JPH0392411A - Active suspension - Google Patents

Abstract

PURPOSE:To eliminate anxiety accompanying an unchanged ground clearance value at acceleration and deceleration in an active suspension device for a vehicle by lowering the ground clearance in acceleration and deceleration than the ground clearance in constant speed straight driving. CONSTITUTION:Acceleration and deceleration speed in the lengthwise direction is detected by a length acceleration sensor 26, and a signal g is put out to a controller 30. The controller 30 operates a pressure command value for each wheel for lowering a ground clearance than that in constant speed straight driving based on this signal g and puts out command currents iFL to iRR separately to each of pressure control valve 20FL to 20RR. Thus, each of the pressure control valves 20FL to 20RR works in the direction to lower the ground clearance. By this constitution, a sense of security in acceleration and deceleration can be improved.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an active suspension, and in particular to a suspension that controls the operating pressure of a fluid pressure cylinder disposed between a vehicle body and wheels in accordance with longitudinal acceleration/deceleration. , relates to an active suspension system that adjusts the vehicle height during acceleration and deceleration.

"Prior Art" The applicant has proposed an active suspension that can control the pitch motion of a vehicle that occurs when starting or braking.
No. 246294 (unpublished) has been filed.

One aspect of the active suspension device described in this application includes:
As described in the example, there is a hydraulic cylinder inserted between the vehicle body and each wheel, a pressure control valve that controls the operating pressure of this hydraulic cylinder according to a command value only, and a longitudinal adjustment of the vehicle body. The vehicle includes a longitudinal acceleration/deceleration sensor that detects speed, and a calculation means that calculates the command value according to the difference between the detected value of the acceleration/deceleration sensor and a changeable acceleration/deceleration neutral value, and the vehicle does not rock. means for setting the detected value of the longitudinal acceleration/deceleration sensor at the time when the initial state of stopping is recognized as the acceleration/deceleration neutral value, and the detected value of the longitudinal acceleration/deceleration sensor calculated every predetermined traveling distance or predetermined traveling time. and means for updating the neutral acceleration/deceleration value with the average value of the acceleration/deceleration.

This achieves highly accurate attitude control by optimizing acceleration/deceleration correction when the vehicle starts from a stopped state on a slope and travels on a flat road, which is the objective of the prior application.

Furthermore, an accumulator is connected to the cylinder chamber of the hydraulic cylinder to absorb hydraulic fluctuations corresponding to high-frequency vibrations in the unsprung resonance region manually applied from the road surface.

By the way, in the above-mentioned active suspension, the relationship between the excitation current (command current) supplied to the pressure control valve and the output pressure P of the pressure control valve (i.e. cylinder pressure) is as shown in Fig. 10. . In other words, when the longitudinal acceleration/deceleration is zero, the neutral excitation current I. is calculated, and when a certain amount of longitudinal acceleration/deceleration is detected during acceleration/deceleration, the rate of change in the rise and fall of the front and rear cylinder pressures is adjusted to be the same. For this reason, an example of the control characteristic is shown in FIG. 11, where the horizontal axis is the longitudinal acceleration/deceleration M (positive value at the time of IT speed) and the vertical axis is the operating pressure P of the hydraulic cylinder. To elaborate on this,
When the longitudinal acceleration/deceleration X=O during constant speed driving, both the front wheel side and rear wheel side working pressures P are at the predetermined neutral pressure P. 4, and as the longitudinal acceleration/deceleration nu1 increases due to acceleration/deceleration driving, the front wheel side. The rear wheel side working pressure P both increases or decreases at the same rate of change, causing pitch stiffness.

[Problem to be solved by the invention]

However, in the active suspension having the control characteristics shown in FIG. 11 described above, the cylinder pressures of each wheel when traveling straight at a constant speed are both at the neutral operating pressure PM, so the vehicle runs at the vehicle height determined by this neutral pressure Ps, and on the other hand, During acceleration and deceleration, the working pressure on the sinking side of the vehicle body and the working pressure on the lifting side of the car body decrease at the same rate, so the vehicle height value during acceleration and deceleration is the average value, that is, approximately the neutral value P8.
When accelerating or decelerating from constant-speed straight-ahead driving, the height of the vehicle's center of gravity remains unchanged and remains at the predetermined vehicle height value, which is determined by !
3. The current situation was such that the passengers, who were used to vehicles with reduced P, felt uneasy. This inconvenience is
This was especially noticeable during nose dive during deceleration.

In addition, as mentioned above, the rate of change in operating pressure is the same for the front and rear wheels, and the pressure increase on the sinking side of the car is large, so the accumulator connected to the cylinder collapses significantly, making it difficult to absorb pressure fluctuations. Therefore, for example, there is an unresolved problem that vibrations picked up by the front wheels during braking due to small irregularities on the road are transmitted to the vehicle body, worsening ride comfort.

The present invention has been made in view of these current circumstances, and its first objective is to eliminate the feeling of anxiety among occupants caused by the unchanged vehicle height during acceleration and deceleration. The objective is to improve ride comfort during acceleration and deceleration while eliminating such uneasiness.

[Means to solve the problem]

In order to solve the first problem above, claims (]) and (3)
As shown in FIG. 1, the invention described in ) includes a fluid pressure cylinder interposed between a vehicle body side member and a wheel side member for each wheel;
A pressure control valve that individually controls the operating pressure of the fluid pressure cylinder according to a command value, a longitudinal acceleration/deceleration detection means for detecting acceleration/deceleration in the longitudinal direction of the vehicle body, and an acceleration/deceleration detection value of the longitudinal acceleration/deceleration detection means. a command value calculation means for calculating, for each wheel, a command value for lowering the vehicle height during at least one of acceleration and deceleration than when traveling straight at a constant speed, based on the above, and a command value calculated by the command value calculation means; and command value output means for respectively outputting the values to the pressure control valves.

Furthermore, in order to solve the second problem, the invention according to claims (2) and (3) includes a fluid pressure cylinder interposed between the vehicle body side member and the wheel side member for each wheel; an accumulator provided in the fluid pressure cylinder to absorb vibrations of the wheel side member; a pressure control valve that individually controls the operating pressure of the fluid pressure cylinder according to a command value; and a pressure control valve that detects longitudinal acceleration/deceleration of the vehicle body. A longitudinal acceleration/deceleration detection means, and a command value for each wheel to lower the vehicle height during at least one of acceleration and deceleration than when traveling straight at a constant speed based on the acceleration/deceleration detection value of the longitudinal acceleration/deceleration detection means. The main part includes a command value calculation means for calculating, and a command value output means for outputting the command values calculated by the command value calculation means to the pressure control valves.

[Effect]

In the inventions described in claims (1) and (3), when the vehicle is traveling straight at a constant speed, the longitudinal acceleration detected value is zero and the command value calculation means calculates the predetermined command value, so that the fluid pressure cylinder The operating pressure is controlled according to this predetermined command value, and a flat predetermined vehicle height value is maintained.

When the state transitions from this state to at least one of acceleration and deceleration, the command value calculation means determines that, for example, as the absolute value of the longitudinal acceleration/deceleration detection value increases, the vehicle body lift side decreases at a predetermined rate of change, and the vehicle body For the sinking side, a command value that increases at a smaller rate of change than the rate of change for the vehicle body lifting side is calculated for each wheel. Then, each command value is outputted to the pressure control valve by the command value output means. As a result, the rate of increase in the operating pressure of the fluid pressure cylinder on the side where the vehicle body sinks is smaller than the rate of decrease in the operating pressure of the fluid pressure cylinder on the side where the vehicle body is raised. As a result, the height of the center of gravity can be improved while allowing a certain degree of moderate pitch condition. In other words, the vehicle height value is moderately lower than when the vehicle is traveling straight at a constant speed.

In addition to the above-mentioned effects, in the inventions described in claims (2) and (3), since the pressure increase rate of the fluid pressure cylinder on the side where the vehicle body sinks is small, the accumulator cylinder connected thereto There is less crushing and the spring constant can be kept at a smaller value. Therefore, the function of the accumulator to absorb vibrations of the wheel-side member can be activated even when the vehicle is accelerating or decelerating, and vibrations can be prevented from being transmitted to the vehicle body.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 2 to 9. The active suspension of this embodiment shows a case where only the pitch control of the vehicle body is performed.

In Fig. 2, 10 is a suspension arm on the vehicle body side, IIFL to IIRR are front left to rear right wheels,
Reference numeral 12 indicates an active suspension.

The active suspension 12 includes a vehicle body side member lO and a wheel 1.
Hydraulic cylinders 18FL to 18FL as fluid pressure cylinders interposed between each wheel side member 14 of 1FL to IIRR.
18RR, pressure control valves 20FL to 20RR that individually adjust the operating pressures of the hydraulic cylinders 18FL to 18RR, a hydraulic power source 22 of the hydraulic system, and pressure control valves 20FL to 2ORR inserted between the hydraulic power source 22 and the pressure control valves 20FL to 2ORR. an accumulator 24.24 for accumulating pressure, a lateral acceleration/deceleration sensor 26 that detects acceleration generated in the lateral direction of the vehicle body, and pressure control valves 20FL to 20F based on the detection signal of the lateral acceleration/deceleration sensor 26.
It has a controller 30 that individually controls the output pressure of ORR. Further, each of the pressure chambers L of the hydraulic cylinders 18FL to 18RR, which will be described later, is connected via a throttle valve 32 to a relatively small-capacity accumulator 34 for absorbing unsprung vibrations. Furthermore, hydraulic cylinder 18F ~ 18RH
Between the unsprung and unsprung portions of each is a coil spring 3 which has a relatively low spring constant and supports the static load of the vehicle body.
6 is arranged.

Each of the hydraulic cylinders 18FL to 18RR has a cylinder tube 18a, and this cylinder tube l8a includes:
A lower pressure chamber L is defined by the piston 18c. The lower end of the cylinder tube 18a is attached to the wheel side member 14, and the piston rod 18b
The upper end of is attached to the vehicle body side member 10. Also,
Each of the pressure chambers L is connected to the pressure control valve 2 via a hydraulic pipe 38.
Connected to output ports from 0FL to 20RR.

Further, each of the pressure control valves 20FL to 20RR is a conventionally well-known three-boat proportional electric 1ifi pressure reducing valve (for example, Japanese Patent Laid-Open No. 1983-1992-1), which has a cylindrical valve housing and a proportional solenoid integrally provided therein. 74111)). By adjusting the command current i (command value) supplied to the excitation coil of the proportional solenoid, the moving distance of the boppet housed in the valve housing, that is, the position of the spool, is controlled, and the supply boat, output boat, or output The hydraulic oil flowing between the hydraulic power source 22 and the hydraulic cylinders 18FL to 18RR can be controlled via the boat and the return boat.

Here, command current i ( : f
FL-1 am) and pressure control valve 20FL (~20RR
) and the control pressure P output from the output boat is as shown in FIG. In other words, when the minimum current value iMIN takes noise into consideration, the minimum control pressure is P8. When the current value i is increased from this state, the control pressure P increases linearly in proportion to the current value l, and the maximum current value i M
When AX, the maximum control pressure P corresponds to the set line pressure.

It becomes AX. iN is a neutral command current, and PM is a neutral control pressure.

On the other hand, a longitudinal acceleration/deceleration sensor 26 is installed at the center of gravity of the vehicle. This longitudinal acceleration/deceleration sensor 26 detects acceleration/deceleration X in the longitudinal direction acting on the vehicle body. For example, the controller 30 sends a voltage signal g corresponding to the amount of displacement when a magnetically suspended mass is displaced by inertial force. Output to. The detection characteristics are as shown in Figure 4.
When the longitudinal acceleration/deceleration x=0, the detection signal g=gN (predetermined neutral value), and when decelerating or accelerating from this state, it increases or decreases in proportion to the longitudinal acceleration/deceleration k. Here, the longitudinal acceleration/deceleration is positive during deceleration and negative during acceleration.

Furthermore, as shown in FIG. 5, the controller 30 includes an A/D converter 70 that converts a detection signal g corresponding to the input analog longitudinal acceleration into a digital quantity, and a microcomputer 72 for arithmetic processing. Digital pressure command value VFL' output from this microcomputer 72
= D/A converters 73A to 73D that individually convert VRII into analog quantities, and pressure command values V, L of these analog quantities.
-V- as the target value, pressure control valves 20FL to 20RR
The command current i FL- i Rll to be output individually to
It has drive circuits 74A to 74D that follow the target value.

Of these, the microcomputer 72 includes at least an interface circuit 76, an arithmetic processing unit 78, a RAM, and a RAM.
The interface circuit 76 includes an I/O port and the like. Further, the arithmetic processing El device 78 is connected via the interface circuit 76. The detection signal gv is read, and based on these, calculations and other processing described later are performed. The storage device 80 stores in advance a predetermined program, fixed data, etc. necessary for execution of processing by the arithmetic processing device 78, and also stores processing results of the arithmetic processing device 78.

The fixed data stored in the storage device 80 includes a storage table corresponding to FIG. This figure shows the characteristics of the pressure command value V yt=V IN (voltage value) from the front left side to the rear right side with respect to the acceleration/deceleration rate. To explain this in detail, when the longitudinal acceleration = O, a predetermined neutral value VN (command value for maintaining the vehicle height when traveling straight) is taken, and when the longitudinal acceleration corresponding to deceleration = 0, the front pressure command value is V, L, V
■〉v8 and rear side pressure command value Vat, vll<vN. At this time, 0<father≦kI (S!1 is, for example, 0.5
CG)), the front pressure command value vFt. ,■■ is■
From 8 ■. ', the rear pressure command values V, 1L, V■ increase at the rate of change αz(I) from V2 to v1.
αzl > l α1 1). Furthermore, X
, <X, ■FL. VFII=VM,
VRL. V**=Vs (71 states are maintained respectively.On the other hand, when the longitudinal acceleration corresponding to the acceleration is X〈O,
Front pressure command value VFL, VFR and rear pressure command value V
Both IL and V■ change symmetrically.

In other words, in the range of acceleration 〈father,〉, saturation occurs from the neutral value v1 at the same rate of change α3 (1α, 1〉1α2 1) {II
increases and decreases to Vf and v,/, then a constant value V
．． and ■, ′ are retained.

In this way, in this embodiment, only during deceleration, the pressure command value VF
The rate of change from L to Vllml is different between the front and rear wheels, allowing pressure commands with different ranges of change to be given to the front and rear wheels, as will be described later.

Next, the operation of the above embodiment will be explained.

When the ignition switch of the vehicle is turned on, the controller 30 is activated and executes the timer interrupt process shown in FIG. 7 at predetermined intervals (for example, 20+ seconds) while a predetermined main program is being executed.

The process shown in FIG. 7 will be explained. First, in step 2 of the same figure, the arithmetic processing unit 78 of the microcomputer 72 reads the detection signal g of the longitudinal acceleration/deceleration sensor 26, and proceeds to step (3). this? In step ■, subtract the neutral value gN from the detection signal g read in step
Find the longitudinal acceleration detection signal Δg. Next, the process moves to step (2), and by referring to a memory table previously stored in the storage device 80, etc., the longitudinal acceleration/deceleration corresponding to the detection signal Δg is calculated.

Next, the process moves to step (2), and the memory table corresponding to FIG.
Read V■ and temporarily store the value. In this setting, if the stored data in the storage table is the value of a bending point in each curve in FIG. 6, the value of the midpoint may be obtained from a calculation based on two known points.

After this, the arithmetic processing unit 78 moves to step (3),
The pressure command values VFL~V■ calculated in step ■ are sent to the D/A converters 73A~73 via the interface circuit 76.
Output to D individually.

For this reason, the deviation of each wheel with respect to the change in longitudinal acceleration/deceleration X obtained by performing the above-mentioned control? The change in pressure P is as shown in FIG.

Next, the overall operation will be explained.

It is now assumed that a vehicle is traveling straight at a constant speed on a flat, smooth road. In this state, pitch movements such as noise dive and scut do not occur, so the detection signal g of the longitudinal acceleration/deceleration sensor 26 is its neutral value gH, and the longitudinal acceleration/deceleration X calculated by the controller 30 is zero (7th (See figure steps ■～■). For this reason, each pressure command value VFL"" is set by referring to the memory table.
V Rll =■8 (see step ■ in Figures 6 and 7), and this neutral value VN is applied to the D/A converters 73A to 73.
They are output to D respectively. And D/A converters 73A to 7
Pressure command f direct VF converted into analog quantity by 3D
L-V■ (=VS) is set as a target value by the drive circuit 74A~
74D, and from these drive circuits 74A to 74D, neutral command currents i. are supplied to pressure control valves 20PL to 20RR, respectively. This results in
The pressure control valves 20FL to 20RR are connected to the hydraulic cylinder 18F.
What is the operating pressure of L-18RR? Since the pressure is controlled to be the neutral pressure PM (see FIG. 3), each of the hydraulic cylinders 18FL to 18RR generates a force corresponding to the neutral pressure Ps, and the vehicle body is held in a flat posture at a predetermined vehicle height.

When the constant-speed straight-ahead state shifts to a decelerating state, for example by stepping on the brake, inertial force acts in the front direction of the vehicle, causing the front side of the vehicle to sink and the rear of the vehicle to rise, resulting in a nose dive.

At this time, the detection signal g of the longitudinal acceleration/deceleration sensor 26 is the neutral value g. Since the value is larger than 4 by the amount corresponding to the amount of brake depression, etc., the controller 30 has a longitudinal acceleration signal Δg>Q, and a positive longitudinal acceleration/deceleration signal according to this Δg. That is, the deceleration is calculated, and pressure command values VFL to VIN are set in accordance with the deceleration k (see steps 1 to 2 in FIG. 7). Pressure command value at this time VFL ~ VR
R is VFLVFR>VRL, V■, and the neutral value■
The range of change from 8 is the pressure command value on the front wheel side “FL+ ■F
l is smaller than the rear wheel side pressure command values V, , , V■, and these command values VFL to VIA are the command currents corresponding to each? Converted to rt= i *, l and pressure control valve 2
Supplied to 0FL~20RR, hydraulic cylinder 18FL~
The operating pressure of 18RH is controlled to a value corresponding to the command current iFL-i*R, that is, the pressure command value VFL''V■.

Therefore, the front wheel side hydraulic cylinder l 8FL, 1 8
The operating pressure of FH is neutral pressure P. The pressure is slightly increased from the neutral pressure Ps to generate a force that suppresses the sinking of the car body to some extent, and the operating pressure of the rear wheel hydraulic cylinders 1811L and 18RR is significantly lowered from the neutral pressure Ps, which helps the car body lift up. (For example, see the point S (=M) in FIG. 8.) As a result, the pitch angle during braking is suppressed to an acceptable and appropriate value.

On the other hand, the vehicle height value in this braking state is determined by the average value of the front and rear wheel pressures, and as shown by the dashed-dotted line H in Figure 8, the vehicle height value is determined by the average value of the front and rear wheel pressures. The pressure is lower than PM. In other words, as the vehicle transitions from a constant speed state to a braking state, the center of gravity height, that is, the overall vehicle height, is lowered by an appropriate amount while allowing a slight pitch angle nose dive, which is especially important during deceleration. ,
It is also possible to accurately avoid situations in which the occupants feel unnecessarily anxious due to the vehicle height not being lowered, and the handling stability is lower than when driving at a constant speed.

In addition, in the above deceleration state, the front wheel side hydraulic cylinder 1
Since the increase rate of the cylinder pressure P of 8FL, 1 BPR is lowered, the increase rate of the cylinder pressure P of the cylinder 1 8FL, 1 BPR is
The accumulators 34 and 34 connected to the pump are less prone to collapse and have sufficient internal capacity to absorb hydraulic oil.
As a result, the accumulators 34 and 34 do not lose their spring function to absorb hydraulic vibrations, so high-frequency vibrations equivalent to the unsprung resonance region, such as vibrations caused by small irregularities on the road surface that are often encountered in front of a crosswalk, can be avoided. Even when using human power, it can reliably absorb the hydraulic vibration that corresponds to the human power.
This suppresses vibrations transmitted to the vehicle body during braking,
It reduces the jerky feeling and ensures good riding comfort during posture control. The reason why this good ride comfort is obtained during posture control is explained in the ninth section.
Let's analyze quantitatively based on Figures (a) and (b).

In the cylinder model shown in FIG. 5(a), the piston cross-sectional area A, the internal pressure P. Internal volume V. When the piston stroke is X and the rod reaction force is F, the spring constant K is K=ΔF/ΔX, F=P-A, ΔF=ΔP-AΔV=A=Δ
Since X, ΔX = ΔV/A, K-ΔF/ΔX = (ΔP-A)/(ΔV/A) = AZ · (ΔP/Δ■). In other words, since the spring constant K is proportional to "ΔP/Δ■", P-v in FIG. 9(b) showing that P-V=constant.
On the lib line, point a is when traveling straight at a constant speed. If a certain braking time is at point b, the spring constant at point b is larger than the spring constant at point a, resulting in a hard state.

In other words, in the active suspension having the characteristics shown in Fig. 10.11 described above, the cylinder pressure P on the front wheel side during braking is high, so when suppressing nose dive, the vibration human power from the front wheel side is transmitted to the vehicle body, and the rider There was a risk that it would make her feel worse. However, in this embodiment, the front wheel side cylinder pressure P during braking is
is lower than that of the prior application, so the spring constant can be kept in a soft state correspondingly small, and the above-mentioned effects can be enjoyed.

In this way, when the pitch rigidity and vehicle height control during braking is finished and the state returns to a constant speed straight-ahead state, the sensor detection signal g=g
N, thereby calculating the longitudinal acceleration/subtraction of 10, and maintaining a flat predetermined vehicle height value as described above.

Furthermore, it is assumed that the vehicle accelerates from the above-mentioned constant speed straight-ahead state. The sensor signal g detected during this acceleration is the neutral value gN
The negative longitudinal acceleration/deceleration, that is, the acceleration, is calculated, and the pressure command value V , , V 1111 corresponding to the acceleration X is calculated by referring to the memory table as described above. , the same rate of change for the front and rear wheels,
While changing, the rear wheel side is set to a higher value. As a result, the rear wheel side hydraulic cylinders 1 8RL, 1 8
The working pressure P of RH is increased and the hydraulic cylinder 1 on the front wheel side
8PL. The operating pressure P of the 18PR is lowered, and pitch rigidity is obtained to resist the scut where the rear part of the vehicle body sinks. In this way, in the case of the scut control in this embodiment, the vehicle can be driven while maintaining the vehicle body in a substantially flat state.

As described above, in this embodiment, the longitudinal acceleration/deceleration sensor 26. A/D
The converter 70 and the processing in steps 1 to 2 in FIG. 7 constitute a longitudinal acceleration/deceleration detection means, the step 2 in FIG.
A to 73D and drive circuits 74A to 74D are monitoring the command value output means.

In addition, in the above embodiment, the hydraulic cylinder tapt, ~18R
Although the accumulator 34 is separately installed in R, this may be removed if necessary.

In addition, the active suspension according to each invention of the present application is
As in the above embodiment, the rate of increase in cylinder pressure on the sinking side of the vehicle is not limited to being set small only during deceleration, but for example, the rate of increase in cylinder pressure on the rear wheel side during acceleration may be set to a small Set it to be smaller than the rate of decrease in cylinder pressure.
The same effect as described above may be obtained by slightly lowering the vehicle height while allowing a certain appropriate level of scut. Furthermore, such a structure may be applied to both acceleration and deceleration, and in that case, in addition to the various effects described above, the maximum value P WAX controlled by the pressure control valves 20FL to 20RR is also Since it is lower than the one described, the discharge amount of the hydraulic pump that controls a part of the hydraulic source 22 can be smaller, and the relief pressure of the relief valve can be lower, so the entire hydraulic source 22 can be made smaller. , weight reduction can be achieved.

Furthermore, each invention of the present application naturally includes vehicle roll control,
It can also be applied to active suspension systems that also perform bounce control.

Furthermore, the fluid pressure cylinder of each invention is not limited to the case where a hydraulic cylinder is applied as in the above-mentioned embodiments, but may be configured to use, for example, a pneumatic cylinder or the like.

Furthermore, in the above embodiment, the controller is equipped with a microcomputer, but this inputs the detection signal of the longitudinal acceleration/deceleration sensor and outputs the voltage value having the characteristic shown in FIG. 6 above. An analog circuit structure may be used in which the output value is sent to the pressure control valve via a drive circuit. On the other hand, as for the processing of the controller, in addition to directly obtaining the pressure command values VFL to Vll from the lookup of the memory table as described above, the calculated longitudinal acceleration/deceleration is multiplied by the control gain, and the neutral value vN is calculated. The pressure command value VFL~■■ may be calculated by adding the pressure command values, and the control gain may be varied so as to obtain the output characteristics shown in FIG. 8 according to the longitudinal acceleration/deceleration. Furthermore, in each invention, the rate of increase in cylinder pressure only needs to be smaller than the rate of decrease, and the rate of change in the increase or decrease curve of cylinder pressure with respect to longitudinal acceleration/deceleration may be arbitrarily changed midway.

[Effects of the Invention] As explained above, in the inventions described in claims (1) and (3), the command value, that is, the working pressure of the fluid pressure cylinder, is set to the sinking of the vehicle body during at least one of acceleration and deceleration. On the other hand, it is raised on the side where the vehicle body lifts up, and it is lowered on the opposite side where the vehicle body lifts up, but the rate of change in the increase in operating pressure is controlled to be smaller than the rate of change in the decrease in operating pressure. When transitioning from the state to the acceleration or deceleration state, it is possible to obtain appropriate pitch rigidity and suppress the pitch angle to an acceptable value, and the vehicle height at the center of gravity can be moderated by reducing the average working pressure of the front and rear wheels. This has the effect of providing a sense of security to the occupants and improving steering stability during acceleration and fIi speeds.

In addition to the above-mentioned effects, the invention according to claims (2) and (3) enables the accumulator that absorbs vibrations of the wheel side member to operate even when the vehicle accelerates or decelerates.
, it is possible to prevent vibrations from being transmitted to the vehicle body, further improving riding comfort.

[Brief explanation of drawings]

Fig. 1 is a diagram corresponding to the claims of the invention (showing the invention described in claims (1) and (3)), Fig. 2 is a schematic configuration diagram showing an embodiment of the invention, and Fig. 3 is the output characteristics of the pressure control valve. A graph showing,
Figure 4 is a graph showing the detection characteristics of the longitudinal acceleration/deceleration sensor.
FIG. 5 is a block diagram showing an example of a controller, FIG. 6 is a characteristic diagram corresponding to a pressure command value storage table, FIG. 7 is a schematic flowchart showing an example of a processing procedure executed in the controller, and FIG. The figure is a characteristic diagram of cylinder pressure.
Figures 9(a) and (b) are explanatory diagrams of the spring function of the accumulator, Figure 10 is a graph showing the output characteristics of the pressure control valve according to the earlier application, and Figure 11 is a graph of the cylinder pressure according to the earlier application. It is a characteristic diagram. In the figure, 10 is a vehicle body side member, 12 is an active suspension, 14 is a wheel side member, 18FL-18RR is a front left to rear right hydraulic cylinder (fluid pressure cylinder), 20FL to 20RR
are the front left to rear right pressure control valves, 26 is the longitudinal acceleration/deceleration sensor,
30 is a controller, 70 is an A/D converter, 73A to 7
3D is a D/A converter, and 74A to 74D are drive circuits.

Claims (3)

[Claims] (1) A fluid pressure cylinder installed for each wheel between the vehicle body side member and the wheel side member, a pressure control valve that individually controls the operating pressure of this fluid pressure cylinder according to a command value, and a longitudinal acceleration/deceleration detection means for detecting acceleration/deceleration in the longitudinal direction;
Based on the acceleration/deceleration detection value of this longitudinal acceleration/deceleration detection means,
a command value calculating means for calculating a command value for each wheel to lower the vehicle height during at least one of acceleration and deceleration than when driving straight ahead at a constant speed; An active suspension comprising command value output means for outputting command values to control valves. (2) A fluid pressure cylinder interposed between the vehicle body side member and the wheel side member for each wheel, an accumulator provided in the fluid pressure cylinder to absorb vibrations of the wheel side member, and A pressure control valve that individually controls the operating pressure according to a command value, a longitudinal acceleration/deceleration detection means that detects the longitudinal acceleration/deceleration of the vehicle body, and a longitudinal acceleration/deceleration detection means that detects acceleration/deceleration during acceleration based on the acceleration/deceleration detected value of the longitudinal acceleration/deceleration detection means. and a command value calculation means for calculating a command value for each wheel to lower the vehicle height during at least one of the driving conditions during deceleration compared to when the vehicle is traveling straight at a constant speed, and the command value calculated by the command value calculation means is applied to the pressure control valve. An active suspension comprising command value output means for respectively outputting command values. (3) The command value calculation means sets a predetermined value when the acceleration/deceleration detection value of the longitudinal acceleration/deceleration detection means is zero, and changes the command value to a predetermined value for the vehicle body lifting side as the absolute value of the acceleration/deceleration detection value increases. Claim (1): means for calculating a command value that decreases at a rate of change and increases at a rate of change for the vehicle body sinking side, which is smaller than the rate of change for the vehicle body lift side.
Or the active suspension described in (2).