JPH01208212A - Damping force control device of shock absorber - Google Patents

Abstract

PURPOSE:To prevent resonance of a car with road surface by returning the damping force characteristic back to the large when a certain period of time has passed after a damping force varying means shifts the damping force characteristic into the small, or when the elongation/contraction speed of the shock absorber sinks below a certain level. CONSTITUTION:When a road surface condition sensing means M2 senses unevenness on the road surface, a damping force varying means M3 switches the damping force characteristic of a shock absorber M1 from the large to small. At the same time, a damping force returning means M5 starts counting of the time. When a certain period of time determined upon the car speed has passed followed by an additional passage of a specified time, or when the elongation/contraction speed of the shock absorber M1 sensed by an elongation/ contraction speed sensing means 4 has sunk below a certain level, the damping force characteristic of the shock absorber M1 is restituted to the large forcedly. This prevents resonance between the car and road surface.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a damping force control device for a shock absorber that controls damping force characteristics of a shock absorber according to the unevenness of a road surface.

[Conventional technology] Conventionally, the damping force characteristics of shock absorbers are normally set to a large (hard) level in order to ensure steering stability of the vehicle, and when there are irregularities on the road surface, the damping force characteristics of the shock absorbers are In order to absorb wheel vibration caused by this unevenness,
A shock absorber damping force control device that switches the damping force characteristic of a shock absorber to a small (soft) state is known.

That is, as described in JP-A-60-183216, unevenness on the road surface is detected from the vibration of the front wheels of the vehicle and the damping force characteristic of the rear wheels is switched from large to small, or JP-A-62-22.
For example, as described in Japanese Patent Application No. 1907, unevenness of the road surface is detected from the expansion/contraction acceleration of the shock absorber and the damping force characteristic of the shock absorber is switched from large to small.

By the way, in conventional devices of this type, the damping force characteristic was configured to return from small to large after a predetermined period of time had passed after changing the damping force characteristic. The damping force characteristics may be returned to a large degree, and wheel vibrations may be suddenly transmitted to the vehicle body, causing a return shock to the vehicle body.

Therefore, the applicant of the present application, in accordance with Japanese Patent Application No. 62-209774, etc., detects the expansion and contraction speed of the shock absorber (■[J damping force), and when a predetermined period of time has elapsed after changing the damping force characteristics, the expansion and contraction speed detected above is We proposed that the damping force characteristics be switched from small to large when the damping force becomes near 0.

[Problems to be Solved by the Invention] According to the damping force control device for a shock absorber proposed above, when the displacement of the shock absorber is substantially stopped, the damping force characteristic can be switched from small to large.
Prevents the return shock that occurs on the vehicle body when switching,
Vehicle ride comfort can be controlled more optimally.

However, when this is done, there is a problem in that depending on the driving condition of the vehicle, the expansion and contraction speed of the shock absorber does not easily reach zero after changing the damping force characteristics, resulting in vibration of the vehicle body.

In other words, for example, if the Hg force characteristic of the shock absorber is switched from large to small and the vehicle runs over a bump with a long period, such as an undulation on the road surface, the vehicle body will resonate with the road surface and the shock absorber will The car body vibration (01
~10H2) may cause the shock absorber to expand and contract slowly, and in such cases, it takes time for the shock absorber to reach the expansion and contraction speed of This causes problems such as the vehicle body continuing to vibrate.

Therefore, in the present invention, if the expansion and contraction speed of the shock absorber does not easily reach around O after changing the damping force characteristics, by forcibly returning the damping force characteristics from small to large,
This was done to prevent the vehicle from resonating with the road surface.

[Means for Solving the Problems] That is, the present invention has been made to achieve the above object, and as illustrated in FIG. a variable damping force shock absorber M1 that can be switched to a damping force variable shock absorber M1; a road condition detecting means M2 that detects unevenness of the road surface; and when the road condition detecting means M2 detects an unevenness of the road surface, the damping force characteristic of the shock absorber M1 is reduced. A damping force control device for a shock absorber, comprising: a damping force changing means M3 for changing the damping force to the shock absorber M1;
After changing the damping force characteristic of
When the expansion/contraction speed of the shock absorber M1 detected in step 4 is below a predetermined value, the shock absorber M1
The gist of the present invention is a damping force control device for a shock absorber, which is characterized by being provided with a damping force return means M5 for returning the damping force characteristic of 1 to a large extent.

[Function] In the shock absorber damping force control device of the present invention configured as described above, when the road surface condition detecting means M2 detects unevenness of the road surface, the damping force changing means M3 increases the Ws force characteristic of the shock absorber M1. The shock absorber M1 absorbs vehicle body vibrations caused by uneven road surfaces. Then, when a predetermined period of time has elapsed, and a further predetermined period of time has elapsed, or when the expansion/contraction speed of the shock absorber detected by the expansion/contraction speed detection means M4 becomes less than a predetermined value, the damping force return means M5 is activated to damp the shock absorber M1. The force characteristic is restored from small to large.

For this reason, the shock absorber Ws force control device of the present invention is effective in cases where it takes time for the shock absorber's expansion/contraction speed to drop below a predetermined value after changing the damping force characteristics (in other words, the vehicle body resonates with the road surface as described above). In such a case), even if the expansion/contraction speed is not below the predetermined value, the damping force characteristic will be forcibly returned from small to large depending on the elapsed time after changing the damping force characteristic, and this will cause the car body to It is possible to prevent resonance with the road surface.

[Example code] Embodiments of the present invention will be described below with reference to the drawings.

First, FIG. 2 is a schematic configuration diagram showing the entire configuration of the damping force control device of the embodiment.

As shown in the figure, the vehicle shock absorber control device 1 of this embodiment is a variable damping force shock absorber (hereinafter simply referred to as a shock absorber).

) 2FL, 2FR, 2RL, 2RR, a vehicle speed sensor 3 that detects the running speed of the vehicle, and an electronic control device 4 that controls these.

Shock absorber 2FL, 2FR, 2RL,
2RR is a shock absorber 2FL as described later.
, 2FR.

A piezo load sensor that detects the damping force acting on 2RL and 2RR, and shock absorbers 2FL and 2FR.
, 2RL, and 2RR are each equipped with a built-in piezo actuator for switching the damping force characteristics into two levels, large and small.

Also, each shock absorber 2FL, 2FR, 2RL
.

2RR has left and right front and rear wheels 5FL, 5FR, and 5R, respectively.
L, 5RR suspension lower arm 6FL,
Coil spring 8FL is installed between 6FR, 6RL, 6RR and car body 7.

It is attached to 8FR, 8RL, and 8RR.

Then, the detection signal from the vehicle speed sensor 3 is manually input to the electronic control device 4, and the electronic control device 4 outputs a control signal to the piezo actuator described above.

Next, each of the above shock absorbers 2PL, 2FR, 2
The structure of RL and 2RR will be explained. Since the structures of the above-mentioned shock absorbers 2FL, 2FR, 2RL, and 2RR are all the same, the shock absorber 2FL on the left front wheel 5FL side will be explained here as an example.

As shown in FIG. 3(A), the shock absorber 2FL has a main piston 12 inside the cylinder 11 in the axial direction (
This is indicated by arrows A and B in the figure. ) is slidably fitted into the
The inside of the cylinder 11 is divided into a first hydraulic chamber 13 and a second hydraulic chamber 14 by a main piston 12 . The main piston 12 is connected to one end of a piston rod 15, and the other end of the piston rod 15 is fixed to a shaft 16. A lower portion (not shown) of the cylinder 11 is connected to a lower arm 6FL of the left front wheel 5FL, and an upper portion (not shown) of the shaft 16 is connected to the vehicle body 7.

Next, a fixed orifice on the extension side 17 and a fixed orifice on the contraction side are bored in the main piston 12 to communicate the first hydraulic chamber 13 and the second hydraulic chamber 14. On the outlet side of the 1st, there is a plate valve 17 that restricts the flow direction to one direction.
a and 18a are provided, respectively.

Therefore, the main piston 12 moves inside the cylinder 11 as shown by the arrow A.
, When sliding in the axial direction shown by B, the hydraulic oil inside the first hydraulic chamber 13 and the second hydraulic chamber 14 mutually flows through the fixed orifice 17 on the extension side and the fixed orifice 18 on the contraction side. Therefore, the damping force of the shock absorber 2FL is determined by the cross-sectional area of the flow path of the hydraulic oil.

On the other hand, the piston rod 15 has a hollow part bored in its axial direction, and a piezo actuator 19 which is an electrostrictive element laminate made of piezoelectric ceramics such as PZT is installed in the hollow part.
Built-in FL. Also piezo actuator 19
A piston 20 is disposed at a position close to and facing the lower end surface of the FL. The piston 20 is usually a plate spring 2
0a in the direction shown by arrow A in the same figure, it can slide inside the hollow portion of the piston rod 15 in its axial direction.

Therefore, when a voltage of several hundred V is applied to the piezo actuators 19F and 19L to extend the piezo actuator 19FL, the piston 20 moves several tens of microns in the direction shown by arrow B in the figure.
When the piezo actuator 19FL is contracted by discharging the charge accumulated in the piezo actuator 19FL by applying a voltage, the piston 20 moves in the direction shown by arrow A in the figure due to the bias of the temporary spring 20a. do. The charging and discharging of piezo actuator 19FL is as follows.
A lead &! arranged in a passage bored inside the shaft 16 in its axial direction. 19a.

Next, the hollow portion of the piston rod 15 and the bottom surface of the piston 20 form an oil-tight chamber 21, and a cylindrical plunger 22 is provided in a through hole bored in the axial direction of the piston rod 15 and communicating with the bottom of the oil-tight chamber 21. The plunger 22 is slidably fitted thereinto, and the lower end of the plunger 22 is connected to the upper part of a spool valve 24, which is slidably fitted into a fitting hole inside a housing 23 fixed to the piston rod 15.

The spool valve 24 is biased by a spring 25 in the direction indicated by the arrow A in the figure, and the lower part of the spool valve 24 has an annular groove 24a carved in the outer circumference, and the lowermost part is shaped into a cylindrical shape. ing.

Further, the piston rod 15 is provided with an auxiliary passage 26 that connects the first hydraulic chamber 13 and the second hydraulic chamber 14. It is blocked by the lower part.

For this purpose, a voltage of several hundred V is applied to the piezo actuator 19FL to extend the piezo actuator 19FL,
When the piston 20 is moved in the direction of arrow B, the oil-tight chamber 21
The internal pressure increases and plunger 22 and spool valve 2
4 also moves in the direction of arrow B, and the sub flow path 26 is connected to the spool valve 24.
The first hydraulic chamber 13 and the second hydraulic chamber 14 communicate with each other via this sub passage 26, and the main piston The flow path cross-sectional area of the hydraulic oil flowing through 12 becomes larger than usual, and its flow rate increases. Therefore, the Wv force characteristic of the shock absorber 2FL at this time becomes smaller than normal.

That is, each of the above-mentioned shock absorbers 2FL, 2FR, 2
RL and 2RR apply a high voltage to the piezo actuators 19FL, 19FR, 19RL, and 19RR provided respectively, so that the piezo actuators 19FL, 1
9FR.

When extending 19RL and 19RR, the damping force characteristics are 4th.
It is switched to the small (soft) side shown in the figure, and is normally maintained at the large (hard) state shown in FIG.

Next, at the top of the shaft 16 is a shock absorber 2F.
A piezo load sensor 31FL that detects the magnitude of the Wx force acting on L is provided, and the piezo load sensor 31FL is fixed to the shaft 16 with a nut 32.

As shown in FIG. 3(B), the piezo load sensor 31FL is constructed by stacking two thin plates 31A and 31B of a piezoelectric element made of piezoelectric ceramics such as PZT with an electrode 31C in between. It is connected to the electronic control device 4 via a lead wire 31a disposed in the bored passage.

As shown in FIG. 5, the electronic control device 4 includes CPUs 4a, R
It is configured as a logic operation circuit centering around OM4b and RAM4c, and is connected to the human power section 4e and the output section 4 via a common bus 4d.
It is connected to f and performs human output with the outside. In addition, the electronic control circuit 4 includes each piezo load sensor 31FL, 31FR,
From the charges generated by 31RL and 31RR, each shock absorber 2FL.

Ws force detection circuit 35 that detects the damping force of 2FR, 2RL, and 2RR and the rate of change of the damping force, and the vehicle speed sensor 3
A waveform shaping circuit 36 is provided for shaping the detection signal from the sensor, and the detection results from each of the sensors are manually input to the human power section 4e through these sections. Furthermore, the electronic control circuit 14 expands and contracts the piezo actuators 19FL, 19FR, 19RL, and 19RR in response to a control signal output from the CPU 4a via the output section 4f, and each of the shock absorbers 2FL, 2FR, 2RL,
A drive circuit 37 is provided to switch the damping force characteristics of the 2RR.

Here, the damping force detection circuit 35 includes piezo load sensors 31FL, 31FR, and 31RL, as shown in FIG.

Four detection circuits 41FL provided corresponding to 31RR
, 41FR, 41RL, and 41RR.

Taking the detection circuit 41FL as an example, each detection circuit 4IFL
, 41FR, 41RL, and 41RR will be explained below.

As shown in the figure, the detection circuit 41FL includes the piezo load sensor 3
A damping force change rate detection circuit 50 that detects the rate of change in damping force from the current flowing in the 1FL, and a damping force change rate signal amplification circuit 52 that amplifies the output signal from the damping force change rate detection circuit 50.
, an A/D converter 54 that A/D converts the damping force change rate signal output from the damping force change rate signal amplification circuit 52, and an output signal from the damping force change rate detection circuit 50. A damping force estimating circuit 56 that estimates the force, an A/D converter that A/D converts the tlis force signal output from the damping force estimating circuit 56, and a voltage generating circuit 60 that generates a reference voltage of 2V. , is composed of.

First, the damping force change rate detection circuit 50 is 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 31FL 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 ftfi damping force change rate detection circuit 50, the current flowing through the resistor R1 is detected by the voltage across the resistor R1, and the detected value is output as a signal representing the damping force change rate of the shock absorber 2FL.

That is, in the damping force change rate detection circuit 50, first, the resistor R
The voltage generated at both ends of the filter 1 is applied via a resistor R2 to a radio noise removal filter EMI consisting of two coils Ll and L2 and a capacitor C1, and high frequency components such as radio noise are removed.

Then, the voltage signal from which radio noise has been removed is converted to the reference voltage (
2V) is applied to a bypass filter HPF consisting of a resistor R3, which removes low frequency components below 0°1Hz, and at the same time raises the frequency by 2V, and a low-pass filter consisting of a resistor R4 and a capacitor C3. After the high frequency components of 100Hz or more are manually removed by the filter LPF,
It is output to the outside via a buffer consisting of an operational amplifier OPI.

Therefore, in the damping force change rate detection circuit 50, as shown in FIG.
As shown in the figure, there is a protrusion on the road surface, the left front wheel 5FL rides on the protrusion, and the shock absorber 2FL expands and contracts.
According to the expansion/contraction acceleration, the voltage across the resistor R1 (voltage at point a in FIG. 1) changes as shown in FIG. 7(B), and 0. A voltage signal as shown in FIG. 7(C) obtained by adding 2v to the signal components of 1 to 100H2 is generated as a damping force change rate signal.

In addition, bypass filter HPF and low pass filter LPF
From the voltage across resistor R1, 0.1 to 10
0H2 frequency component voltage signal.

The reason for this is that the shock absorber 2FL is structurally capable of expanding and contracting in this frequency range. In addition, in Fig. 6, the diode D1.02 is connected to the operational amplifier OP.
This is a protection diode for protecting the operational amplifier OPI so that the input terminal of I is in the range of 0 to 5V.

Next, the damping force change rate signal amplifying circuit 52 is for amplifying the damping force change rate signal output from the damping force change rate detection circuit 50 and outputting it to the A/D converter 54. A reference voltage (2V) from the voltage generation circuit 60 is applied to the non-inverting input terminal via the inverting input terminal, and the inverting input terminal is connected to the output terminal of the damping force change rate signal amplification circuit 52 via the capacitor C4 and the resistor R6. , an operational amplifier OP2 whose inverting input terminal and output terminal are connected via a resistor R7 constitutes an inverting amplifier.

Therefore, from the damping force change rate signal amplification circuit 52, ? li
The output signal of the force change rate detection circuit 50 is inverted and amplified around 2V to output a damping force change rate signal VFL as shown in FIG. 7(D).

Note that this damping force change rate signal amplification circuit 52 includes a capacitor C
4 and resistor R7, it also functions as a bypass filter, and removes low frequency components (several Hz to 10F (frequency components below z) of the damping force change rate signal output from the damping force change rate detection circuit 50. It is being done.

In other words, the damping force change rate signal VFL output from the damping force change rate signal amplification circuit 52 is used to detect unevenness on the road surface and softly switch the damping force of the shock absorber. If the low frequency component corresponding to long-cycle irregularities is also taken in as the damping force change rate signal VFL, the damping force of the shock absorber will be softly switched even for such irregularities, and the vehicle body will resonate with the irregularities on the road surface. This is because the riding comfort of the vehicle is adversely affected.

Next, the damping force estimating circuit 56 integrates the damping force change rate signal output from the damping force change rate detection circuit 50 to obtain a damping force signal representing the damping force of the shock absorber. A reference voltage (2V) from the voltage generation circuit 60 is applied to the terminal via the resistor R8, and the inverting input terminal is connected to the output terminal of the damping force change rate signal amplification circuit 52 via the capacitor C5 and the resistor R9. , an operational amplifier OP3 whose inverting input terminal and output terminal are connected through a resistor R7 and a capacitor C6, respectively.

This damping force estimating circuit 56 has an overall bandwidth of 01 to
It constitutes a band pass filter of about 10 Hz, and the capacitor C5 cuts the DC component of the damping force change rate signal output from the damping force change rate detection circuit 50, and the human power signal is constituted by the capacitor C6 and resistor R9. The integrated circuit integrates the signal and outputs it to the A/D converter 58. Therefore, the damping force estimating circuit 56 outputs 01 to 10 Hz of the damping force change rate signal from the damping force change rate detection circuit 50.
Ws as shown in FIG. 7(E) where the frequency components of are integrated.
The force signal VaFL will be output.

The damping force estimating circuit 56 is configured to integrate only the frequency components of 01 to 10 Hz of the damping force change rate signal, as described below.
This is because the control for returning the damping force characteristic from small to large is executed by the Hg force signal output from 6, and it is sufficient to detect a low frequency component that affects vehicle body vibration as the damping force signal.

Next, the voltage generation circuit 60 is for generating a reference voltage of 2V as described above, and in this embodiment, the power supply voltage of 5V is divided by resistors R11 and R12, and the operational amplifier OP4
It is configured to output a reference voltage of 2V via a buffer consisting of.

In this way, the Mi force detection circuit 35 includes four detection circuits 41FL, 41FR, 41 corresponding to each piezo load sensor 31F [4, 31FR, 31RL, 31 RR].
R.L.

41RR is provided, and each detection circuit 4. I FL,
41 FR.

Each shock absorber 2FL from 41RL and 41RR.

Detection signals representing the damping force and damping force change rate of 2FR, 2RL, and 2RR are output.

Incidentally, since the shock absorber expands and contracts due to the Ws force detected above, each of the detection circuits 41FL, 4IFR, 41
The damping force signals output from RL and 41RR represent the expansion and contraction speed of each shock absorber, and the damping force change rate signal represents the expansion and contraction acceleration of the shock absorber.In this embodiment, this damping force detection circuit and the piezo load sensor are used. The expansion/contraction speed detection means M4 is constituted by these.

Next, the drive circuit 37 outputs each shock absorber 2FL, 2FR, 2RL, from the CPU 4a via the output section 4f.
Each shock absorber 2FL, 2FR, 2RL according to the WH force switching signal output every 2RR.

Piezo actuator 19FL installed in 2RR.

19FR, 19RL, and 19RR, as shown in FIG. High voltage is applied to each piezo actuator 19FL, 19FR, 19RL.

It is composed of charging/discharging circuits 47FL, 47FR, 75RL, and 47RR for applying voltage to 19RR and conversely discharging it.

Here, the high voltage generation circuit 47 converts the battery voltage to 600V.
It is composed of a DC/D(, I) inverter 47a that converts the high voltage into a DC/D inverter 47a, and a capacitor 74b that stores the converted high voltage.

In addition, each charging/discharging circuit 47FL, 47FR, 75RL,
47RR applies a high voltage to each piezo actuator 19FL, 19FR, 19RL, and 19RR when a low-level signal is manually applied as a damping force switching signal, and conversely, when a high-level signal is manually applied as an Rs force switching signal. When each piezo actuator is 19FL,
It is configured to discharge the high voltage charged in 19FR, 19RL, and 19RR.

That is, taking the charging/discharging circuit 47FL as an example, in the charging circuit 47FL, when a low-bell signal is input as a damping force switching signal, the transistor Tri is turned off and the transistor Tr2 is turned on, so that the transistor T
r2. High voltage generation circuit 45 and piezo actuator 19FL are connected via resistor R20, and a high voltage is applied to piezo actuator 19FL. Conversely, when a high-level signal is input as a damping force switching signal, the transistor Tri is turned on and the transistor Tr2 is turned off, so the high voltage generation circuit 45 and the piezo actuator 19FL are cut off, and the resistor R20 and the diode The electric charge charged in the piezo actuator 19FL is discharged via DIO and the transistor Tri.

[Following] Each of the above shock absorbers 2FL, 2FR
.

The damping force characteristics of 2RL and 2RR are piezo actuators 19FL, 19FR, 19RL, and 19RR.
By applying a high voltage to the piezo actuator 19FL,
When 19FR, 19RL, and 19RR are extended, they become small (soft), and piezo actuators 19FL,
Discharge the charges stored in 19FR, 19RL, and 19RR to actuate the piezo actuators 19FL, 19FR,
When 19RL and 19RR are contracted, they become large (hard), so each shock absorber 2FL, 2F
When making the damping force characteristics of R, 2RL, and 2RR small (soft), each charging/discharging circuit 47FL, 47FR, 75
All you need to do is manually input a low-level damping force switching signal to RL and 47RR, and conversely, each shock absorber 2FL,
When making the Mi force characteristics of 2FR, 2RL, and 2RR large (hard), each charging/discharging circuit 47FL, 47F
All you have to do is manually input a high-level Mi force switching signal to R, 75RL, and 47RR.

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

Figure 9 shows each shock absorber 2FL, 2FR, 2
C to switch and control the damping force of RL and 2RR.
This shows the damping force switching process that is repeatedly executed by the PU 4a.

As shown in FIG. 9(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 steps 110 to 130. , based on the detection signals from the vehicle speed sensor 3 and the damping force detection circuit 35, the vehicle speed S, each shock absorber 2FL, 2FR, 2RL, 2R
R(7) Damping force change rate signal VFL, VFR, VRL
, VRR, and damping force signal VaFL.

Read V aFR, V aRL, V aRR.

Then, in the following step 140, a matrix as shown in FIG.
upper and lower limit values V refl and V ref2 of the damping force change rate signal according to the vehicle speed S are set using the damping force change rate signal, and in steps 150 to 180, the set upper and lower limit values V ref1 . Each shock absorber 2FL based on Vref2.

The damping force switching control is performed every 2FR, 2RL, and 2RR, and the process returns to step 110. This procedure is repeated.

Note that the upper limit value Vref1 and lower limit value Vref2 set in step 140 are thresholds for detecting road surface irregularities based on the damping force change rate signal.

Next, in steps 150 to 180, each shock absorber 2FL, 2FR, 2RL, 2
The damping force switching control executed for each RR is shown in Fig. 9 (B
) is executed as shown below. In addition, Fig. 9 (B) shows step 1.
Shock absorber 2 installed on the left front wheel 5FL in 50
This shows the damping force switching control executed on the FL, and here, the Ha force switching control of the shock absorber 2FL executed in step 150 is taken as an example.
The processing of each step 150 to 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 it is determined whether the vehicle speed S determined in step 110 is greater than 0 and the vehicle is in a running state. And this step 200
If it is determined that the vehicle is stopped, step 210
The process then proceeds to step 280 to reset time counters CTI and C70, which will be described later.

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 12 described above is performed.
It is determined whether the damping force change rate signal VFL of the shock absorber 2FL read in step 0 exceeds the upper limit value Vrefl set according to the vehicle speed S in step 140 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 set lower limit value Vref2.

Note that the processing in steps 220 and 230 is performed so that the damping force change rate signal VFL changes from the lower limit value Vref2 to the upper limit value Vref2.
This is a process for detecting road surface irregularities depending on whether or not they are within the range of l, and corresponds to the road surface condition detection means M2 described above.

Next, if it is determined in step 220 that V FL>V reft, or in step 230, VFL<Vr
If it is determined to be ef2, it is determined that there are irregularities on the road surface, and the process moves to step 240, where the time counters CTI and Cr2 are set according to the vehicle speed S using a map as shown in FIG. time T1 and T2 (TI
<T2), the process moves to step 250 and outputs a low-level damping force switching signal to the charging/discharging circuit 47FL to switch the Ks force of the shock absorber 2FL to a small (soft) state.

Note that the time counters CTFLI and CTFL2, to which the times T1 and T2 are set in step 240, are counters that are counted down to 0 at predetermined time intervals in a time measurement process (not shown).
By setting 2, the elapsed time (soft elapsed time) after the damping force is switched to small (soft) is measured.

Next, if the damping force of the shock absorber 2FL is switched to small (soft) in step 250, or if it is determined that VFL≧V ref2 in step 230, the process moves to step 260, and the time counter CTI Determine whether or not the value is 0. In other words, the time counter CTI is set to time T1 when the $i damping force is switched to small, and is then counted down at predetermined time intervals in a time measurement process (not shown), so here, the time counter CTFLI is set to 0. By determining whether or not the attenuation cull (soft) state has passed for a predetermined time T1 or more, it is determined whether or not the attenuation cull (soft) state has elapsed for a predetermined time T1 or more.

If it is determined in this step 260 that the time counter CTI is not 0, this process is temporarily terminated, and vice versa.
If T1=O, the process moves to step 270, and it is determined whether the damping force VaFL read in step 130 is within 2±ΔV, that is, the expansion/contraction speed of the shock absorber 2FL is below a predetermined value near O. Determine whether or not the

And in this step 270, the shock absorber 2FL
When it is determined that the expansion/contraction speed of is below the predetermined value,
Moving on to the following step 280, the shock absorber 2F
In order to return the damping force characteristic of L to high (hard), a high level damping force switching signal is output to the charging/discharging circuit 47FL to stop driving the piezo actuator 19FL,
Terminate the process once.

On the other hand, if it is determined in step 270 that the expansion/contraction speed of the shock absorber 2FL is not below the predetermined value, the process moves to step 290 and step 24 is performed.
It is determined whether or not the time counter CT2 set at 0 has reached 0, that is, whether a predetermined time T2 or more has elapsed after the Mff force characteristic of the shock absorber 2FL was switched to small (soft). If an affirmative determination is made in step 290, step 280 is executed, and if a negative determination is made, the process is immediately terminated.

In this way, in the damping force switching control of this embodiment, as shown in FIG. When the damping force change rate signal VFL exceeds the upper limit value VreflFL or falls below the lower limit value Vref2FL, it is determined that the road surface is uneven and vehicle body vibration increases, resulting in worsening of the vehicle ride comfort, and the shock absorber 2FL is damped. Switch the force characteristics from large (hard) to small (soft) and set the time counter CTI.
and Cr2 are set to start measuring the subsequent elapsed time (soft elapsed time). Furthermore, since detection of unevenness is performed every time the damping force change rate signal VFL exceeds the upper limit value V refl or falls below the lower limit value V ref2, the unevenness of the road surface is detected at time t1, and the damping force characteristic becomes small (soft). When the unevenness of the road surface is detected again while the timer is switched to , the timers CTI and C70 are set again, and timekeeping starts from the time t2. Finally, after the unevenness of the road surface is detected (at time t2 in this case), a predetermined time T1 has elapsed, and then a predetermined time (T2-Tl) has elapsed or the damping force signal VaFL has become 2V±ΔV. When the expansion and contraction speed of the shock absorber 2FL becomes equal to or less than a predetermined value near 0, the damping force characteristic of the shock absorber 2FL is switched from small (soft) to large (hard).

Therefore, according to the damping force control device of this embodiment, as shown in FIG. 7, after the detection of road surface irregularities, the shock absorber is When the expansion/contraction speed of the shock absorber becomes less than a predetermined value near 0, the damping force characteristic of the shock absorber is restored from small to large at time t3, and it is possible to suppress the return shock that occurs in the vehicle body at the time of this return. .

Furthermore, as shown in Fig. 12, when it takes time for the damping force signal VaFL to reach 2v±ΔV after changing the damping force characteristics, in other words, the vehicle body resonates with the unevenness of the road surface and the expansion/contraction speed of the shock absorber becomes 0. If it takes a long time for the nearby clay to become below a predetermined level, the predetermined time T after detecting the unevenness of the road surface.
At time t4, when 2 elapses, the ms force characteristic of the shock absorber is restored from small (soft) to large (hard), and as a result, it becomes possible to suppress resonance of the vehicle body with the road surface.

Here, in the above embodiment, the expansion and contraction speed of the shock absorber was configured to be detected using a piezo load sensor.
The expansion/contraction speed of the shock absorber can also be detected using a stroke sensor conventionally used for vehicle height control of automobiles.

In other words, as shown in Fig. 13, each wheel 5FL, 5FR
.

5RL, 5RR suspension lower arm 6F
L.

Stroke sensors 70FL, 70 are provided between 6FR, 6RL, 6RR and the vehicle body 7 to detect the distance therebetween.
F.R.

70RL and 70RR are provided, and the electronic control device 4 differentiates the detection signals from the stroke sensors 70FL, 70FR, 70RL, and 70RR and outputs the shock absorber 2F.

By providing a differentiating circuit 72 that outputs damping force signals representing the expansion and contraction speeds of 2FR, 2RL, and 2RR, damping force switching control of the shock absorber can be performed in the same manner as in the above embodiment.

In this case, the circuit that processes the detection signal from the piezo load sensor may be configured to output only the damping force change rate signal of the shock absorber, and the damping force estimation circuit 35 of the above embodiment may be used to output the damping force change rate signal of the shock absorber. A configuration in which the circuit 56 and the A/D converter 58 are removed may be used.

In addition, the damping force change rate signal for detecting road surface irregularities is
Since it represents the expansion/contraction acceleration of the shock absorber, the damping force change rate signal is obtained by further differentiating the damping force signal obtained by differentiating the detection signal from the stroke sensor without using a piezo load sensor. You can.

Next, in the above embodiment, the upper and lower limits for detecting road surface irregularities from the damping force change rate signal are set according to the vehicle speed S using the map shown in FIG.
These upper and lower limits may be further corrected based on the acceleration state of the vehicle, the turning angle, the brake depression state, etc.

In other words, under such driving conditions, the vehicle body leans forward and backward or left and right, and in such cases, if the damping force characteristics are changed to a small value in the same way as when the vehicle is normally traveling straight, the running stability of the vehicle can be improved. Therefore, by correcting the upper and lower limit values to larger values depending on the driving condition of the vehicle, it is possible to improve the driving stability of the vehicle.

[Effects of the Invention] As detailed above, according to the shock absorber damping force control device of the present invention, after changing the damping force characteristic of the shock absorber from large to small, the expansion/contraction speed of the shock absorber is lower than the predetermined value. If it takes a long time for the damping force characteristic to change, the damping force characteristic is forcibly restored from small to large over an appropriate period of time after changing the damping force characteristic, even if the expansion/contraction speed is not below the predetermined value. Therefore, when the vehicle body resonates with the road surface, the damping force characteristic can be returned from low to high to suppress vehicle body vibration.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing the configuration of the invention, Figures 2 to 1
3 shows an embodiment of the present invention, FIG. 2 is a schematic configuration diagram showing the overall structure of a damping force control device, FIG. 3 is a partial sectional view showing the structure of a variable damping force type shock absorber, and FIG. A characteristic diagram showing the damping force characteristics of the shock absorber, Fig. 5 is a block diagram showing the configuration of the electronic control device, Fig. 6 is an electric circuit diagram showing the damping force detection circuit, and Fig. 7 shows the operation and operation of the detection circuit. A time chart explaining the operation of the damping force switching control, Fig. 8 is an electric circuit diagram showing the configuration of the drive circuit, Fig. 9 is a flowchart showing the damping force switching control, and Fig. 10 shows how the road surface is determined from the damping force change rate signal. A diagram showing a map for setting upper and lower limits for detecting irregularities, Figure 11 shows soft elapsed times T1 and T of damping force characteristics.
Figure 12 is a time chart explaining the operation of reducing FF force switching control in the same way as Figure 7. Figure 13 is a diagram showing the map for two settings. Figure 13 is a diagram showing the stroke when obtaining a damping force signal using a stroke sensor. FIG. 3 is an explanatory diagram illustrating a state in which the sensor is attached to a vehicle. Ml, 2FL, 2FR, 2RL, 2RR... Variable damping force type shock absorber M2... Road surface condition detection means M3... Damping force changing means M4... Extension/contraction speed detection means M5... Damping force return means 4...Electronic control device 31FL, 31FR, 31RL, 31RR...
・ Piezo load sensor 35... Damping force detection circuit 50... Damping force change rate detection circuit 52... Damping force change rate signal amplification circuit 56... Damping force estimation circuit Agent: Patent attorney Tsutomu Sadate (and 2 others) Figure 1 Figure 3 Figure 3 (B) Figure 4 (kg) (kg) Figure 7 Figure 8 Figure '0 (km/h) Figure 11↑ Vehicle speed S→ (km/h) Figure 12

Claims (1)

[Scope of Claims] A variable damping force shock absorber provided between a vehicle wheel and a vehicle body and capable of switching damping force characteristics in at least two stages, large and small; road surface condition detection means for detecting unevenness of the road surface; A damping force control device for a shock absorber, comprising: a damping force changing means for changing the damping force characteristic of the shock absorber to a small value when the road surface condition detecting means detects an unevenness of the road surface; an expansion/contraction speed detection means for detecting; and a predetermined time elapses after the damping force changing means changes the damping force characteristic of the shock absorber to a small value; A damping force control device for a shock absorber, comprising: damping force return means for restoring the damping force characteristic of the shock absorber to a large level when the expansion/contraction speed of the shock absorber becomes less than a predetermined value.