JPH08142627A - Suspension control device - Google Patents

Abstract

PURPOSE: To reduce the shock in changing and controlling the damping force to be generated in a fluid cylinder by controlling the upper limit of the change of the damping force by a damping force changing means to the side where the damping force is reduced following the reduction of the detected inner pressure. CONSTITUTION: A hydrodynamic type active suspension 10 controls the upper limit of the damping force (the target step number of the damping force) which is once determined from the viewpoint of the steering stability and the riding comfort to the guard value to be determined according to the inner pressure of an actuator 36 and the relative speed of a piston 62. This upper limit is controlled to the side where the damping force is reduced if the inner pressure of the actuator 36 is dropped, and to the side where the damping force is reduced if the relative speed is increased. The cavitation in changing the damping force can be prevented, and the riding comfort of the vehicle can be improved by avoiding the generation of disagreeable shock such as this cavitation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a suspension control device capable of changing the damping force of a suspension via a fluid pressure cylinder.

[0002]

2. Description of the Related Art As a suspension control device of this type, for example, JP-A-4-201614 can be exemplified. This publication proposes an active suspension that uses a fluid pressure cylinder that actively changes the attitude of the vehicle body by controlling the supply and discharge of working fluid, and an active suspension that uses a gas spring to realize variable damping force control. Is actively controlled and damping force is adjusted.

[0003]

However, in the above-mentioned conventional suspension control device, the flow of the working fluid between the gas spring and the fluid pressure cylinder passes through the throttle (variable throttle or fixed throttle) of the gas spring pipeline. Because of the fact that I'm awake,
The following problems remain. Since this problem is associated with the variable damping force control, first, this problem will be described by taking a hydropneumatic suspension in which the variable damping force control is performed only by a gas spring as an example.

As shown in the schematic view of FIG. 10, the suspension is provided with a variable throttle 206 in a gas spring conduit 204 which connects the gas spring 200 and the fluid pressure cylinder 202. Further, the piston 208 of the fluid pressure cylinder 202 has a through hole 210 communicating with the upper and lower chambers in the cylinder. In this suspension, the piston 208
Damping force of the fluid pressure cylinder 202 itself due to the flow of the working fluid through the flow hole 210 of the gas spring 200 due to the flow of the working fluid through the variable throttle 206 of the gas spring conduit 204.
And the damping force of Here, if the diameter of the through hole 210 is set to be relatively large, the damping force generated in the suspension can be approximated to the damping force of the gas spring 200.

The maximum damping force FFIN generated on the extension side of this suspension is the pressure Pg in the gas spring 200 and the pressure Pup in the upper chamber of the fluid pressure cylinder 202.
Is expressed by the following mathematical formula. Note that A in the following mathematical expression is the pressure receiving area of the piston 208.

FFIN = (Pg-Pup) .A

The variable throttle 206 is driven to change the damping force according to the running state of the vehicle such as acceleration / deceleration and turning.
Therefore, when the variable throttle 206 is driven to generate a damping force that exceeds the maximum damping force FFIN, the upper chamber pressure Pup of the fluid pressure cylinder 202 becomes a negative pressure. Therefore, the pressure change of the fluid before and after the variable throttle becomes large, and cavitation occurs.

Next, the problem that cavitation occurs as described above will be described in an active suspension such as Japanese Patent Laid-Open No. 4-201614 in which a gas spring and a fluid pressure cylinder are used together.

For example, in order to actively suppress a change in posture during turning of the vehicle, the internal pressure of the fluid pressure cylinder of the turning inner wheel is usually controlled to be lowered. In this situation,
Furthermore, when trying to generate a higher damping force by narrowing the variable throttle between the gas spring and the fluid pressure cylinder in order to improve the suppression of posture changes, the cylinder internal pressure drops considerably relative to the gas spring internal pressure. To do. Therefore, even in this case, the pressure change of the fluid before and after the variable throttle becomes large, and cavitation occurs in the fluid.

The present invention has been made to solve the above problems, and it is an object of the present invention to reduce the impact such as cavitation when changing and controlling the damping force generated in a fluid pressure cylinder and to improve the riding comfort of a vehicle. And

[0011]

In order to achieve the above object, the means adopted by the suspension control device according to claim 1 is a suspension control device capable of changing the damping force of the suspension, and A fluid pressure cylinder, which is interposed between the unsprung part and which can increase or decrease the vehicle height of a corresponding portion by supplying and discharging the fluid, and a damping force generated by the fluid pressure cylinder are applied to the running state of the vehicle. The damping force changing means for changing the damping force, the pressure detecting means for detecting the internal pressure of the fluid pressure cylinder, and the upper limit of the damping force change by the damping force changing means. It is a gist of the present invention to provide damping force limiting means for limiting the pressure according to the detected internal pressure on the side of reduction.

The means adopted by the suspension control device according to claim 2 is a suspension control device capable of changing the damping force of the suspension, which is interposed between the unsprung and unsprung parts of the vehicle. A fluid pressure cylinder that can increase or decrease the vehicle height of the corresponding portion by supplying and discharging
Damping force changing means for changing the damping force generated in the fluid pressure cylinder according to the running state of the vehicle; and relative speed detecting means for detecting the relative speed in the vertical direction of the sprung and unsprung parts, A damping force limiting unit that limits the upper limit of the damping force change by the damping force changing unit on the side where the damping force decreases in accordance with the increase in the detected relative velocity, according to the detected relative velocity. The summary will be given.

[0013]

In the suspension controller having the above-mentioned structure, when the damping force generated in the fluid pressure cylinder is changed by the damping force changing means, the upper limit of the damping force change is set by the damping force limiting means. It is limited according to the internal pressure detected by the pressure detecting means. The upper limit is limited to the side where the damping force decreases as the internal pressure of the fluid pressure cylinder decreases. Therefore, when the internal pressure of the fluid pressure cylinder decreases, the damping force is not increased carelessly, and the damping force is the soft side damping force.

In the suspension control device according to the second aspect, when changing the damping force by the damping force changing means, the upper limit of the damping force change is set by the damping force limiting means according to the relative speed detected by the relative speed detecting means. Restrict. This upper limit is imposed on the side where the damping force decreases as the relative speed in the vertical direction of the sprung and unsprung parts increases. Therefore,
When the relative speed increases and the internal pressure fluctuation in the fluid pressure cylinder is large, the damping force is not increased and changed carelessly.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the suspension control device according to the present invention will be described with reference to the drawings. The suspension control device of the present embodiment is configured as the fluid pressure active suspension 10 using a fluid pressure cylinder as follows.

FIG. 1 is a schematic configuration diagram showing a fluid circuit of a fluid pressure type active suspension 10 of an embodiment. As shown, the fluid pressure type active suspension 10
Includes a reservoir 11 that stores oil as a working fluid, and one end of a connection passage 12 and one end of a working fluid discharge passage 14 are connected to the reservoir 11. The other end of the connection passage 12 is connected to the suction side of a pump 18 driven by the engine 16. The pump 18 is a variable displacement pump in the illustrated embodiment, and one end of a working fluid supply passage 20 is connected to the discharge side thereof. The other end of the working fluid supply passage 20 and the other end of the working fluid discharge passage 14 are pilot-operated type 3 constituting a pressure control valve 22.
The port 3 position switching type switching control valve 24 is connected to the P port and the R port, respectively. The pressure control valve 2 is provided in the middle of each working fluid discharge passage 14 rather than the communication connection portion 14a where the working fluid discharge passages for other wheels join.
A check valve 15 is provided on the 2 side. Therefore, in the working fluid discharge passage 14, due to the check valve 15,
Only the flow of the working fluid from the pressure control valve 22 to the reservoir 11 is allowed.

The pressure control valve 22 includes a switching control valve 24, a branch passage 26 that branches from the working fluid supply passage 20 to reach the reservoir 11, and a fixed throttle 2 provided in the middle of the passage.
8 and a variable throttle 30 that changes the effective passage cross-sectional area of the branch passage 26 by a built-in solenoid. The variable throttle 30 of the pressure control valve 22 is connected to an electronic control unit 100 described later, and when the electronic control unit 100 controls the current to the solenoid, it cooperates with the fixed throttle 28 to change the fixed throttle 28. Branch passage 26 to the throttle 30
The internal pressure Pp is changed. A connection passage 32 leading to an actuator 36 that is interposed between the vehicle body and the wheels and suspends the vehicle body is connected to the A port of the switching control valve 24. The switching control valve 24 of the pressure control valve 22 is a spool valve that takes in the pressure Pp as a pilot pressure through the fixed throttle 28 and the variable throttle 30 and the pressure Pa in the connection passage 32 through the throttle 34 of the passage. Yes, pressure Pp and pressure P
The direction of the oil flow is switched according to the balance with a, and the oil is supplied to and discharged from the actuator 36.

The other end of the connection passage 32 is communicatively connected to a working fluid chamber 38 of an actuator 36 provided corresponding to the wheel. As shown in the figure, the actuator 36 is a kind of cylinder piston device and is arranged between the suspension member 35 supporting the wheels Wh and the vehicle body to suspend the vehicle body. Then, the actuator 36 variably generates a force that causes vertical displacement of the vehicle body by supplying and discharging the working fluid to and from the working fluid chamber 38, and accordingly, the vehicle height of the corresponding portion is set as follows. Increase or decrease.

Generally, the variable diaphragm 30 is an electronic control unit 100.
The solenoid is controlled to change the effective passage area of the branch passage 26. If the pressure Pp in the branch passage 26 and the pressure Pa in the connection passage 32 are equal when the effective passage cross-sectional area of the branch passage 26 has a certain value, the switching control valve 2
4 has a switching position 24b that shuts off communication with all ports.

When the variable throttle 30 is controlled by the electronic control unit 100 so that the pressure Pp becomes low, the pressure P
Since a becomes higher than the pressure Pp, the switching control valve 24 switches to the switching position 24c that connects and connects the port R and the port A, and keeps this position until the pressure Pa and the pressure Pp become equal. Therefore, the working fluid chamber 3 of the actuator 36
Oil is discharged from No. 8, and the actuator 36 reduces the force that causes vertical displacement of the vehicle body to reduce the supporting load of the wheels. Accordingly, the actuator 36
Will reduce the vehicle height.

On the other hand, the variable throttle 3 is used to increase the pressure Pp.
When 0 is controlled, the pressure Pa becomes lower than the pressure Pp, so that the switching control valve 24 switches to the switching position 24a that connects and connects the port P and the port A, and the pressure Pa and the pressure Pp.
Take this position until are equal. Therefore, oil is supplied from the pump 18 to the working fluid chamber 38 of the actuator 36, and the actuator 36 increases the force that causes vertical displacement of the vehicle body to increase the supporting load of the wheels. Along with this, the actuator 36 increases the vehicle height.

A gas-liquid spring device 42 is connected to the working fluid chamber 38 by a passage 40.
Is a gas spring that utilizes the elasticity of the enclosed nitrogen gas. A variable diaphragm 44 is provided in the passage 40, and the variable diaphragm 44 includes a variable diaphragm actuator 45.
The effective passage cross-sectional area is changed by changing the passage amount of the working oil in the passage 40. Therefore, the gas-liquid spring device 4
Not only does 2 act as a suspension spring or an auxiliary suspension spring, but also cooperates with the variable throttle 44 of the passage 40 to variably generate the damping force of the suspension. On the other hand, the piston 62 in the working fluid chamber 38 is fixed to the suspension member 35 at the lower end of the rod, and the piston 62 has a working oil circulation hole 64 that allows the working oil to flow through the upper and lower oil chambers. Is empty. Therefore, the actuator 36 changes the damping force of the suspension characteristic with the gas-liquid spring device 42 via the variable throttle 44. The variable diaphragm actuator 45 is connected to an electronic control unit 100, which will be described later, and is drive-controlled by the electronic control unit 100.

Further, as shown in the figure, the actuator 3
6, a pressure sensor 37 for detecting the pressure in the working fluid chamber 38 is provided, and a vehicle height sensor 118 for detecting the vehicle height of the vehicle body is provided between the suspension member 35 and the vehicle body. There is.

A pilot operated shutoff valve 46 is provided in the middle of the connection passage 32.
A pilot pressure Pc controlled by a pilot pressure control device 48 described later is taken in. And the shutoff valve 46 is
The valve opens when the pilot pressure Pc exceeds a predetermined valve opening value, and closes when the pilot pressure falls below a predetermined valve closing value. A pilot pressure control device 48 is provided in a connection passage 50 that connects the working fluid supply passage 20 and the reservoir 11 to each other. The pilot pressure control device 48 includes a fixed throttle 52 provided in the middle of the passage. And a variable throttle 54 that changes the effective passage cross-sectional area of the connection passage 50 with a built-in solenoid. The variable throttle 54 is connected to an electronic control unit 100 described later, and when the electronic control unit 100 controls the current to the solenoid, the fixed throttle 52 is connected.
The pressure Pc in the connecting passage 50 between the fixed throttle 52 and the variable throttle 54 is changed in cooperation with the above. Therefore, the pilot pressure control device 48 controls the pilot pressure P by the variable throttle 54.
c is changed and supplied to the shutoff valve 46, and the shutoff valve 46 opens or shuts off the connection passage 32 according to the pilot pressure Pc.

Further, in the middle of the working fluid supply passage 20,
A check valve 58 is provided which allows only the flow of working fluid from the filter 56 and pump 18 towards the pressure control valve 22. An accumulator 60 is connected to the working fluid supply passage 20 downstream of the check valve 58.

The pressure control valve 22, the connecting passage 32,
Variable throttle 44, actuator 36, pressure sensor 37,
The gas-liquid spring device 42, the variable diaphragm actuator 45, etc. are provided corresponding to each wheel. In addition, each wheel (front right wheel,
These constituent members of the left front wheel, the right rear wheel, and the left rear wheel are represented by adding reference numerals FR, FL, RR, RL, respectively. For example, the pressure control valve 22 includes 22FR, 22FL, 2
They will be referred to as 2RR and 22RL.

Next, the electrical construction of the fluid pressure type active suspension 10 will be described. As shown in FIG. 2, the pilot pressure control device 48 and the pressure control valve 22FL are used.
~ 22RR and variable diaphragm actuator 45FL ~ 4
The 5RRs are each connected to the electronic control unit 100. The electronic control unit 100 drives and controls the pilot pressure control device 48 and the variable throttle 54, the variable throttle 30, and each variable throttle actuator 45 included in each pressure control valve. The electronic control unit 100 includes a microcomputer 102 mainly including a central processing unit (CPU) 104. This microcomputer 10
2 is a CPU 104, a read-on memory (ROM) 106, and a random access memory (RA).
M) 108, an input port device 110, and an output port device 112, which are bidirectional common buses 114.
Are connected to each other by.

The input port device 110 is provided with various sensors and switches, such as a pressure sensor 37FL for each wheel.
~ 37RR and ignition switch (IGSW) 1
16 and vehicle height sensors 118FL to 118RR for each wheel,
A vehicle speed sensor 120 that detects the vehicle speed, a front-rear G (acceleration) sensor 122 that detects the longitudinal acceleration of the vehicle body, a lateral G sensor 124 that detects the lateral acceleration of the vehicle body, and a steering that detects the steering angle of the steering wheel. An angle sensor 126, a vehicle height setting switch 128 for setting the vehicle height control mode to either a high mode or a low mode, and a left front wheel, a left rear wheel, and a right rear wheel, which are provided corresponding to these wheels. Vertical G sensors 140, 142, 14 for detecting vertical acceleration
4 and a brake sensor 148 for detecting the state of the depression operation of the brake are connected.

The electronic control unit 100 then uses various signals from these switches and sensors, specifically, the internal pressure Pi of the actuator 36 corresponding to each wheel (left front wheel, right front wheel, left rear wheel and right rear wheel). (I = 1,2,3,4), a signal indicating whether or not the ignition switch is in an on state, a signal indicating the vehicle height Xi of a portion corresponding to each wheel,
A signal indicating the vehicle speed V, a signal indicating the longitudinal acceleration Gx of the vehicle body,
A signal indicating the lateral acceleration Gy of the vehicle body, a signal indicating the steering angle θ of the steering wheel, a signal indicating whether the vehicle height control mode is the high mode or the low mode, each wheel (left front wheel, left rear wheel and right rear) Vertical acceleration Gza, Gzb and Gzc corresponding to the wheel)
, A signal indicating the state of the brake pedal operation, etc. are input.

The input port device 110 appropriately processes the above-mentioned input signal and outputs the processed signal to the CPU and the RAM 108 according to an instruction of the CPU 104 based on a program stored in the ROM 106. The ROM 106 stores maps corresponding to the graphs shown in FIGS. 6 to 9 in addition to the control flows shown in FIGS. 3 to 5 and the control flows not shown, and the CPU stores signals based on the respective control flows. It is designed to perform the processing of. Further, the output port device 112 outputs a control signal to the variable restrictor 54 of the pilot pressure control device 48 via the drive circuit 130 according to the instruction of the CPU 104, and the drive circuit 1
The control signals are output to the variable throttles 30 of the pressure control valves 22FL to 22RR via 32-138 to drive circuits 150 to 15
Variable aperture actuator 45 of each variable aperture 44
A control signal is output to FL to 45RR.

Next, regarding suspension control performed by the fluid pressure type active suspension 10 of this embodiment,
This will be described with reference to the flowcharts of FIG. The suspension control shown is based on the ignition switch 11
It is started by turning on the ignition switch 6, and is ended shortly after the ignition switch is turned off.

In the first step S50, R
The AM 108 is initialized, and respective initial values are set to parameters used in target damping force step number calculation, active calculation, etc., which will be described later. Then, step S10
Go to 0.

In step S100, a control signal is output to the solenoid of the variable throttle 54 of the pilot pressure control device 48 to gradually reduce the effective passage sectional area of the variable throttle, thereby gradually increasing the pilot pressure Pp. In this process, the shutoff valve 46 is opened, the pressure of the working fluid in the working fluid supply passage 20 reaches a predetermined pressure, and the shutoff valve 46 is fully opened, that is, the actuator 3
In the state in which the oil can be supplied to and discharged from 6, the process proceeds to the next step S150.

In step S150, the ignition switch 116, the pressure sensor 37 for each wheel,
In addition to the vehicle height sensor 118, a vehicle speed sensor 120, a longitudinal G sensor 122, a lateral G sensor 124, a steering angle sensor 126,
Vehicle height setting switch 128 and vertical G sensors 140 to 14
4, scan the brake sensor 148 and the like, read the corresponding signal from each switch and sensor, and then proceed to step S200. That is, this step S
At 150, a signal indicating the internal pressure Pi of the actuator 36 corresponding to each wheel, a signal indicating whether the ignition switch 116 is in the ON state, a signal indicating the vehicle height Xi of each wheel, a signal indicating the vehicle speed V, A signal indicating the longitudinal acceleration Gx, a signal indicating the lateral acceleration Gy, a signal indicating the steering angle θf of the steering wheel, a signal indicating whether the set mode is the high mode or the low mode, each wheel (front left wheel, rear left wheel) Vertical acceleration Gza, Gzb and Gzc corresponding to the wheel and the right rear wheel)
And various signals such as a signal indicating the state of the brake pedal depression operation.

Subsequent to step S150, in order to change the damping force from the viewpoint of steering stability and riding comfort in step S200, the target damping force step number (each variable throttle) is changed based on various signals read in step S150. Four
The drive control amount of each variable diaphragm actuator 45 when changing and controlling the damping force via 4 is calculated.

Now, the calculation of the target damping force step number in step S200 will be described with reference to the flow chart shown in FIG.

In step S202, which is the initial step of this target damping force step number calculation, the damping force step number Cso for the purpose of ensuring steering stability is calculated as follows. First, it is determined whether the turning situation of the vehicle is slow or fast based on the detection signals θf, V from the steering angle sensor 126 and the vehicle speed sensor 120, and the damping force (anti-roll) required to suppress the posture change of the vehicle in the turning situation. Calculate the number of steps of. When calculating this damping force step number,
As shown in FIG. 6, a map corresponding to the graph of the product value of the vehicle speed V and the steering angle θf and the damping force step number is used. As a result, the damping force step number calculated for the anti-roll becomes a larger step number as the value of the product of the vehicle speed V and the steering angle θf exceeds the predetermined value α1 and the roll becomes larger. The calculation of the damping force step number for this anti-roll is replaced with the vehicle speed V multiplied by the steering angle θf.
It is also possible to use the multiplication value of and the steering angular velocity.

[0038] Further, based on the detection signals from the vehicle speed sensor 120 and the brake sensor 148, it is discriminated whether the dive is slow or fast, which is the difference between the vehicle height before and after, and the damping necessary for suppressing the attitude change of the vehicle in the situation of the dive. Calculate the number of steps of force (anti-dive). Also in this case, as shown in FIG. 7, a map corresponding to the graph of the vehicle height front-back difference and the damping force step number is used. As a result, the damping force step number calculated for the anti-dive gradually increases as the vehicle height front-back difference exceeds the predetermined value α 2. In addition, the vehicle height sensor 118 for each wheel
It can also be obtained from the detection signals Xi of FL to 118RR. Also, instead of the vehicle height front-back difference, the vehicle longitudinal acceleration Gx
Can also be used.

Further, based on the detection signals from the vehicle speed sensor 120 and the throttle opening sensor (not shown), it is judged whether the vehicle squart is slow or abrupt, and the damping force necessary for suppressing the vehicle attitude change in the squat situation. Calculate the number of steps of (anti-squat). Even in this calculation, as shown in FIG. 8, a map corresponding to the graph of the throttle opening speed and the damping force step number is used. As a result, the damping force step number calculated for the anti-squat gradually increases as the throttle opening speed exceeds the predetermined value α3. It is also possible to correct this throttle opening speed by the vehicle speed V from the vehicle speed sensor 120 and obtain the damping force step number from the corrected throttle opening speed. Further, the longitudinal acceleration Gx of the vehicle can be used instead of the throttle opening speed.

The largest of these three damping force step numbers is adopted as the damping force step number Cso for the purpose of ensuring steering stability.

In the following step 204, the damping force step number Cno for the purpose of ensuring riding comfort is calculated as follows. That is, based on the detection signals Xi from the vehicle height sensor 118 and the corresponding vertical G sensor and Gza, Gzb, Gzc, the vertical movement of the vehicle body reflected by the unevenness of the road surface is detected, and the damping force necessary for suppressing the vertical movement is detected. The number of steps of (road surface input suppression) is calculated. Then, the calculated number of steps is
The damping force step number Cno is used to ensure riding comfort.

In the subsequent step S206, the damping force step number Cso and the damping force step number C calculated above are calculated.
No is compared, and the maximum value (MAX (Cso, Cno)) is set as the final target damping force step number CF FINAL. After that, the process proceeds to step S250 and the subsequent processes are performed.

Step S following step S200
At 250, the detailed processing is the damping force guard processing shown in the flowchart of FIG. In this damping force guard processing, first, in step S252, the vehicle height X for each wheel that has been read in step S150.
From i, the relative velocity DX of the piston 62 of the actuator 36 is calculated according to the following equation.

DXi = Xi (n) -Xi (n-1)

That is, step S1 of this routine
Vehicle height Xi (n) read at 50 and vehicle height Xi (n-1) read at step S150 of the previous routine.
The relative speed DX of the piston 62 is calculated from the difference between and.
The relative speed DX of the piston 62 corresponds to the relative speed of the vehicle body on the spring, the suspension member 35 under the spring, and the wheels Wh in the vertical direction.

In the following step S254, the piston 62
It is determined whether the direction of relative movement of is relative to the actuator 36 or the gas-liquid spring device 42 on the extension side or the compression side based on the calculated relative speed DX. Here, after it is determined that the force is on the extension side, the guard value C of the damping force is determined in step S256.
Select GARD. The guard value CGARD of this damping force is shown in FIG.
As shown in FIG. 5, it is determined according to the internal pressure Pi of the actuator 36 and the relative speed DX of the piston 62, and is set to take a smaller value as the internal pressure Pi of the actuator 36 decreases or the relative speed DX increases. Therefore, in this step S256, the damping force guard is calculated from the map corresponding to the graph shown in FIG. 9, the internal pressure Pi of the actuator 36 read in step S150, and the relative speed DX of the piston 62 calculated in step S252. Select the value CGARD.

Step S258 following step S256
Then, the target damping force step number CFINAL determined in step S206 described above is compared with the guard value CGARD selected in step S256. If it is determined that the target damping force step number CFINAL falls below the guard value CGARD, the target damping force step number CFINAL is set to the output damping force step number COUT in step S260, and then the process proceeds to step S300. On the other hand, step S2
At 58, the target damping force step number CF FINAL is the guard value CGARD
When it is determined that the above is the case, the guard value CGARD is set to the output damping force step number COUT in step S262, and then the process proceeds to step S300.

After it is determined in step S254 that the direction of relative movement of the piston 62 is the compression side, the process proceeds to step S260 and the target damping force step number CFINA
L is set to the output damping force step number COUT, and thereafter, the process proceeds to step S300.

Therefore, steps S252 to S252 shown in FIG.
By the processing up to 262, the damping force is limited as follows. That is, as shown in FIG. 9, the damping force (target damping force step number CFINAL) once determined from the viewpoint of steering stability and riding comfort is a guard value determined by the internal pressure Pi of the actuator 36 and the relative speed DX of the piston 62 at that time as shown in FIG. If CGARD is exceeded, the guard value CGARD is used instead of the target damping force step number CFINAL. Thus, the upper limit of the target damping force step number CF FINAL is set according to the internal pressure Pi of the actuator 36 and the relative speed DX of the piston 62. Moreover, the upper limit is limited to the side where the damping force is reduced when the internal pressure Pi of the actuator 36 is reduced, and to the side where the damping force is reduced when the relative speed DX is increased.

In step S300 following step S250, active calculation is performed based on various signals read in step S150 in order to perform vehicle height maintenance control, posture control, and vehicle riding comfort control. In other words, by controlling the supply and discharge of hydraulic oil to and from the actuator 36 through the drive control of the pressure control valve 22, the vehicle body is positively displaced, and the vehicle body height maintenance control, posture control, and vehicle ride comfort control are performed. Plan. In this active calculation, the pressure control valves 22FL to 22FL ... The active control amount (control target pressure Puj in each actuator 36 controlled by each pressure control valve) output to the variable throttle 30 of 22 RR is calculated.

This control target pressure Puj (j = 1, 2, 3, 4)
Is the standard pressure Pbj in the working fluid chamber of each actuator stored in the ROM (the pressure in the working fluid chamber when the vehicle in the standard loading state is stopped) and the displacement feedback control amount Pxj based on the displacement of the vehicle body. , A feedforward control amount Pgj based on longitudinal acceleration and lateral acceleration,
Although it is calculated as the sum of the feedback control amount Pzj based on the vertical acceleration, the details of the active calculation of these control amounts are omitted because they are not directly related to the gist of the present invention.

Step S350 following step S300
In, the control signal corresponding to the active control amount is
Drive circuit 1 corresponding to each pressure control valve 22FL to 22RR
32 to 138, and output damping force step number COUT (target damping force step number CF FINAL or guard value C
GARD) control signals corresponding to the drive circuits 150 to 15 corresponding to the variable diaphragm actuators 45FL to 45RR.
6 is output. Through the output of this control signal, the pressure control valve 2
2FL to 22RR and variable diaphragm actuator 45F
L-45RR is driven and controlled, and then step S15
Return to 0.

In the fluid pressure type active suspension 10 of the present embodiment described above, the damping force (target damping force step number CFINA) once determined from the viewpoint of steering stability and riding comfort.
The upper limit of (L) is limited to a guard value CGARD determined according to the internal pressure Pi of the actuator 36 and the relative speed DX of the piston 62. In addition, the upper limit is limited to the side where the damping force decreases when the internal pressure Pi of the actuator 36 decreases, and to the side where the damping force decreases when the relative speed DX increases.

Therefore, the gas-liquid spring device 42 and the actuator 36 generate a damping force on the soft side of the once determined damping force. Therefore, when the internal pressure P of the actuator 36 is reduced by the active calculation for performing the vehicle height maintenance control of the vehicle body, the posture control, and the ride comfort control of the vehicle, for example, the actuator 3 for the inner wheel when the vehicle turns.
When the internal pressure P of 6 is lowered, the damping force is limited to the guard value CGARD and the damping force is not increased unintentionally. Further, the higher the relative speed DX of the piston 62, the greater the internal pressure fluctuation in the actuator 36. Even in such a case, however, the damping force is limited to the guard value CGARD and careless changes in the damping force can be made. Do not do. Then, the damping force is softened by limiting the damping force to the guard value CGARD, and the flow of the hydraulic oil between the gas-liquid spring device 42 and the actuator 36 is changed.
Does not hinder the expansion of the effective area of Therefore, since the pressure difference between the gas-liquid spring device 42 and the actuator 36 is not increased, the internal pressure of the actuator 36 with respect to the gas-liquid spring device 42 is not accidentally lowered. Therefore, according to the fluid pressure type active suspension 10 of the present embodiment,
Cavitation can be prevented when changing the damping force, and the riding comfort of the vehicle can be improved by avoiding the occurrence of unpleasant impact such as cavitation.

Further, when the internal pressure Pi of the actuator 36 is high or when the relative speed DX of the piston 62 is low, the guard value CGARD is set to a large value. Therefore, according to the fluid pressure type active suspension 10 of the present embodiment, when the internal pressure Pi of the actuator 36 is high or the relative speed DX of the piston 62 is low, the gas-liquid spring device 42 is used.
The variable width of the damping force generated by the actuator 36 and the actuator 36 can be made relatively wide, and the damping force can be effectively changed.

Further, in the fluid pressure type active suspension 10 of the present embodiment, the damping force on the compression side of the piston 62 is not limited to the guard value CGARD. On the compression side of the piston 62, the variable width of the damping force that can be generated by the gas-liquid spring device 42 and the actuator 36 is originally narrower than on the extension side. That is, even if the guard value CGARD is not limited, the damping force on the compression side is naturally limited to some extent. Therefore, according to the fluid pressure type active suspension 10, it is possible to reduce the calculation load by omitting the restriction calculation of the damping force on the compression side of the piston 62, and avoid unnecessary driving of the variable throttle actuator 45. You can In addition, on the compression side of the piston 62, the damping force can be effectively changed over the variable width of the damping force that can be generated by the gas-liquid spring device 42 and the actuator 36.

Although one embodiment of the present invention has been described above, the present invention is not limited to such an embodiment, and can be implemented in various modes without departing from the scope of the present invention. Of course.

For example, in the fluid pressure type active suspension 10 in the above embodiment, the damping force guard value C
Although the limit to GARD is adopted according to the internal pressure Pi of the actuator 36 and the relative speed DX of the piston 62,
It is not limited to this. That is, the guard value CGA of the damping force
It is also possible to limit the RD only in accordance with the internal pressure Pi of the actuator 36 or only in accordance with the relative speed DX of the piston 62.

Further, in this embodiment, the variable diaphragm 44
Is provided in the passage 40 connecting the actuator 36, which is a fluid pressure cylinder, and the gas-liquid spring device 42, the variable throttle 44 is provided in the piston 62 of the actuator 36, or the passage 40 and the piston 6 are provided.
Needless to say, it is also possible to implement the configuration provided in both of the two.

Further, in the present embodiment, the control valve is constructed as the pressure control valve 22 which directly introduces the pressure in the connection passage 32 and the branch passage 26 to perform switching, but this control valve is provided in the working fluid chamber 38. Needless to say, the pressure sensor 37 may be configured as a flow control valve that is detected by the pressure sensor 37 and is electrically switched by a solenoid or the like based on the detected value.

Further, in limiting the damping force to the guard value CGARD in accordance with the internal pressure Pi of the actuator 36, the internal pressure Pi of the actuator 36 is directly detected by the pressure sensor 37, but the following may be done. That is, the target control current value I of the pressure control valve 22 for each wheel is
It is also possible to adopt a configuration in which the internal pressure Pi of the actuator 36 is estimated and calculated using i (i = 1, 2, 3, 4). In this case, the pressure sensor 37 for each wheel becomes unnecessary,
By reducing the number of parts, the structure can be simplified and the cost can be reduced.

Further, in the above embodiment, the fluid pressure type active suspension 10 for positively displacing the vehicle body by using the fluid pressure cylinder has been described as an example, but it is applied to the hydropneumatic suspension using the gas spring. Of course, you can do that.

[0063]

As described above in detail, in the suspension control device according to the first aspect, the damping force upper limit is limited in accordance with the internal pressure of the fluid pressure cylinder, so that the damping force is inadvertently increased when the internal pressure of the fluid pressure cylinder decreases. Do not change or inadvertently lower the internal pressure of the fluid pressure cylinder with respect to the gas spring. Therefore, according to the suspension control device of claim 1,
Cavitation can be prevented when changing the damping force, and the riding comfort of the vehicle can be improved by avoiding the occurrence of unpleasant impact such as cavitation.

In the suspension control device according to the second aspect of the present invention, the damping force upper limit is set according to the relative speed in the vertical direction of the sprung and unsprung parts, so that when the relative speed is high and the internal pressure fluctuation of the fluid pressure cylinder is large. Does not inadvertently increase the damping force or inadvertently decrease the internal pressure of the fluid pressure cylinder with respect to the gas spring. Therefore, according to the suspension control device of the second aspect, it is possible to prevent cavitation at the time of changing the damping force, and it is possible to improve the riding comfort of the vehicle by avoiding the occurrence of an unpleasant impact such as this cavitation. .

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a fluid pressure type active suspension 10 which is one embodiment of a suspension control device according to the present invention.

2 is a block diagram showing an electronic controller for controlling the pilot pressure controller and the pressure control valve shown in FIG. 1. FIG.

FIG. 3 is a general flow chart showing a suspension control flow achieved by the electronic control device shown in FIG.

FIG. 4 is step S2 of the flowchart shown in FIG.
10 is a flowchart showing a routine for calculating a target damping force step number performed at 00.

FIG. 5 is a step S2 of the flowchart shown in FIG.
6 is a flowchart showing a routine of a damping force guarding process performed in 50.

6 is a graph for explaining the contents of the process in step S202 of FIG. 4, and is a graph showing the relationship between the vehicle speed V and the product of the steering angle θf and the damping force step number.

7 is a graph for explaining the content of the process in step S202 of FIG. 4, and is a graph showing the relationship between the vehicle height front-back difference and the damping force step number.

8 is a graph for explaining the content of the process in step S202 of FIG. 4, and is a graph showing the relationship between the throttle opening speed and the number of damping force steps.

9 is a graph for explaining the content of the process in step S256 of FIG. 5, and is a graph showing the relationship between the cylinder internal pressure and the damping force guard step number.

FIG. 10 is an explanatory diagram for explaining a problem of the conventional technique.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Fluid pressure type active suspension 14 ... Working fluid discharge passage 14a ... Communication connection part 15 ... Check valve 16 ... Engine 18 ... Pump 20 ... Working fluid supply passage 22 ... Pressure control valve 24 ... Switching control valve 26 ... Branch passage 28 ... Fixed throttle 30 ... Variable throttle 32 ... Connection passage 34 ... Throttle 35 ... Suspension member 36 ... Actuator 37 ... Pressure sensor 38 ... Working fluid chamber 40 ... Passage 42 ... Gas-liquid spring device 44 ... Variable throttle 45 ... Variable throttle actuator 46 ... Cut off Valve 48 ... Pilot pressure control device 50 ... Connection passage 52 ... Fixed throttle 54 ... Variable throttle 60 ... Accumulator 62 ... Piston 64 ... Hydraulic oil flow hole 100 ... Electronic control device 116 ... Ignition switch 118 ... Vehicle height sensor 120 ... Vehicle speed sensor 122 ... front and rear G sensor 124 ... lateral G sensor 26 ... steering angle sensor 140, 142, 144 ... vertical G sensor 148 ... brake sensor Wh ... wheel

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshihiko Yamanaka 2-chome, Asahi-cho, Kariya city, Aichi Aisin Seiki Co., Ltd.

Claims (2)

[Claims] 1. A suspension control device capable of changing the damping force of a suspension, which is interposed between a sprung part and an unsprung part of a vehicle and supplies and discharges fluid to adjust a vehicle height of a corresponding portion. A fluid pressure cylinder capable of increasing and decreasing, a damping force changing means for changing a damping force generated in the fluid pressure cylinder according to a running state of a vehicle; a pressure detecting means for detecting an internal pressure of the fluid pressure cylinder; A damping force limiting unit that limits the upper limit of the damping force change by the damping force changing unit on the side where the damping force decreases in accordance with the decrease in the detected internal pressure is provided. Suspension control device. 2. A suspension control device capable of changing a damping force of a suspension, which is interposed between a sprung part and an unsprung part of a vehicle and supplies and discharges fluid to adjust a vehicle height of a corresponding portion. A fluid pressure cylinder capable of increasing / decreasing, a damping force changing means for changing a damping force generated in the fluid pressure cylinder according to a running state of a vehicle, and a relative speed in a vertical direction with respect to the sprung and unsprung portions. Relative speed detection means to detect, the upper limit of the damping force change by the damping force changing means, to the side where the damping force decreases following the increase in the detected relative speed,
A suspension control device comprising: a damping force limiting unit that limits the detected relative velocity according to the relative velocity.