JPH11139132A - Damping force control device for vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve comfortableness and maneuvering stability of a vehicle by damping vibration generated between a sprung member and an unsprung member of the vehicle, detecting a relative displacement state in a low speed area of the relative speed, and controlling damping force on the basis of a relative displacement direction and the change of speed. SOLUTION: Shock absorbers 10 provided with actuators 2 damping vertical vibration are disposed between a vehicle body 200 and lateral suspension arms 210 so as to adjust generated damping force. A stroke sensor 220 is disposed corresponding to each wheel. A sensor body is fixed to the vehicle body 200, and the tip of a detecting rod 221 is connected to the suspension arm 210 to detect the relative stroke quantity of wheels L, R to the vehicle body 206. An electronic control unit executes driving control of the actuators 2 of the shock absorbers 10 on the basis of the computed result based on the detected result of sensors for the stroke quantity of each wheel, vehicle speed, vertical acceleration, and the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a damping force control device for a vehicle for controlling a damping force of a hydraulic shock absorber (shock absorber) disposed between a sprung member and a unsprung member of a vehicle.

[0002]

2. Description of the Related Art An example of a conventional damping force control device is disclosed in, for example, Japanese Patent Laid-Open No. 5-294122. This damping force control device employs the so-called skyhook control theory to control the damping force of the hydraulic pressure damping device. The relative speed between the sprung member and the unsprung member of the vehicle and the vertical direction of the sprung member are controlled. The damping force is controlled based on the speed, thereby increasing the effect of suppressing the vertical vibration of the sprung member based on the vertical input from the road surface.

[0003] In addition, in order to ensure the riding comfort of the vehicle,
It is desirable that the damping force be small in a region where the displacement speed of the piston rod that constitutes the hydraulic shock absorber is low. On the other hand, in order to ensure good steering stability of the vehicle, it is desirable that the damping force be large in a region where the displacement speed of the piston rod is high.
Generally, the displacement speed of the piston rod is 0.1 to 0.3.
It is known that at a point exceeding m / s, the riding comfort and the steering stability can be made compatible by reducing the gradient of the damping force characteristic (characteristic indicating the relationship between the displacement speed of the piston rod and the damping force). ing.

[0004]

As a result of research, it has been found that the riding comfort and the steering stability of a vehicle are limited to a region where the displacement speed of the piston rod is extremely low (for example, a region of 0.02 m / s or less; It is also found that it greatly depends on the damping force characteristic in the above.

However, such a large change in the riding comfort and the driving stability of the vehicle depending on the damping force characteristics in the low speed range has not been recognized so far, and the riding comfort and the steering stability of the vehicle have not been recognized. It is important to control the damping force characteristic in the low-speed region in order to improve the damping force.

Accordingly, an object of the present invention is to provide a vehicle damping force control device that can further improve the riding comfort and steering stability of a vehicle by controlling the damping force characteristics in this low speed range.

[0007]

Accordingly, a vehicle damping force control device according to a first aspect of the present invention damps vibration generated between a sprung member and a unsprung member of a vehicle with a predetermined damping force, A hydraulic buffer having a damping force variable function in a region where the relative speed between the upper member and the unsprung member is low; and a relative displacement between the sprung member and the unsprung member provided corresponding to the hydraulic buffer. And a control means for controlling the damping force of the hydraulic pressure buffer means based on the relative displacement direction and the change state of the relative displacement speed obtained from the detection result of the displacement state detection means. I do.

From the detection result of the displacement state detecting means, an acceleration at which the relative displacement direction and relative displacement speed between the sprung member and the unsprung member are changed is obtained. Based on these results, the control means determines whether the hydraulic pressure buffer means is in the expansion stroke or the contraction stroke, and determines whether the relative displacement speed is in the acceleration tendency or in the deceleration tendency. Then, damping force control according to the determination result is performed.

According to a second aspect of the present invention, in the control means according to the first aspect, the damping force of the hydraulic pressure buffer is increased when the relative displacement speed is in an accelerating state, and the damping force is increased in a decelerating state. Is controlled to decrease the damping force of the hydraulic buffer.

The control means increases the damping force when the relative displacement speed is in an accelerating state and decreases the damping force when the relative displacement speed is in a decelerating state, so that the fluctuation of the relative displacement speed between the sprung member and the unsprung member is reduced. Restrained, thereby improving the riding comfort and steering stability of the vehicle.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described.
This will be described with reference to the accompanying drawings.

FIG. 1 schematically shows a vehicle equipped with a damping force control device according to a first embodiment. Wheels L and R are connected to the left and right sides of the vehicle body 200 via suspension arms 210, respectively. A shock absorber 1 is provided between the vehicle body 200 and the left and right suspension arms 210 to attenuate vertical vibration generated in the vehicle body 200.
0 is arranged. The shock absorber 10 includes an actuator 2 as described later, and has a mechanism capable of adjusting a generated damping force by controlling the drive of the actuator 2. The steering shaft 202 connected to the steering handle 201 is provided with a steering angle sensor 203 for detecting an operation amount of the steering handle 201.

A stroke sensor 220 is provided corresponding to each wheel. The sensor body is fixed to the vehicle body 200, and the tip of a detection rod 221 extending from the sensor body is connected to the suspension arm 210. The detection rod 221 swings with the swing of the suspension arm 210, and the movement of the detection rod 221 is detected by a potentiometer built in the sensor body. Therefore, the stroke sensor 220 detects the relative stroke amounts of the wheels L and R with respect to the vehicle body 200. The detection rod 2 for the suspension arm 210
Since the connecting portion 21 is located at a position from the center of the vehicle body 200, the actual relative stroke amount of the wheel is a constant multiple of the detection result of the stroke sensor 220. Therefore, a value obtained by multiplying the detection result of the stroke sensor 220 by a predetermined constant is obtained as the relative stroke amount Y of the wheel.

FIG. 1 schematically shows only the configuration of the front wheels, but the wheels L, R, the shock absorber 10, the suspension arm 210, the stroke sensor 220, and the like have the same configuration on the rear wheels. . Then, as shown in FIG. 2, an electronic control unit (hereinafter, referred to as “ECU”).
230 includes a steering angle sensor 203, a stroke sensor 220 for each wheel, and a vehicle speed sensor 20 for detecting a vehicle speed.
4. A detection result from each sensor, such as a vertical acceleration sensor 205 that detects vertical acceleration acting on the vehicle body 200 as a sprung member, is given. In the ECU 230,
Based on these detection results, the following processing is executed,
Based on the calculation result, drive control of the actuator 2 in the shock absorber 10 corresponding to each wheel is performed.

Here, the shock absorber 10 will be described. As shown in FIG. 3, the shock absorber 10
Has a piston rod 16 and an outer cylinder 18. A guide 10a is fixed to the outer periphery of the outer cylinder 18, and a bracket 10b is hung on the upper end of the piston rod. Also, between the guide 10a and the bracket 10b,
A coil spring 10c is provided, and the vehicle body is elastically supported by the coil spring 10c.

Inside the outer cylinder 18, an inner cylinder 20 is provided.
And are arranged coaxially. An annular chamber 21 is formed between the outer cylinder 18 and the inner cylinder 20. A rod guide 22 is fitted into the upper end of the outer cylinder 18. The rod guide 22 is a columnar rigid member having a large diameter portion 22a and a small diameter portion 22b. The outer peripheral surface of the small diameter portion 22b is engaged with the inner peripheral surface of the inner cylinder 20, and the outer peripheral surface of the large diameter portion 22a is engaged with the inner peripheral surface of the outer cylinder 18. The rod guide 22 has a through hole at the center thereof. The piston rod 16 is slidably inserted through the through hole in a liquid-tight manner. A cap 24 is fixed to the upper end of the outer cylinder 18 so that the piston rod 16 passes through the center of the cap 24.

The piston rod 16 is a columnar member whose lower end has a small diameter. The piston rod 16 is arranged so that its small diameter portion is housed inside the inner cylinder 20. A rebound stopper 26 and a rebound stopper plate 28 are mounted on the piston rod 16 at positions accommodated inside the inner cylinder 20.

The rebound stopper plate 28 is an annular rigid member, and is fixed to the outer periphery of the piston rod 16. The rebound stopper 26 is an annular member having elasticity, and is mounted on an upper part of the rebound stopper plate 28. When the piston rod 16 is displaced upward by a predetermined distance, the rebound stopper 26 comes into contact with the rod guide 22, and further displacement of the piston rod 16 is restricted.

A sub piston 30 and a main piston 32 are fixed to a lower end portion of the piston rod 16, and the sub piston 30 and the main piston 32 are attached in this order from the upper side. The inner space of the inner cylinder 20 is formed by the sub piston 30 and the main piston 32 by the sub piston 30.
The upper chamber 34 is partitioned into an upper chamber 34, a middle chamber 36 between the sub piston 30 and the main piston 32, and a lower chamber 38 below the main piston 32.

Sub piston 30 and main piston 32
Are provided with orifices and valve mechanisms that allow fluid to flow between the upper chamber 34 and the middle chamber 36 and between the middle chamber 36 and the lower chamber 38, respectively. A damping force is generated according to. Details of the configuration of the sub piston 30 and the main piston 32 will be described later.

A passage 40 penetrating in the axial direction is provided inside the piston rod 16. Passage 40
A large-diameter portion 40a and a small-diameter portion 4 extending below the large-diameter portion 40a
0bb. A step 40c is formed at the boundary between the large diameter portion 40a and the small diameter portion 40b of the passage 40. The large diameter portion 40a of the passage 40 has an adjustment rod 42
Is inserted.

A base valve 41 is fixed to a lower end of the outer cylinder 18. The base valve 41 is configured to allow a fluid to flow between the lower chamber 38 and the annular chamber 21. The working fluid is contained inside the outer cylinder 18 so as to fill the inner space of the inner cylinder 20 and fill the annular chamber 21 to a predetermined height.

The upper end of the adjusting rod 42 reaches the upper part of the piston rod 16 and is engaged with the actuator 2 mounted on the vehicle body 200. Actuator 2
Is provided with, for example, a stepping motor as a drive source, and adjusts the adjustment rod 42 according to a signal from the ECU 230.
To rotate.

Next, referring to FIG.
The configuration of the main piston 32, the main piston 32, and its peripheral parts will be described. FIG. 4 is an enlarged view of the sub-piston 30, the main piston 32, and a peripheral portion thereof. The left half of FIG. 4 shows a component that allows fluid to flow from the upper chamber 34 to the lower chamber 38, and the right half of FIG. Fig. 2 shows components that allow fluid to flow through.

As shown in FIG. 4, the adjusting rod 42 is one of damping force variable mechanisms, and includes a small diameter portion 42a having an outer diameter smaller than the inner diameter of the large diameter portion 40a of the passage 40, and a small diameter portion 42a. And a conical portion 42b formed at a lower end portion. The adjusting rod 42 is configured such that the tip of the conical portion 42 b is
It is arranged so as to enter the small-diameter portion 40b of zero. A clearance C is formed between the outer peripheral surface of the conical portion 42b and the step 40c of the passage 40.

An O-ring 43 is mounted on the outer periphery of the adjusting rod 42 above the small diameter portion 42a. The O-ring 43 defines an annular communication space 44 between the outer periphery of the small diameter portion 42 a of the adjustment rod 42 and the inner periphery of the large diameter portion 40 a of the passage 40. The communication space 44 communicates with the internal space of the small diameter portion 40b of the passage 40 via the clearance C.

A communication passage 46 extending in the radial direction of the piston rod 16 and communicating the upper chamber 34 with the communication space 44.
Is provided. Further, the piston rod 16 is provided with a communication passage 47 extending in the radial direction and communicating the internal space of the small diameter portion 40 b of the passage 40 with the middle chamber 36.

The adjusting rod 42 is screwed with a large diameter portion 40a of the passage 40 at a screw portion (not shown), and the upper end thereof is engaged with the actuator 2. Therefore, the clearance C can be adjusted by rotating the adjustment rod 42 by the actuator 2 and thereby changing the opening position (up-down position) of the adjustment rod 42.

A stopper plate 48, a leaf seat 49, and a leaf valve 5 are arranged on the outer periphery of the small diameter portion of the piston rod 16 in order from the large diameter portion 16a side (the upper side in FIG. 4).
0, the sub piston 30, the leaf valve 54, and the leaf seat 56 are fitted.

The leaf valves 50 and 54 are members having a low bending rigidity made of a thin plate. The upper and lower ends of the sub-piston 30 have annular grooves 58 respectively.
And 60 are provided. Leaf valves 50 and 54
Are arranged to close the annular grooves 58 and 60, respectively. The sub-piston 30 has an annular groove 5.
A through passage 62 that connects the internal space of No. 8 to the middle chamber 36 and a through passage 64 that connects the internal space of the annular groove 60 to the upper chamber 34 are provided.

The leaf valve 50 opens by flexing and deforming when the hydraulic pressure in the middle chamber 36 becomes higher than the hydraulic pressure in the upper chamber 34 by a predetermined valve opening pressure P1. To the upper chamber 34 from the working fluid. The leaf valve 54 opens by flexing and deforming when the hydraulic pressure of the upper chamber 34 becomes higher than the hydraulic pressure of the middle chamber 36 by a predetermined valve opening pressure P2. The flow of the working fluid toward the middle chamber 36 is allowed.

A piston ring 66 is mounted on the outer periphery of the sub piston 30. The seal between the sub-piston 30 and the inner cylinder 20 is ensured by the piston ring 66. Leaf sheet 5 around piston rod 16
6, a communication member 68, a leaf seat 70, a spacer 72, a spring seat 74,
And a spacer 76 are fitted.

The communication member 68 has a communication passage 77 penetrating in the radial direction and communicating with the communication passage 47 of the piston rod 16. A spring seat 78 is fitted on the outer periphery of the spacer 76 so as to be slidable in the axial direction. A spring 80 is provided between the spring seat 74 and the spring seat 78.

The spacer 76 on the outer periphery of the piston rod 16
A leaf valve 82, a main piston 32, and a leaf valve 86 are fitted in order from the upper side further below. A plurality of seat surfaces 92 are provided on the upper end surface of the main piston 32. Also, the main piston 32
A plurality of sheet surfaces 94 are provided at positions not corresponding to the sheet surface 92 at the lower end surface of the. The leaf valves 82 and 86 are members formed by laminating a plurality of thin plate members, and are disposed so as to contact the top surfaces of the seat surfaces 92 and 94, respectively. A piston ring 95 is mounted on the outer periphery of the main piston 32. Piston ring 95
Thereby, the sealing property between the main piston 32 and the inner cylinder 20 is ensured.

The main piston 32 is provided with through passages 96 and 98 penetrating in the axial direction. The through-passage 96 is configured to open at a concave portion between the seat surfaces 92 at an upper end thereof, and to open at a top surface of the seat surface 94 at a lower end thereof. In addition, the through passage 98
At the upper end, an opening is formed on the top surface of the seat surface 92, and at the lower end, an opening is formed in a concave portion between the seat surfaces 94.

A first orifice (see FIG. 3) that connects the through passage 98 to the middle chamber 36 in a state where the leaf valve 82 is in contact with the seat surface 92 is formed on the thin plate material on the side of the main piston 32 constituting the leaf valve 82. (Not shown). A second orifice (shown in the drawing) that connects the through passage 96 and the lower chamber 38 in a state where the leaf valve 86 is in contact with the seat surface 94 is provided on the thin plate material closest to the main piston 32 that constitutes the leaf valve 86. Are formed.

A spacer 99 is fitted below the leaf valve 86 on the outer periphery of the piston rod 16.
A thread 16c is formed at the lower end of the piston rod 16, and a spring seat 100 is screwed to the thread 16c. A spring seat 102 is fitted on the outer periphery of the spacer 99 so as to be slidable in the axial direction. Spring seat 102 and spring seat 10
A spring 104 is provided between the spring 104 and the spring.

At the lower end of the small diameter portion of the piston rod 16, a screw 105 for closing the passage 40 is mounted. Therefore, communication between the passage 40 and the lower chamber 38 is interrupted, and the passage 40 communicates only with the upper chamber 34 and the middle chamber 36.

The member disposed on the outer periphery of the small diameter portion at the lower portion of the piston rod 16 is pressed by the spring seat 100 toward the step surface at the boundary between the large diameter portion 16a and the small diameter portion. 16 are integrally fixed.

The leaf valves 82 and 86 are pressed toward the top surfaces of the seat surfaces 92 and 94 of the main piston 32 by the urging forces of the springs 80 and 104.
When the hydraulic pressure of the lower chamber 38 becomes higher than the hydraulic pressure of the intermediate chamber 36 by a predetermined valve opening pressure P3 or more, the leaf valve 82 bends upwardly against the urging force of the spring 80 to be deformed. The valve is opened to allow the flow of the working fluid from the lower chamber 38 to the middle chamber 36. When the hydraulic pressure in the middle chamber 36 becomes higher than the hydraulic pressure in the lower chamber 38 by a predetermined valve opening pressure P4 or more, the leaf valve 86 bends and deforms downward against the urging force of the spring 104. Thus, the valve is opened, and the flow of the working fluid from the middle chamber 36 to the lower chamber 38 is allowed.

In the present embodiment, since the leaf valves 50 and 54 are formed of low rigidity thin plate members,
These valve opening pressures P1 and P2 are set to very small values. On the other hand, since the leaf valves 82 and 86 are pressed by the springs 80 and 104, respectively, the valve opening pressures P3 and P4 are set to relatively large values.

Next, the operation of the shock absorber 10 will be described. FIG. 5 shows a damping force characteristic realized by the shock absorber 10. In FIG. 5, the horizontal axis shows the displacement speed V of the piston rod 16, and the vertical axis shows the damping force F generated by the shock absorber 10. In FIG. 5, the piston rod 16 is
The damping force F when displacing in the direction of retreating from 0, that is, in the extension direction, is shown as positive.

When the piston rod 16 is displaced in the extending direction, the volume of the upper chamber 34 decreases and the volume of the lower chamber 38 increases. In order to compensate for these volume changes, the working fluid flows from the upper chamber 34 through the middle chamber 36 to the lower chamber 38. Further, when the piston rod 16 retreats from the inner cylinder 20, the volume of the inner cylinder 20 increases. In order to compensate for the increase in the volume of the inner cylinder 20, the working fluid flows from the annular chamber 21 into the lower chamber 38 via the base valve 41.

When the displacement speed V of the piston rod 16 is sufficiently low, the differential pressure between the upper chamber 34 and the middle chamber 36 and the differential pressure between the middle chamber 36 and the lower chamber 38 are small. Both the leaf valve 54 and the leaf valve 86 are kept in a closed state. Therefore, the working fluid in the upper chamber 34 flows through the communication passage 46 of the piston rod 16, the communication space 44, the clearance C, the small diameter portion 40 b of the passage 40, the communication passage 47, and the communication passage 77 of the communication member 68. The air flows into the intermediate chamber 36 through a road (hereinafter, referred to as a bypass passage). The working fluid in the middle chamber 36 flows into the lower chamber 38 through the through passage 96 of the main piston 32 and the second orifice.

In this case, when the working fluid flows through the bypass passage and the second orifice, a damping force is generated due to the flow resistance. The damping force F exerted by the shock absorber 10 includes a damping force Fa generated according to the flow resistance R1 when the working fluid flows from the upper chamber 34 to the middle chamber 36, and a damping force F generated from the middle chamber 36 to the lower chamber 38. This is the sum with the damping force Fb generated according to the flow resistance R2 when flowing. For this reason. As shown by reference numeral A1 in FIG. 5, the damping force F rises with a large gradient as the displacement speed V increases.

When the flow resistance R1 when the working fluid flows from the upper chamber 34 to the middle chamber 36 increases, the upper chamber 34 and the middle chamber 36
And the pressure difference between them rises. Further, when the flow resistance R2 when the working fluid flows from the middle chamber 36 to the lower chamber 38 increases,
The pressure difference between the middle chamber 36 and the lower chamber 38 increases. And
When the displacement speed V increases until the pressure difference between the upper chamber 34 and the middle chamber 36 reaches the valve opening pressure P2 of the leaf valve 54, the leaf valve 54 opens. Hereinafter, the displacement speed V of the piston rod 16 when the leaf valve 54 is opened and the damping force F generated by the shock absorber 10 will be referred to as a first force, respectively.
These are referred to as a valve opening speed V1 and a first valve opening damping force F1. As described above, the first valve opening damping force F1 has a very small value, for example,
The valve opening pressure P2 of the leaf valve 54 is set sufficiently small so as to be 3 to 5 kgf. When the valve opening pressure P2 of the leaf valve 54 is set as described above, the first valve opening speed V1 becomes a very low speed of 0.05 m / s or less.

When the leaf valve 54 opens, the upper chamber 34
The movement of the fluid from the inner chamber 36 to the inner chamber 36 is performed through the through passage 64 together with the bypass passage. For this reason,
The flow resistance R1 when the working fluid flows from the upper chamber 34 to the middle chamber 36 decreases. Then, as the flow resistance R1 decreases, the increasing gradient of the damping force F decreases in a region where the displacement speed V exceeds the first valve opening speed V1, as indicated by reference numeral A2 in FIG.

When the displacement speed V further increases and the pressure difference between the middle chamber 36 and the lower chamber 38 reaches the valve opening pressure P4 of the leaf valve 86, the leaf valve 86 opens. Hereinafter, the displacement speed V and the damping force F when the leaf valve 86 opens are referred to as a second valve opening speed V2 and a second valve opening damping force F2, respectively.
Called. In the present embodiment, the valve opening pressure P4 of the leaf valve 86 is set such that the second valve opening damping force F2 is, for example, about 50 kgf. In this case, the second valve opening speed V2 has a value of about 0.2 m / s.

When the leaf valve 86 is opened, the middle chamber 36
By increasing the flow passage area of the flow passage from the lower chamber 38 to the lower chamber 38,
The flow resistance R2 when the working fluid flows from the middle chamber 36 to the lower chamber 38 is reduced. For this reason, FIG.
In the region where the displacement speed V exceeds the second valve opening speed V2, the increasing gradient of the damping force F further decreases as shown by.

On the other hand, when the piston rod 16 is displaced in the direction of entering the inner cylinder 20, that is, in the contraction direction,
As the volume of the upper chamber 34 increases, the volume of the lower chamber 38 decreases. In order to compensate for these volume changes, the working fluid flows from the lower chamber 38 via the middle chamber 36 into the upper chamber 34. In addition, as the piston rod 16 enters the inner cylinder 20, the volume of the inner cylinder 20 decreases. In order to compensate for the decrease in the volume of the inner cylinder 20, the working fluid flows out from the lower chamber 38 to the annular chamber 21 via the base valve 41.

In this embodiment, the valve opening pressure P1 of the leaf valve 50 is provided so as to substantially coincide with the valve opening pressure P2 of the leaf valve 54. Therefore, when the displacement speed V reaches v1 substantially equal to the first valve opening speed V1, and the damping force F becomes f1 substantially equal to the first valve opening damping force F1,
The leaf valve 50 opens. Also, the leaf valve 82
The valve opening pressure P3 is set to be slightly smaller than the valve opening pressure P4 of the leaf valve 86. Therefore, the displacement speed V reaches v2 (for example, about 0.15 m / s) smaller than the second valve opening speed V2, and the damping force F becomes f2 (for example, about 30 kgf) smaller than the second valve opening damping force F2. At this point, the leaf valve 82 opens. Note that
The displacement speeds v1 and v2 of the piston rod 16 when the leaf valves 50 and 82 open are also referred to as a first valve opening speed and a second valve opening speed, respectively. F1 and f2, which are the damping forces F at the time of performing, are also referred to as a first valve opening damping force and a second valve opening damping force, respectively.

Therefore, even when the piston rod 16 is displaced in the contracting direction, similarly to the case where the piston rod 16 is displaced in the extending direction, until the displacement speed V of the piston rod 16 reaches the first valve opening speed v1. 5, the damping force F rises with a relatively large gradient, as indicated by reference numeral B1 in FIG. Then, the displacement speed V becomes equal to the first valve opening speed v1.
, The leaf valve 50 is opened, and FIG.
, The increasing gradient of the damping force F decreases. Further, when the displacement speed V reaches the second valve opening speed v2, the leaf valve 82 is opened, so that the increasing gradient of the damping force F is further reduced as indicated by reference numeral B3 in FIG.

As described above, according to the shock absorber 10, the displacement speed V of the piston rod 16 is in a low speed range (first range).
Damping such that the increasing gradient of the damping force F gradually decreases in accordance with the transition from the valve opening speed V1, v1 or lower region to the high speed region (region exceeding the first valve opening speed V1, v1). Force characteristics are realized.

The degree of opening of the bypass passage changes according to the size of the clearance C. As the opening degree of the bypass passage increases, the flow resistance of the working fluid flowing through the bypass passage decreases. When the flow resistance when flowing through the bypass passage decreases, the differential pressure between the upper chamber 34 and the middle chamber 36 generated for a constant displacement speed V decreases, and the damping force F decreases. That is, the gradient of the damping force characteristic is small as shown by the broken lines with the reference numerals a1 and b1 in FIG.

Therefore, by adjusting the clearance C, the displacement speed V of the piston rod 16 becomes equal to the first valve opening speed V.
1, while the damping force characteristic in a region larger than v1, that is, a high-speed region is maintained substantially constant, the first valve opening speed V
It is possible to change the damping force characteristic at 1, v1 or less. As described above, the first valve opening speed V1, v1 is 0.05
It is set to a low value of m / s or less. Therefore, according to the shock absorber 10 according to the present embodiment, by changing the clearance C, the damping of the shock absorber 10 in the low-speed region of 0.05 m / s or less without affecting the damping force characteristics in the high-speed region. Only the force characteristics can be adjusted. Further, by controlling the driving of the actuator 2 to change the clearance C stepwise, it is possible to change the gradient of the damping force characteristic of the shock absorber 10 stepwise in the low speed range of the piston rod 16.

The shock absorber 10 according to the present embodiment
According to the experiment performed using the vehicle, it is known that the riding comfort and the steering stability of the vehicle greatly change depending on the damping force characteristics in a low speed range. For example, if the clearance C is reduced to increase the gradient of the damping force characteristic in the low speed range, the steering holding force at the time of cornering increases, and the feeling of steering response increases. In addition, the responsiveness of the vehicle's rolling speed during turning and the responsiveness of the vehicle's yawing change during steering are sensitive to changes in the damping force characteristics in the low speed range. Therefore, according to the shock absorber 10 according to the present embodiment, by adjusting the clearance C and changing the damping force characteristic in the low speed range, more optimal riding comfort and steering stability can be obtained. In each of the embodiments described below, ECU 230 mainly controls the damping force characteristic in the low speed range.

Here, the damping force change control (damping force change routine) of the shock absorber 10 performed by the ECU 230 will be described with reference to the flowchart of FIG. Note that the flowchart of FIG. 6 representatively shows the damping force change control of the shock absorber 10 corresponding to the wheel L in FIG. 1, and the same damping force control is performed for the other three wheels. .

The routine shown in FIG. 6 is repeatedly executed from when an ignition switch (not shown) is turned on until it is turned off.

First, in step 100 (hereinafter referred to as "S"), the number of control steps for determining the damping force generated by the shock absorber 10 is provisionally set. This will be described based on the flowchart shown in FIG.

First, the process proceeds to S102, where the steering angle sensor 20
3, stroke sensor 220, vertical acceleration sensor 20
4. The detection result of each sensor indicating the running state of the vehicle, such as the vehicle speed sensor 205, is read.

At S104, the stroke sensor 22
Based on the relative stroke amount Y of the wheel L detected at 0,
A relative stroke speed (hereinafter, referred to as a stroke speed) Vi of the wheel L is calculated, and a sprung speed Zd, which is a vertical speed of the vehicle body 200, is calculated from a detection result of the vertical acceleration sensor 205 mounted on the vehicle body 200.

In the following S106, the speed ratio Zd / stroke speed between the stroke speed Vi calculated in S104 and the sprung speed Zd is calculated.
Based on Vi and the vehicle speed read in S102, the control step number step is set based on the skyhook control theory. The control step number step is used to set a stop position of the stepping motor serving as a drive source of the actuator 2 in the shock absorber 10.
This corresponds to the vertical position of the adjustment rod 42 within 0. As the number of control steps increases, the clearance C of the oil passage formed by the adjustment rod 42 decreases, and the damping force increases (the damping force shifts to the hard side).
The smaller the number of control steps, the larger the clearance C of the oil passage and the lower the damping force (the damping force shifts to the soft side).

At S108, it is determined whether or not the vehicle is turning, based on the detection result of the steering angle sensor 203 read at S102. For example, assuming that the detected steering angle is θ, when | θ | is larger than a predetermined turning determination constant θs, it is determined that the vehicle is in a turning state.

If "No" in S108 (the vehicle is traveling straight), the number of control steps set in S106 is maintained, and S100 is terminated as it is.

If "Yes" in S108, S11
The process proceeds to 0, and it is determined whether or not the stroke speed Vi is Vi> 0. If “Yes” is determined in S110,
This is an extension stroke in which the piston rod 16 of the shock absorber 10 is displaced to the extension side. In this case, the process proceeds to S112, where the control step number set in S106 is 1 step.
The increased value is updated as a new control step number step.

On the other hand, if “No” is determined in S110, the process proceeds to S114, and the stroke speed Vi becomes less than Vi <
It is determined whether it is 0. If “No” is determined in S114, the control step number step set in S106
Is maintained as it is, and S100 ends. If "Yes" is determined in S114, it is a contraction stroke in which the piston rod 16 of the shock absorber 10 is displaced to the contraction side. In this case, the process proceeds to S116, and the control step number set in S106 is 1 step. The reduced value is updated as a new control step number step.

During turning of the vehicle, the shock absorber 10 on the turning outer wheel side is in a contraction stroke due to the load movement,
The shock absorber 10 on the turning inner wheel side is extended. Therefore, in S100, the damping force is increased in S112 for the turning inner wheel side of the turning inner wheel, which is an extension stroke, and the damping force is increased in S116, for the turning outer wheel side of the turning outer wheel, which is in a contraction stroke. The number of control steps st so that the force decreases
ep is set. By changing the number of control steps as described above, the amount of extension of the shock absorber 10 on the turning inner wheel side is suppressed, and the shock absorber 1 on the turning outer wheel side is suppressed.
The amount of shrinkage of 0 increases. By such an operation, the height of the center of gravity of the vehicle body 200 is reduced at the time of turning, and the maneuverability at the time of turning can be improved.

After S100 is performed as described above, the process proceeds to S202 in FIG. 6, and the determination flag Fc is set according to the stroke speed Vi. When Vi is equal to or greater than the speed determination constant Vs, Fc = 1 is set, and when Vi is equal to or less than the speed determination constant -Vs, Fc = −1 is set.
When Vs <Vi <Vs, Fc = 0 is set.

At S204, the acceleration dVi of the wheel L is obtained.
/ Dt is calculated. The calculated acceleration dVi / d
t is a relative acceleration between the vehicle body 200 and the wheel L.

In subsequent S206, it is determined whether the determination flag Fc is 1, that is, whether the shock absorber 10 is in the extension stroke, and if it is determined "Yes", S2 is determined.
08, the acceleration dVi of the wheel L calculated in S204
It is determined whether / dt is 0 or more.

If "Yes" is determined in S208, the stroke speed Vi of the shock absorber 10 in the extension direction is in an accelerating state. In such a case, the process first proceeds to S210, and the current time is S210. The control step number step temporarily set in the routine is compared with the control step number step old set in the previous routine. S21
If the control step number is 0 and the control step number step is larger than the control step number step old (“Yes” in S210), the process proceeds to S212 and the control step number temporarily set in the current routine.
Step is set as the number of control steps step. Thereafter, the process proceeds to S214, and the value of the control step number step set in the current routine is stored as step old. On the other hand, when “No” is determined in S210,
Number of control steps temporarily set in this routine step
Is the number of control steps set in the previous routine step old
In the following cases, the process proceeds to S216, in which the value of the temporarily set control step number step is replaced with the previous control step number step old which is equal to or greater than the current value.
Step 14 is executed.

On the other hand, if "No" is determined in S208, the stroke speed Vi of the shock absorber 10 in the extension direction is in a decelerating state. In such a case, the process proceeds to S218. Then, the control step number step temporarily set in the current routine is compared with the control step number step old set in the previous routine.
In step S218, the control step number step becomes the control step number step.
If smaller than old (“Yes” in S218), S21
The process proceeds to step 2 and the control step number step temporarily set in the current routine is set as the control step number step.
Thereafter, the process proceeds to S214, and the value of the control step number step set in the current routine is stored as step old.
On the other hand, if “No” is determined in S218, that is, the number of control steps provisionally set in this routine
step is the number of control steps set in the previous routine
If it is equal to or more than old, the process proceeds to S216, and the value of the temporarily set control step number step is replaced with the previous control step number step old that is equal to or less than the current value, and thereafter, the above-described S214 is executed.

By executing S208 to S218 in this manner, when the shock absorber 10 is in the extension stroke,
When the stroke speed Vi is in the accelerating state, the control step number step is increased to suppress the tendency of the stroke speed Vi to accelerate, and when the stroke speed Vi is in the decelerating state, the control step number step is decreased. The tendency of the stroke speed Vi to decelerate is suppressed. Therefore, the fluctuation of the stroke speed Vi is suppressed, and the amplitude of the vertical movement of the vehicle body 200 as the sprung member is also suppressed, so that it is possible to improve both the riding comfort and the steering stability of the vehicle.

On the other hand, if "No" is determined in S206, the process proceeds to S220, and it is determined whether the determination flag Fc is -1, that is, whether the shock absorber 10 is in a contraction stroke. If “Yes” is determined in S220, the process proceeds to S222, and it is determined whether the acceleration dVi / dt of the wheel L calculated in S204 is 0 or less.

If "Yes" is determined in S222, the stroke speed Vi of the shock absorber 10 in the contraction direction is in an accelerating state. In such a case, the process first proceeds to S224, and The control step number step temporarily set in the routine is compared with the control step number step old set in the previous routine. S22
In step S4, if the control step number step is larger than the control step number step old (“Yes” in step S224), the process proceeds to step S226, where the control step number temporarily set in the current routine is set.
Step is set as the number of control steps step. Thereafter, the process proceeds to S228, in which the value of the control step number step set in this routine is stored as step old. On the other hand, when “No” is determined in S222,
Number of control steps temporarily set in this routine step
Is the number of control steps set in the previous routine step old
In the following cases, the process proceeds to S230, in which the value of the provisionally set control step number step is replaced with the previous control step number step old which is equal to or greater than the current value.
Execute 28.

On the other hand, if "No" is determined in S222, the stroke speed Vi of the shock absorber 10 toward the contraction direction is in a decelerating state. In such a case, the process proceeds to S232 and Is compared with the control step number step temporarily set in the previous routine and the control step number step old set in the previous routine. S23
If the control step number step is smaller than the control step number step old in step S2 (“Yes” in step S232), the process proceeds to step S226, where the control step number temporarily set in the current routine is set.
Step is set as the number of control steps step. Thereafter, the process proceeds to S228, in which the value of the control step number step set in this routine is stored as step old. On the other hand, when it is determined “No” in S232,
Number of control steps temporarily set in this routine step
Is the number of control steps set in the previous routine step old
In the above case, the process proceeds to S230, in which the value of the temporarily set control step number step is replaced with the previous control step number step old having a value equal to or less than the current value.
Execute 28.

By executing S222 to S232 in this manner, when the shock absorber 10 is in the contraction stroke,
When the stroke speed Vi is in the accelerating state, the control step number step is increased to suppress the tendency of the stroke speed Vi to accelerate, and when the stroke speed Vi is in the decelerating state, the control step number step is decreased. The tendency of the stroke speed Vi to decelerate is suppressed. Therefore, the fluctuation of the stroke speed Vi is suppressed, and the amplitude of the vertical movement of the vehicle body 200 as the sprung member is also suppressed, so that it is possible to improve both the riding comfort and the steering stability of the vehicle.

If "No" is determined in S220, that is, if Fc = 0, the process proceeds to S234, and
The number of control steps temporarily set to the number of control steps
The value is set as step old, and the process proceeds to S236, where the value of the control step number step set in the current routine is stored as step old.

By performing the damping force change control of the shock absorber 10 in this manner, in the graph shown in FIG. 8, in both the expansion and contraction strokes, the damping force of the shock absorber 10 is increased in the hatched region where the stroke speed Vi is accelerated. The force is increased, and the number of control steps is reduced in the area indicated by the satin finish where the stroke speed Vi is reduced.

In the embodiment described above, in the flowchart shown in FIG. 7, one step is exemplified as the number of steps to be increased or decreased in S112 or S116. However, the present invention is not limited to this example. The predetermined number of steps may be increased or decreased during the contraction stroke, and the number of steps to be increased or decreased may be set according to the magnitude of the stroke speed Vi.

[0081]

As described above, according to the vehicle damping force control device of the first aspect, the control for controlling the damping force of the hydraulic pressure buffer means based on the relative displacement direction and the change state of the relative displacement speed. Providing the means makes it possible to carry out optimal control for each stroke of expansion and contraction of the hydraulic pressure buffer means.

In the vehicle damping force control device according to the second aspect, the control means increases the damping force when the relative displacement speed is in the accelerating state and decreases the damping force in the decelerating state. , The fluctuation of the relative displacement speed between the sprung member and the unsprung member is suppressed, and a sudden change in the vehicle height is suppressed, thereby improving the riding comfort and steering stability of the vehicle. It becomes possible.

[Brief description of the drawings]

FIG. 1 is a front view schematically showing a vehicle equipped with a damping force control device according to a first embodiment.

FIG. 2 is a block diagram showing an input / output target in damping force change control and an ECU that performs control calculation.

FIG. 3 is a longitudinal sectional view of a shock absorber used in each embodiment.

FIG. 4 is an enlarged sectional view showing a main part of the shock absorber.

FIG. 5 is a graph showing a relationship between a displacement speed V of a piston rod and a generated damping force F.

FIG. 6 is a flowchart illustrating damping force change control.

FIG. 7 is a flowchart showing S100 in FIG. 6;

FIG. 8 is a graph showing an example of transition of a stroke speed, a vehicle height, and a speed derivative of the stroke speed.

[Explanation of symbols]

2 ... actuator, 10 ... shock absorber, 20
0: body, 201: steering wheel, 203: steering angle sensor, 210: suspension arm, 220: stroke sensor, 230: electronic control unit.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masahiro Murata 1 Toyota Town, Toyota City, Aichi Prefecture, Toyota Motor Corporation (72) Inventor Satoshi Suzuki 1 Toyota Town, Toyota City, Aichi Prefecture, Toyota Motor Corporation ( 72) Inventor Yoshiyuki Hashimoto 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation

Claims (2)

[Claims] 1. A vibration generated between a sprung member and a unsprung member of a vehicle is damped by a predetermined damping force, and the damping force is variable in a region where the relative speed between the sprung member and the unsprung member is low. A hydraulic pressure buffer having a function; a displacement state detecting means disposed corresponding to the hydraulic pressure buffer to detect a relative displacement between the sprung member and the unsprung member; and detection of the displacement state detecting means. A damping force control device for a vehicle, comprising: control means for controlling a damping force of the hydraulic pressure buffer means based on a relative displacement direction and a change state of a relative displacement speed obtained from the result. 2. The control means increases the damping force of the hydraulic pressure buffer when the relative displacement speed is in an accelerating state,
2. The vehicular damping force control device according to claim 1, wherein the damping force of the hydraulic pressure buffer is reduced in a deceleration state.