JPH09309310A - Vehicle suspension device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve barking performance by heightening frictional resistance between a tire and a road surface by slipping a center of wheel load variation at least at the time of braking a vehicle. SOLUTION: At least a damping force characteristic changing means (a) of a front wheel side shock absorber b1 of the shock absorbers b1 , b2 interposed between the side of a car body and the side of each wheel and having the damping force characteristic changing means (a) free to change a damping force characteristic is structured free to change a first characteristic which a contraction stroke side damping farce characteristic becomes a larger value than a extension stroke side damping force characteristic and the least another second characteristic over to each other, end it is furnished with a braking state detection means (c) to detect a braking state of a vehicle and a damping force characteristic control means (d) to control to change at least the damping force characteristic changing means (a) of the front wheel side shock absorber b1 over to the first characteristic side when the backing state of the vehicle is detected by the braking state detection means (c).

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 a damping force characteristic of a shock absorber.

[0002]

2. Description of the Related Art Conventionally, as a vehicle suspension system for controlling a damping force characteristic of a shock absorber, for example, Japanese Patent Publication No.
The one described in Japanese Patent No. 502439 is known.
This conventional vehicle suspension system detects the absolute speed of the vehicle body (the sprung vertical speed) and the relative piston speed of the damper (the relative speed between the sprung and unsprung parts), and detects the relative speed between the sprung vertical speed and the unsprung part. In the damping range where the speed direction identification codes match, the damping force characteristics of the shock absorber are controlled to the hard side to increase the vehicle damping force, and in the vibration range where the direction identification codes do not match. Is to control the switching of damping force characteristics based on the Karnop control theory (skyhook control theory), such as damping the vehicle excitation force by controlling the damping force characteristics of the shock absorber to the soft side. Met.

[0003]

However, in the conventional vehicle suspension system, the damping force characteristic control based on the skyhook control theory has the effect of improving the riding comfort of the vehicle, but the braking effect during braking of the vehicle. It may not be possible to improve. That is, generally, the damping force characteristic of the shock absorber is set so that the compression side damping force characteristic is smaller than the extension side damping force characteristic, so that the shock absorber contracts (the vehicle height decreases). As a result, the center of the wheel load fluctuation caused by the road surface input during braking deviates in the wheel load decreasing direction, so that the frictional force between the tire and the road surface decreases, and as a result, the braking force decreases.

The present invention has been made in view of the above-mentioned conventional problems, and at least at the time of braking of the vehicle, the center of the wheel load fluctuation is shifted in the wheel load increasing direction so as to increase the friction resistance between the tire and the road surface. It is an object of the present invention to provide a vehicle suspension device capable of improving the braking performance by improving the braking performance.

[0005]

In order to achieve the above-mentioned object, the vehicle suspension system according to claim 1 of the present invention is arranged between the vehicle body side and each wheel side as shown in the claim correspondence diagram of FIG. Of the shock absorbers b ₁ and b ₂ which are interposed and have damping force characteristic changing means a capable of changing the damping force characteristic, at least the damping force characteristic changing means a of the front wheel side shock absorber b ₁ is better than the extension stroke side damping force characteristic. Also, a braking state detecting means c for detecting the braking state of the vehicle, which has a structure capable of switching between the first characteristic in which the pressure stroke side damping force characteristic has a larger value and at least one other second characteristic, When the braking state of the vehicle is detected by the braking state detecting means c, at least a damping force characteristic control means d for controlling the switching of the damping force characteristic changing means a of the front wheel side shock absorber b ₁ to the first characteristic side. Prepare It was a means you are. In addition, claim 2
In the vehicle suspension system described above, at least the first characteristic of the damping force characteristic changing means a of the front wheel side shock absorber b ₁ is the compression stroke side damping force characteristic rather than the extension stroke side damping force characteristic only in the low piston velocity range side. Is configured to have a large value. Further, in the vehicle suspension system according to the third aspect, the anti-skid control device is provided, and the braking state detecting means c is configured to detect the braking state from the operation of the anti-skid control device.
Further, in the vehicle suspension system according to the fourth aspect, a brake switch is provided, and the braking state detecting means c is configured to detect the braking state from the operation state of the brake pedal. Further, in the vehicle suspension system according to claim 5, a brake switch and a wheel speed detecting means are provided, and the braking state detecting means c detects the braking state from the operation state of the brake pedal and the change rate of the wheel speed. It has been configured means. Further, in the vehicle suspension system according to the sixth aspect, the brake fluid pressure detecting means is provided, and the braking state detecting means c is configured to detect the braking state from the brake fluid pressure. Further, in the vehicle suspension system according to the seventh aspect, the vehicle acceleration / deceleration detecting means is provided, and the braking state detecting means c is configured to detect the braking state from the longitudinal acceleration of the vehicle. The vehicle suspension system according to claim 8 further comprises a wheel speed detecting means for detecting a wheel speed or a sprung up / down behavior detecting means for detecting a sprung up / down behavior, and the wheel speed detecting means or the up / down behavior detecting means The damping force characteristic control means d is extracted only when the detected wheel speed or 1-8 Hz component of the sprung vertical motion is extracted and the component exceeds a predetermined threshold value.
The means for controlling the switching to the first characteristic by means of. Further, in the vehicle suspension system according to claim 9, a sprung vertical velocity detecting means for detecting a sprung vertical velocity is provided, and the damping force characteristic changing means a of the shock absorbers b ₁ and b ₂ is provided on one stroke side. When the damping force characteristic is variably controlled, the reverse stroke side has a low damping force characteristic. When the braking state of the vehicle is not detected by the braking state detecting means c, the damping force characteristic controlling means d When the direction identification code of the sprung vertical velocity signal detected by the sprung vertical velocity detecting means is upward, the shock absorber b
The damping force characteristics ₁ and b _{2 on} the extension stroke side are variably controlled based on the sprung vertical velocity signal when the damping force characteristics on the compression stroke side are downward, and the braking state of the vehicle is detected by the braking state detecting means c. When is detected, at least the damping force characteristic changing means a of the front wheel side shock absorber b ₁ is fixedly controlled so that the damping force characteristic on the pressure stroke side becomes a high damping force characteristic.

[0006]

Since the vehicle suspension system according to claim 1 of the present invention is configured as described above, when the braking state of the vehicle is detected by the braking state detecting means c, at least the damping force characteristic control means d is By controlling the damping force characteristic changing means a of the front wheel side shock absorber b _{1 to} the _first characteristic in which the compression stroke side damping force characteristic is larger than the extension stroke side damping force characteristic, the center of wheel load fluctuation is controlled. Can be shifted in the wheel load increasing direction, whereby the frictional resistance between the tire and the road surface is increased and the braking performance can be improved.

Further, in the vehicle suspension system according to claim 2,
On the low piston speed range where the sprung mass behavior is the main component, as described above, the center of wheel load fluctuation is shifted in the direction of increasing wheel load to increase the frictional resistance between the tire and the road surface while improving braking performance. In the high piston velocity range where unsprung behavior is the main component, the damping force characteristics not only on the compression stroke side but also on the extension stroke side should be at least equal to or greater than the compression stroke side. The unsprung behavior is suppressed, whereby the ground contact force of the tire is increased and the braking performance can be improved.

Further, in the vehicle suspension system according to claim 8,
The damping is performed only when the 1 to 8 Hz component of the wheel speed or the sprung vertical behavior exceeds a predetermined threshold value, that is, when the frequency band component of the sprung behavior having a large influence on the wheel load fluctuation during braking is detected. The force characteristic control means d controls the switching to the first characteristic, whereby when the sprung mass behavior is the main component, the center of wheel load fluctuation is shifted in the wheel load increasing direction as described above. As a result, the frictional resistance between the tire and the road surface can be increased to improve the braking performance, and when the sprung mass behavior is small and the unsprung mass behavior is the main component, not only the compression stroke side but also the extension stroke side. The damping force characteristics of the tire are at least equal to or higher than those on the pressure stroke side, so that unsprung behavior is suppressed, which increases the ground contact force of the tire and improves braking performance. So that it is.

Further, in the vehicle suspension system according to claim 9,
During normal running of the vehicle (during non-braking), when the direction discrimination code of the sprung vertical velocity is upward in the damping force characteristic control means d, the damping force characteristic on the extension side of the shock absorbers b ₁ and b ₂ is When it is downward, the damping force characteristic on the compression stroke side is variably controlled based on the sprung vertical velocity signal, while the reverse stroke side is fixedly controlled to the low damping force characteristic. Therefore, in the damping region where the direction discrimination codes of the sprung vertical velocity and the sprung unsprung relative velocity match, the shock absorbers b ₁ and b at that time are
The damping force of the vehicle is enhanced by variably controlling the stroke side of ₂ on the high damping force characteristic side, and in the vibration range where the direction discrimination codes of the two do not match, the shock absorbers b ₁ and b ₂ at that time are A basic damping force characteristic switching control is performed based on the skyhook theory, such as weakening the vehicle's excitation force by making the stroke side a low damping force characteristic, which allows the vehicle to run normally (non-braking). At the time), it is possible to suppress the sprung behavior to secure the riding comfort and steering stability of the vehicle.

At the time of braking the vehicle, at least the damping force characteristic changing means a of the front wheel side shock absorber b ₁ is fixedly controlled so that the damping force characteristic on the pressure stroke side becomes a high damping force characteristic, and vice versa. The damping force characteristic on the extension side of the stroke is a low damping force characteristic.This allows the center of wheel load fluctuation to be shifted in the direction of increasing wheel load, increasing the frictional resistance between the tire and the road surface and braking. The performance can be improved.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described with reference to the drawings. (Embodiment 1) FIG. 2 shows Embodiment 1 of the present invention.
FIG. 2 is an explanatory view showing the configuration of the vehicle suspension device of FIG. 1, which is interposed between a vehicle body and four wheels, and is provided with four shock absorbers S.
A _FL , SA _FR , SA _RL , SA _RR (Note that in describing the shock absorber, these four are collectively referred to, and when describing their common configuration, they are simply indicated as SA. The lower reference numbers indicate the wheel position, _FL indicates the front wheel left, _FR indicates the front wheel right, _RL indicates the rear wheel left, and _RR indicates the rear wheel right.) Each wheel position has a vertical acceleration G (G _FL ,
_GPR , _GRL , _GRR ) sprung vertical acceleration sensor (hereinafter referred to as vertical G sensor) 1 ( _1FL , _1FR , _1RL ,
1 _RR ) and wheel speed sensors 2 _FL , 2 _FR for detecting wheel speeds W _V-FL , W _V-FR of the front wheel side left and right wheels, respectively. , rear differential wheel speed sensors 2 _RS for detecting a wheel speed W _V-RS of the rear wheel side is provided in the further in the vicinity of the driver's seat, the vertical G sensors _{1 (1 FL, 1 FR,} 1 RL , 1 _RR ) and signals from each wheel speed sensor 2 (2 _FL , 2 _FR , 2 _RS ) are input to drive control the pulse motor 3 of each shock absorber SA _FL , SA _FR , SA _RL , SA _RR. A control unit 4 that outputs a signal is provided.

The system block diagram of FIG. 3 shows the above configuration. The control unit 4 includes an interface circuit 4a, a CPU 4b, and a drive circuit 4c, and the interface circuit 4a includes the vertical G sensor 1 (1).
_FL , 1 _FR , 1 _RL , 1 _RR )
_FL , G _FR , G _RL , G _RR ) signal, each wheel speed sensor 2
Wheel speed W _V (W _V-FL , W from (2 _FL , 2 _FR , 2 _RS )
_V-FR , W _V-RS ) signals are input, and the control unit 4 controls the damping force characteristics of each shock absorber SA (SA _FL , SA _FR , SA _RL , SA _RR ) based on these input signals, Skid control is performed. An anti-skid control operation detection circuit for detecting anti-skid control operation is provided in the control unit 4. It should be noted that description of specific contents of the anti-skid control is omitted.

The control unit 4 includes:
The sprung sprung at each wheel position based on the sprung vertical acceleration G (G _FL , G _FR , G _RL , G _RR ) signals from the vertical G sensors 1 (1 _FL , 1 _FR , 1 _RL , 1 _RR ). A signal processing circuit (FIG. 14) for obtaining the vertical speed signal and the sprung unsprung relative speed signal is provided. The details of this signal processing circuit will be described later. Further, an anti-skid control operation detection circuit for detecting an operation state of the anti-skid control device is provided in the control unit.

Next, FIG. 4 is a sectional view showing the structure of the shock absorber SA.
A is a cylinder 30, a piston 31 defining the cylinder 30 into an upper chamber A and a lower chamber B, an outer cylinder 33 having a reservoir chamber 32 formed on the outer periphery of the cylinder 30, a lower chamber B and a reservoir chamber 32. Defining the base 34 and the piston 31
A guide member 35 for guiding the sliding of the piston rod 7 connected to the outer cylinder 33, a suspension spring 36 interposed between the outer cylinder 33 and the vehicle body, and a bump rubber 37.

Next, FIG. 5 is an enlarged sectional view showing a portion of the piston 31. As shown in FIG. 5, the piston 31 is formed with through holes 31a and 31b, and each through hole is formed. A compression side damping valve 20 and an expansion side damping valve 12 that open and close 31a and 31b respectively are provided. Further, a stud 38 penetrating the piston 31 is screwed and fixed to the bound stopper 41 screwed to the tip of the piston rod 7, and the stud 38 bypasses the through holes 31a and 31b. Communication for forming a flow path (an expansion-side second flow path E, an expansion-side third flow path F, a bypass flow path G, and a compression-side second flow path J described later) that connects the upper chamber A and the lower chamber B with each other. A hole 39 is formed and this communication hole 3
An adjuster 40 for changing the flow passage cross-sectional area of the flow passage is rotatably provided inside the passage 9. Also, the stud 38
The communication hole 3 is formed on the outer periphery of the communication hole 3 in accordance with the direction of fluid flow.
An expansion-side check valve 17 and a compression-side check valve 22 that allow and shut off the flow on the flow path side formed by 9 are provided. It should be noted that this adjuster 40 corresponds to the pulse motor 3
Is rotated through the control rod 70 (see FIG. 4). Also, the stud 38 has
A first port 21, a second port 13, a third port 18, a fourth port 14, and a fifth port 16 are formed in this order from the top.

On the other hand, in the adjuster 40, a hollow portion 19 is formed, a first lateral hole 24 and a second lateral 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.
b, the inside of the extension side damping valve 12 is opened to open 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
, The pressure-side second flow path J that opens the pressure-side check valve 22 to reach the upper chamber A through the air passage, and the bypass flow that reaches the upper chamber A through the hollow portion 19, the second horizontal hole 25, and the third port 18. Road G
And three flow paths.

That is, the shock absorber SA is constructed so that the damping force characteristic can be changed in multiple stages on both the extension side and the compression side by the characteristic as shown in FIG. 6 by rotating the adjuster 40. That is, as shown in FIG.
The state in which both pressure sides are soft (hereinafter, soft area SS
When the adjuster 40 is rotated counterclockwise from
When the damping force characteristic can be changed in multiple stages only on the extension side and the compression side is a region fixed to the low damping force characteristic (hereinafter referred to as the extension side hard region HS). Conversely, when the adjuster 40 is rotated clockwise, Only the compression side has a structure in which the damping force characteristic can be changed in multiple stages, and the extension side is a region fixed to the low damping force characteristic (hereinafter referred to as a compression side hard region SH).

Incidentally, in FIG. 7, when the adjuster 40 is arranged in the position of, the KK section, the LL section and the MM section, the NN section in FIG. 8, FIG. 9, and FIG. 10, and the damping force characteristics at each position are shown in FIGS.

Next, in the control operation of the control unit 4, the configuration of the signal processing circuit for obtaining the sprung vertical velocity Δx and the sprung-unsprung relative velocity (Δx-Δx ₀ ) is shown in the block diagram of FIG. It will be described with reference to the drawings.

First, in B1, the phase delay compensation formula is used,
Each vertical G sensors _{1 (1 FL, 1 FR,} 1 RL, 1 RR) on each spring is detected by the vertical acceleration _{G (G FL, G FR,} G RL, G RR)
Is converted into a sprung vertical speed signal at each tower position.

The general equation for phase delay compensation can be expressed by the following transfer function equation (1). G _(S) = (AS + 1) / (BS + 1) ... (1) (A <B) And the frequency band (0.5 Hz to 3) required for damping force characteristic control.
Hz), has the same phase and gain characteristics as the case of integration (1 / S), and as a phase lag compensation equation for lowering the gain on the low frequency side (up to 0.05 Hz), the following transfer function equation (2 ) Is used.

G _(S) = (0.001 S + 1) / (10 S + 1) × γ (2) Note that γ is a signal and gain characteristic in the case of speed conversion by integration (1 / S). Is a gain for matching, and is set to γ = 10 in the first embodiment of the present invention. As a result, as shown in the solid line gain characteristics in FIG. 15A and the solid line phase characteristics in FIG. 15B, the frequency band (0.5 Hz to 3 Hz) required for damping force characteristic control is obtained.
2), only the gain on the low frequency side is reduced without deteriorating the phase characteristics. Note that FIG.
Dotted lines (a) and (b) show the gain characteristic and phase characteristic of the sprung vertical velocity signal that has been velocity-converted by integration (1 / S). In B2, band-pass filter processing is performed to cut off components other than the target frequency band to be controlled. That is, the band-pass filter BPF is composed of a second-order high-pass filter HPF (0.3 Hz) and a second-order low-pass filter LPF (4 Hz), and has a sprung vertical velocity that targets a sprung resonance frequency band of the vehicle. Δx (Δx _FL , Δ
x _FR , Δx _RL , Δx _RR ) signal.

On the other hand, in B3, as shown in the following equation (3),
The vertical acceleration G (G _FL , G _FR , G _RL , G _{RR )} detected by each vertical G sensor 1 using the transfer function Gu _(S) from each sprung vertical acceleration to the relative speed between the sprung and unsprung _portions. ) Signal, the relative speed (Δx
−Δx ₀ ) [(Δx−Δx ₀ ) _FL , (Δx−Δx
₀ ) _FR , (Δx−Δx ₀ ) _RL , (Δx−Δx ₀ ) _RR ] signals are obtained. Gu _(S) =-ms / (cs + k) (3) where m is the sprung mass, c is the damping coefficient of the suspension, and k is the spring constant of the suspension.

That is, in the first embodiment of the present invention, the sprung vertical velocity detecting means for detecting the sprung vertical velocity at each wheel position is detected by the vertical G sensor 1 and the signal processing circuit of FIG. It is composed.

Next, of the damping force characteristic control operation of the shock absorber SA in the control unit 4, the contents of the normal control by the basic control unit will be described with reference to the flowchart of FIG. Note that this normal-time control is performed for each shock absorber SA _FL , SA _FR , SA _RL , SA.
_It is performed for each _RR .

In step 101, the sprung vertical velocity Δx
Is determined to be a positive value. If YES, the flow proceeds to step 102 to control each shock absorber SA to the extension-side hard region HS. If NO, the flow proceeds to step 103.

In step 103, the sprung vertical speed Δx
Is determined to be a negative value. If YES, the routine proceeds to step 104, where each shock absorber SA is controlled to the pressure-side hard area SH, and if NO, the routine proceeds to step 105.

Step 105 is a processing step when NO is determined in steps 101 and 103, that is, when the value of the sprung vertical velocity Δx is 0,
At this time, each shock absorber SA is
To control.

Next, the operation of the damping force characteristic control will be described with reference to the time chart of FIG. The sprung vertical velocity Δx is
When changing as shown in this figure, as shown in the figure, when the value of the sprung vertical velocity Δx is 0, the shock absorber SA is controlled to the soft region SS.

Further, when the value of the sprung vertical velocity Δx becomes a positive value, the compression side damping force characteristic is controlled to the soft side while controlling to the extension side hard region HS, while the expansion side damping force characteristic (target The damping force characteristic position P _T ) is changed in proportion to the sprung vertical velocity Δx based on the following equation (4). P _T = α · Δx · K (4) where α is a constant on the extension side, and K is a relative speed between the sprung and unsprung (Δx −Δx ₀ ).

When the value of the sprung vertical velocity Δx becomes a negative value, the compression side hard region SH is controlled to fix the extension side damping force characteristic to the soft characteristic, while the compression side damping force characteristic (target damping force The characteristic position P _C ) is calculated based on the following equation (5).
It changes in proportion to the sprung vertical speed Δx. P _C = β · Δx · K (5) where β is a pressure-side constant.

Next, among the damping force characteristic control operations of the control unit 4, mainly the switching operation state of the control region of the shock absorber SA will be described with reference to the time chart of FIG.

In the time chart of FIG.
Is a state in which the sprung vertical speed Δx is reversed from a negative value (downward) to a positive value (upward). At this time, the relative speed (Δx−Δx ₀ ) is still a negative value (shock absorber SA).
Is a pressure stroke side), and at this time, the shock absorber SA is controlled to the extension side hard region HS based on the direction of the sprung vertical speed Δx,
Therefore, in this area, the shock absorber SA at that time is
The pressure stroke side, which is the stroke of, has soft characteristics.

In the region b, the sprung vertical velocity Δx remains a positive value (upward), and the relative velocity (Δx-Δx ₀ ) is a negative value to a positive value (the stroke of the shock absorber SA is the extension stroke). Side), the shock absorber SA is controlled to the extension side hard area HS based on the direction of the sprung vertical velocity Δx at this time, and the stroke of the shock absorber is also the extension stroke. Therefore, in this region, therefore, the extension 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 Δx.

In region c, the sprung vertical velocity Δx is reversed from a positive value (upward) to a negative value (downward), but at this time, the relative velocity (Δx-Δx ₀ ) is still positive. Since this is the region where the value of is (the stroke of the shock absorber SA is the extension side), at this time, the sprung vertical velocity Δx
The shock absorber SA is controlled in the compression side hard region SH based on the direction of the above, and therefore, in this region, the extension side, which is the stroke of the shock absorber SA at that time, has a soft characteristic.

In the area d, the sprung vertical velocity Δx remains a negative value (downward), and the relative velocity (Δx-Δx ₀ ) is a positive value to a negative value (the stroke of the shock absorber SA is the extension stroke). Side), the shock absorber SA is controlled to the compression side hard region SH based on the direction of the sprung vertical velocity Δx at this time, and the stroke of the shock absorber is also the pressure stroke. In this region, the pressure stroke side, which is the stroke of the shock absorber SA at that time, has a hardware characteristic proportional to the value of the sprung vertical velocity Δx.

As described above, in the first embodiment of the present invention, when the sprung vertical velocity Δx and the relative velocity (Δx-Δx ₀ ) have the same sign (region b, region d), the shock absorber at that time is obtained. Damping force characteristic control based on the skyhook theory, in which the stroke side of the SA is controlled to the hard characteristic, and when the different sign (area a, area c), the stroke side of the shock absorber SA at that time is controlled to the soft characteristic. The same control as above will be performed. Further, in the first embodiment of the present invention, when the stroke of the shock absorber SA is switched, that is, when the region a shifts to the region b and the region c shifts to the region d (soft characteristic to hard characteristic), Since the damping force characteristic position on the stroke side to be switched is already switched to the hard characteristic side in the previous regions a and c, the switching from the soft characteristic to the hard characteristic can be performed without a time delay.

Next, of the damping force characteristic control operation in the control unit 4, the switching control between the normal control by the normal control section and the braking control by the braking control section and the content of the braking control will be described. A description will be given based on the flowchart of 18 and the time chart of FIG.

First, in the flow chart of FIG.
In step 201, according to the anti-skid control operation state detected by the anti-skid control operation detection circuit,
If it is YES (anti-skid control operation = braking state), it is determined whether the vehicle is in the braking state.
In the compression side hard region SH side A, and fixed control the damping force characteristics of the compression phase to the maximum position P _{C-ma x} (switching to the first characteristic of the claims) (see FIG. 13). NO
When (the anti-skid control is not operated = the non-braking state), the routine proceeds to step 203 where the normal control is performed, and the normal control (skyhook control) by the normal control unit (the second characteristic of the claims is applied). Switching is performed, and the control flow for one time is completed as described above, and the above control flow is repeated thereafter.

That is, in the control during braking, as shown in FIG.
As shown in, the shock absorber SA is located on the compression side hard region SH side, and the damping force characteristic on the compression stroke side is set to the maximum position P.
By fixing control to the _{C-ma x,} as shown in FIG. 13, the extension phase is soft characteristic damping force characteristics of the compression phase is the reverse stroke hard characteristic (extension phase damping force <compression phase damping As a result, as shown by the solid line in the wheel load characteristic diagram of FIG. 20, the center of the wheel load fluctuation is displaced in the increasing direction, and the frictional force between the tire and the road surface (grip of the tire). Force), braking performance is improved,
As a result, as shown by the solid line in FIG. 21, the braking distance can be shortened as compared with the case of the conventional damper CONV (extension stroke side damping force> pressure stroke side damping force) shown by the dotted line in the figure. 22. FIG. 22 is a diagram showing the stop distance characteristic with respect to the input frequency. Compared to the case of the conventional damper CONV (extension stroke side damping force> pressure stroke side damping force) shown by the polygonal line of this figure, diamond points are shown. As indicated by the polygonal line, the stop distance can be shortened in the frequency range of sprung mass behavior (input frequency 1 to 8 Hz), which greatly affects the wheel load fluctuation during braking.

As described above, the vehicle suspension system according to the first embodiment of the present invention has the following effects. When the vehicle is not braking, the ride performance and steering stability of the vehicle are ensured by controlling the damping force characteristics of the shock absorber SA based on the skyhook control theory. Can be shortened.

In normal-time control based on the skyhook control theory, since switching to the soft characteristic and the hardware characteristic is performed without a time delay, high control response is obtained, and switching from the hard characteristic to the soft characteristic is pulsed. This is performed without driving the motor 3, which makes it possible to improve the durability of the pulse motor 3 and save power consumption.

(Second Embodiment of the Invention) A vehicle suspension system according to a second embodiment of the present invention is different from the vehicle suspension system according to the first embodiment of the present invention in that the number of switching steps of the damping force characteristic in the shock absorber SA is two. Only the steps are different, and other points are almost the same as those of the vehicle suspension system according to the first embodiment of the present invention. Therefore, only the differences will be described.

That is, the damping force characteristic changing means of the shock absorber SA used in the vehicle suspension system according to the second embodiment of the present invention has a pressure stroke as shown by a dotted line in FIG. 23 (damping force characteristic diagram with respect to piston speed). The damping force characteristic position for normal time control (the second characteristic of the claims) in which the damping force characteristic on the extension stroke side is larger than that on the compression stroke side, and as shown by the solid line in FIG. Damping force characteristic position for braking control where the damping force characteristic is large (first in the claims)
It has a structure that can be switched in two steps.

When the vehicle is running normally (when the vehicle is not braking), the normal control damping force characteristic position is switched. When the vehicle is braking, the braking control damping force characteristic position is switched to the normal control damping force characteristic position. Switching is performed.

Therefore, also in the vehicle suspension system according to the second embodiment of the present invention, the riding performance and the steering stability of the vehicle are ensured when the vehicle is not braked, and the braking performance is improved when the vehicle is braked. The braking distance can be shortened.

(Third Embodiment of the Invention) A vehicle suspension system according to a third embodiment of the present invention is different from the vehicle suspension systems according to the first and second embodiments of the present invention in terms of damping force for braking control in a shock absorber SA. The damping force characteristic of the characteristic position is different, and other points are the same as in the first embodiment of the invention.
Or, since it is almost the same as the vehicle suspension device of No. 2, only different points will be described.

That is, FIG. 24 shows the shock absorber SA.
FIG. 6 is a damping force characteristic diagram for the piston speed at the damping force characteristic position for braking during braking, as shown in this damping force characteristic diagram, in the low piston velocity range side, the compression stroke side damping force is more than the extension stroke side damping force characteristic. Although the characteristic has a larger value, the extension stroke side damping force characteristic has a larger value than the pressure stroke side damping force characteristic on the high piston speed range side.

With the above configuration, on the low piston speed range side where the sprung mass behavior is the main component, as described above, the center of the wheel load fluctuation is shifted in the wheel load increasing direction so that the distance between the tire and the road surface is increased. It is possible to improve the braking performance by increasing the frictional resistance of the piston, and at the high piston speed range where unsprung behavior is the main component, the damping force characteristics not only on the compression stroke side but also on the extension stroke side are at least the compression stroke side. By setting the damping force characteristics to be equal to or higher than, it is possible to suppress the behavior of the unsprung part, and thereby the ground contact force of the tire is increased and the braking performance can be improved.

(Fourth Embodiment of the Invention) A vehicle suspension system according to a fourth embodiment of the present invention is different from the vehicle suspension system according to the first and second embodiments of the present invention in switching between normal control and braking control. The contents of control are different, and other points are almost the same as those of the vehicle suspension device of the first or second embodiment of the present invention, and therefore only the differences will be described.

That is, in the vehicle suspension system according to the fourth embodiment of the present invention, the vertical G sensor 1 (1 _FL , 1 _FR , 1 _RL , 1).
_Sprung vertical acceleration G (G _FL , G _FR , G _RL , G from _RR )
_RR ) signal, or each wheel speed sensor 2 (2 _FL ,
2 _FR , 2 _RS ) wheel speed W _V (W _V-FL , W _V-FR , W
_V-RS ) signal is used to extract a frequency band component (1 to 8 Hz) of sprung mass behavior that greatly affects wheel load fluctuations during braking, and when the vehicle is braking, the 1 to 8 Hz frequency component is predetermined. Only when the threshold value is exceeded, the damping force characteristic of the shock absorber SA is controlled to be switched to the damping force characteristic position for braking control.

With the above configuration, when the sprung mass behavior is the main component, the center of wheel load fluctuation is shifted in the wheel load increasing direction as described above to reduce the frictional resistance between the tire and the road surface. When the sprung behavior is small and the unsprung behavior is the main component, the damping force characteristics not only on the compression stroke side but also on the extension stroke side should be at least on the compression stroke side. By setting the damping force characteristics to be equal to or higher than that, it is possible to suppress the behavior under the spring, and thereby the ground contact force of the tire is increased and the braking performance can be improved.

Note that FIG. 25 is a one-wheel model diagram of the wheel load, and the wheel load F is obtained by the following equation (6). F = m ₁ · Δ ² x ₁ + m ₂ · Δ ² x ₂ + (m ₁ + m ₂ ) ... (6) In addition, m ₁ is sprung weight, m ₂ Is unsprung weight, Δ ² x ₁
Is the sprung acceleration, and Δ ² x ₂ is the unsprung acceleration (where Δ ² is the second derivative).

That is, in the above equation (6), the unsprung weight m
_{Since the} sprung mass m _{1 is} greater than ₂ , the unsprung mass acceleration Δ ² x ₂ has a greater influence on the sprung mass acceleration Δ ² x ₁ than the frequency band component (1 to 8 Hz) is detected. It can be said that the effect of suppressing wheel load fluctuations is large by making the stroke side larger than the extension side.

Although the embodiments of the present invention have been described above, the specific configurations are not limited to the embodiments of the present invention, and even if there are design changes and the like within the scope not departing from the gist of the present invention, the present invention Included in the invention.

For example, in the first embodiment of the invention, the braking state detecting means detects the braking state from the operation of the anti-skid control device. However, in addition to that, a brake switch is provided and the operation state of the brake pedal is detected. From the brake fluid pressure by detecting the braking state from the brake fluid, detecting the braking state from the brake pedal operating state and the rate of change of the wheel speed, and providing the brake fluid pressure detecting means. It is also possible to detect the braking state, or to provide a longitudinal acceleration detecting means to detect the braking state from the longitudinal acceleration of the vehicle.

In the first embodiment of the invention, the soft area SS is controlled only when the sprung vertical velocity signal is 0. However, a predetermined dead zone centered at 0 is provided within the dead zone. Control hunting can be prevented by maintaining the damping force characteristic in the soft region SS while the sprung vertical velocity is changing.

[0059]

As described above, the first aspect of the present invention is as follows.
In the vehicle suspension device described above, as described above, the damping of at least the front wheel-side shock absorber among the shock absorbers having the damping force characteristic changing means that is interposed between the vehicle body side and each wheel side and that can change the damping force characteristic. The force characteristic changing means has a structure capable of switching between the first characteristic in which the compression stroke side damping force characteristic is larger than the extension stroke side damping force characteristic and at least one other second characteristic, and A braking state detecting means for detecting a braking state, and a damping force for controlling at least the damping force characteristic changing means of the front wheel side shock absorber when the braking state of the vehicle is detected by the braking state detecting means. The characteristic control means and the configuration including, by the time of braking the vehicle, it is possible to shift at least the center of the wheel load fluctuation on the front wheel side in the wheel load increasing direction, The Le, the effect is obtained that it is possible to improve the braking performance by increasing the frictional resistance between the tires and the road surface.

Further, in the vehicle suspension system according to claim 2,
At least the first characteristic of the damping force characteristic changing means of the front wheel side shock absorber is configured such that the compression stroke side damping force characteristic is larger than the extension stroke side damping force characteristic only in the low piston speed region side. In the low piston speed range where sprung mass is the main component, at least the center of the wheel load fluctuation on the front wheel side is shifted in the wheel load increasing direction to increase the frictional resistance between the tire and the road surface, as described above. While improving braking performance, on the high piston speed range where unsprung behavior is the main component, the damping force characteristics not only on the compression stroke side but also on the extension stroke side are at least equal to or greater than the damping stroke side. By providing the characteristics, it is possible to suppress the unsprung behavior, thereby increasing the ground contact force of the tire and enhancing the braking performance.

Further, in the vehicle suspension system according to claim 8,
Damping force only when the 1-8 Hz component of wheel speed or sprung vertical behavior exceeds a predetermined threshold value, that is, when the frequency band component of sprung behavior that has a large effect on wheel load fluctuations during braking is detected. By performing the switching control to the first characteristic by the characteristic control means, when the sprung mass behavior is the main component, the first characteristic causes the center of the wheel load fluctuation to be in the wheel load increasing direction as described above. It is possible to increase the frictional resistance between the tire and the road surface to improve the braking performance by shifting it to the lower side, and when the sprung mass behavior is small and the unsprung mass behavior is the main component, the second characteristic causes Not only the damping force characteristic on the extension side but also the damping force characteristic on the extension side is at least equal to or more than that on the compression stroke side, whereby the unsprung behavior can be suppressed.
The effect that the ground contact force of the tire is increased and the braking performance can be improved is obtained.

Further, in the vehicle suspension system according to claim 9,
When the damping force characteristic changing means of the shock absorber variably controls the damping force characteristic on one stroke side, the structure is such that the reverse stroke side has a low damping force characteristic, and the braking state detection means does not detect the braking state of the vehicle. In the damping force characteristic control means, when the direction discrimination code of the sprung vertical velocity signal detected by the sprung vertical velocity detecting means is upward, the damping force characteristic on the extension side of the shock absorber is set downward. At certain times, the damping force characteristic on the pressure stroke side is variably controlled based on the sprung vertical velocity signal, and when the braking state of the vehicle is detected by the braking state detecting means, at least the damping force characteristic of the front wheel side shock absorber is changed. The means is fixedly controlled so that the damping force characteristic on the pressure stroke side becomes a high damping force characteristic, so that when the vehicle is not braking, the damping force characteristic is reduced based on the skyhook control theory. By controlling the switching of force characteristics, it is possible to ensure the riding comfort and steering stability of the vehicle, and at the time of braking the vehicle, the center of wheel load fluctuation can be shifted at least on the front wheel side in the wheel load increasing direction. Friction resistance between the tire and the road surface is increased, and braking performance can be improved.

[Brief description of drawings]

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

FIG. 2 is a configuration explanatory view showing a vehicle suspension device according to the first embodiment of the present invention.

FIG. 3 is a system block diagram illustrating the vehicle suspension device according to the first embodiment of the present invention.

FIG. 4 is a sectional view showing a shock absorber applied to the vehicle suspension system according to the first embodiment of the present invention.

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 damping force characteristic diagram corresponding to the 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 a perspective view of the shock absorber shown in FIG.
It is a -L cross section and a MM cross section.

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 circuit for obtaining a sprung vertical velocity and a sprung unsprung relative velocity signal from sprung vertical acceleration in the vehicle suspension system according to the first embodiment of the present invention.

FIG. 15 is a diagram showing a gain characteristic (a) and a phase characteristic (b) of the sprung vertical velocity signal converted by using the phase lag compensation equation.

FIG. 16 is a flowchart showing a normal control operation of the damping force characteristic of the control unit in the vehicle suspension system according to the first embodiment of the present invention.

FIG. 17 is a time chart illustrating damping force characteristic normal control operation of the control unit in the vehicle suspension system according to the first embodiment of the present invention.

FIG. 18 is a flowchart showing the contents of switching control between normal time control by the normal time control unit and slip time control by the slip control unit in the vehicle suspension system according to the first embodiment of the present invention.

FIG. 19 is a time chart showing the content of braking control by the braking control section in the vehicle suspension system according to the first embodiment of the present invention.

FIG. 20 is a time chart showing wheel load characteristics in the vehicle suspension system according to the first embodiment of the present invention.

FIG. 21 is a stop distance characteristic diagram with respect to an input frequency in the vehicle suspension system according to the first embodiment of the present invention.

FIG. 22 is a time chart showing braking distance characteristics in the vehicle suspension system according to the first embodiment of the present invention.

FIG. 23 is a characteristic diagram of damping force with respect to piston speed of the shock absorber applied to the vehicle suspension system according to the second embodiment of the present invention.

FIG. 24 is a damping force characteristic diagram with respect to a piston speed at a damping force characteristic position for braking control in a shock absorber applied to the vehicle suspension system according to the third embodiment of the present invention.

FIG. 25 is a one-wheel model diagram of wheel load fluctuations in the vehicle suspension system according to the fourth embodiment of the present invention.

[Explanation of symbols]

a damping force characteristic changing means b ₁ front wheel side shock absorber b ₂ rear wheel side shock absorber c braking state detecting means d damping force characteristic controlling means

Claims (9)

[Claims] 1. A damping force characteristic changing means of at least a front wheel side shock absorber of a shock absorber having a damping force characteristic changing means capable of changing a damping force characteristic interposed between a vehicle body side and each wheel side. The braking state for detecting the braking state of the vehicle has a structure capable of switching between the first characteristic in which the compression stroke side damping force characteristic has a larger value than the side damping force characteristic and at least one other second characteristic. Detection means, and damping force characteristic control means for switching and controlling at least the damping force characteristic changing means of the front wheel side shock absorber when the braking state of the vehicle is detected by the braking state detecting means. A vehicle suspension device characterized in that 2. A damping characteristic characteristic of the damping force characteristic changing means of at least the front wheel side shock absorber has a larger value in the compression stroke side damping force characteristic than in the extension stroke side damping force characteristic only in the low piston velocity range side. The vehicle suspension system according to claim 1, wherein the vehicle suspension system is configured as described above. 3. The anti-skid control device is provided, and the braking state detecting means is configured to detect the braking state from the operation of the anti-skid control device. Vehicle suspension system. 4. A brake switch is provided, and the braking state detecting means is configured to detect a braking state from an operating state of a brake pedal.
Alternatively, the vehicle suspension device according to item 2. 5. A brake switch and a wheel speed detecting means are provided, and the braking state detecting means is configured to detect the braking state from the operation state of the brake pedal and the rate of change of the wheel speed. The vehicle suspension system according to claim 1 or 2. 6. A brake fluid pressure detecting means is provided, and the braking state detecting means is configured to detect a braking state from the brake fluid pressure.
The vehicle suspension device described in. 7. The longitudinal acceleration detecting means is provided, and the braking state detecting means is configured to detect the braking state from the longitudinal acceleration of the vehicle. Vehicle suspension system. 8. A wheel speed detecting means for detecting a wheel speed or a sprung up / down behavior detecting means for detecting a sprung up / down behavior, the wheel speed or spring detected by the wheel speed detecting means or the up / down behavior detecting means. It is characterized in that a 1 to 8 Hz component of upward and downward behavior is extracted, and switching control to the first characteristic by the damping force characteristic control means is performed only when the component exceeds a predetermined threshold value. The vehicle suspension device according to claim 1. 9. A sprung vertical velocity detecting means for detecting a sprung vertical velocity is provided, and when the damping force characteristic changing means of the shock absorber variably controls the damping force characteristic on one stroke side, the opposite stroke side is set. When the braking state of the vehicle is not detected by the braking state detecting means, in the damping force characteristic control means, the sprung vertical velocity signal of the sprung vertical velocity signal detected by the sprung vertical velocity signal is detected. When the direction identification code is upward, the damping force characteristic on the extension side of the shock absorber is variably controlled based on the sprung vertical velocity signal when it is downward, and the damping state characteristic is detected. When the braking state of the vehicle is detected by the means, at least the damping force characteristic changing means of the front wheel side shock absorber is fixedly controlled so that the damping force characteristic on the pressure stroke side becomes a high damping force characteristic. Vehicle suspension of claim 1, wherein that there were Unishi.