JPH045116A - Shock absorber for change in damping force of automobile - Google Patents

Abstract

PURPOSE:To prevent application of a shock due to a rapid change in the damping force by providing a valve member in a piston member sectioning the interior of the cylinder member into upper/lower fluid chambers, and advancing this valve member via an auxiliary piston driver through operation of an actuator to thereby secure a sufficient length of reset time. CONSTITUTION:A shock absorber for any change in damping force of an automobile comprises a cylinder member 1 in which a viscous fluid is sealed. The interior of this cylinder member 1 is sectioned by a piston member 2 into fluid chambers 1a, 1b. The piston member 2 is interiorly formed with a main flow passage 11 communicating the fluid chambers 1a and 1b with each other, the main flow passage 11 being provided with a valve member 3 for changing the cross-sectional area of the flow passage. In this case, a plunger 4 is provided in a manner that one end thereof abuts on the valve member 3 to drive this valve member 3, the other end of the plunger 4 being exposed in a closed chamber 2a. Further, an auxiliary piston 5 is provided which is larger in size than the plunger 4 and which is to be driven by an actuator 6. A part of the side wall of the closed chamber 2a is formed in the auxiliary piston 5, whereby the valve member 3 is advanced in accordance with the extending operation of the actuator 6 so as to make small the cross-sectional area of the flow passage in accordance with the amount advanced of the valve member 3.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a variable damping force shock absorber for a vehicle.
In particular, it relates to improvements in its structure.

[Prior Art] Shock absorbers with variable damping force are used, which can change the damping force generated depending on the running condition of the vehicle, and can always provide good ride comfort and steering stability. As shown in FIG. 2, this shock absorber S has a piston member 2 slidably disposed within a cylinder member 1 filled with hydraulic oil. It is divided into a side fluid chamber 1b.

The piston member 2 has a cylindrical shape extending vertically, and a throttle flow path 12 that is opened and closed by a check valve and communicates the two fluid chambers is formed on the outer periphery of the lower end, and a main flow passage 12, which will be described in detail later, is formed in the center of the lower end. A channel 11 is formed.

This shock absorber S is connected to a suspension arm (not shown) via a bushing arranged in an eye 13 at the lower end of the cylinder member 1, and the tip of a piston rod 9 extending upward from the piston member 2 is fixed to a vehicle body having a concave road. has been done. In the figure, reference numeral 14 designates a spring support member, and a coil spring is provided between this and the vehicle tenon.

A cross section of the main part of the piston member 2 is shown in FIG.
1a, and this vertical portion 11a extends below the valve member 3, passing through the valve member 3 to reach the fluid chamber 1a above the left and right horizontal portions 11b.

The valve member 3 is a cylindrical body having a partition wall 31 in the middle part,
It is held in the piston member 2 so as to be able to freely slide up and down, and is biased upward by a coil spring 32 whose one end is in contact with the lower surface of the partition wall 31, so that the lower end flange 33 of the coil spring 32 is brought into contact with the channel wall and the above-mentioned The space between the vertical portion 11a and the horizontal portion 11b is closed.

The lower end of a plunger 4, which is held movably up and down and is urged downward by a coil spring 41, is in contact with the upper surface of the partition wall 31. It is exposed to chamber 2a.

This sealed chamber 2a is constituted by a large-diameter auxiliary piston 5 on the side opposite to the exposed side of the plunger 4, and the piston 5, which is vertically movable, is urged upward by a disc spring 21 in the sealed chamber 2a. At the same time, the tip of a pressing member 61 having a piezo actuator 6 installed therein is in contact with the back surface thereof.

A flow path communicating with the space in which the coil spring 41 is disposed is formed in the sealed chamber 2a, and a check valve 7 is provided in the middle of the flow path. This check valve 7 opens when the pressure on the sealed chamber 2a side decreases.

In the variable damping force shock absorber having such a structure, when the piezo actuator 6 is energized to extend it, the auxiliary piston 5 moves downward and fills the sealed chamber 2a.
The volume of the plunger 4 is reduced, and the plunger 4 is moved downward to compensate for this reduction. Since the plunger 4 has a sufficiently smaller diameter than the auxiliary piston 5, its movement amount becomes large.

Due to the downward movement of the plunger 4, the valve member 3 is activated by the coil spring 3.
It moves downward against the spring force of No. 2, and the flange 33 moves away from the channel wall, and the flow cross-sectional area of the main channel 11 increases in accordance with the amount of movement. As a result, the flow resistance of the hydraulic oil flowing between the upper and lower fluid chambers 1a and 1b via the main flow path is reduced, and the damping force generated by the shock absorber is accordingly reduced.

By the way, when the plunger 4 is moved downward and the valve member 3 is kept at a predetermined opening degree, oil leaks from the sealed chamber 2a through the outer periphery of the plunger 4, and if this is left unattended, the plunger 4 will move upward. The valve member 3 moves back and the opening degree of the valve member 3 changes. Conventionally, the piezo actuator 6 is contracted to its original position at regular intervals (hereinafter referred to as "reset"), and the pressure in the sealed chamber 2 is reduced by the amount of the insufficient hydraulic fluid.
Hydraulic oil is replenished into the tank a by opening the check valve 7.

The variable damping force shock absorber is, for example, disclosed in Japanese Patent Application Laid-open No. 6
An example thereof is described in Japanese Patent No. 1-85210.

[Problems to be Solved by the Invention] By the way, if the piezo actuator is rapidly contracted and re-extended during reset, a shock may be applied to the vehicle tenon due to a sudden change in the generated damping force, causing abnormal noise. It is necessary to operate the piezo actuator over a certain period of time. Furthermore, in order to completely replenish the leaked hydraulic oil, it is necessary to maintain the contracted state of the piezo actuator for a certain period of time in order to ensure sufficient operating time for the auxiliary piston.

However, in the above conventional shock absorber,
During this reset, the valve member closes and the generated damping force becomes large, or hard, so if high-frequency vibrations are input during this period, this vibration will be transmitted to the vehicle body, causing discomfort to the occupants. Therefore, it is necessary to shorten the contraction state of the piezo actuator. As described above, it has been difficult to balance the conflicting demands of wanting to lengthen the reset time to prevent abnormal noise and the like and making the reset time as short as possible to prevent the transmission of vibrations.

The present invention solves this problem by effectively preventing the transmission of high-frequency vibrations during reset operation, thereby ensuring sufficient reset time to avoid shocks caused by two changes in damping force, and allowing An object of the present invention is to provide a variable damping force shock absorber for a vehicle that can effectively replenish insufficient hydraulic oil.

[Means for Solving the Problems] To explain the present invention in detail, a piston member 2 moves the inside of a cylinder member 1 containing a viscous fluid into upper and lower fluid chambers 1a,
1b, and forms a main flow path 11 in the piston member 2 that communicates between the upper and lower fluid chambers 1a and 1b, and is interposed in the main flow path 11 to change its flow cross-sectional area. A plunger 4 is provided, one end of which abuts against the valve member 3 to drive it forward, and the other end is exposed to a sealed chamber 2a formed within the piston member 2. 6
The auxiliary piston 5 driven by the auxiliary piston 5 moves the valve member 3, which forms a part of the side wall of the sealed chamber 2a and is driven to advance as the actuator 6 extends, to the flow cross-sectional area according to the amount of advance. It is molded to make it smaller.

[Function] In the above configuration, when the actuator 6 is extended, the auxiliary piston 5 is activated and the volume of the sealed chamber 2a is reduced, and the plunger 4 is moved to compensate for this, causing the valve member 3 to advance, thereby reducing the volume of the sealed chamber 2a. The flow cross-sectional area becomes smaller in accordance with the amount of advancement, producing a predetermined damping force.

When the actuator 6 is retracted to its original position at the time of reset, the auxiliary piston 5 is retracted, and the plunger 4 is accordingly retracted, and viscous fluid is supplied to the low pressure sealed chamber 2a via the check valve 7. Ru. At this time, the valve member 3 moves back together with the plunger 4, and the flow cross-sectional area of the main flow path 11 increases accordingly. As a result, the damping force generated by the shock absorber becomes small, that is, soft.

Therefore, even if the reset operation takes a sufficient amount of time, high-frequency vibrations are not transmitted during this time, and the operation of the valve member 3 is made sufficiently slow to prevent shocks caused by sudden changes in the generated damping force. By holding the piston 5 in the retracted position for a sufficient period of time, the viscous fluid can be effectively replenished into the sealed chamber 2a.

Note that at the time of this reset, the vibration damping force decreases, or since the large vibration has a low frequency, its period is sufficiently long compared to the reset time, and there is no substantial effect.

[Embodiment] An embodiment of the present invention will be described below with reference to FIG. 1 showing the main parts of a shock absorber.

In the figure, a valve member 3 that slides up and down is disposed inside the piston member 2, and this valve member 3 has a partition wall 31 in the middle part.
It is a cylindrical body with The vertical portion 1 of the main flow path 11 is inserted into the lower half of the valve member 3 from the lower fluid chamber 1b (FIG. 2).
1a, and a coil spring 32 for biasing the valve member 3 upward is provided in this lower half.

A groove-shaped port portion 34 is formed on the outer periphery of the lower half of the valve member 3, and the boat portion 34 communicates with the inside of the lower half through a through hole 35. Therefore, the main flow path 11 passes from the vertical portion 11a through the through hole 35 and the boat portion 34 to the horizontal portion 11.
b, and reaches the upper fluid chamber 1a.

A plunger 4 extends from above into the upper half of the valve member 3, which communicates with the lower half through a through hole 36 provided in the partition wall 31, and its lower end abuts the upper surface of the partition wall 31. The plunger 4 is held movable up and down, and the flange 42 formed on the outer periphery abuts against the earthen wall of the space in which the valve member 3 is housed, and is positioned at the retreating end, and its upper end is located in the sealed chamber 2a formed at the upper position. exposed on the lower wall of the In the illustrated state in which the plunger 4 is at the retracted end, the boat portion 34 on the outer periphery of the valve member 3 communicates between the vertical portion 11a and the horizontal portion 11b of the main stream B11 with the maximum flow cross-sectional area.

The earthen wall of the sealed chamber 2a is constituted by an auxiliary piston 5 that is movable up and down, and the movable end of a piezo actuator 6 is in contact with the back surface of the piston 5. A flow path 71 is formed connecting the sealed chamber 2a and the space above the valve member 3, and a check valve 7 is disposed in the flow path. 20 The check valve 7 opens when the pressure on the sealed chamber 2a side becomes low.

In the shock absorber having the above structure, the piezo actuator 6 is extended by a predetermined amount during damping force control;
Along with this, the plunger 4 and the valve member 3 move downward, and the flow cross-sectional area of the main flow path 11 that communicates with the port portion 34 becomes a predetermined small value.

At the time of reset, the piezo actuator 6 is contracted to its original position, and the auxiliary piston 5, plunger 4, and valve member 3 are also moved upward and backward. Then, as the pressure in the sealed chamber 2a decreases, the check valve 7 opens, and after the insufficient hydraulic oil is replenished, the piezo actuator 6 is again extended by the predetermined amount.

During this reset operation, the flow cross-sectional area of the main flow path 11 increases as the valve member 3 retreats, and the damping force generated by the shock absorber decreases, shifting to a soft characteristic.

Even if high-frequency micro-vibrations are input during this period, they are well absorbed and are not transmitted to the vehicle body side, so that the contraction and re-extension of the piezo actuator 6 are made sufficiently gradual. Therefore, shocks due to sudden changes in the generated damping force will not occur.

In addition, by ensuring sufficient time for contraction of the actuator 6, it is possible to reliably replenish the hydraulic oil to the sealed chamber 2a.

During the above-mentioned reset operation, the characteristics of the shock absorber shift to the soft side, so the damping performance against low-frequency, large-amplitude vibrations at this time decreases, but the period of such vibrations is long, and the time required for reset is compared to this. is short enough to have no real effect.

An example of damping force control using the above-mentioned shock absorber will be explained below with reference to FIG.

As shown in FIG. 4, the electronic control device 8 includes CPUs 8a, R
It is configured as a logic operation circuit centered around OM8b and RAM8c, and is connected to an input section 8e and an output section 8 via a common bus 8d.
It is connected to f and performs input/output with the outside. The electronic control device 8 also includes piezo load sensors 31FL, 31FR131RL, and 31R built into the shock absorber.
From the electric charge generated by R, each shock absorber 2FL,
A damping force change rate detection circuit 85 that detects the rate of change in the damping force of 2PR12RL and 2RR, and a waveform shaping circuit 86 that shapes the waveform of the detection signal from the vehicle speed sensor 81 are provided. The results are input to the input section 8e. Furthermore, the electronic control device 8 is configured to control each piezo actuator 19F by a control signal representing a target charge of each piezo actuator 19FL to 19RR outputted from the CPU 8a via an output section 8f.
A driving recess 687 is provided that controls the amount of electric charge of L to 19RR to expand and contract each piezo actuator 19FL to 19RR, thereby switching the damping force characteristics of each shock absorber 2FL to 2RR.

Here, the damping force change rate detection circuit 35 detects each shock absorber 2FL, 2FR12 based on the detection signal from each piezo load sensor 31FL, 31FR131RL, 31RR.
The road surface condition is detected by the expansion/contraction acceleration of RL and 2RR, and as shown in Fig. 5, each piezo load sensor 31FL
, 31FR131RL, 4 detection circuits 41FL, 41FR141RL, 41R provided corresponding to 31RR.
R and each detection circuit 41FL, 41FR141RL, 41
It is composed of A/D converters 42FL, 42FR142RL, and 42RR that convert the output signal from RR into a digital signal.

Taking the detection circuit 41FL as an example, each detection circuit 41FL
, 41FR141RL, and 41RR operations will be explained.

As shown in FIG. 5, the detection circuit 41FL is first provided with a resistor R1 connected in parallel to the piezo load sensor 31FL. Since electric charges corresponding to the damping force are generated at both ends of the piezo load sensor 3IFL due to the expansion and contraction of the shock absorber 2FL, the generated electric charges move through the resistor R1, and the damping force of the shock absorber 2FL is transferred to the resistor R1. A current flows every time the value changes, and the current value becomes a value representing the rate of change in the damping force of the shock absorber 2FL. Therefore, in this embodiment, detection diagram #! 41FL
The current flowing through the resistor R1 is detected by the voltage across the resistor R1, and the value is sent to the A/D converter 42FL as a detection signal representing the damping force change rate of the shock absorber 2PL.
It is designed to output to .

That is, in the detection circuit 41FL, a voltage signal across the resistor R1 is first passed through the resistor R2, and then connected to the two coils L1,
The signal is input to a radio noise removal filter EMI consisting of L2 and capacitor C1, and high frequency components such as radio noise are removed. The voltage signal from which radio noise has been removed is then input to a bypass filter HPF consisting of a coupling capacitor C2 and a resistor R3 applied to an offset voltage (2V), where low frequency components of 0.1Hz or less are removed. At the same time, it is increased by 2V, and further resistor R4 and capacitor C
It is input to a low pass filter LPF consisting of 100
After high frequency components above Hz are removed, the operational amplifier OP
It is output to the A/D converter 42FL via a buffer consisting of I.

Therefore, in the detection circuit 41FL, when there is a protrusion on the road surface as shown in FIG. (voltage at point a in Fig. 5) changes, and 0.1 to 0.1 of the voltage signal
A voltage signal as shown in FIG. 6(B) obtained by adding 2.times. to the 100 Hz signal component is generated as the damping force change rate signal VFL.

In addition, bypass filter HPF and low pass filter L
By PF, from the voltage across resistor R1, 0.1~
The reason why the voltage signal of the frequency component of 100 Hz is extracted is because the shock absorber 2FL expands and contracts in this frequency range.

Further, in FIG. 5, diodes D1 and D2 are protection diodes for protecting the operational amplifier OPI so that the input voltage of the operational amplifier OP1 is in the range of 0 to 5V.

Next, as shown in FIG.
The high voltage generation circuit 761 is configured to convert the voltage into a high voltage and store it in the capacitor 741.
Charge control circuits 80FL and 80FR that control the amount of charge of R
It consists of 180RL and 80RR.

Each of the charge control circuits ff1OFL to ff80RR will be described below, taking the charge control circuit 80FL as an example.

First, the charge control circuit 80FL includes a capacitor C8 connected in series to the piezo actuator 19FL, and a CPU
A D/A converter 821 for converting the control signal from 4a into a voltage signal is provided.

The capacitor C8 is for detecting an amount equivalent to the electric charge of the piezo actuator 19FL, and has a capacitance sufficiently larger than that of the piezo actuator 19FL.

The voltage of this capacitor C8 (capacitor voltage) Vc is
A voltage (command voltage) Vs that is input to the comparator 861 via the buffer 84] and obtained by the D/A converter 821 and represents the target charge amount of the piezo actuator 19FL.
It is compared in size. The output end of the comparator 861 is connected to the photocoupler 881 via the NOT circuit NOT 1, and to the photocoupler 90 via the NOT circuits N0T2 and N0T3. The comparator 861 turns off the photocoupler 881 and turns on the photocoupler 90 when the command voltage Vs is larger than the capacitor voltage Vc, so that the capacitor voltage Vc is between the command voltage and
'S or more, the photocoupler 881 is turned on,
The photocoupler 90 is turned off.

The photocouplers 881 and 90 are charging FETs that supply electric charge to the piezo actuator 19FL.
92 and the piezo actuator 19FL. When the photocoupler 881 is turned off, the charging FET 92 is turned on, and when the photocoupler 90 is turned off, the discharge FET 94 is turned on and off. E, T 94 are turned on.

When the charging FET 92 is in the on state, the voltage across the resistor R21 provided in the charging path from the charging FET 92 to the piezo actuator 19FL is set to be determined by the variable resistor VRI that divides the battery voltage. The charging current to the piezo actuator 19FL is controlled by an operational amplifier 96 consisting of an operational amplifier ○P5 that controls the bias voltage of the charging FET 92 so that the
When the discharge FET 94 is in the on state, the voltage across the resistor R22 provided in the discharge path from the piezo actuator 19FL to the ground becomes the set voltage determined by the variable resistor VR2 that divides the battery voltage. Operational amplifier O that controls the bias voltage of discharge FET94
A differential amplifier 98 composed of P6 controls the discharge current from the piezo actuator 19FL.

In the charge control circuit 80FL configured in this way, when the capacitor voltage Vc becomes approximately equal to the command voltage Vs, each FET 9 is controlled at a frequency determined by the characteristics of the control system.
2.94 turns on and off, piezo actuator 19F
The amount of charge of L is controlled to the target amount of charge set by the CPU 4a. In addition, each FET92 is included in the operational amplifier OP5 and ○P6.
．． Resistors R2B and R24 and capacitors C9 and CIO provided in the signal system to 94 create a time delay when each FET 92. This is to reduce power consumption when the amount is reached.

Next, the shock absorber damping force switching control executed by the CPU 4a will be explained.

Figure 8 shows each shock absorber, 2PL, 2FR2RL
, CPt to switch and control the damping force characteristics of 2RR.
This shows the damping force switching process repeatedly executed in J4a.

As shown in FIG. 8(A), in the damping force switching process, first, in step 100, an initialization process is performed to initialize counters, etc. used in subsequent processes, and then in step 1
At 10.120, based on the detection signals from the vehicle speed sensor 3 and the damping force change rate detection circuit 35, the vehicle speed S and the damping force change rate signals VFL, VFRlVRL, and VRR of each shock absorber 2FL, 2FR12RL, and 2RR are read.

In the subsequent step 130, soft switching upper limit values Vr, efl and soft switching lower limit value Vref2 of the damping force change rate signal according to the vehicle speed S are set using a map as shown in FIG. Subsequently, in step 10, a speed switching upper limit value Vsrefl and a speed switching lower limit value Vsref2 of the damping force change rate signal according to the vehicle speed S are set using the same map. Next, in steps 150 to 180, each shock absorber 2
The switching control of the damping force characteristics is performed for each of F, L, 2FR52RL, and 2RR, and the process returns to step 110, which is repeated.

Note that the soft switching upper limit value V set in step 130 above
refl and the soft switching lower limit value Vref2 are thresholds for detecting road surface irregularities based on the damping force change rate signal. Also, the speed switching upper limit value Vsrefl and the speed switching lower limit value Vsref2 set in step 140 above.
is for each shock absorber 2 based on the damping force change rate signal.
This is a threshold value for setting the switching speed when switching the damping force characteristics of FL, 2FR12RL, and 2RR to small (soft) (corresponding to the time it takes to change the damping force characteristics from large to small).

Further, the damping force switching control executed for each shock absorber 2PL, 2FR12RL, and 2RR in steps 150 to 180 is executed as shown in FIG. 8(B). In addition, in Fig. 8 (B), the left front wheel is 5F at step 150.
This shows the damping force switching control executed for the shock absorber 2FL provided at the shock absorber 2FL, taking the damping force switching control of the shock absorber 2PL executed at step 150 as an example, and each step 150 to The process of step 180 will be explained.

As shown in the figure, in the damping force switching control of the shock absorber 2FL, step 200 is first executed, and the step 1 described above is executed.
It is determined whether the vehicle speed S determined in step 10 is greater than 0 and the vehicle is in a running state. If it is determined in step 200 that the vehicle is stopped, the process proceeds to step 210, where a time counter CT4, which will be described later, is reset, and the process proceeds to step 300.

On the other hand, if it is determined in step 200 that the vehicle is in a running state, the process moves to step 220, and the step 120 described above proceeds to step 220.
It is determined whether the damping force change rate signal VFL of the shock absorber 2F-L read in step 130 exceeds the soft switching upper limit value Vrefl set according to the vehicle speed S in step 130 above. If VFL≦Vrefl, the process moves to step 230, and it is then determined whether the damping force change rate signal VFL has fallen below the soft switching lower limit value V r e f 2 set above.

Next, if it is determined in step 220 that VFL>Vre41, or in step 230, VFL<Vref2.
If so, it is determined that there are irregularities on the road surface, and the process moves to step 240, where the time counter CT1 is programmed with software that is set according to the vehicle speed S using a map as shown in FIG. Set the holding time TS. Next, the process moves to step 250, and it is determined whether the damping force change rate signal VFL exceeds the speed switching upper limit value Vsrefl, which was set in step 140 according to the vehicle speed S.
If ≦Vsrefl, the process moves to step 260, and it is then determined whether the damping force change rate signal VFL has fallen below the set speed switching lower limit value Vsref2. VFL
<Vsref2 or VF L>Vs in step 250
If it is determined that r e f 1, the process moves to step 270, and the charge control circuit 80 described above is activated to quickly switch the damping force characteristic of the shock absorber 2FL to small (soft).
Outputs a control signal to FL. That is, Figure 6 (D)
As shown at time t1, the command voltage Vs (D/
The fall time (time t1) of the output voltage of the A converter 82
to time t2) to quickly switch to the low level. At this time, the piezo actuator 19
Since the charging voltage applied to FL corresponds to this command voltage ■S, the piezo actuator 19FL is charged at that speed, and the damping force characteristic is switched quickly and softly.

If it is determined in step 260 that VFL≧Vsref2, that is, if Vsrefl≧VFL≧Vsref2, the process moves to step 280, and the shock absorber 2F
A control signal is output to the charge control circuit 80FL in order to slowly switch the damping force characteristic of L to small (soft). That is, as shown at time t5 in FIG. 6(D), the command voltage V
The falling time of S (the time from time t5 to time t6) is lengthened to slowly charge the piezo actuator 19FL.

Note that the time counter CTI for which the soft hold time TS is set in step 240 is a counter that is counted down at predetermined time intervals until it reaches 0 in a time measurement process (not shown). As a result, the elapsed time after the damping force characteristic is switched to soft is measured.

Next, in step 270 or step 280, if the damping force characteristic of shock absorber 2 F L is switched to small (soft), or in step 230, VFL≧
If it is determined to be Vref2, the process moves to step 290, and it is determined whether the time counter CTI is 0 or not.

In other words, the time counter CTI is set to the soft holding time TS when the damping force characteristic is switched to small, and thereafter counted down at predetermined time intervals in a time measurement process (not shown). Therefore, here, by determining whether the time counter CT1 is 0 or not, the damping force change rate signal VFL is set to the soft switching upper and lower limit value Vre f 1
, Vre f 2, it is determined whether or not the time within the predetermined range set by Vre f 2 continues for longer than the soft retention time TS.

If it is determined in this step 290 that the time counter CTI is not 0, this process is temporarily terminated, and conversely
If T1=0, the process moves to step 300, and a control signal is output to the charge control circuit 80FL in order to restore the damping force characteristic of the shock absorber 2FL to a large (hard) level. As shown, when it is determined that the time counter CTI is 0 at time t3 (or time t7), the command voltage Vs is slowly switched to a high level (lengthening the time from time t3 to time t4).

At this time, in step 310, counting of time TH (for example, several seconds) is started from time t7, and the hardware state time T
If H has passed, refresh processing is performed. During processing, the piezo actuator is operated at a speed that does not cause oil hammering noise. In this case t9~tlo
The time is approximately 50m5. tlo ~ tll (about 50
In m5), the soft state is maintained until the hydraulic oil is reliably replenished, and the piezo actuator is charged at a speed that does not generate oil hammering noise again (t11 to t12>).

Here, if the hard damping force and the soft damping force are frequently switched, the oil seal chamber is replenished with oil when the soft damping force is applied, so the refresh process is not performed (if NO in step 310).

In addition, when controlling the damping force continuously, the time during which the movement of the spool is held by the hydraulic oil (i.e., the applied voltage of the piezo actuator is in a state other than zero) is measured, and refreshed when a predetermined period of time has elapsed. Process.

[Effects of the Invention] As described above, according to the variable damping force shock absorber of the present invention, sufficient reset time for the actuator can be ensured while preventing the transmission of high-frequency vibrations, so that shocks caused by sudden changes in the damping force generated due to reset can be prevented. will not occur,
Furthermore, it is possible to reliably replenish the viscous fluid leaked from the sealed chamber and prevent fluctuations in the damping characteristics.

[Brief explanation of drawings]

Figures 1 and 2 show an embodiment of the present invention, Figure 1 is an enlarged sectional view of the main parts of a shock absorber, Figure 2 is a longitudinal sectional view of the entire shock absorber, and Figure 3 shows a conventional structure. 4 is a block diagram of the electronic control unit, 5 is a circuit diagram of the damping force change rate detection circuit, 6 is a signal time chart, and 7 is a circuit diagram of the drive circuit. Figure 8 is a program flowchart, Figure 9 is an explanatory diagram showing a map for setting the threshold value from the damping force change rate signal, and Figure 10 is a map for setting the soft holding time from the vehicle speed. The explanatory diagram, FIG. 11, is an explanatory diagram showing a map for setting the switching speed based on the vehicle speed. 1... Cylinder members 1a, 1b... Fluid chamber 11... Main flow path 2... Piston member 2a... Sealed chamber 3... Valve member 4... Plunger 5... Auxiliary piston No. Figure 1 Figure 3 Figure 7 Figure 8 (A) Figure 8 (B) Figure 9 Speed Figure 10 Medium speed S Figure 11 Skewer speed

Claims (1)

[Claims] The inside of a cylinder member containing a viscous fluid is divided into upper and lower fluid chambers by a piston member, and a main flow path that communicates between the upper and lower fluid chambers is formed within the piston member, and a A valve member for changing the cross-sectional area of flow is provided, and a plunger is provided with one end abutting the valve member and driving the valve to move forward, and the other end is exposed to a sealed chamber formed within the piston member, and the plunger has a lower end than the plunger. A large auxiliary piston driven by an actuator constitutes a part of the side wall of the sealed chamber, and the valve member is driven to advance as the actuator extends, and the flow cross-sectional area is adjusted according to the amount of advance of the valve member. A variable damping force shock absorber for a vehicle, characterized by being formed to be small.