JP2748121B2 - Variable damping force type hydraulic shock absorber - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a variable damping force type hydraulic shock absorber for a vehicle such as an automobile, and more particularly, to a variable damping force capable of changing a damping force for each cycle of road surface vibration. The present invention relates to a mold hydraulic shock absorber.

(Prior Art) In recent years, there has been a tendency for compatibility between comfort and running stability to be required in accordance with sophistication of requirements for vehicles. for that reason,
A damping force variable type hydraulic pressure that increases or decreases the damping force according to the running condition and generates a low damping force that improves riding comfort during normal driving and a high damping force that enhances running stability when a vehicle roll occurs Shock absorbers are also widespread.

As this kind of conventional variable damping force type hydraulic shock absorber,
For example, one described in JP-A-61-85210 is known. In this device, a single piezoelectric element (that is, four) provided in each of the four shock absorbers detects the hydraulic pressure in the cylinder generated in response to the road surface vibration, and the controller determines the magnitude of the hydraulic pressure. Based on the above, the voltage is ignited to the piezoelectric element to switch the damping force from software to hardware. The switching of the damping force between software and hardware is performed at a low vibration frequency that causes displacement of the vehicle body and when the magnitude of the electromotive force generated by two of the four piezoelectric elements exceeds a set value,
It is continued for a predetermined time.

That is, the damping force is maintained hard during the predetermined time regardless of the pressure stroke and the extension stroke, and the hydraulic pressure is not detected within the predetermined time.

(Problems to be Solved by the Invention) However, in such a conventional variable damping force type hydraulic pressure buffer device, a single piezoelectric element is used as a hydraulic pressure sensing device and an actuator for increasing and decreasing the damping force by applying a voltage. Since it is configured to switch and use and make the damping force characteristic hard for a predetermined time according to the detection signal, it is not possible to perform sensing within the above-mentioned predetermined time, so if independent control is performed for each of the pressure stroke and the extension stroke, In addition, there is a problem that sufficient control cannot be performed on the second and subsequent input vibrations among the continuous input from the road surface. For example, for the pressure-side input after the first time, a high damping force acts as a vibration source on the contrary, and the vibration damping property is deteriorated. As a result, it is impossible to achieve both riding comfort and running stability.

In addition, since the magnitude of the hydraulic pressure, that is, the speed of the vibration is used as the vibration information, and the magnitude of the vibration is determined, the hardware is maintained when the hydraulic pressure is equal to or higher than the set value. If the vibration having a large vibration speed is continuously input, the hydraulic pressure is maintained at a high level, and the hardware is maintained for a long time, thereby deteriorating the riding comfort.

(Objects of the Invention) Accordingly, the present invention detects the hydraulic pressure on the compression side and the hydraulic pressure on the extension side separately, and makes the damping force variable based on the detected value of the hydraulic pressure or the detected value and the rate of change thereof. Provided is a hydraulic pressure absorbing device having a configuration that improves responsiveness, precisely changes a damping force for each vibration cycle of a vehicle, and achieves both riding comfort and running stability even with continuous vibration input. . It is intended to be.

(Means for Solving the Problems) In order to achieve the above object, a variable damping force type hydraulic shock absorber according to the present invention is characterized in that, in claim 1, only the hydraulic pressure on the pressure side of the shock absorber is independently used as a first pressure signal. A first detecting means for detecting, a second detecting means for independently detecting only a hydraulic pressure on the extension side of the shock absorber as a second pressure signal, and a first for changing the damping force on the compression side of the shock absorber.
Operating means, a second operating means for changing the extension-side damping force of the shock absorber, and the first or second pressure signal detected by the first or second detecting means, and (2) calculating the rate of change of the pressure signal and selectively driving one of the first or second operating means based on the rate of change and the first or second pressure signal corresponding thereto; Control means for outputting a control value to be stopped.

Further, the invention according to claim 2 is characterized in that the control means continuously determines the magnitude of the change rate from the change rate obtained by calculation, and when the control means confirms that the extreme value has been reached, the first or the second is performed. 2
Is energized, and when it is confirmed that the rate of change is equal to or less than a predetermined value, the energization of the first or second operating means is stopped.

Further, the invention according to claim 3 is characterized in that the predetermined value is zero.

(Operation) The hydraulic pressure on the compression side during the compression stroke is independently detected by the first detection means, and the hydraulic pressure on the compression side during the extension stroke is independently detected by the second detection means.

The control means, which has received the hydraulic pressure signal detected in this manner, differentiates the hydraulic pressure signal with respect to time to calculate the rate of change of hydraulic pressure, that is, the acceleration of vibration. Alternatively, energization / stop is performed for one of the second operation means, and the damping force is switched between hardware and software. At this time,
The determination is made based on whether the first or second operating means is driven or whether the hydraulic pressure signal itself becomes zero to determine whether the stroke changes. By driving each operating means in this way, the damping force is continuously controlled based on the hydraulic pressure detected continuously during the extension / pressure stroke.

Hereinafter, the present invention will be described with reference to the drawings.

2 to 5 are views showing one embodiment of a variable damping force type hydraulic pressure buffer device according to the present invention.

First, the configuration will be described. FIG. 2 is an overall configuration diagram of the shock absorber, FIG. 3 is a sectional view of a main part thereof, FIG. 4 is an overall configuration diagram of the system, and FIG. 5 is a diagram showing a control circuit of a part thereof.

In FIG. 2, reference numeral 1 denotes a variable damping force type shock absorber. The shock absorber 1 is a sealed outer cylinder 2
A cylinder 3 built in the outer cylinder 2, a piston 4 sliding axially on the inner wall of the cylinder 3, a bottom valve 5 provided at a lower end of the cylinder 3, and a piston rod 6 supporting the piston 4. , A reservoir chamber 7 formed by the inner wall of the outer cylinder 2 and the cylinder 3, a rod guide 8 for supporting the piston rod 6, a piston seal 9 provided on the upper part of the rod guide 8, and closing the upper part of the outer cylinder 2 And a stopper plate 10.

The cylinder 3 has a bottom body 12 having a communication hole 11 at a lower end.
The opening is closed by the rod guide 8. The inside of the cylinder 3 is moved by the piston 4 to the upper liquid chamber 14.
And the lower liquid chamber 15, and the hydraulic fluid in the two chambers mutually flows through communication holes 46 to 48 provided in the piston 4, which will be described later.

The piston 4 has an extension valve that generates damping force during the extension stroke.
A spring 17 for urging the expansion valve 16 and the extension side valve 16 upward is provided. The lower end of the spring 17 is fixed to the piston 4 by an adjust nut 18 and a lock nut 19, and an adjust nut 20 is screwed to the lower end of the piston 4.

The bottom valve 5 includes a check valve 21 that opens during the extension stroke,
Port through which hydraulic fluid flows in when check valve 21 opens
22, a pressure side valve 23 that opens in the pressure stroke, an orifice 24 that allows the hydraulic fluid in the reservoir chamber 7 to flow from the lower liquid chamber 15 when the pressure side valve 23 opens, and a stopper plate 25 that regulates the opening of the check valve 21. And a caulking pin 26 for fixing the check valve 21 and the like to the bottom body 12. In the extension stroke, the hydraulic fluid in the reservoir chamber 7 opens the check valve 21 by the negative pressure in the lower liquid chamber 15 and flows into the lower liquid chamber 15. At this time, the check valve 21 is regulated by the stopper plate 25 so as not to open more than a certain amount. In the pressure stroke, the hydraulic fluid in the lower liquid chamber 15 opens the pressure valve 23 to generate a damping force corresponding to the positive pressure in the lower liquid chamber 15, and passes through the communication hole 11 to the reservoir chamber 7. Inflow. The pressure in the upper liquid chamber 14 and the lower liquid chamber 15 is generated according to the magnitude of the vibration of the vehicle. By detecting the pressure, the input state of the vibration to the vehicle, that is, the running state can be detected.

A retainer 27 is fixed to the piston rod 6,
The collision between the piston 4 and the rod guide 8 is mitigated by the retainer 27 together with the elastic rebound stopper 28 provided on the upper part.

The lower portion of the stopper plate 10 is fitted to the upper end of the cylinder 3, and the piston rod 6 passes through the central through hole 10a.

The outer cylinder 2 accommodates the cylinder 3, the rod guide 8 and the piston seal 9 inside, and is formed by caulking the upper end. The inner periphery of the piston seal 9 is provided with a main lip 29 which elastically contacts the piston rod 6 to maintain the liquid tightness inside and a dust lip 30 for preventing muddy water and the like from the outside. An eye bush 31 and an eye 32 for attachment to an axle or the like of a vehicle are fixed to the lower end of the outer cylinder 2. The wiring 35 drawn from the upper end of the piston rod 6 is connected to the control unit 100.

FIG. 3 shows a cross section around the piston 4. The upper side in the figure is the vehicle body side, and the lower side in the figure is the wheel side. In the figure, a wiring passage 41 for accommodating the wiring 35 is provided at the center of the piston rod 6, and the wiring passage 41 is screwed with the piston 4 with a gradually enlarged lower end screw portion 41a. Piston body 42
A large diameter portion and a small diameter portion are formed on the outer circumference, and a sealing member 44 made of a low friction member such as Teflon is fitted to the large diameter portion, whereby the upper and lower liquid chambers 14 and 15 are formed in the cylinder 3 as described above.
It is segregated. A male screw is formed at the distal end of the small diameter portion, and is screwed to the piston rod 6 as described above. Furthermore, the piston body 42 is hollow,
An adjust screw 52 having an adjust nut 53 screwed therein is formed at the end on the small diameter side, and a slightly larger accommodation hole 49 is formed below the adjust screw 52 following the step. A first piezoelectric element 60 sandwiched between a cap 55 and a slider 71 at the top and bottom is fitted into the accommodation hole 49, and their upper portions are locked to the step portion via a length adjusting plate 54. ing. The lower part of the accommodation hole 49 is a large-diameter portion 45 having two further steps, which are pressed against the two-step shoulders so that the valve body 73 is pressed.
Is inserted, and the valve body 73 is sandwiched between the stepped portion by a sleeve 43 screwed into a female screw portion formed on the end side of the large diameter portion 45. Space on the top side of this valve body 73
79 is defined and communicates with the upper liquid chamber 14 by a communication hole 46 formed in the piston main body 42, while a space 80 is defined between the sleeve 43 on the lower surface side and formed in the sleeve 43. The communication hole 48 communicates with the lower liquid chamber 15, and the opening of the communication hole 48 on the lower liquid chamber side is covered with the extension valve 16. An annular groove 73a is formed on the outer periphery of the valve body 73, and the annular groove 73a communicates with the lower liquid chamber 15 through a communication hole 47 formed in the piston body. The valve body 73 has an orifice 76 communicating the upper space 79 and the annular groove 73a, and an orifice 77 communicating the upper space 79 and the lower space 80.These orifices 76,
A pressure-side disc valve 74 is provided on the upper surface of the valve body 73 and a growth-side disc valve 75 is provided on the lower surface thereof so as to cover the respective 77s.

The sleeve 43 is formed in a hollow shape and has a receiving hole.
50 includes a valve core 72 and a second piezoelectric element 9 in order from the top.
0, a cap 94 is inserted, and these are accommodated in the accommodation hole 50 so as to be vertically movable by an adjusting screw 20 screwed at a lower end of the sleeve 43. The valve core 72 has a hollow shaft portion projecting from the center of the upper surface of the large diameter portion inserted into the housing hole 50. The hollow shaft portion passes through the center hole of the valve body 73, and the upper portion of the slider 71 It penetrates the central hole.

Thus, the compression-side disc valve 74 is sandwiched between the lower surface of the slider 71 and the upper surface of the sleeve 43 via the valve body 73, and the set load is adjusted on the upper surface of the valve body 73 in accordance with the adjustment of the adjust nut 53, The slider 71 functions as a transmitting member that transmits the electrostriction when a voltage is applied to the first piezoelectric element 60 to the pressure side disk valve 74 and presses it. The extension-side disc valve 75 is also sandwiched between the upper surface of the valve core 72 and the shoulder of the large-diameter portion 45 of the piston body 42 via the valve body 73, and the valve body 73 is adjusted in accordance with the adjustment of the adjust screw 20. The set load is adjusted on the lower surface, and the valve core 72 acts as a transmission member for transmitting the electrostriction of the second pressure element 90 to the extension-side disk valve 75. Further, an inclined surface 71b is provided at the lower end of the slider 71 to receive the pressure of the upper liquid chamber 14 introduced into the space 79 and transmit the pressure to the first piezoelectric element 60. The slider 71 functions as a pressure-sensitive member. Further, a pressure hole 95 is formed on the lower surface of the adjusting screw 20, and the lower liquid chamber 15 is formed.
Is a pressure-sensitive member that guides the pressure to the lower surface of the cap 94 and pushes the cap 94 to transmit the pressure to the second piezoelectric element 90. In the present embodiment, the communication hole 48 covered by the extension side valve 16 is partially notched, and the space 80 always communicates with the lower liquid chamber 15, so that the valve core 72 is also a pressure-sensitive member. Act as Thus, it is sufficient that one pressure-sensitive member is provided for one voltage piezoelectric element.

The first and second piezoelectric elements 60 and 90 are provided with harnesses 61 and 62 and 91 and 92, respectively.
2, piston body 42, cap 55, adjust nut 53
Of the piston rod 6
The harnesses 61 and 91 are grounded, and the harnesses 62 and 92 are connected to the I / D port 101 of the control unit 100 as shown in FIG.

110 and 110 'are arithmetic circuits for detecting signals from the first piezoelectric element 60 and the second piezoelectric element 90, respectively, in which only the AC component is input by the capacitors C and C, and the buffers 112 and 112 amplify the AC component. The extension signal S _P and the compression signal S _{S at} 120
As an input circuit.

The arithmetic circuit 120 is constituted by, for example, a microcomputer or the like, captures external data according to a program written in the internal memory, and based on the captured data and data written in the internal memory,
The processing value required for the variable control of the damping force is calculated. That is, the arithmetic circuit 120 based on the input signal calculates the rate of change of the input signal, performs a predetermined determination from the detection signal S _P or S _S and its rate of change [Delta] S _P or [Delta] S _S, depending on the determination result, the pressure side and outputs one of control signals S _a or the extension side control signal S _B. Or output nothing. For example, the drive circuit 130 when the compression side control signals S _A are input transistor Tr ₁ is turned ON in the buffer 131, the drive voltage of the drive power supply circuit 140 I / O
Via the diode D ₁ of the port 101 is applied to the first piezoelectric element 60, switched to the hard damping force from the soft. Also,
Driving circuit 130 when the compression side release signal S _'A is input transistor Tr ₂ is turned ON in the buffer 132, the first piezoelectric element 60
Discharge through the diode D ₂ of the I / O port 101,
Return the damping force from hard to soft. The drive circuit 13
The same applies to the case where the expansion side control signal S _B and the expansion side release signal S ′ _B are input to 0 ′. The driving power supply circuit 140 is, for example, a DC-D
First and second piezoelectric elements 6 formed by a C converter
It outputs a DC high voltage (hereinafter referred to as a drive voltage) that can extend 0 and 90.

Next, the flow of the hydraulic fluid when the shock absorber performs the expansion / contraction stroke, and the operation of detecting and driving the first and second piezoelectric elements 60 and 90 will be described with reference to FIG.

Now, when the vehicle body bounces due to the wheels riding on the projections or the like and the piston rod 6 moves downward with respect to the cylinder 3, the hydraulic fluid in the lower liquid chamber 15 is filled with the invading body of the piston rod 6. The liquid flows into the liquid chamber 14. That is,
From the lower liquid chamber 15, the pressure-side disc valve 74 is pushed open through the communication hole 47, the annular groove 73a, and the orifice 76, and flows into the upper liquid chamber 14 through the space 79 and the communication hole 46. At this time, the pressure-side disc valve 74 bends in accordance with the flow rate passing therethrough.
15 becomes high pressure by that amount and acts as a compression side damping force. The pressure of the lower liquid chamber 15 is the as so introduced from the pressure hole 95 on the lower surface of the cap 94, the second piezoelectric element 90 is distorted depending on the pressure, control power corresponding to the distortion as compression side signal S _S Output to unit 100.

At this time, since the valve body 73 is engaged with the shoulder of the large-diameter concave portion 45, no force is transmitted to the upper first piezoelectric element 60 even when pressed from below. Therefore, at this time, the first
The piezoelectric element 60 is in a state where it can operate as an actuator for the time being.

When the piston rod 6 moves upward with respect to the cylinder 3 in the rebound after the vehicle body sinks, for example, after the wheel rides on a projection or the like, the hydraulic fluid in the upper liquid chamber 14 becomes the piston rod 6 Flows into the lower liquid chamber 15 of the invading body integral. That is, the upper liquid chamber 14 passes through the communication hole 46, the space 79, and the orifice 77, pushes and opens the extension-side disc valve 75, and
0, flows into the lower liquid chamber 15 through the communication hole 48. At this time, since the expansion-side disk valve 75 bends in accordance with the flow rate passing therethrough, a differential pressure corresponding to the bent spring force is generated in the hydraulic fluid before and after the passage, and the upper liquid chamber 14 becomes high pressure by that amount, and the expansion side Acts as a damping force. The pressure in the upper liquid chamber 14 is increased from the space 79 to the slider 71.
And acts on the inclined surface 71b to move the slider 7
Since biasing the 1 upwards, the first piezoelectric element 60 is distorted depending on the pressure, and outputs to the control unit 100 a voltage corresponding to the distortion as the extension side signal S _P.

At this time, even if the valve body 73 abuts the shoulder of the piston 4 and is pressed from above, it does not transmit a force to the lower second piezoelectric element 90 via the valve core 72. Therefore, at this time, the second piezoelectric element 90 is in a state where it can operate as an actuator for the time being.

Next, a method of applying the variable damping force type hydraulic shock absorber according to the present invention to a suspension will be described with reference to a time chart of FIG.

FIG. 6B shows the detected values of the pressures of the upper and lower liquid chambers 14 and 15, which are detected by the first and second piezoelectric elements 60 and 90, respectively.
The ag and the section km are the pressures during the extension stroke and are detected by the first piezoelectric element 60, and the section gk is the pressure during the compression stroke and are detected by the second piezoelectric element 90.

The pressure detection area multiplied by the pressure receiving area of each stroke is the sixth
This is the damping force shown in FIG.

In the figures (a) and (b), (Aa), (Gg), (Kk),
At each point of (Mm), the damping force and pressure become “0”. Among them, A and K are the bottom dead center of vibration at the point where the damping force moves from the pressure stroke to the extension stroke, and G and M are the same. Becomes top dead center. Between these upper and lower dead points, there are extreme values of the pressures b, d, f, j, l, and among them, b, j, l is the neutral position of the piston (position at rest).

Since d and f reach the maximum speed at the neutral point of the piston and then enter the deceleration range toward the top dead center, c
There is an external input to increase the piston speed at the point, weakening the deceleration, reaching the minimum value at d, entering the speed increasing region again, indicating that the speed decreased after reaching the extreme value at f ing.

As described above, the switching between the extension stroke and the pressure stroke can be determined by the pressure signal becoming “0”, but it is difficult to determine the fluctuation of the piston speed in the external input during each stroke by the pressure signal. It is.

Therefore, when the detection signal shown in FIG. 2B is differentiated with respect to time to obtain a rate of change (corresponding to acceleration), and FIG.
All the extrema in the detection signal shown in FIG. 6B have a change rate of “0” shown in FIG. 9C, and both the extrema of the top and bottom dead center and the extremum due to the composite input from outside have a change rate of “0”. 0 "can be detected. Further, all the inflection points in FIG. 8B are detected as extreme values in FIG.

That is, a, g, k, and m in FIG. 7B are inflection points of the stroke switching, and c and e are inflection points of the speed due to the external input during the stroke. ) Are all extreme values. Therefore, if the "0" point and the extreme value of the rate of change shown in FIG. (C) are obtained and the pressure detection signal value shown in FIG. (B) is added to the judgment, all suspension states can be determined, and an appropriate damping force can be obtained. Control becomes possible.

In FIG. 6, the speed increase sections (ab) and (kl) of the extension stroke from the neutral position of the piston to the top dead center, and the speed increase section (gj) of the compression stroke are extreme values in FIG. In this case, a voltage is applied to a piezoelectric element operable as an actuator so as to harden the damping force in order to reduce the piston speed. In this case, since the extremum in FIG. 9C corresponds to the switching of the stroke, the pressures of the upper and lower fluid chambers 14 and 15 in the hydraulic buffer also switch at the extremum as a boundary. The piezoelectric element to which a voltage is applied is a piezoelectric element that has not been detected so far.

Next, the (jk) section is a section where the speed from the neutral position to the bottom dead center is reduced from the neutral position, and the (lm) section is a section where the speed from the neutral position to the top dead center is reduced. Stop and soften the damping force of the hydraulic shock absorber.

The section (bc) is a section of the piston speed from the neutral position to the top dead center as in the section (lm), but the input at the point c decreases the deceleration rate of the piston from the point c. And the velocity curve changes downwardly convexly.
This is detected as an extreme value C '(minimum value) in FIG. 9C, and after the next extreme value E' (maximum value), the rate of change is "0".
The damping force can be controlled in the vibration section by the composite input until F ′ as in the other simple vibration sections described above.

As described above, in the variable damping force type hydraulic buffer according to the embodiment of the present invention, since the two piezoelectric elements 60 and 90 are configured to detect the pressures of the upper and lower liquid chambers 14 and 15, respectively, the stroke is reduced. Since the pressure can always be detected even when switching, and since the other piezoelectric element does not always detect the pressure, it can be operated as an actuator, so it can continuously detect every state during traveling and according to the detection result Can be properly controlled.

In the above embodiment, when the rate of change of the pressure signal becomes “0”, the control is performed such that the energization is stopped. However, the present invention is not limited to this, and the rate of change is close to “0”. When the predetermined value is reached, the energization may be stopped.

(Effect) According to the present invention, the hydraulic pressure on the pressure side during the pressure stroke is independently detected by the first detection means, and the hydraulic pressure on the expansion side during the extension stroke is independently detected by the second detection means. The control means, which has received the detected hydraulic pressure signal, calculates the change rate of the hydraulic pressure, that is, the acceleration, by differentiating the hydraulic pressure signal with respect to time, and obtains the first or the second according to the change rate. One of the operating means is energized and stopped, and the damping force is switched between hard and soft. At this time, it is determined whether the first or second operating means is driven by setting the hydraulic pressure signal itself to zero. It is determined whether or not the process changes depending on whether or not it becomes true. By driving each operating means in this way, the damping force is continuously controlled based on the hydraulic pressure detected continuously during the extension / pressure stroke.

As a result, every state during running is continuously detected,
Damping force control can be appropriately performed in accordance with the detection result, and both riding comfort and running stability with respect to continuous vibration input can be achieved.

[Brief description of the drawings]

FIG. 1 is a basic conceptual diagram of the present invention, and FIGS. 2 to 6 are views showing an embodiment of a shock absorber having a variable damping force type liquid according to the present invention. FIG. 2 is an overall view of the shock absorber. FIG. 3 is a cross-sectional view of a main part of the system, FIG. 4 is a diagram of the entire system, FIG. 5 is a circuit diagram of a part of the system, and FIG. 6 is a time chart showing its operation. DESCRIPTION OF SYMBOLS 1 ... Shock absorber, 3 ... Cylinder, 4 ... Piston, 60 ... First piezoelectric element, 70 ... Damping means, 71 ...
... Slider, 72 ... Valve core, 73 ... Valve body,
74: Compression side valve, 75: Extension side valve, 76, 77 ... Orifice, 90 ... Second piezoelectric element, 100 ... Control unit (control means), 101 ... I / O port, 110 ... Input circuit, 120 arithmetic circuit, 130 drive circuit, 140
Power supply circuit for driving.

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Junichi Emura 1370 Onna, Atsugi-shi, Kanagawa Prefecture Inside Atsugi Automotive Parts Co., Ltd. (56) References JP-A-61-85210 (JP, A)

Claims (3)

(57) [Claims] 1. A first detecting means for independently detecting only the hydraulic pressure on the pressure side of a shock absorber as a first pressure signal, and independently detecting only a hydraulic pressure on the expanding side of the shock absorber as a second pressure signal. A second operating means for changing the damping force on the compression side of the shock absorber, a second operating means for changing the damping force on the extension side of the shock absorber, and the first or second detecting means. The first or second detected
A pressure signal is input, and a change rate of the first or second pressure signal is obtained by calculation, and the first or second pressure signal is calculated based on the change rate and the first or second pressure signal corresponding thereto.
And a control means for outputting a control value for selectively driving / stopping one of the operation means. 2. The control means according to claim 1, wherein said control means continuously determines the magnitude of said change rate from said change rate obtained by calculation, and when it is confirmed that said change rate has reached an extreme value, said first or second operation means. 2. The variable damping force according to claim 1, wherein the power supply to any one of the first and second operation means is stopped, and when it is confirmed that the rate of change is equal to or less than a predetermined value, the power supply to the first or second operation means is stopped. Type hydraulic shock absorber. 3. The variable damping force type hydraulic shock absorber according to claim 2, wherein said predetermined value is zero.