JPH0648142A - Suspension device for vehicle - Google Patents

Abstract

PURPOSE:To suppress the transmission of high frequency road surface input to a body so as to improve riding comfortableness by setting the upper limit value of the damping characteristic on the stroke side, in the same direction as a control signal, of a shock absorber to the low damping characteristic until the direction of the control signal is reversed from the time of an acceleration signal reaching the threshold value or more. CONSTITUTION:When an acceleration signal having passed a high-pass filter (e) is less than the specified threshold value, the basic control part (f) of a damping characteristic control means (g) outputs a control signal to a damping characteristic changing means (a) so that the stroke side of a shock absorber (b) in the same direction as a control signal based on the sprung vertical speed detected by a sprung vertical speed detecting means is controlled to have an optimum damping characteristic according to the control signal. When the acceleration signal having passed the high-pass filter (e) reaches the specified threshold value or more, an upper limit value setting processing part (h) sets the upper limit value of the damping characteristic on the stroke side, in the same direction as the control signal, of the shock absorber (b) to the specified low damping characteristic until the direction of the control signal is reversed from the time of the acceleration signal reaching the specified threshold value or more.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle suspension system for optimally controlling the damping characteristics of a shock absorber.

[0002]

2. Description of the Related Art Conventionally, as a vehicle suspension system for controlling a damping characteristic of a shock absorber, for example, Japanese Patent Laid-Open No. 64-64-
The one described in Japanese Patent No. 60411 is known.

This conventional apparatus detects the damping force generated by the shock absorber, estimates the relative speed from the signal strength of the shock absorber, and the relative speed exceeds a predetermined threshold value to enter a bad road or a single-shot input. When it is determined that the shock absorber has a damping characteristic, the damping characteristic of the shock absorber is switched to the high damping characteristic side in order to ensure the running performance of the vehicle during a predetermined interval.

[0004]

However, in the conventional device, as described above, when it is determined that the road is rough, the shock absorber has a high damping characteristic for a predetermined interval regardless of the movement on the spring. Since the vehicle is maintained in the state, there is a problem that the ride comfort of the vehicle cannot be ensured when traveling on a rough road or when a single protruding input is performed.

The present invention has been made by paying attention to the above-mentioned conventional problems, and suppresses vibration of the vehicle during traveling on a good road to ensure riding comfort and steering stability of the vehicle, and also on a bad road. An object of the present invention is to provide a vehicle suspension device capable of suppressing the transmission of a high-frequency road surface input to the vehicle body during traveling or when a single projection-like input is made to improve the riding comfort of the vehicle.

[0006]

As shown in the claim correspondence diagram of FIG. 1, a vehicle suspension system of the present invention is interposed between the vehicle body side and each wheel side, and the damping characteristic is changed by the damping characteristic changing means a. A possible shock absorber b, a sprung vertical acceleration detecting means for detecting the sprung vertical acceleration of the vehicle, and c
A sprung vertical velocity detecting means d for detecting a sprung vertical velocity of the vehicle; a high-pass filter e for cutting low frequency components including a sprung resonance frequency from a signal obtained from the sprung vertical acceleration detecting means c; When the acceleration signal passed through the high pass filter e is less than a predetermined threshold value,
The shock absorber b has the same direction as the direction of the control signal based on the sprung vertical velocity detected by the sprung vertical velocity detecting means d.
A damping characteristic control means g having a basic control section f for outputting a signal for controlling the stroke side of the damping characteristic to the optimal damping characteristic in accordance with a control signal, and a high pass filter provided in the damping characteristic control means g. When the acceleration signal passing through e becomes equal to or higher than a predetermined threshold value, the upper limit value of the damping characteristic on the stroke side of the shock absorber b which is the same as the direction of the control signal from that point until the direction of the control signal is reversed is set. And the upper limit value setting processing unit h for setting the low attenuation characteristic of the above.

[0007]

In the vehicle suspension system of the present invention, when the road surface is a good road with a low frequency input state, the sprung vertical acceleration signal indicating the unsprung motion is less than the predetermined threshold value, so that the damping characteristic control is performed. The basic control part of the means controls the stroke direction side of the shock absorber, which is the same as the direction of the control signal based on the sprung vertical velocity at that time, to the optimum damping characteristic in accordance with the control signal, which makes it possible to drive on a good road. It is possible to suppress the vibration of the vehicle and secure the riding comfort and the steering stability of the vehicle.

Further, when the road surface is a bad road with a high-frequency input state or when there is a single spiking input, the sprung vertical acceleration signal indicating the unsprung movement exceeds a predetermined threshold value. In the upper limit value setting processing unit of the damping characteristic control means, the upper limit value of the damping characteristic on the stroke direction side of the shock absorber, which is the same as the direction of the control signal from that point until the direction of the control signal is reversed, is set to a predetermined value. The process of setting to a low damping characteristic is performed, which can suppress the transmission of the high frequency road surface input to the vehicle body when the vehicle is traveling on rough roads or when there is a sporadic input of a bump, thereby improving the riding comfort of the vehicle. it can.

[0009]

Embodiments of the present invention will be described with reference to the drawings. First, the configuration of the vehicle suspension system according to the embodiment of the present invention will be described. FIG. 2 is a configuration explanatory view showing a vehicle suspension system of an embodiment of the present invention, in which four shock absorbers SA are provided between the vehicle body and each wheel. Then, a sprung vertical acceleration sensor (hereinafter referred to as vertical G sensor) 1 for detecting vertical acceleration is provided on the vehicle body in the vicinity of the mounting position of each shock absorber SA on the vehicle body, and further, in the driver's seat. A control unit 4 that receives a signal from each sensor 1 and outputs a drive control signal to the pulse motor 3 of each shock absorber SA is provided in the vicinity of the position.

The above configuration is shown in the system block diagram of FIG. 3, in which the control unit 4 comprises an interface circuit 4a, a CPU 4b, and a drive circuit 4c, and the interface circuit 4a receives signals from the respective vertical G sensors 1. A signal is input. And this interface circuit 4
As shown in FIG. 14, a set of five filter circuits is provided for each upper and lower G sensor 1 in a. That is, L
PF1 is a low-pass filter circuit for removing noise of a high frequency (30H _Z or higher) from the sprung mass vertical accelerations G sent from the vertical G sensor 1. The HPF 1 removes low-frequency components including the sprung resonance frequency from the sprung vertical acceleration G to generate a high-frequency acceleration signal G including the unsprung resonance frequency.
A high pass filter for obtaining _1, are used those 6H _Z in this embodiment. The LPF 2 is a low-pass filter that integrates the sprung vertical acceleration G and converts it into a sprung vertical velocity Vn. HPF2 is the cutoff frequency
The LPF 3 is a 1.0H _Z high-pass filter and the LPF 3 is a low-pass filter having a cut-off frequency of 1.5H _Z , and both filters form a bandpass filter that obtains a sprung vertical velocity Vn including a sprung resonance frequency.

Next, FIG. 4 shows each shock absorber SA.
FIG. 3 is a cross-sectional view showing the configuration of the shock absorber SA in which a cylinder 30, a piston 31 that defines the cylinder 30 into an upper chamber A and a lower chamber B, and a reservoir chamber 32 are formed on the outer periphery of the cylinder 30. An outer cylinder 33, a base 34 that defines the lower chamber B and the reservoir chamber 32, a guide member 35 that guides the sliding of the piston rod 7 having a piston 31 connected to the lower end, and an outer cylinder 33 and the vehicle body. The suspension spring 36 interposed between the bumper bar 3 and
7 and 7.

Next, FIG. 5 is an enlarged sectional view showing a portion of the piston 31. As shown in FIG. 5, the piston 31 has through holes 31a and 31b formed therein and the through holes 31a and 31b. A compression side damping valve 20 and an expansion side damping valve 12 that open and close 31a and 31b respectively are provided. In addition, the bound stopper 41 screwed to the tip of the piston rod 7 has a stud 3 penetrating the piston 31.
8 is screwed and fixed, and this stud 38 is
A communication hole 39 that connects the upper chamber A and the lower chamber B is formed, and further, an adjuster 40 for changing the flow passage cross-sectional area of the communication hole 39 and the fluid communication depending on the direction of fluid flow. Extension side check valve 1 that allows and blocks the flow of holes 39
7 and a pressure side check valve 22 are provided.
The adjuster 40 is rotated by the pulse motor 3 via the control rod 70 (see FIG. 4). Further, the stud 38 is formed with a first port 21, a second port 13, a third port 18, a fourth port 14, and a fifth port 16 in order from the top.

On the other hand, in the adjuster 40, a hollow portion 19 is formed, a first horizontal hole 24 and a second horizontal hole 25 which communicate the inside and the outside are formed, and a vertical groove 23 is formed in the outer peripheral portion. There is.

Therefore, a through hole 31 is provided between the upper chamber A and the lower chamber B as a flow passage through which a fluid can flow in the extension stroke.
The inside of the extension side damping valve 12 is opened through b and the lower chamber B
To the extension side first flow path D, the second port 13, the vertical groove 23,
Via the expansion side second flow path E, which opens the outer peripheral side of the expansion side damping valve 12 to the lower chamber B via the fourth port 14, the second port 13, the vertical groove 23, and the fifth port 16. Then, the extension side check valve 17 is opened to reach the lower chamber B by way of the third side flow passage F extending to the lower chamber B and the third port 18, the second lateral hole 25, and the hollow portion 19. There are four channels, channel G. Further, as a flow path through which the fluid can flow in the pressure stroke, the pressure side first valve that opens the pressure side damping valve 20 through the through hole 31a is used.
Flow path H, hollow portion 19, first lateral hole 24, first port 21
Via the pressure side check valve 22 to the upper chamber A, and the bypass flow to the upper chamber A via the hollow portion 19, the second lateral hole 25, and the third port 18. Road G
There are three channels.

That is, the shock absorber SA is constructed so that the damping characteristic can be changed in multiple stages with the characteristics shown in FIG. 6 on both the extension side and the compression side by rotating the adjuster 40. That is, as shown in FIG. 7, when the adjuster 40 is rotated counterclockwise from a region in which both the extension side and the compression side are soft (hereinafter referred to as the soft region SS),
Only the expansion side can change the damping characteristic to the hard side in multiple stages, and the compression side becomes a softly fixed area (hereinafter referred to as the expansion side hard area HS). Conversely, when the adjuster 40 is rotated clockwise, the compression side Only the damping characteristic can be changed to the hard side in multiple steps, and the extension side is softly fixed (hereinafter, compression side hard area SH
That is) the structure.

By the way, in FIG. 7, the KK cross section, the LL cross section and the MM cross section, and the NN cross section in FIG. 8, FIG. 9, and FIG. 10, and the damping force characteristics at each position are shown in FIGS.

Next, the operation of the damping characteristic control section in the control unit 4 will be described with reference to the flowchart of FIG. 15 and the time chart of FIG.

In the flowchart of FIG. 15, step 101 is a step of detecting the sprung vertical acceleration G from the vertical G sensor 1.

In step 102, the sprung vertical acceleration G is integrated to calculate the sprung vertical velocity Vn. The sprung vertical velocity Vn is given as a positive value in the upward direction and a negative value in the downward direction, and is used as it is as the control signal V of the shock absorber SA of each wheel.

Step 103 is a step of determining whether or not the sprung vertical velocity Vn is a positive value (upward). If YES (upward), the routine proceeds to step 104, and NO.
(Downward) proceeds to step 105.

Step 104 is a step for judging whether or not the previous sprung vertical velocity Vn _-1 is a negative value. If YES, the routine proceeds to step 106, and if NO, step 1
Proceed to 07. That is, in this step, the sprung vertical velocity V
It determines whether the direction of n has been reversed.

In step 106, the threshold V _S1 of the upward sprung vertical velocity Vn is initialized to a predetermined value, and a flag for determining whether the direction of the sprung vertical velocity Vn is reversed is 0 ( This is a step for setting the "non-reverse", and then the process proceeds to step 107.

Step 107 is a step of judging whether or not the sprung vertical velocity Vn becomes equal to or more than a predetermined threshold value V _S1 , and if YES (or more), the process proceeds to step 108,
If NO (less than), the process proceeds to step 109.

Step 108 is a step for updating the initially set value of the threshold value V _{S1 to} the value of the sprung vertical velocity Vn at that time, and then proceeds to step 109.

Step 109 is a shock absorber S
This is a step of setting a target damping position Pn on the extension side in A and driving the pulse motor 3 toward the set target position Pn. This target damping position Pn is (P _{+ MAX} / V _S1 ) × Vn It is calculated based on the arithmetic expression of. It should be noted that P _{+ MAX} is a position where the damping force on the extension side becomes maximum, as shown in FIG.

Step 110 is a step for judging whether or not the flag is 0. If YES (reverse rotation of Vn direction), the process proceeds to step 111, and if NO (not reverse rotation), step 112.
Go to.

Step 111 is the absolute value of the acceleration signal |
This is a step for determining whether or not G ₁ | exceeds a predetermined threshold value Gn, and if YES, then the routine proceeds to step 112, where N
Return to step 101 with O.

Step 112 is a step in which the flag is set to 1 (reverse rotation), and then the process proceeds to step 113.

Step 113 is a step of judging whether or not the target position Pn exceeds a predetermined upper limit value Xn ₁ , and if YES, the routine proceeds to step 114, where N
Return to step 101 with O.

Step 114 is a step of updating the upper limit value Xn ₁ to the target position Pn at that time.

Step 105 is a step for determining whether or not the previous sprung vertical velocity Vn _-1 is a positive value. If YES, the process proceeds to step 115, and if NO, step 1
Proceed to 16. That is, this step is the sprung vertical velocity V
It determines whether the direction of n has been reversed.

In step 115, the threshold value V _S2 of the downward sprung vertical velocity Vn is initialized to a predetermined value, and a flag for determining whether the direction of the sprung vertical velocity Vn is reversed is 0 ( This is a step for setting to (non-reverse), and then the process proceeds to step 116. It is a step.

Step 116 is a step of judging whether or not the absolute value │Vn│ of the sprung vertical velocity is equal to or more than the absolute value │V _S2 │ of a predetermined threshold value. If YES, the routine proceeds to step 117, If NO, the process proceeds to step 118.

Step 117 is a step of updating the initially set threshold value V _{S2 to} the value of the sprung vertical velocity Vn at that time.

Step 118 is a shock absorber S
This is a step of setting a target damping position Pn on the pressure side in A and driving the pulse motor 3 toward the set target position Pn. This target damping position Pn is defined as (P- _MAX / V _S2 ) × Vn. It is calculated based on the calculation formula. It should be noted that P- _MAX is the position where the damping force on the compression side is maximized, as shown in FIG.

In step 119, the flag is 0 (not reversed).
This is a step for determining whether or not, and if YES, step 1
20. If NO, proceed to step 121.

Step 120 is the absolute value of the acceleration signal |
This is a step of determining whether or not G ₁ | exceeds a predetermined threshold value Gn, and if YES, the routine proceeds to step 121, where N
Return to step 101 with O.

Step 121 is a step in which the flag is set to 1 (reverse rotation), and then the process proceeds to step 122.

Step 122 is a step of judging whether or not the absolute value | Pn | of the target position exceeds the absolute value | Xn ₂ | of the predetermined upper limit value. If YES, the routine proceeds to step 123, and if NO. Return to step 101.

Step 123 is a step for updating the upper limit value Xn ₂ to the target position Pn at that time.

With the above, one control flow is completed, and the control unit 4 repeats the above control flow.

Next, the operation of the control unit 4 will be described with reference to the time chart of FIG. That is, FIG.
6 is a time chart showing the operation when the vehicle is running, showing the acceleration signal G ₁ , the sprung vertical velocity Vn, and the target position Pn in order from the top.

(A) When running on a good road with a small unsprung vibration: The acceleration signal G ₁ obtained by cutting the sprung vertical acceleration G from the low frequency component including the sprung resonance frequency is a predetermined threshold value Gn.
When the value is less than the value, the unsprung vibration is not severe (running on a good road), so that the stroke side of the shock absorber SA, which is the same as the direction of the sprung vertical velocity Vn at that time, is high in proportion to the sprung vertical velocity Vn. Switching control (high-proportional proportional control) of the damping characteristic that becomes the damping characteristic is performed. That is, a) As shown by r ₁ in FIG. 16, the acceleration signal G ₁ (unsprung high frequency component) is below a predetermined threshold value Gn,
And when the direction of the sprung vertical velocity Vn is upward,
The extension side, which is in the same direction as the sprung vertical velocity Vn, has a high damping position [Pn = proportional to the sprung vertical velocity Vn].
(P _{+ MAX} / V _S1 ) × Vn], the pressure side of the reverse stroke is switched to the extension side hard region HS (characteristic of FIG. 11) side where a predetermined low damping characteristic is obtained.

B) As indicated by r ₂ in FIG. 16, the absolute value of the acceleration signal | G ₁ | (unsprung high frequency component) is less than or equal to a predetermined threshold value Gn, and the sprung vertical velocity Vn Is downward, the pressure side, which is in the same direction as the sprung vertical velocity Vn, is at a high damping position [Pn = (P- _MAX / V _S2 ) × Vn] proportional to the sprung vertical velocity Vn.
The extension side of the reverse stroke is switched to the compression side hard region SH (characteristic of FIG. 13) side where a predetermined low damping characteristic is obtained.

Therefore, the unsprung state is accurately grasped by the acceleration signal G ₁ from which the low frequency component including the sprung resonance frequency is removed, and when the unsprung vibration is not severe, the sprung vertical velocity Vn at that time is determined. By controlling the stroke direction of the shock absorber SA, which is the same as the direction of the shock absorber SA, to the high damping characteristic side proportional to the sprung vertical velocity Vn, vibration on the spring is suppressed to ensure steering stability, and at the same time, sprung at that time. The stroke of the shock absorber SA in the direction opposite to the direction of the vertical velocity Vn is set to a predetermined low damping characteristic to absorb the road surface input in the direction opposite to the stroke direction during vibration control and prevent the transmission of vibration to the vehicle body. The ride comfort can be secured.

(B) When traveling on a bad road with a large amount of unsprung vibration or when inputting a single projection, the acceleration signal value G ₁ obtained by cutting the low-frequency component including the sprung resonance frequency from the sprung vertical acceleration G is a predetermined value. Threshold G
When n is exceeded, unsprung vibration is severe (during traveling on a rough road or when a single spiking input is made). In this case, until the direction of the sprung vertical velocity Vn reverses. ,
Upper limit limits Xn ₁ and Xn ₂ are set to the target position Pn by the basic control unit, and upper limit control is performed so that the damping position does not become higher than a predetermined low damping characteristic. That is, a) As shown by s ₁ and s ₂ in FIG. 16, the acceleration signal G ₁
When the (unsprung high frequency component) exceeds the predetermined threshold value Gn and the target position by the basic control unit exceeds the upper limit Xn ₁ or Xn ₂ , the sprung vertical velocity Vn Until the direction is reversed, the damping position in the same stroke direction as the direction of the sprung vertical velocity Vn at that time is fixed to the upper limit Xn ₁ , Xn ₂ .

B) As shown at t ₁ and t ₂ in FIG. 16, after the acceleration signal G ₁ (unsprung high frequency component) exceeds a predetermined threshold value Gn, and by the basic control unit. When the target position Pn becomes less than or equal to the upper limit Xn ₁ , Xn ₂ , until the direction of the sprung vertical velocity Vn reverses, the same stroke side as the direction of the sprung vertical velocity Vn at that time is the basic control unit. It is controlled according to the target position Pn calculated by

Accordingly, the unsprung state is accurately grasped by the acceleration signal G ₁ from which the low-frequency component including the sprung resonance frequency is removed, and when the unsprung vibration is severe, it is the same as the sprung vertical velocity Vn at that time. The upper limit of the damping characteristic of the shock absorber SA on the stroke side is set to a predetermined low damping characteristic (Xn ₁ , X
By limiting to n ₂ ), it is possible to suppress the transmission of the high-frequency road surface input to the vehicle body when the vehicle is traveling on a rough road or when there is a single spiking input, and it is possible to improve the riding comfort of the vehicle.

Next, the operation of the control unit 4 at the time of running on a good road in which the acceleration signal G ₁ is within the threshold value Gn will be described with reference to the time chart of FIG. , Damping force F and relative speed, control direction (stroke) of shock absorber SA,
The target position Pn is shown, and the sprung vertical velocity Vn is shown.
That is, the control signal V travels in a sine curve alternately on the extension side and the compression side, and the peak values P ₁ and P ₂ in the vertical direction exceed the threshold values V _S1 and V _S2 of the initial setting values, respectively. The case where it changes is shown.

In the figure, region a is the sprung vertical velocity V
This is a region where n is upward and less than the initial threshold value V _S1 . In this case, the target extension-side target position Pn is controlled in proportion to the sprung vertical velocity Vn.
At this time, since the stroke of the shock absorber SA is the pressure stroke, the push-up of the vehicle body due to the road surface input can be suppressed by the soft characteristic on the pressure side (minimum damping position).

The next region b is a region until the sprung vertical velocity Vn becomes equal to or higher than the initial threshold value V _S1 and reaches the peak value P ₁ , and in this case, the flow of steps 107 to 108 in FIG. As a result, the threshold V _S1 is made to coincide with the sprung vertical velocity at all times, and as a result, the target position is held at the maximum extension side damping position P _{+ MAX} until the peak value P ₁ is reached. By thus increasing the damping characteristic on the extension side, it is possible to suppress vibration in the upward direction of the vehicle body.

The next region c is a region from the peak value P _{1 of the} sprung vertical velocity Vn to the reverse of the direction of the sprung vertical velocity Vn. In this case, the sprung vertical velocity Vn is the peak value P ₁ At that time, the threshold value V _S1 also reaches the peak value P.
_Since it is equal to ₁ , step 10 in FIG.
When the sprung vertical velocity Vn falls below the peak value P ₁ based on the arithmetic expression shown in Fig. 9, the target position Pn on the extension side decreases from that point in proportion to the reduction of the sprung vertical velocity Vn.

The next area d is an area from when the direction of the sprung vertical velocity Vn is reversed to when the downward downward threshold V _S2 or more is reached. In this case, the target position P
Although n is controlled in proportion to the sprung vertical velocity Vn, at this time, since the stroke of the shock absorber SA is the extension stroke, the soft characteristic on the extension side (minimum damping position) is used for road surface input. It is possible to suppress the sinking of the vehicle body based on this.

The next region e is a region in which the sprung vertical velocity Vn reaches or exceeds the initial threshold value V _S2 and reaches the peak value P ₂ , and in this case, the flow of steps 116 to 117 in FIG. As a result, the threshold value V _S2 is made to coincide with the sprung vertical velocity at all times, and as a result, the target position Pn is set to the compression side maximum damping position P until the peak value P ₂ is reached.
_-Hold to _MAX . By thus increasing the damping characteristic on the compression side, it is possible to suppress downward vibration of the vehicle body.

The next region f is a region from the peak value P _{2 of the} sprung vertical velocity Vn to the reverse of the direction of the sprung vertical velocity Vn. In this case, the sprung vertical velocity Vn is the peak value P ₂ Threshold value V _S2 peak value P ₂
Since it is equal to, step 118 in FIG.
When the sprung vertical velocity Vn changes upward from the peak value P ₂ based on the arithmetic expression shown in, the target position Pn on the extension side decreases from that point in proportion to the change in the sprung vertical velocity Vn.

Further, in the time chart of FIG.
In the region g, the sprung vertical velocity Vn based on the sprung vertical velocity Vn is reversed from a negative value (downward) to a positive value (upward), but at this time, the relative velocity is still a negative value (shock). Since the stroke of the absorber SA is on the pressure stroke side), at this time, the shock absorber SA is extended on the extension side hard area HS based on the direction of the sprung vertical velocity Vn.
Therefore, in this region, the pressure stroke side, which is the stroke of the shock absorber SA at that time, has a soft characteristic.

Further, in the region h, the sprung vertical velocity Vn remains a positive value (upward), and the relative velocity is switched from a negative value to a positive value (the stroke of the shock absorber SA is on the extension side). Since it is a region, at this time, the sprung vertical velocity Vn
The shock absorber SA is controlled in the extension side hard region HS based on the direction of, and the stroke of the shock absorber is also the extension stroke. Therefore, in this area, the extension side which is the stroke of the shock absorber SA at that time is The hard characteristic is proportional to the value of the sprung vertical velocity Vn.

In the region j, the sprung vertical velocity Vn is reversed from a positive value (upward) to a negative value (downward), but at this time, the relative velocity is still positive (shock absorber SA). Since the stroke is on the extension side), the shock absorber SA is controlled to the compression side hard area SH based on the direction of the sprung vertical velocity Vn at this time. The extension side, which is the stroke of the shock absorber SA, has soft characteristics.

The region k is a region in which the sprung vertical velocity Vn remains a negative value (downward) and the relative velocity changes from a positive value to a negative value (the stroke of the shock absorber SA is the extension stroke side). Therefore, at this time, the shock absorber SA moves in the compression side hard area SH based on the direction of the sprung vertical velocity Vn.
Is controlled and the stroke of the shock absorber is also a pressure stroke. Therefore, in this region, the pressure stroke side, which is the stroke of the shock absorber SA at that time, has a hard characteristic proportional to the value of the sprung vertical velocity Vn. .

As described above, in this embodiment, when the sprung vertical speed and the relative speed between the sprung portion and the unsprung portion have the same sign (region h, region k), the shock absorber S at that time is detected.
Attenuation characteristic control based on the skyhook theory, that is, the stroke side of A is controlled to have a hard characteristic and the stroke side of the shock absorber SA at that time is controlled to have a soft characteristic when the signs are different (area g, area j). The same control will be performed without detecting the relative speed between sprung and unsprung. Further, in this embodiment, when the region g is changed to the region h and the region j is changed to the region k, the attenuation characteristics are switched without driving the pulse motor 3.

As described above, in this embodiment, the effects listed below can be obtained. While suppressing the vehicle vibration when traveling on a good road to ensure the riding comfort and steering stability of the vehicle, it suppresses the transmission of high frequency road surface input to the vehicle body when traveling on a bad road or when there is a single spurious input. It is possible to improve the riding comfort of the vehicle.

When performing the damping characteristic control based on the skyhook theory, the upper and lower G sensors 1 are used as the detection means.
Since only one is used, the number of parts can be reduced and the cost can be reduced, and the assembling labor, assembling space and weight can be reduced.

As compared with the conventional damping characteristic control based on the skyhook theory, the frequency of switching the damping characteristic is reduced, so that the control response can be improved and the durability of the pulse motor 3 can be improved.

Although the embodiment has been described above, the specific structure is not limited to this embodiment, and a design change and the like within the scope not departing from the gist of the invention are included in the invention.

For example, in the embodiment, the control content is such that the stroke for controlling to the hardware characteristic side is determined depending on whether the sprung vertical velocity is a positive value or a negative value. A value is set, and while the sprung vertical velocity is within this positive / negative threshold, the soft region SS is controlled so that both the extension side and the compression side have soft characteristics, and when the positive / negative threshold is exceeded, the hard characteristic (extension It is also possible to control to the side hard region HS or the pressure side hard region SH) side.

Further, in the embodiment, the target position is calculated based on the arithmetic expression, but it may be calculated based on the map shown in FIG. In this figure, (a) is a map for extension side and (b) is a map for compression side, and the target position corresponding to the value of the sprung vertical velocity is set.

In the embodiment, the sprung vertical velocity of each wheel is used as it is as the control signal of each shock absorber, but the control is performed based on the sprung vertical velocity difference between the front and rear wheels and the left and right wheels. You may make it request | require a signal.

Further, in this embodiment, when controlling one side of both the extension and compression strokes to the high damping characteristic side, a shock absorber having a structure in which the reverse stroke side is fixed to a predetermined low damping characteristic is provided. Although used, a shock absorber having a structure in which both extension and compression strokes change at the same time can be used.

Further, the upper limit value may be changed in proportion to the sprung vertical acceleration and the vehicle speed.

[0070]

As described above, in the vehicle suspension system of the present invention, when the acceleration signal passing through the high-pass filter is less than a predetermined threshold value, the sprung up / down direction detected by the sprung up / down speed detecting means. While controlling the stroke side of the shock absorber, which is the same as the direction of the control signal based on speed, to the optimum damping characteristic according to the control signal, the direction of the control signal reverses from that point when the acceleration signal exceeds the specified threshold value. The upper limit value of the damping characteristic on the stroke side of the shock absorber, which is the same as the direction of the control signal, is set to a predetermined low damping characteristic until the The damping characteristics ensure the damping of the vehicle and the steering stability of the vehicle, while the riding characteristics of the vehicle are reduced due to the low damping characteristics that are reduced when driving on a rough road or when a single protruding input is applied. Effect is obtained that it is possible to improve the land.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of a claim showing a vehicle suspension device of the present invention.

FIG. 2 is a structural explanatory view showing a vehicle suspension device of an embodiment of the present invention.

FIG. 3 is a system block diagram showing a vehicle suspension system of the embodiment.

FIG. 4 is a cross-sectional view showing a shock absorber applied to the apparatus of the embodiment.

FIG. 5 is an enlarged cross-sectional view showing a main part of the shock absorber.

FIG. 6 is a damping force characteristic diagram corresponding to the piston speed of the shock absorber.

FIG. 7 is a characteristic diagram of damping characteristics corresponding to a step position of the pulse motor of the shock absorber.

FIG. 8 is a K of FIG. 5 showing a main part of the shock absorber.
FIG.

FIG. 9 is an L of FIG. 5 showing a main part of the shock absorber.
It is a LM sectional view.

FIG. 10 is a sectional view taken along line NN of FIG. 5, showing a main part of the shock absorber.

FIG. 11 is a damping force characteristic diagram of the shock absorber when the extension side is hard.

FIG. 12 is a damping force characteristic diagram of the shock absorber in a soft state on the extension side and the compression side.

FIG. 13 is a damping force characteristic diagram of the shock absorber in a compression side hard state.

FIG. 14 is a block diagram showing a signal processing unit of a control unit.

FIG. 15 is a flowchart showing the operation of the control unit.

FIG. 16 is a time chart showing the operation of the control unit.

FIG. 17 is a time chart showing the operation of the control unit during basic control.

FIG. 18 is a map showing another example of how to obtain a target position.

[Explanation of symbols]

 a damping characteristic changing means b shock absorber c sprung vertical acceleration detecting means d sprung vertical velocity detecting means e high-pass filter f basic control section g damping characteristic control section h upper limit setting processing section

Claims (1)

[Claims] 1. A shock absorber interposed between a vehicle body side and each wheel side and capable of changing a damping characteristic by a damping characteristic changing means; a sprung vertical acceleration detecting means for detecting a sprung vertical acceleration of a vehicle; A sprung vertical velocity detecting means for detecting the sprung vertical velocity, a high-pass filter for cutting low-frequency components including a sprung resonance frequency from a signal obtained from the sprung vertical acceleration detecting means, and the high-pass filter. When the passed acceleration signal is less than a predetermined threshold value, the stroke side of the shock absorber, which is the same as the direction of the control signal based on the sprung vertical velocity detected by the sprung vertical velocity detecting means, is optimized according to the control signal. A damping characteristic control means having a basic control section for outputting a signal for controlling the damping characteristic to the damping characteristic changing means, and a high-pass filter provided in the damping characteristic control means. When the acceleration signal passing through the filter exceeds a predetermined threshold value, the upper limit value of the damping characteristic on the stroke side of the shock absorber that is the same as the direction of the control signal from that point until the direction of the control signal reverses A vehicle suspension device comprising: an upper limit value setting processing unit for setting a low damping characteristic.