frequency input when the flexible disc 515 is fully bent and there is no change in the volume of oil flowing into the intermediate chamber 147. In other words, when the frequency of the piston 18 exceeds a predetermined frequency, the volume variable mechanism 185D including the flexible disc 515 enters a state in which the flow rate of oil to the sub-valve 110 of the second damping force generating mechanism 183D is restricted.

[0167] Of the first damping force generating mechanism 42D and the second damping force generating mechanism 173D, both of which are on the compression side, the main valve 71D of the first damping force generating mechanism 42D has higher rigidity and a higher valve opening pressure than the sub-valve 107 of the second damping force generating mechanism 173D. Therefore, the damping force change characteristics during the compression stroke are the same as those during the extension stroke. Here, the slope of the deflection of the flexible disk 515 relative to the load can be adjusted by varying the rigidity, which can be adjusted by the thickness of the flexible disk 515, etc. As a result, the slope of the damping force change until the second damping force generating mechanisms 173D, 183D open can be adjusted.

[0168] If the load gradient relative to the deflection of the flexible disc 515 is too small (the spring constant is too low) during low-frequency input, the delay until the second damping force generating mechanisms 173D, 183D open will be large. As a result, the extremely low-speed damping force will not be generated even at low frequencies, and the sprung vibration damping function that the second damping force generating mechanisms 173D, 183D are intended to achieve may not be fully achieved. For this reason, it is necessary to set the rigidity of the flexible disc 515 appropriately high and the spring constant of the variable volume mechanisms 185D, 561 high.

[0169] Furthermore, if the gradient of the load relative to the deflection of the flexible disk 515 is too large (the spring constant is too high) during high-frequency input, the load will rise quickly relative to the amount of oil flowing into the intermediate chamber 147 and the communication chamber 149 of the volume variable mechanisms 185D, 561, and will reach the valve-opening pressure of the second damping force generating mechanisms 173D, 183D. As a result, even with small-amplitude vibration (high frequency), the second damping force generating mechanisms 173D, 183D will approach certain characteristics, reducing the effectiveness of the volume variable mechanisms 185D, 561. For this reason, it is necessary to set the rigidity of the flexible disk 515 appropriately low and the spring constant of the volume variable mechanisms 185D, 561 low.

[0170] Therefore, the spring constant of the variable volume mechanism 185D, 561 needs to be appropriately adjusted according to the specifications of the second damping force generating mechanism 173D, 183D so that the internal pressure is high at low frequencies and low at high frequencies, which is the target for low damping. While it can be difficult to achieve both low and high frequencies with linear spring characteristics, the shock absorber 700A2 increases support rigidity by shifting the fulcrum of the O-rings 551, 552 that support the flexible disk 515 toward the inner diameter according to the amount of deflection of the flexible disk 515, as described above. This results in nonlinear spring characteristics that provide high rigidity for large deflections, allowing for a large spring constant at low frequencies and a small spring constant at high frequencies.

[0171] Conversely, if the valve opening pressure of the second damping force generating mechanisms 173D, 183D is high, or if the delay in opening the valves of the second damping force generating mechanisms 173D, 183D is too great, once the flexible disc 515 has bent to a certain extent, the bending of the flexible disc 515 is suppressed to allow a high load. Once the flexible disc 515 has bent to a certain extent, the above-mentioned discs 511-514 and discs 516-519 come into contact with the flexible disc 515 to suppress the bending of the flexible disc 515.

[0172] In this way, it is possible to generate a reliable ultra-low-speed damping force for low-frequency sprung vibration damping, such as for responsiveness during slight steering inputs and a smooth ride on good roads, which require an ultra-low-speed damping force. Furthermore, for high-frequency, small-amplitude inputs that generate abnormal noise due to rod acceleration, the ultra-low-speed damping force can be weakened and the connection between the valve openings of the second damping force generating mechanisms 173D and 183D can be improved. This makes it possible to suppress the generation of abnormal noise due to rod acceleration. Therefore, it is possible to achieve both improved performance of the ultra-low-speed damping force during low-frequency inputs and suppression of abnormal noise during high-frequency inputs.

[0173] The shock absorber 700A may be a damping force adjustable shock absorber that uses an actuator such as a solenoid to vary the rate at which the damping force increases in response to an increase in piston speed. Such a damping force adjustable shock absorber is disclosed in, for example, Japanese Patent No. 7129565. Figures 23-25 ​​show one embodiment of the above-described damping force adjustable shock absorber 700A3. The shock absorber 700A3 is a so-called control valve side-mounted type damping force adjustable shock absorber, in which the damping force adjustment mechanism 821 is mounted next to the cylinder 702. The cylinder 702 includes an inner cylinder 703 and an outer cylinder 704 that is coaxially disposed relative to the inner cylinder 703. A reservoir 706 is formed between the inner cylinder 703 and the outer cylinder 704. The inner cylinder 703 is filled with hydraulic fluid, and the reservoir 706 is filled with hydraulic fluid and gas.

[0174] A piston 718 is slidably fitted within the inner tube 703 of the cylinder 702. The piston 718 divides the inner tube 703 into two chambers: an upper cylinder chamber 702A (first chamber) and a lower cylinder chamber 702B (second chamber). The lower end (one end) of a piston rod 721 is connected to the piston 718. The upper end (the other end) of the piston rod 721 passes through the upper cylinder chamber 702A and extends to the outside of the cylinder 702 through a rod guide 722 and a seal member 723 attached to the upper end of the cylinder 702. The piston rod 721 has a main shaft portion 727 guided by the rod guide 722 and a mounting shaft portion 728 to which the piston 718 is attached. A step portion 729 is formed between the main shaft portion 727 and the mounting shaft portion 728. A thread portion 731 is formed at the lower end of the mounting shaft portion 728.

[0175] 24 , the piston 718 is provided with passages 737 and 739 that allow communication between the upper cylinder chamber 702A and the lower cylinder chamber 702B. Passage 737 (extension-side passage) opens to the inner periphery of the piston 718 on the side of the lower cylinder chamber 702B and opens to the outer periphery of the piston 718 on the side of the upper cylinder chamber 702A. Passage 738 (compression-side passage) opens to the outer periphery of the piston 718 on the side of the lower cylinder chamber 702B and opens to the inner periphery of the piston 718 on the side of the upper cylinder chamber 702A.

[0176] An extension-side damping force generating mechanism 741 is provided on the cylinder lower chamber 702B side of passage 737 (extension-side passage). The extension-side damping force generating mechanism 741 generates a damping force by controlling the flow of hydraulic fluid from the cylinder upper chamber 702A to the cylinder lower chamber 702B via passage 737. On the other hand, a compression-side damping force generating mechanism 742 is provided on the cylinder upper chamber 702A side of passage 739 (compression-side passage). The compression-side damping force generating mechanism 742 generates a damping force by controlling the flow of hydraulic fluid from the cylinder lower chamber 702B to the cylinder upper chamber 702A via passage 739.

[0177] Compression-side damping force generating mechanism 742 has an annular seat portion 750 formed on the outer periphery of the end face of piston 718 on the cylinder upper chamber 702A side. Between clamp portion 747 of piston 718 and step portion 729 of piston rod 721, provided in this order from the piston 718 side are a retainer 762, a disk valve 763 consisting of multiple disks, multiple retainers 764, a spacer 765, a retainer 766, and an annular member 767, which constitute compression-side damping force generating mechanism 742.

[0178] The compression-side damping force generating mechanism 742 has an intake valve 771 (first low-speed valve) that allows hydraulic fluid to flow from the cylinder lower chamber 702B (second chamber) to the cylinder upper chamber 702A (first chamber) via a passage 739. The intake valve 771 is made up of an annular seat 750 and a disc valve 763 that can be seated on and removed from the seat 750. The passage 739, located on the inner periphery of the seat 750, opens to the upper chamber 702A side.

[0179] The extension-side damping force generating mechanism 741 has an annular seat portion 748 formed on the outer periphery of the end face of the piston 718 on the cylinder lower chamber 702B side. Between a clamp portion 747 of the piston 718 and a cap 801 (described later), provided in this order from the piston 718 side are a retainer 782, a disk valve 783 consisting of multiple disks, a spacer 784, and a retainer 785, which constitute the extension-side damping force generating mechanism 741. The extension-side damping force generating mechanism 741 has a main valve 791 that allows hydraulic fluid to flow from the cylinder upper chamber 702A (first chamber) side to the cylinder lower chamber 702B (second chamber) side via a passage 737.

[0180] The main valve 791 comprises an annular seat portion 748 and a disc valve 783 that can be seated on and removed from the seat portion 748. The retainer 782 is provided with an orifice 788 (notch) that constantly communicates the passage 737 with a passage 730 formed in the mounting shaft portion 728 of the piston rod 721 via an annular passage 746 formed between the mounting shaft portion 728 and the large diameter portion of the insertion hole 744 (shaft hole) of the piston 718. The passage 730 is provided by forming a width across flats in the mounting shaft portion 728.

[0181] On the opposite side of the main valve 791 from the piston 718 of the extension-side damping force generating mechanism 741, there are provided, in order from the main valve 791 side, the above-mentioned cap 801, passage member 802, retainer 803, spacer 804, compression-side extremely low speed valve 805 (fifth low speed valve) made up of multiple discs, and valve body 806. The cap 801 is formed in a generally cylindrical shape with a bottom that is open on the side opposite the piston 718 side. An annular seal member 807 seals the gap between the inner circumferential surface of the cap 801 and the valve body 806.

[0182] On the opposite side of the valve body 806 from the compression side ultra low speed valve 805 of the extension side damping force generating mechanism 741, provided in this order from the ultra low speed valve 805 side are an extension side ultra low speed valve 808 (third low speed valve) made up of multiple discs, multiple spacers 809, a retainer 810, and an annular member 811. Components, including the piston 718, through which the mounting shaft portion 728 passes between the annular members 767 and 811 are fixed by a nut 812 tightened to a threaded portion 731 of the mounting shaft portion 728.

[0183] The valve body 806 has a clamp portion 834 in which an axial hole 831 is formed. An annular seat portion 836 is formed on the outer periphery of the end face of the valve body 806 facing the piston 718, against which the outer periphery of the compression-side extremely low speed valve 805 can be seated and released. An annular seat portion 835 is formed between the clamp portion 834 and the seat portion 836 on the end face of the valve body 806 facing the piston 718, against which the intermediate position of the compression-side extremely low speed valve 805 can be seated and released. On the other hand, an annular seat portion 839 is formed on the end face of the valve body 806 opposite the piston 718, against which the outer periphery of the extension-side extremely low speed valve 808 can be seated and released.

[0184] The valve body 806 is provided with passages 841, 843 that penetrate the valve body 806 in the axial direction (up and down direction). The multiple passages 841 on the inner peripheral side have their ends (lower ends) on the extension-side extremely low speed valve 808 side opening to the inner peripheral side of the seat portion 839, and their ends (upper ends) on the compression-side extremely low speed valve 805 side opening to the inner peripheral side of the seat portion 835. On the other hand, the multiple passages 843 on the outer peripheral side have their ends (lower ends) on the extension-side extremely low speed valve 808 side opening to the cylinder lower chamber 702B, and their ends (upper ends) on the compression-side extremely low speed valve 805 side opening between the seats 835, 836.

[0185] A cap chamber 846 is formed between the cap 801 and the valve body 806. The cap chamber 846 is constantly connected to the cylinder upper chamber 702A via a passage 853 formed in the passage member 802, a passage 830 formed in the mounting shaft portion 728, an annular passage 746 formed on the inner periphery of the piston 718, an orifice 788 in the retainer 782, and an extension-side passage 737 formed in the piston 718. The cap chamber 846 is also constantly connected to a passage 841 in the valve body 806 via a passage 861 formed in the compression-side extremely low speed valve 805. The extremely low speed valve 805 functions as a check valve that allows the flow of hydraulic fluid from the cylinder lower chamber 702B to the cap chamber 846.

[0186] 23 , a base valve 725 is provided at the bottom of the cylinder 702. The base valve 725 includes a valve body 891 that separates the cylinder lower chamber 702B from the reservoir 706, an extension disc valve 892 provided on the reservoir 706 side (lower end side) of the valve body 891, a compression disc valve 893 (second low-speed valve) provided on the cylinder lower chamber 702B side (upper end side) of the valve body 891, and a mounting pin 894 that mounts the extension disc valve 892 and compression disc valve 893, which are suction valves, to the valve body 891.

[0187] The valve body 891 is formed with passages 895 and 896 that penetrate the valve body 891 in the axial direction (up and down). The extension-side disc valve 892 functions as a check valve that allows hydraulic fluid to flow from the cylinder lower chamber 702B to the reservoir 706 via multiple passages 895 on the inner periphery. The extension-side disc valve 892 is provided with an orifice 898 that constantly communicates between the cylinder lower chamber 702B and the reservoir 706. On the other hand, the compression-side disc valve 893 functions as a suction valve that allows hydraulic fluid to flow from the reservoir 706 to the cylinder lower chamber 702B via multiple passages 896 on the outer periphery. The valve body 891 is also provided with a notch 897 that constantly communicates between the space at the lower end of the valve body 891 and the reservoir 706.

[0188] As shown in FIG. 23 , a separator tube 710 is attached to the outer periphery of the inner cylinder 703 via a pair of seal members 709, 709. An annular oil passage 711 is formed between the separator tube 710 and the inner cylinder 703. The annular oil passage 711 is connected to the upper cylinder chamber 702A via multiple passages 712 provided in the side wall at the upper end of the inner cylinder 703. A cylindrical connection port 713 (opening) that protrudes laterally and has an open tip is provided in the side wall at the lower end of the separator tube 710. A mounting hole 714 is provided in the side wall of the outer cylinder 704 at a position opposite the connection port 713. The mounting hole 714 is arranged coaxially with the connection port 713 and has an inner diameter larger than the outer diameter of the connection port 713. A substantially cylindrical case 715 that surrounds the mounting hole 714 is provided in the side wall of the outer cylinder 704. The case 715 accommodates a damping force adjusting mechanism 821 .

[0189] 25 shows the hydraulic circuit of damping force adjustable shock absorber 700A3. Piston 718 is provided with a passage 920 that connects upper cylinder chamber 702A and lower cylinder chamber 702B. Passage 920 includes passage 739, and passage 920 is provided with intake valve 771 (first low-speed valve) that allows hydraulic fluid to flow from lower cylinder chamber 702B to upper cylinder chamber 702A. Piston 718 is also provided with a third passage 923 that is arranged in parallel with intake valve 771.

[0190] The third passage 923 is provided with an extension-side extremely low speed valve 808 (third low speed valve) that allows hydraulic fluid to flow from the upper cylinder chamber 702A to the lower cylinder chamber 702B. The extremely low speed valve 808 opens at a lower pressure than the intake valve 771 (first low speed valve). The third passage 923 is also provided with a compression-side extremely low speed valve 805 (fifth low speed valve) that is arranged in parallel with the extension-side extremely low speed valve 808. Furthermore, an orifice 788 is provided in the third passage 923 on the upper cylinder chamber 702A side of the extremely low speed valves 808, 805. An orifice 888 is also provided in parallel with the extension-side extremely low speed valve 808 and the compression-side extremely low speed valve 805.

[0191] The third passage 923 is formed by the extension-side passage 737 formed in the piston 718, the orifice 788 of the retainer 782, the annular passage 746 formed on the inner periphery of the piston 718, the passage 730 formed in the mounting shaft portion 728, the passage 853 formed in the passage member 802, the cap chamber 846, the passage 861 formed in the compression-side extremely low speed valve 805, the passage 841 of the valve body 806, and the extension-side extremely low speed valve 808 (third low speed and a compression-side path that passes through a passage 843 in the valve body 806, a compression-side extremely low speed valve 805 (fifth low speed valve), a cap chamber 846, a passage 853 formed in the passage member 802, a passage 730 formed in the mounting shaft portion 728, an annular passage 746 formed on the inner periphery of the piston 718, an orifice 788 in the retainer 782, and an extension-side path 737 formed in the piston 718.

[0192] Cylinder lower chamber 702B and reservoir 706 are connected by a second passage 922. Second passage 922 includes passages 895, 896 and a notch 897 formed in base valve 725. A compression side disc valve 893 (second low-speed valve) is provided in second passage 922 (base valve 725). Also, second passage 922 is provided with an orifice 898 arranged in parallel with compression side disc valve 893.

[0193] The cylinder upper chamber 702A (first chamber) and the reservoir 706 are connected by a first passage 921. The first passage 921 includes a main passage 925 formed in the damping force adjustment mechanism 821, a pilot passage 926, and a communication passage 927 that communicates between the main valve 822 and the pilot passage 926. The main passage 925 is provided with the main valve 822 of the damping force adjustment mechanism 821. The pilot passage 926 is provided with an inlet orifice 755.

[0194] The introduction orifice 755 is disposed on the upper cylinder chamber 702A side of a connection 928 between the pilot passage 926 and the communication passage 927. A pilot valve 823 is also provided in the pilot passage 926. The opening pressure of the pilot valve 823 is controlled by changing the value of the current passed through the solenoid 901. The pilot valve 823 is disposed on the reservoir 706 side of the connection 928. Furthermore, the pilot passage 926 is provided with an extremely low speed valve 855 (fourth low speed valve) that allows the flow of hydraulic fluid from the upper cylinder chamber 702A (first chamber) to the reservoir 706. The extremely low speed valve 855 is disposed on the reservoir 706 side of the pilot valve 823.

[0195] The piston speed when the extension-side extremely low speed valve 808 (third low speed valve) arranged on the piston 718 opens is slower than the piston speed when the extremely low speed valve 855 (fourth low speed valve) arranged on the pilot passage 926 opens. In addition, the piston speed when the compression-side extremely low speed valve 805 (fifth low speed valve) arranged on the piston 718 opens is slower than the piston speed when the extremely low speed valve 855 (fourth low speed valve) arranged on the pilot passage 926 opens. In addition, the piston speed when the compression-side extremely low speed valve 805 opens is slower than the piston speed when the intake valve 771 (first low speed valve) arranged on the piston 718 opens.

[0196] FIG. 26 is a graph showing the damping force characteristics of the damping force adjustable shock absorber 700A3 during the compression stroke. In hard mode, which generates a hard-characteristic damping force, a damping force F1 (axial force) is generated due to friction between the sliding parts in the friction region from piston speed 0 to H1. When the piston speed reaches H1 and the extremely low speed valve 805 (fifth low speed valve) on the compression side of the piston 718 opens, a damping force with valve characteristics due to the extremely low speed valve 805 is generated in the initial stage. Thereafter, in the extremely low speed region up to H2, when the pilot valve 823 (control valve) of the damping force adjustment mechanism 821 opens, a damping force with orifice characteristics mainly due to the orifice 788 of the piston 718 is generated. Note that the damping force of the extremely low speed valve 805 in the extremely low speed region becomes saturated. Furthermore, in the extremely low speed region, the pilot valve 823 of the damping force adjustment mechanism 821 is in a closed state.

[0197] In the low-speed range where the piston speed is from H2 (the opening point of the pilot passage 926) to H3, at which the main valve 822 of the damping force adjustment mechanism 821 opens, the pilot valve 823 and the extremely low-speed valve 855 (fourth low-speed valve) open, and a damping force is generated mainly by the inlet orifice 755 of the damping force adjustment mechanism 821. Note that the damping force of the extremely low-speed valve 855 in the low-speed range has a saturated characteristic. Then, in the medium-speed range where the piston speed is H3 or higher after the main valve 822 of the damping force adjustment mechanism 821 opens, a damping force with valve characteristics of the main valve 822 is generated.

[0198] In the soft mode, which generates a soft-characteristic damping force, friction between the sliding parts generates a damping force F1 (axial force) in the friction range from piston speed 0 to S1. In the extremely low-speed range from when the piston speed reaches S1 to when the extremely low-speed valve 855 (fourth low-speed valve) of the damping force adjustment mechanism 821 opens, the hydraulic fluid in the upper cylinder chamber 702A (first chamber) expands, generating a pressure difference between the upper cylinder chamber 702A and the lower cylinder chamber 702B (second chamber) of the compression-side extremely low-speed valve 805 (fifth low-speed valve). As a result, the compression-side extremely low-speed valve 805 opens, and the extremely low-speed valve 805 generates a damping force with valve characteristics in the extremely low-speed range from S1 to S2. In the extremely low-speed range, the pilot valve 823 of the damping force adjustment mechanism 821 remains open.

[0199] In the extremely low speed range from when the piston speed reaches S2 to S3 at which the main valve 822 of the damping force adjustment mechanism 821 opens, the intake valve 771 (first low speed valve) opens first, and then the extremely low speed valve 855 (fourth low speed valve) of the damping force adjustment mechanism 821 generates a damping force with valve characteristics. When the orifice pressure difference in the orifice 788 of the piston 718 increases and a pressure difference occurs in the inlet orifice 755 of the damping force adjustment mechanism 821, the main valve 822 of the damping force adjustment mechanism 821 opens. In the low speed range at piston speeds S3 and above after the main valve 822 of the damping force adjustment mechanism 821 opens, a damping force with valve characteristics is generated by the main valve 822. Note that in the medium speed range of the piston speed, the intake valve 771 (first low speed valve) of the piston 718 opens, and thus a damping force with valve characteristics is generated by the intake valve 771.

[0200] On the other hand, in the extremely low-speed range of the piston speed during the extension stroke in soft mode, the hydraulic fluid in the cylinder upper chamber 702A (first chamber) is compressed, generating a pressure difference between the cylinder upper chamber 702A side and the cylinder lower chamber 702B (second chamber) side of the extension-side extremely low-speed valve 808 (third low-speed valve). As a result, the extremely low-speed valve 808 opens, and a damping force with valve characteristics is generated by the extremely low-speed valve 808 in the extremely low-speed range of the extension stroke. Furthermore, when the orifice pressure difference at the orifice 788 of the piston 718 increases and the extremely low-speed valve 855 (fourth low-speed valve) of the damping force adjustment mechanism 821 opens, a damping force with valve characteristics is generated by the extremely low-speed valve 855. Thereafter, when the pressure difference at the inlet orifice 755 of the damping force adjustment mechanism 821 increases, the main valve 822 of the damping force adjustment mechanism 821 opens, and the main valve 822 generates a damping force with valve characteristics.

[0201] In damping force adjustable shock absorber 700A3, main valve 822 of damping force adjustment mechanism 821 constitutes a first damping force generation mechanism, and a valve called a low speed valve (low speed valve) constitutes a second damping force generation mechanism that operates when steering in a low speed range (first speed range) of piston speed with the first damping force generation mechanism not operating, and operates together with the first damping force generation mechanism in a high speed range (second speed range) of piston speed. Then, when the damping ratio ζ and the natural angular frequency ωn are variable, steering control device 630 (vehicle response characteristic setting section 632) can output a control signal to solenoid 901 to switch to a hard mode in which a hard-characteristic damping force is generated when, for example, damping ratio ζ is reduced to increase responsiveness, and conversely, output a control signal to solenoid 901 to switch to a soft mode in which a soft-characteristic damping force is generated when damping ratio ζ is increased to decrease responsiveness.

[0202] 27 to 30 show shock absorber 700B1 as one embodiment of shock absorber 700B in which two valves that open in the same stroke are arranged in series. For ease of explanation, the top and bottom of shock absorber 700B1 shown in FIG. 27 will be simply referred to as "top" and "bottom" unless otherwise specified. As shown in FIG. 27, shock absorber 700B1 includes a cylindrical cylinder 401 with a bottom, a piston 402 that is slidably inserted into cylinder 401, and a piston rod 403 whose bottom end is connected to piston 402 and whose top end protrudes outside cylinder 401.

[0203] Shock absorber 700B1 also includes an annular cylinder head 410 that closes the upper end of cylinder 401 and slidably supports piston rod 403. Meanwhile, the lower end of cylinder 401 is closed by bottom 401a. In this manner, the inside of cylinder 401 is an enclosed space. A free piston 411 is slidably inserted into cylinder 401 on the opposite side of piston 402 from piston rod 403.

[0204] A liquid chamber L filled with a liquid such as hydraulic oil is formed above the free piston 411 inside the cylinder 401. On the other hand, a gas chamber G filled with air or a compressed gas such as nitrogen gas is formed below the free piston 411 inside the cylinder 401. In this way, the inside of the cylinder 401 is divided into the liquid chamber L and the gas chamber G by the free piston 411.

[0205] When the shock absorber 700B1 extends, the piston rod 403 retracts from the cylinder 401, and the internal volume of the cylinder increases by the volume of the retracted piston rod 403, so the free piston 411 moves upward within the cylinder 401, expanding the gas chamber G. Conversely, when the shock absorber 700B1 contracts, the piston rod 403 moves into the cylinder 401, and the internal volume of the cylinder decreases by the volume of the retracted piston rod 403, so the free piston 411 moves downward within the cylinder 401, reducing the gas chamber G.

[0206] The fluid chamber L in the cylinder 401 is divided into an extension-side chamber L1 on the piston rod 403 side and a compression-side chamber L2 on the opposite side (opposite the piston rod side) by the piston 402. The piston 402 is sandwiched between a step 403a formed on the outer periphery of the piston rod 403 and a nut 430 that screws onto the tip end of the piston rod 403, and includes two valve discs 404 and 405 that are held vertically aligned on the outer periphery of the piston rod 403.

[0207] Of the two valve discs 404, 405, the upper valve disc 404 (on the expansion-side chamber L1 side) is fitted with expansion-side and compression-side main valves 406, 407. On the other hand, the lower valve disc 405 (on the compression-side chamber L2 side) is fitted with an extremely low speed valve 408. The two valve discs 404, 405, the expansion-side and compression-side main valves 406, 407, and the extremely low speed valve 408 constitute a damping valve V. Each of the components that constitute this damping valve V will be described in detail below.

[0208] 28 , the upper valve disc 404 includes an annular main body portion 404b having a mounting hole 404a formed in the center thereof for allowing insertion of the piston rod 403, and a cylindrical skirt portion 404c protruding downward from the outer periphery of the lower end of the main body portion 404b. Furthermore, the main body portion 404b is formed with extension-side and compression-side ports 404d, 404e that open to the inner periphery of the skirt portion 404c and penetrate the main body portion 404b in the axial direction. The extension-side port 404d is opened and closed by an extension-side main valve 406 stacked on the lower side of the main body portion 404b, and the compression-side port 404e is opened and closed by a compression-side main valve 407 stacked on the upper side of the main body portion 404b.

[0209] The lower valve disc 405 has a mounting hole 405a formed in its center to allow insertion of the piston rod 403, and also includes an annular fitting portion 405b that fits onto the inner periphery of a skirt portion 404c of the upper valve disc 404, a tubular portion 405c that protrudes downward from the outer periphery of the lower end of the fitting portion 405b, and an annular opposing portion 405d that protrudes radially inward from the lower end of the tubular portion 405c. A seal 405e seals the gap between the fitting portion 405b and the skirt portion 404c, and a communication hole 405f that communicates between the inside of the skirt portion 404c and the inside of the tubular portion 405c is formed in the fitting portion 405b. Furthermore, a valve stopper 409 and an extremely low speed valve 408 are stacked below the fitting portion 405b, and this extremely low speed valve 408 is arranged to block the opening of the opposing portion 405d located at the lower end of the cylindrical portion 405c.

[0210] As a result, the fluid flowing from the main valves 406, 407 to the compression-side chamber L2 flows through the inside of the skirt portion 404c of the upper valve disc 404, the inside of the communication hole 405f and the cylindrical portion 405c of the lower valve disc 405, and the extremely low speed valve 408, in that order. Conversely, the fluid flowing from the compression-side chamber L2 to the main valves 406, 407 flows in the opposite direction through the above-mentioned path. In this way, the extremely low speed valve 408 (second pressure generating mechanism) is provided in series with the main valves 406, 407 (first pressure generating mechanism) in the passage connecting the expansion-side chamber L1 and the compression-side chamber L2. Hereinafter, the space extending from the inside of the skirt portion 404c to the inside of the cylindrical portion 405c, which is located between the main valves 406, 407 and the extremely low speed valve 408, will be referred to as the intermediate chamber L3.

[0211] The expansion-side and compression-side main valves 406, 407 each include one or more leaf valves. These leaf valves are thin, elastic annular plates. Each main valve 406, 407 has its inner periphery fixed to the valve disc 404 while allowing deflection of its outer periphery. Its outer periphery is seated and released from the valve disc 404 to open and close the outlet of the corresponding port 404d, 404e. The inlet of the expansion-side port 404d opens to the expansion-side chamber L1, and pressure in the expansion-side chamber L1 deflects the outer periphery of the expansion-side main valve 406 downward, thereby opening the expansion-side port 404d. Meanwhile, the inlet of the compression-side port 404e opens to the intermediate chamber L3, and pressure in the intermediate chamber L3 deflects the outer periphery of the compression-side main valve 407 upward, thereby opening the compression-side port 404e.

[0212] Furthermore, of the leaf valves constituting the extension-side and compression-side main valves 406, 407, notches 406a, 407a are formed in the outer periphery of the first leaf valve located closest to the valve disc 404. As a result, even when the extension-side and compression-side main valves 406, 407 are closed, an orifice is formed by the notches 406a, 407a, and liquid passes through the orifice to move back and forth between the extension-side chamber L1 and the intermediate chamber L3.

[0213] 29, the extremely low speed valve 408 is configured to include a leaf valve 408a and first and second sub-leaf valves 408b, 408c stacked above and below it. The leaf valve 408a and the first and second sub-leaf valves 408b, 408c are each thin, elastic annular plates, and the outer diameters of the first and second sub-leaf valves 408b, 408c are smaller than the outer diameter of the leaf valve 408a.

[0214] Furthermore, one or more spacers 480a, 480b, each having an outer diameter smaller than that of the leaf valve 408a and the first and second sub-leaf valves 408b, 408c, are stacked above and below the extremely low speed valve 408. The inner periphery of the extremely low speed valve 408 is sandwiched between the spacers 480a, 480b and fixed to the valve disc 405. On the other hand, the outer periphery of the extremely low speed valve 408 on the side closer to the spacers 480a, 480b is allowed to flex both above and below.

[0215] Furthermore, the leaf valve 408a is provided such that its outer peripheral surface f1, which forms the end face of its free end in an undeflected state, faces the inner peripheral surface f2 of the facing portion 405d. In other words, the facing portion 405d of the valve disc 405 protrudes toward the outer peripheral surface (end face of the free end) f1 of the leaf valve 408a in an undeflected state, and the inner peripheral surface f2 of the facing portion 405d faces the outer peripheral surface f1 of the leaf valve 408a. Note that the "undeflected state" refers to a state in which no load is applied.

[0216] Even when the leaf valve 408a is not bent and the outer peripheral surface f1 of the leaf valve 408a and the inner peripheral surface f2 of the opposing portion 405d face each other, a gap P is formed between the outer periphery of the leaf valve 408a and the opposing portion 405d. This gap P allows the outer periphery (free end) of the leaf valve 408a to move up and down relative to the opposing portion 405d. However, because the gap P is very narrow, almost no liquid moves through the gap P.

[0217] The pressure in the contraction-side chamber L2 acts in a direction that deflects the outer periphery of the leaf valve 408a upward. On the other hand, the pressure in the intermediate chamber L3 acts in a direction that deflects the outer periphery of the leaf valve 408a downward. Then, when the outer periphery of the leaf valve 408a is deflected up and down by the pressure in the contraction-side chamber L2 or the intermediate chamber L3, and the outer periphery surface f1 and the inner periphery surface f2 of the opposing portion 405d are displaced up and down and no longer face each other, the greater the deflection of the leaf valve 408a, the wider the gap P that is formed between the outer periphery and the opposing portion 405d.

[0218] Furthermore, the leaf valve 408a and the second sub-leaf valve 408c overlapping it below are apertured leaf valves, and each of these has a mounting hole (not shown) that allows the piston rod 403 to pass through, as well as a communication hole that passes through the wall of each valve. Hereinafter, in order to distinguish between the hole formed in the leaf valve 408a and the hole formed in the second sub-leaf valve 408c, the former will be referred to as the through hole h1 and the latter as the through hole h2. Furthermore, the state in which the components that make up the damping valve V are attached to the outer periphery of the piston rod 403 will be referred to as the attached state.

[0219] The leaf valve 408a has a circular through-hole h1 in a plan view, and multiple through-holes h1 are formed around the leaf valve 408a in the circumferential direction, while the second sub-leaf valve 408c has an arc-shaped through-hole h2 in a plan view, and multiple through-holes h2 are formed around the second sub-leaf valve 408c in the circumferential direction. As shown in Figure 29, when the leaf valve 408a and the second sub-leaf valve 408c are in an attached state, two or more through-holes h1 are communicated with one through-hole h2 without the need for circumferential alignment. This prevents the lower end of the through-hole h1 from being blocked by the second sub-leaf valve 408c, and keeps the lower end of the through-hole h1 always open.

[0220] On the other hand, the first sub-leaf valve 408b overlapping the upper side of the leaf valve 408a is a holeless leaf valve that has no holes other than an attachment hole (not shown) that allows insertion of the piston rod 403. When the leaf valve 408a and the first sub-leaf valve 408b are attached to each other, as shown in Figure 29, the outer periphery of the first sub-leaf valve 408b is located more outer periphery than the upper opening of the through-hole h1 of the leaf valve 408a.

[0221] As a result, when the outer periphery of the first sub-leaf valve 408b is in contact with the upper surface of the leaf valve 408a, the upper end of the through-hole h1 is blocked by the first sub-leaf valve 408b. Furthermore, when the outer periphery of the leaf valve 408a shown in Fig. 29 is deflected upward by the pressure of the compression-side chamber L2, the outer periphery of the first sub-leaf valve 408b also deflects upward in response to this, so that the outer periphery of the first sub-leaf valve 408b is maintained in contact with the upper surface of the leaf valve 408a, and the upper end of the through-hole h1 is maintained in a blocked state by the first sub-leaf valve 408b.

[0222] 30, when the outer periphery of the leaf valve 408a bends downward due to the pressure of the intermediate chamber L3, the outer periphery of the first sub-leaf valve 408b separates from the upper surface of the leaf valve 408a, opening the upper end of the through-hole h1. When the outer periphery of the leaf valve 408a bends downward, the outer periphery of the second sub-leaf valve 408c also bends downward in response, so that the outer periphery of the second sub-leaf valve 408c is maintained in contact with the lower surface of the leaf valve 408a, but the lower end of the through-hole h1 is opened downward by the through-hole h2.

[0223] This allows liquid in the intermediate chamber L3 to flow into the through hole h1 from between the first sub-leaf valve 408b and the leaf valve 408a, and to move through the through hole h1 and the through hole h2 to the compression-side chamber L2. In other words, the through hole h1 and the through hole h2 form a passage B that is parallel to the gap P formed between the outer periphery (free end) of the leaf valve 408a and the opposing portion 405d. This passage B is opened and closed by the first sub-leaf valve 408b, and when the leaf valve 408a is bent downward, the first sub-leaf valve 408b opens passage B, allowing liquid to flow through passage B from the intermediate chamber L3 to the compression-side chamber L2. In this way, the ultra-low speed valve 408 constituting the second force generating mechanism (second damping force generating mechanism) has a disk valve with one radial end fixed and the other radial end formed as a free end, and opens and closes communication holes (holes h1, h2) that connect the upstream side and downstream side of the disk valve.

[0224] Furthermore, when the leaf valve 408a and the first sub-leaf valve 408b are deflected upward to a certain extent, one or both of the leaf valve 408a and the first sub-leaf valve 408b come into contact with the valve stopper 409, preventing further deflection. In this way, the valve stopper 409 limits the upward deflection of the leaf valve 408a and the first sub-leaf valve 408b. Conversely, when the leaf valve 408a and the second sub-leaf valve 408c are deflected downward to a certain extent, one or both of the leaf valve 408a and the second sub-leaf valve 408c come into contact with the nut 430, preventing further deflection. In this way, the nut 430 functions as a valve stopper that limits the downward deflection of the leaf valve 408a and the second sub-leaf valve 408c.

[0225] Furthermore, a groove 430a is formed in the radial direction at the upper end of the nut 430. This groove 430a prevents communication between passage B and the compression-side chamber L2 from being blocked when the leaf valve 408a or the second sub-leaf valve 408c abuts against the nut 430. Note that such a groove 430a may also be formed in the extremely low speed valve 408. Also, instead of the groove 430a, a hole may be formed in the nut (valve stopper) 430, and this hole may ensure communication with passage B when the first sub-leaf valve 408b opens passage B.

[0226] The operation of the shock absorber 700B1 will now be described. When the shock absorber 700B1 extends, the piston 402 moves upward within the cylinder 401, compressing the extension-side chamber L1, and the liquid in the extension-side chamber L1 moves to the compression-side chamber L2 through the damping valve V. Resistance is applied to the flow of liquid by the extension-side main valve 406, the orifices formed by the notches 406a and 407a of the main valves 406 and 407, and the extremely low speed valve 408, so that the pressure in the extension-side chamber L1 increases, and the shock absorber 700B1 exerts an extension-side damping force that impedes the extension operation.

[0227] Conversely, when the shock absorber 700B1 contracts, the piston 402 moves downward within the cylinder 401 to compress the compression-side chamber L2, and the liquid in the compression-side chamber L2 passes through the damping valve V and moves to the extension-side chamber L1. Resistance is applied to the flow of the liquid by the compression-side main valve 407, the orifices formed by the notches 406a and 407a of the main valves 406 and 407, or the extremely low speed valve 408, so that the pressure in the compression-side chamber L2 rises, and the shock absorber 700B1 exerts a compression-side damping force that hinders the contraction operation.

[0228] In shock absorber 700B1, extension-side and compression-side main valves 406, 407 open depending on the piston speed, and the outer periphery of leaf valve 408a of extremely low speed valve 408 bends up and down, thereby changing the damping force characteristics (the damping force characteristics relative to piston speed). More specifically, when the speed (piston speed) of piston 402 is extremely low, such as when shock absorber 700B1 starts to move, and the piston speed is in an extremely low speed range close to 0 (zero), the extension-side and compression-side main valves 406, 407 are closed. On the other hand, the outer periphery of leaf valve 408a of extremely low speed valve 408 bends downward when shock absorber 700B1 extends and upward when shock absorber 700B1 contracts, causing the outer periphery f1 of leaf valve 408a and the inner periphery f2 of opposing portion 405d to be displaced up and down and no longer face each other.

[0229] In this case, the liquid moving back and forth between the expansion-side chamber L1 and the compression-side chamber L2 passes through the orifice formed by the notches 406 a, 407 a of each main valve 406, 407, the intermediate chamber L3, and the gap P formed between the outer periphery of the vertically offset leaf valve 408 a and the inner periphery of the opposing portion 405 d. Furthermore, when the shock absorber 700B1 extends, the outer periphery of the first sub-leaf valve 408 b separates from the upper surface of the leaf valve 408 a that bends downward, thereby opening passage B. In the extremely low speed range, the opening area of ​​the flow path formed by the combination of passage B and gap P during extension and the opening area of ​​gap P during contraction each increase with increasing piston speed, but are smaller than the opening area of ​​all the orifices formed by the notches 406 a, 407 a of each main valve 406, 407.

[0230] For this reason, when the piston speed is in the extremely low speed range, the pressure loss when the liquid moves between the expansion-side chamber L1 and the compression-side chamber L2 is dominated by the pressure loss caused by the flow path that combines the gap P formed between the outer periphery of the leaf valve 408a and the inner periphery of the opposing portion 405d and the passage B during extension, and the pressure loss caused by the gap P becomes dominant during contraction.The damping force characteristics in the extremely low speed range are valve-specific characteristics that are proportional to the piston speed both during extension and contraction.Next, when the piston speed increases and leaves the extremely low speed range and enters the low speed range, the expansion-side and compression-side main valves 406, 407 are closed, just as when the piston speed is in the extremely low speed range. On the other hand, the amount of deflection of the outer periphery of the leaf valve 408a in the ultra-low speed valve 408 becomes larger, and the opening area of ​​the flow path consisting of the gap P and the passage B when expanded and the opening area of ​​the gap P when contracted become larger than the opening area of ​​the entire orifice formed by the notches 406a and 407a of each main valve 406 and 407, respectively.

[0231] Therefore, when the piston speed is in the low-speed range, the pressure loss caused by the orifice formed by the notches 406a and 407a when the liquid moves between the expansion-side chamber L1 and the compression-side chamber L2 is dominated by the pressure loss caused by the orifice. The damping force characteristics in the low-speed range are proportional to the square of the piston speed, which is characteristic of an orifice. Next, when the piston speed increases further and moves beyond the low-speed range into the medium-to-high-speed range, the expansion-side main valve 406 opens when the shock absorber 700B1 expands, and the compression-side main valve 407 opens when the shock absorber 700B1 contracts. Furthermore, the amount of deflection of the leaf valve 408a of the very low-speed valve 408 becomes larger than in the low-speed range, and the gap P formed between the outer periphery of the vertically shifted leaf valve 408a and the inner periphery of the opposing portion 405d becomes wider.

[0232] In this case, the liquid flowing between the expansion-side chamber L1 and the compression-side chamber L2 passes through a gap (opening) formed between the outer periphery of the expansion-side or compression-side main valve 406, 407 and the valve disc 404 when the expansion-side or compression-side main valve 406, 407 is open, the intermediate chamber L3, a gap P formed between the outer periphery of the vertically offset leaf valve 408a and the inner periphery of the opposing portion 405d, and a passage B formed in the leaf valve 408a during expansion. In the medium to high speed range, the gap P is wide, allowing the liquid to pass through relatively without resistance. Therefore, when the piston speed is in the medium to high speed range, the pressure loss caused by the opening of the expansion-side or compression-side main valve 406, 407 when the liquid moves between the expansion-side chamber L1 and the compression-side chamber L2 is dominated by the pressure loss. The damping force characteristics in the medium to high speed range are valve-specific characteristics proportional to the piston speed, and the slope is smaller than in the low speed range. Furthermore, when the main valves 406, 407 are fully opened in the middle to high speed range, the damping force characteristics become port-specific characteristics at the boundary of the fully opened speed, and the slope becomes large again.

[0233] Incidentally, in vehicle 500 in which the above-mentioned model following control is implemented, if the friction coefficient of the road surface or tires is low, when the steering angle command δtg (target steering angle) is set by model following control, the grip limit of the tires may be exceeded, making it impossible to obtain the required cornering force and resulting in a failure to fully utilize the performance of the model following control. To address this issue, if longitudinal G control is implemented to increase the wheel load of front wheels 501, 502, which are the steered wheels (in other words, to shift the load of vehicle 500 toward front wheels 501, 502), the performance of the model following control can be fully utilized and emergency avoidance performance can be improved.

[0234] Figure 31 is a schematic diagram showing one aspect of a vehicle 500 to which the above-described longitudinal G control is applied, and the same elements as in Figure 1 are given the same reference numerals and detailed description thereof will be omitted. The vehicle 500 shown in Figure 31 has a braking device 650 that applies braking force to the wheels of the vehicle 500, and a drive device 660 that applies drive force to the wheels of the vehicle 500.

[0235] The braking device 650 may include a friction braking mechanism such as a hydraulic or electric braking mechanism, a regenerative braking mechanism that utilizes regeneration in the motor, and a braking control device that controls the braking force applied to the wheels. The driving device 660 may include a power generation mechanism such as an internal combustion engine or a motor, and a driving control device that controls the driving force applied to the wheels.

[0236] Then, steering control device 630 performs model following control to intervene in steering device 600 to increase the amount of steering of front wheels 501, 502 in relation to the amount of operation of steering operation member 611, and at the same time performs front-rear G control to control the braking / driving force applied to the wheels by brake device 650 and / or drive device 660 to generate vehicle deceleration G and increase the wheel load of front wheels 501, 502. When front-rear G control is performed and the wheel load of front wheels 501, 502 increases, the grip limit of front wheels 501, 502 can be increased to compensate even under driving conditions where the friction coefficient of the road surface and tires is low, and therefore the high avoidance steering performance achieved by model following control can be fully achieved.

[0237] Furthermore, in a combination of shock absorber 700 and steering angle control based on the target dynamic characteristics, shock absorber 700 can smooth the vehicle behavior, so that there is no trade-off between ride comfort and steering angle control and longitudinal G control, and steering angle control and longitudinal G control can be set with emphasis on avoidance performance. Braking device 650 and driving device 660 are wheel speed adjusting devices that can adjust the rotation of the wheels of vehicle 500 and control the wheel speed, and longitudinal G control that increases the wheel load on front wheels 501, 502 can be rephrased as wheel speed adjustment control that adjusts the wheel speed so as to increase the wheel load on front wheels 501, 502.

[0238] FIG. 32 is a graph showing the difference in cornering force (grip) with and without longitudinal G control, with the horizontal axis representing slip angle and the vertical axis representing cornering force (grip). FIG. 33 shows the difference in the driving trajectory of the vehicle 500 with and without longitudinal G control in an obstacle avoidance scenario. Under driving conditions where the friction coefficient of the road surface and tires is low, the grip force required to follow the target trajectory for obstacle avoidance cannot be obtained, making it difficult to follow the target trajectory. In this case, if the wheel load of the front wheels 501, 502 is increased by longitudinal G control, the insufficient grip force is compensated for, making it possible to follow the target trajectory for obstacle avoidance.

[0239] In vehicle 500 in which the above-described longitudinal G control for increasing the wheel load of front wheels 501, 502 is implemented, shock absorber 700, which is a force generating device whose generated force can be changed by relative movement between a cylinder and a rod, is preferably provided on the front wheels 501, 502 side, and ultra-low speed valve 408 (second force generating mechanism) of shock absorber 700 provided on the front wheels 501, 502 side is preferably provided so as to be operable when shock absorber 700 operates in the direction of contraction. Such shock absorber 700 can suppress pitch behavior (sinking of the front wheels 501, 502 side) of vehicle 500 when load shift occurs to the front wheels 501, 502 side due to longitudinal G control, and can ensure a sense of security for the driver by smoothing the initial movement.

[0240] Furthermore, the shock absorber 700 provided on the front wheel 501, 502 side has, as second force generating mechanisms, an extension-side second force generating mechanism 183 that operates when the shock absorber 700 operates in the extension direction and a compression-side second force generating mechanism 173 that operates when the shock absorber 700 operates in the compression direction (see FIG. 18 , etc.), and it is preferable that the extension-side sub-valve 110 that constitutes the extension-side second force generating mechanism 183 is provided so as to generate a force greater than that of the compression-side sub-valve 107 that constitutes the compression-side second force generating mechanism 173. In other words, the opening pressure until the extension-side sub-valve 110 opens is set higher than the opening pressure until the compression-side sub-valve 107 opens, and setting this valve opening pressure makes it easier to control the forward sagging of the vehicle 500 (sinking on the front wheel 501, 502 side).

[0241] Furthermore, when the aforementioned front-rear G control that increases the wheel loads of the front wheels 501, 502 is implemented, shock absorbers 700, which are force generating devices whose generated force can be changed by relative movement between a cylinder and a rod, can be provided on the rear wheels 503, 504 side of the vehicle 500, thereby making it easier to control the forward sagging of the vehicle 500. In the shock absorbers 700 provided on the rear wheels 503, 504 side, the second force generating mechanism has an extension-side second force generating mechanism 183 that operates when the shock absorber 700 operates in the extension direction, and a compression-side second force generating mechanism 173 that operates when the shock absorber 700 operates in the compression direction, and the compression-side sub-valve 107 that constitutes the compression-side second force generating mechanism 173 is configured to generate a larger force than the extension-side sub-valve 110 that constitutes the extension-side second force generating mechanism 183. In other words, the opening pressure until the compression side sub-valve 107 opens is set higher than the opening pressure until the extension side sub-valve 110 opens, and by setting this opening pressure, it becomes easier to control the vehicle 500 from tilting forward (sinking on the front wheels 501, 502 side).

[0242] Furthermore, in vehicle 500 in which front-rear G control is implemented to increase the wheel load on front wheels 501, 502, in the vibration region in which the second force generating mechanism operates and the first force generating mechanism does not operate, it is preferable that the shock absorber 700 (force generating device) on the front wheel 501, 502 side is configured so that axial force fluctuation due to the load input to the wheel position is smaller than that of shock absorber 700 (force generating device) on the rear wheel 503, 504 side. Such a setting also makes it easier to control the forward sagging of vehicle 500 (sinking on the front wheel 501, 502 side).

[0243] The wheel position is the axial force (ground load) at the tire position, not the axial force at the damper or suspension spring. The lever ratio in the suspension (the ratio between the wheel stroke and the shock absorber expansion / contraction amount) differs depending on the vehicle 500 and between the front and rear wheels, so the tire position is used as the reference.

[0244] The technical ideas described in the above embodiments can be used in appropriate combinations as long as no contradictions arise. Furthermore, although the contents of the present invention have been specifically described with reference to preferred embodiments, it is obvious that a person skilled in the art can adopt various modified embodiments based on the basic technical ideas and teachings of the present invention.

[0245] For example, shock absorber 700 may be any shock absorber capable of realizing a characteristic in which the rise rate (slope) of the damping force in a low-speed region where the piston speed is near zero is faster than in a high-speed region where the piston speed is faster, as shown in Fig. 4 , and any known shock absorber capable of realizing such a characteristic may be appropriately adopted. Furthermore, in variable control of the steering gear ratio using an MFC, the drive mode is not limited to one associated with the output characteristics of the drive source of vehicle 500, but may also be a mode dedicated to steering characteristics that specifies the gain and phase (responsiveness and convergence) of the yaw rate in response to the driver's steering operation. In other words, a system may be provided in which the driver can freely specify the settings of damping ratio ζ and natural angular frequency ωn.

[0246] 500...vehicle, 501, 502...front wheels (steered wheels), 501a-504a...wheel speed sensors, 540...yaw rate sensor, 550...drive mode selection switch, 560...acceleration sensor, 600...steering device, 610...steering input device, 611...steering operation member, 613...operation angle sensor, 620...steering mechanism, 621...steering motor, 630...steering control device, 630A...MCU, 700...shock absorber

Claims

1. A vehicle having: a steering device that varies the ratio of the amount of operation of a steering operating member to the amount of steering of the vehicle's steered wheels; and a force generating device that is provided between the vehicle body and the steered wheels and that can change the force generated by the relative movement of a cylinder and a rod, the force generating device comprising a first force generating mechanism and a second force generating mechanism, the second force generating mechanism operating during steering when the movement speed of the rod relative to the cylinder is in a first speed range and the first force generating mechanism is not operating, and operating together with the first force generating mechanism when the movement speed is in a second speed range that is faster than the first speed range.

2. A vehicle according to claim 1, wherein the second force generating mechanism operates without power from an external actuator.

3. A vehicle as claimed in claim 1, wherein the steering device has a dynamic characteristic information generation unit that calculates dynamic characteristic information indicating target dynamic characteristics of the vehicle relative to the amount of operation of the steering operation member, and controls the steering of the steered wheels based on the dynamic characteristic information and the amount of operation of the steering operation member.

4. A vehicle according to claim 1, wherein the steering operation member and the steered wheels are mechanically separated.

5. A vehicle according to claim 1 or 2, wherein the force generated by the first force generating mechanism is adjustable by an actuator.

6. A vehicle as claimed in claim 1, wherein the second force generating mechanism has a disk valve with one radial end fixed and the other radial end formed as a free end, and opens and closes a communication hole provided in the disk valve that connects the upstream side and downstream side.

7. A vehicle comprising: a steering device that varies the ratio of the amount of operation of a steering operation member to the amount of steering of the vehicle's steered wheels; and a force generating device that is provided between the vehicle body and the steered wheels and is capable of changing the generated force by the relative movement of a cylinder and a rod, wherein when the movement speed of the rod relative to the cylinder, which changes as the steered wheels are steered, is in a first speed range, the rate of change of the generated force is greater than when the movement speed is in a second speed range that is faster than the first speed range.

8. A vehicle as claimed in claim 1 or claim 7, comprising a wheel speed adjusting device capable of adjusting the rotation of the wheels of the vehicle to control the wheel speed, wherein the wheel speed adjusting device adjusts the wheel speed so that the load of the vehicle shifts to the front wheel side of the vehicle when the steering device operates so that the amount of steering of the steered wheels increases in relation to the amount of operation of the steering operation member.

9. A vehicle as set forth in claim 8, wherein the force generating device is provided on the front wheel side of the vehicle, and the second force generating mechanism is provided so as to be operable when the force generating device operates in a retracting direction.

10. A vehicle as described in claim 9, wherein the second force generating mechanism has an extension-side second force generating mechanism that operates when the force generating device operates in the extension direction and a compression-side second force generating mechanism that operates when the force generating device operates in the contraction direction, and the extension-side sub-valve that constitutes the extension-side second force generating mechanism is configured to generate a greater force than the compression-side sub-valve that constitutes the compression-side second force generating mechanism.

11. A vehicle as described in claim 8, wherein the force generating device is provided on the rear wheel side of the vehicle, the second force generating mechanism has an extension side second force generating mechanism that operates when the force generating device operates in the extension direction, and a compression side second force generating mechanism that operates when the force generating device operates in the contraction direction, and the compression side sub-valve that constitutes the compression side second force generating mechanism is arranged to generate a larger force than the extension side sub-valve that constitutes the extension side second force generating mechanism.

12. A vehicle as claimed in claim 8, wherein the vehicle is configured such that, in a vibration region in which the second force generating mechanism operates and the first force generating mechanism does not operate, the axial force fluctuation due to a load input to the wheel position is smaller in the force generating device on the front wheel side than in the force generating device on the rear wheel side.

Images