JPH04345518A - Suspension device for vehicle - Google Patents

Abstract

PURPOSE:To improve the performance of a spring for restraining the transmission of a high-frequency vibration to a body by improving the response of the spring to the vibration, regarding the vehicle suspension device where fluid cylinders are fitted respectively between each wheel and the body, and gas springs are connected respectively to each fluid cylinder. CONSTITUTION:At least two gas springs, or the first and second gas springs 5 and 6 are connected to each fluid cylinder. The first gas spring 5 is free piston type having a fluid chamber 5d and a gas chamber 5c separated from each other with a free piston 5d so laid in a gas spring body 5a as to be freely slidable. On the other hand, the second gas spring 6 is of metal bellows type having a free telescopic metal bellows 6d constituting a gas chamber 6 with gas sealed internally.

Description

[Detailed description of the invention]

0001

[Industrial Field of Application] The present invention relates to a suspension system for a vehicle, and more particularly, to a vehicle suspension system, which has fluid cylinders between each wheel and the vehicle body, and which adjusts suspension characteristics by supplying and discharging fluid to each of these fluid cylinders. The present invention relates to a variable suspension device for a vehicle.

0002

2. Description of the Related Art As an automobile suspension system, for example, as described in Japanese Patent Application Laid-Open No. 63-130418, a suspension system is used between the sprung mass and the unsprung mass of a vehicle, that is, between each wheel and the vehicle body. A so-called active suspension device is known, which is configured to have fluid cylinders respectively and to be able to vary suspension characteristics by supplying and discharging fluid to each fluid cylinder according to operating conditions.In this type of active suspension device, Usually, the vehicle height displacement detection means detects the vehicle height displacement, the pressure detection means detects the pressure of the fluid cylinder device, and the vertical acceleration detection means detects the vertical acceleration applied to the vehicle. Based on the detection signal detected by
By controlling the amount of fluid supplied to and discharged from each of the fluid cylinders, bouncing, pitching, and roll of the vehicle are suppressed to improve ride comfort and stability.

[0003] Furthermore, the above active suspension device is provided with a gas spring connected to each fluid cylinder, and this gas spring is connected to a hydraulic pressure chamber that communicates with the hydraulic pressure chamber of the fluid cylinder via a communication passage. and a gas chamber filled with gas at a predetermined pressure, and absorbs particularly high-frequency vibrations among the vibrations transmitted to the vehicle body due to the buffering effect of the gas sealed in the gas chamber. This is designed to improve ride comfort.

0004

[Problems to be Solved by the Invention] By the way, the above-mentioned gas spring usually has a hydraulic chamber in which the gas spring body is communicated with a fluid cylinder by a free piston that is slidably provided in the gas spring body. A free piston type gas spring is used, which is divided into a gas chamber and a gas chamber filled with gas.
A free piston and gas spring are used to improve airtightness in the hydraulic pressure chamber and gas chamber to prevent liquid leakage from the hydraulic pressure chamber side to the gas chamber side, or conversely from the gas chamber side to the hydraulic pressure chamber side. It is necessary to improve the sealing performance between it and the main body. However, if the sealing performance between the free piston and the gas spring body is improved, the sliding resistance of the free piston during vibration transmission will increase, making the free piston less responsive to high-frequency vibrations. It does not slide well, and as a result, the gas spring's ability to suppress the transmission of high-frequency vibrations to the vehicle body deteriorates.

The present invention addresses the above-mentioned situation in an active suspension system for a vehicle, which has fluid cylinders provided between each wheel and the vehicle body, and gas springs connected to each of these fluid cylinders. The purpose is to improve the gas spring's ability to suppress transmission of high-frequency vibrations to the vehicle body by increasing the responsiveness of the gas spring to high-frequency vibrations.

[0006]

[Means for Solving the Problems] In order to solve the above problems, the present invention is characterized by the following structure.

First, the invention according to claim 1 of the present application (hereinafter referred to as the first invention) improves suspension characteristics by supplying and discharging fluid to fluid cylinders provided between each wheel and the vehicle body. In the vehicle suspension system, at least two gas springs each include a hydraulic pressure chamber communicating with the hydraulic pressure chamber of the fluid cylinder and a gas chamber separated from the hydraulic pressure chamber and filled with gas. and at least one of these gas springs is a metal bellows type having a metal bellows with gas sealed inside to form a gas chamber, and the other gas spring partitions the hydraulic pressure chamber and the gas chamber. It is characterized by being of a free piston type with a freely slidable free piston.

[0008] Furthermore, the invention according to claim 2 of the present application (hereinafter referred to as the second invention) has the structure of the second invention described above,
A feature is that the volume of the metal bellows is set smaller than the volume of the free piston.

Furthermore, the invention according to claim 3 of the present application (hereinafter referred to as the third invention) has the structure of the first invention,
It is characterized in that the internal pressure of the gas chamber in the metal bellows type gas spring is set higher than the internal pressure of the gas chamber in the free piston type gas spring.

0010

[Operation] In any of the first to third inventions,
At least one of the gas springs is a metal bellows type gas spring, and unlike a free piston type gas spring, the response to high frequency vibrations is reduced due to the sliding resistance of the free piston. The metal bellows responds extremely well to high-frequency micro-vibrations, thereby effectively suppressing the transmission of high-frequency micro-vibrations to the vehicle body.

By the way, due to the structure of the metal bellows type gas spring, it is difficult to set a large amount of displacement of the metal bellows. However, according to the first to third aspects of the invention, the metal bellows type gas spring and the free piston type gas spring can be suppressed. Since a spring is also used, the free piston type gas spring responds with good response to vibrations with relatively large amplitudes, and the transmission of the vibrations to the vehicle body is suppressed. In this way, since a metal bellows type gas spring and a free piston type gas spring are used together, the overall size of the gas spring is not increased compared to a case where the gas spring is configured only with a metal bellows type gas spring. Furthermore, high frequency vibrations can be effectively suppressed.

In particular, according to the second invention, vibrations with a relatively large amplitude are effectively absorbed by the free piston type gas spring whose volume is set larger than that of the metal bellows. High-frequency micro-vibrations can be adequately dealt with by a metal bellows-type gas spring, which has a smaller volume than a free-piston type gas spring, and this allows the overall structure of the gas spring to be more compact. Become.

Further, in the third invention, the internal pressure of the gas chamber constituted by the metal bellows is set higher than the internal pressure of the gas chamber partitioned by the free piston in the free piston type gas spring. With the displacement of the metal bellows, the dynamic spring constant of the metal bellows increases rapidly, and the vibration damping effect of the metal bellows type gas spring decreases, thereby suppressing the roll speed when the vehicle body rolls. At the same time, the free piston type gas spring suppresses the transmission of relatively large amplitude vibrations to the vehicle body. In particular, since a damping force is generated by the sliding resistance of the free piston, vibrations are damped more effectively.

[0014]

Embodiments Hereinafter, embodiments of the present invention will be explained based on the drawings.

FIG. 1 is an overall schematic diagram of a vehicle including a vehicle suspension system according to the present invention. In FIG. 1, only the left side of the vehicle body 1 is shown, but the right side of the vehicle body 1 is similarly configured. has been done. In FIG. 1, fluid cylinders 3, 3 are provided between the vehicle body 1 and the left front wheel 2FL, and between the vehicle body 1 and the left rear wheel 2FR, and each fluid cylinder 3 includes a cylinder body 3a. A hydraulic chamber 3c is formed by the piston 3b fitted therein. The upper end of the piston rod 3d connected to the piston 3b of each fluid cylinder 3 is connected to the vehicle body 1, and each cylinder body 3a is connected to the left front wheel 2FL or the left rear wheel 2FR, respectively.

As shown in FIG. 1, gas spring units 4...4 are connected to each of the fluid cylinders 3, and each gas spring unit 4 is connected to a first gas cylinder 3, as shown in FIG. A spring 5 and a second gas spring 6 are provided, and bodies 5a and 6a of each gas spring 5 and 6 are respectively connected to hydraulic chambers 5b and 6.
b and gas chambers 5c and 6c filled with a predetermined gas, and a hydraulic chamber 5 in each gas spring 5 and 6.
b, 6b are communicated with the hydraulic pressure chamber 3c of each fluid cylinder 3 via a communication passage 7 and branch passages 7a, 7b branched from the communication passage 7, respectively.

Each of the fluid cylinders 3 includes a
A hydraulic pump 8 for supplying fluid to each fluid cylinder 3 is connected via a fluid passage 9 to the fluid passage 9.
A proportional flow control valve 10 that controls the flow rate of fluid supplied to the
The hydraulic pump 8 is also provided with a discharge pressure gauge 11 that detects the discharge pressure of the fluid, and a hydraulic pressure sensor 12 that detects the hydraulic pressure in the hydraulic chamber 3c of each fluid cylinder 3. is provided.

Furthermore, a vehicle height displacement sensor 13 detects the cylinder stroke amount of each fluid cylinder 3 and detects the vertical displacement of the vehicle body 1 with respect to each wheel, that is, the vehicle height displacement.
13 is provided, and vertical acceleration sensors 14a, 14b, and 14c are provided to detect the vertical acceleration of the vehicle, that is, the vertical acceleration on the springs of the wheels. , above each of the left and right front wheels 2FL, 2FR (only one shown) on a substantially horizontal plane of the vehicle, and the remaining one vertical acceleration sensor 14c detects the vehicle width between the left and right rear wheels 2RL, 2RR (only one shown). They are arranged so as to be located in the center of each direction. Further, a lateral acceleration sensor 15 is provided at the center of gravity of the vehicle body 1 to detect lateral acceleration applied to the vehicle.
A steering angle sensor 16 and a vehicle speed sensor 17 are provided.

[0019]Then, the discharge pressure gauge 11 and the hydraulic pressure sensor 1
2. Vehicle height displacement sensor 13, vertical acceleration sensor 14a, 1
Detection signals from 4b, 14c, lateral acceleration sensor 15, steering angle sensor 16 and vehicle speed sensor 17 are input to a control unit 18 which has a CPU etc. inside, and this control unit 18 performs a predetermined process based on each of the above detection signals. Calculations are performed according to the program, and the operation of each of the proportional flow rate control valves 10 is controlled to achieve desired suspension characteristics.

Next, a description will be given of the hydraulic pressure supply circuit for supplying and discharging working hydraulic pressure to each of the fluid cylinders 3. As shown in FIG. An accumulator 22 is connected to a discharge pipe 8a that is arranged in parallel with a hydraulic pump 21 for a power steering device driven by a power source 20 and discharges working fluid from the hydraulic pump 8 to each fluid cylinder 3. is branched into a front wheel side pipe 23F and a rear wheel side pipe 23R on the downstream side of the connection part of the accumulator 22, and the front wheel side pipe 23F is connected to the left front wheel side on the downstream side of the branch part with the rear wheel side pipe 23FR. Branched into piping 23FL and right front wheel side piping 23FR, each front wheel side piping 23FL, 23
FR communicates with hydraulic chambers 3c, 3c of a fluid cylinder 3FL for the left front wheel and a cylinder 3FR for the right front wheel, respectively. Similarly, the rear wheel side pipe 23R is connected to the left rear wheel side pipe 23RL and the right rear wheel side pipe 23RR on the downstream side of the branching part.
The rear wheel side pipes 23RL and 23RR are connected to hydraulic pressure chambers 3c and 3c of a fluid cylinder 3RL for the left rear wheel and a cylinder 3RR for the right rear wheel, respectively.

[0021] Each of the above fluid cylinders 3FL, 3F
As mentioned above, the hydraulic pressure chambers 5b and 6b of the first and second gas springs 5 and 6 are connected to the communication path 7 in the hydraulic pressure chambers 3c of R, 3RL, and 3RR.
and are connected to each other via branch passages 7a and 7b, and the hydraulic chamber 5b of the first gas spring 5 and the hydraulic chamber 3c of each fluid cylinder 3FL, 3FR, 3RL, 3RR.
An orifice 25 is provided between the orifice 25 and the high-frequency waves applied to the vehicle are The aim is to reduce vibrations.

Further, the communication passage 7 connecting each of the first gas springs 5 and the hydraulic pressure chambers 3c of the respective fluid cylinders 3FL, 3FR, 3RL, and 3RR has an open position in which the communication passage 7 is opened and a position in which the passage 7 is opened. The switching valve 26 adjusts the passage cross-sectional area of the communication passage 7 and switches the damping force of each gas spring unit 4 into two stages by switching the valve to the closed position where the passage cross-sectional area is narrowed.
...26 are provided.

An unload relief valve 28 is connected to the discharge pipe 8a of the hydraulic pump 8 on the upstream side of the connection portion of the accumulator 22. The discharge pressure is a predetermined upper limit, for example, 160Kgf/cm2.
In this case, the hydraulic pump 8 is switched to the open position.
The hydraulic oil discharged from the tank is directly returned to the reserve tank 29, while the hydraulic oil is kept at a predetermined lower limit value, for example, 120 Kgf/cm2.
In the following cases, the valve is switched to the closed position and hydraulic oil is supplied to the accumulator 22, and the pressure accumulation value of the accumulator 22 is controlled to be maintained at a predetermined value. In this way, each fluid cylinder 3FL, 3FR, 3RL, 3F
The fluid is supplied to R by accumulating pressure in the accumulator 22, which is maintained at a predetermined accumulated pressure value.

In FIG. 2, the unload relief valve 28 is shown in the closed position.

Here, since the hydraulic circuits for the left and right front wheels and the left and right rear wheels are constructed in the same way, the left front wheel 2F will be described below.
Only the L hydraulic circuit will be explained, and other details will be omitted.

That is, the proportional flow rate control valve 10 is a three-way valve, which has a closed position where all ports are closed, a supply position where the left front wheel side piping 23FL is opened to the hydraulic pressure supply side, and a fluid cylinder 3FL of the left front wheel side piping 23FL. and a discharge position communicating with the return pipe 32, and FIG. 2 shows the closed position. Further, the proportional flow control valve 10 includes pressure compensation valves 10a, 10a, and these pressure compensation valves 1
0a and 10a allow the hydraulic pressure in the hydraulic pressure chamber 3c of the fluid cylinder 3FL to be maintained at a predetermined value when the proportional flow rate control valve 10 is in the supply position or the discharge position.

Further, on the fluid cylinder 3FL side of the proportional flow rate control valve 10, there is provided a pilot pressure responsive on-off valve 33 that can open and close the left front wheel side piping 23FL. When the solenoid valve 34 that guides the hydraulic pressure of the left front wheel side piping 23FL on the hydraulic pump 8 side of the control valve 10 is opened, the hydraulic pressure of the solenoid valve 34 is introduced as pilot pressure, and when this pilot pressure is equal to or higher than a predetermined value, , on-off valve 33
Open the left front wheel side piping 23FL and open the proportional flow control valve 10.
The flow rate of fluid to the fluid cylinder 3FL is controlled by the fluid cylinder 3FL.

[0028] Furthermore, the hydraulic pressure chamber 3 of the fluid cylinder 3FL
A relief valve 35 that opens when the internal pressure of the hydraulic pressure chamber 3c rises abnormally and returns the working oil in the hydraulic pressure chamber 3c to the return pipe 32, is connected to the discharge pipe 8a of the hydraulic pump 8 near the downstream side of the connection part of the accumulator 22, Open when the ignition is turned off,
The ignition key interlocking valve 36 returns the working oil stored in the accumulator 22 to the reservoir tank 29 and releases the high pressure state in the accumulator 22, and when the discharge pressure of the hydraulic pump 8 increases abnormally, A hydraulic pump relief valve 37 and return piping 32 return the hydraulic oil to the reservoir tank 29 to lower the discharge pressure.
Return accumulators 38 and 38 are provided, respectively, which are connected to the hydraulic cylinder 3FL and perform a pressure accumulation function when the hydraulic oil is discharged from the fluid cylinder 3FL.

On the other hand, in the control unit 18, each proportional flow rate control valve 10 is controlled to control each fluid cylinder 3.
A fluid control amount calculation circuit 39 is provided for controlling the amount of fluid supplied and discharged to and from FL, 3FR, 3RL, and 3RR. As shown in FIGS. 3 to 5, this fluid control amount calculation circuit 39 Vehicle height displacement sensor 13 for each wheel...
A control system A that controls the vehicle height to the target vehicle height based on the vehicle height displacement signals Xfr, Xfl, Xrr, and Xrl of No. 13, and a vehicle obtained by differentiating the vehicle height displacement signals Xfr, Xfl, Xrr, and Xrl. High displacement speed signal Yfr, Yfl, Yrr, Y
a control system B that controls vehicle height displacement speed based on rl;
A control system C that aims to reduce vertical vibration of the vehicle based on vertical acceleration signals Gfr, Gfl, and Gr from three vertical acceleration sensors 14a, 14b, and 14c, and a hydraulic pressure sensor 12 for each wheel.
...Control system D that calculates the torsion of the vehicle body based on the 12 pressure signals Pfr, Pfl, Prr, Prl and suppresses it.
and a control system E that aims to reduce vibrations in the lateral direction of the vehicle based on the lateral acceleration detection signal Gh of the lateral acceleration sensor 15.

The control system A includes a vehicle height sensor 1 for each wheel.
In order to cut the noise of the vehicle height displacement signal detected by 3...13, low-pass filters 40...40 are provided that cut high frequency components, and the high-frequency components of the left and right front wheels 2FL, 2FR are cut by each low-pass filter 40. The outputs Xfr and Xfl of each vehicle height sensor 13 are added together, and the outputs Xrr and Xrl of each vehicle height sensor 13 of the left and right rear wheels 2RL and 2RR whose high frequency components have been cut by each low-pass filter 40 are added together. a bounce component calculation unit 41 that calculates the bounce component of the left and right front wheels 2FL,
Pitching in which the pitching component of the vehicle is calculated by subtracting the added value of the outputs Xrr and Xrl of the respective vehicle height sensors 13 of the left and right rear wheels 2RL and 2RR from the added value of the outputs Xfr and Xfl of the respective vehicle height sensors 13 of the 2FR. The component calculation unit 42, the output Xfr of each vehicle height sensor 13 of the left and right front wheels 2FL, 2FR,
Difference in Xfl (Xfr-Xfl) and left and right rear wheels 2RL
.

The control system A also includes a bounce component calculation section 4.
A bounce control unit 44 receives the vehicle bounce component and target average vehicle height Th calculated in step 1, and calculates the amount of hydraulic oil supplied to the fluid cylinder 3 of each wheel in bounce control based on the gain Kb1; Section 42
The pitching component of the vehicle calculated in is input, and the pitching control unit 45 and roll component calculation unit 43 calculate the amount of hydraulic oil supplied to the fluid cylinder 3 of each wheel in pitching control based on the gain Kp1. The component and the target roll displacement amount Tr are input, and the gain K
A roll control unit 46 is provided that calculates the amount of hydraulic oil supplied to the fluid cylinders 3 of each wheel in roll control based on rf1 and Krr1 so that the vehicle height corresponds to the target roll displacement amount Tr.

In this way, each control amount calculated by the bounce control section 44, pitching control section 45, and roll control section 46 is reversed in sign for each wheel, that is, detected by each vehicle height sensor 13...13. Vehicle height displacement signals Xfr, Xf
l, Xrr, and Xrl are reversed so that their positive and negative signs are opposite, and then the bounce, pitching, and roll control amounts for each wheel are added, respectively, to control the proportional flow rate control valve for each wheel in control system A. Control signals QFL1, QFR1, QRL1, QRR1 to 10 are obtained.

Here, dead band circuits 47...47 are provided between each low-pass filter 40 and the bounce calculation section 41, pitching calculation section 42, and roll calculation section 43. Vehicle height displacement signals Xfr, Xfl, Xrr, X input through 40
Only when rl exceeds the preset dead zone Xh...Xh, these vehicle height displacement signals Xfr, Xfl, Xrr
, Xrl, the bounce calculation unit 41 and the pitching calculation unit
2 and the roll calculation unit 43.

The control system B receives vehicle height displacement signals Xfr, Xfl, Xrr,
It has differentiating circuits 50...50 that differentiate Xrl and calculate vehicle height displacement speed signals Yfr, Yfl, Yrr, Yrl according to the formula shown in Equation 1.

[0035]

[Equation 1] Here, Xn is the amount of vehicle height displacement at time t, and Xn-1 is the amount of vehicle height displacement at time t.
-1 is the vehicle height displacement amount, and T is the sampling time.

Furthermore, the control system B controls the left and right front wheels 2FL, 2
From the added value of the vehicle height displacement speed signals Yfl and Yfr on the FR side, the vehicle height displacement speed signal Yrl on the left and right rear wheels 2RL and 2RR side is determined.
, Yrr to calculate the pitch component of the vehicle, and the left and right front wheels 2FL, 2.
Difference between vehicle height displacement speed signals Yfl and Yfr on the FR side (Yf
1-Yfr) and the difference (Yrl-Yrr) between the vehicle height displacement speed signals Yrl and Yrr of the left and right rear wheels 2RL and 2RR to calculate the roll component of the vehicle. We are prepared.

The pitch component calculated by the pitch component calculation unit 51 is inputted to the pitch control unit 53, and the flow rate control amount to each proportional flow rate control valve 10 in pitch control is calculated based on the gain Kp2. Further, the roll component calculated by the roll calculation section 52 is input to the roll control section 54, and based on the gains Krf2 and Krr2, the vehicle height is adjusted so that the vehicle height corresponds to the target roll displacement amount Tr.
The flow control amount to each proportional flow control valve 10 in roll control is calculated.

Each control amount calculated by the pitch control section 53 and the roll control section 54 is further reversed in sign for each wheel, that is, the vehicle height displacement speed signal Yfr calculated by each differentiating circuit 50 is obtained. , Yfl, Yrr, and Yrl are reversed so that their positive and negative signs are opposite, and then each control amount of pitch and roll for each wheel is added to M, and the proportional flow rate control valve 1 of each wheel in control system B is
Flow signal QFR2, QFL2, QRR2, QRL to 0
2 is obtained.

The control system C includes a low-pass filter 60...
60, a bounce component calculation unit 61 calculates the bounce of the vehicle by adding the vertical acceleration signals Gfr, Gfl, and Gr detected by the vertical acceleration sensors 14a, 14b, and 14c from which high frequency components have been cut; front wheel 2
The output Gr of the vertical acceleration sensor 14c installed at the center of the left and right rear wheels in the vehicle width direction is subtracted from the average value of the outputs Gfr and Gfl of the vertical acceleration sensors 14a and 14b installed above FL and 2FR. Then, the pitch component calculating section 62 calculates the pitch component of the vehicle, and the roll component of the vehicle is calculated by subtracting the output Gfl of the vertical acceleration sensor 14b on the left front wheel side from the output Gfr of the vertical acceleration sensor 14a on the right front wheel side. The bounce component calculation unit 63 receives the calculation value of the bounce component calculated by the bounce component calculation unit 61 and calculates the control amount of hydraulic fluid to each proportional flow rate control valve 10 in bounce control based on the gain Kb3. A pitch control unit 65 receives the calculated value of the pitch component calculated by the pitch component calculation unit 62 and calculates the control amount of hydraulic fluid to the proportional flow rate control valve 10 in pitch control based on the gain Kp3. The roll control unit 66 receives the calculated value of the pitch component calculated by the roll component calculation unit 63 and calculates the control amount of hydraulic oil to the proportional flow rate control valve 10 in pitch control based on the gains Krf3 and Krr3. ing.

In this way, the control amounts calculated by the bounce control section 64, pitch control section 65, and roll control section 66 are reversed for each wheel, and then the bounce and pitch for each wheel are Flow rate signals QFR3, QFL3, QR to each proportional flow rate control valve 10 are outputted by control system C.
R3 and QRL3 are obtained.

Note that dead band circuits 67 . . . 67 are provided between each low-pass filter 60 that cuts high frequency components and the bounce component calculation section 61, pitch component calculation section 62, and roll component calculation section 63, respectively. , vertical acceleration signals Gfr, Gf input from the vertical acceleration sensors 14a, 14b, 14c through each low-pass filter 60.
Only when l, Gr exceed a preset dead zone Xg...Xg, these vertical acceleration signals Gfr, Gfl, G
r is output to a bounce component calculation section 61, a pitch component calculation section 62, and a roll component calculation section 63.

The control system D receives the hydraulic pressure detection signals detected by the hydraulic pressure sensors 12, 12 of the fluid cylinders 3 of the left and right front wheels 2FL, 2FR, and has its high frequency components cut by the low-pass filters 70, 70. Afterwards, the difference in hydraulic pressure between the hydraulic pressure chambers 3c and 3c of the fluid cylinders 3 of the left and right front wheels (P
fr-Pfl) and their addition value (Pfr+Pfl)
The ratio of Pf{(Pfr-Pfl)/(Pfr+Pfl)
}, and if the calculated hydraulic pressure ratio Pf satisfies -ωl<Pf<ωl with respect to a predetermined threshold hydraulic pressure ωl, the calculated hydraulic pressure ratio Pf is output as is, and on the other hand, Pf
When <-ωl or Pf>ωl, the front wheel side hydraulic pressure ratio calculating section 71a outputs the threshold hydraulic pressure ratio ωl, and the hydraulic pressure sensor 1 of the fluid cylinder 3 of the left and right rear wheels 2RL, 2RR.
2 and 12, and its high frequency components are cut by low-pass filters 70 and 70.
The ratio Pr{(Prr-Prl) of the difference in hydraulic pressure between c and 3c (Prr-Prl) and their addition value (Prr+Prl)
)/(Prr+Prl)}, and increases the rear wheel hydraulic pressure ratio Pr by a predetermined multiplier based on the gain ωf, and then increases this as the front wheel hydraulic pressure. The output gain ωa of the warp control unit 71 is used to increase the ratio Pf by a predetermined magnification, and then on the front wheel side, the gain ωc is used to increase the ratio Pf by a predetermined magnification. Furthermore, one of the left and right wheels is reversed so that the controlled amount of hydraulic fluid supplied to each wheel is opposite in positive and negative, and the flow signals QFR4, QFL4, QRR4 and QRL4 is obtained.

Further, the control system E receives the lateral acceleration detection signal applied in the lateral direction of the vehicle detected by the lateral acceleration sensor 15, and after its high frequency component is cut by the low-pass filter 80, the signal is inputted based on the gain Kg. The control amount is calculated, and for the left and right front wheels 2FL and 2FR,
Furthermore, it is increased by a predetermined magnification based on the gain Agf,
After that, the fluid supply control amount for the left front wheel 2FL is reversed so that the fluid supply control amount for the left and right wheels is opposite in positive and negative. The fluid supply control amount of the left rear wheel 2RL is reversed so that the supply control amount of
R5, QFL5, QRR5 and QRL5 are obtained.

Each of the control systems A and B obtained as described above
, C, D, and E are added to each wheel, and further multiplied by a gain Af for the left and right front wheels to provide a total flow signal to each proportional flow control valve 10. QFR, QFL, QRR and QR
L is obtained.

Here, each of the control systems A, B, C, D and E stored in the control unit 18
An example of the control gain reference map used in
It is shown in Table 1. This map has seven modes set according to driving conditions.

[0046]

[Table 1] In Table 1, mode 1 is the value of each control gain for 60 seconds after the engine has stopped, and mode 2 is the state where the ignition switch is on but the vehicle is stopped and the vehicle speed is 0. The value of each control gain in mode 3 is
The values of each control gain are shown in a straight-ahead state where the vehicle's lateral acceleration Gh is 0.1 or less, and mode 4 is the vehicle's lateral acceleration Gh when the reverse roll mode is selected by a roll mode switch (not shown). Indicates the value of the control gain selected in place of mode 5 in a slow turning state where the value exceeds 0.1 and is less than or equal to 0.3, and the vehicle speed is 120 km/h.
When the number of rolls exceeds h, the mode is automatically switched to mode 5 even if the reverse roll mode is selected. Mode 5 is for each control gain value in a slow turning state where the vehicle's lateral acceleration Gh exceeds 0.1 and is 0.3 or less, and mode 6 is for the vehicle's lateral acceleration Gh.
The value of each control gain in a medium turning state where h exceeds 0.3 and 0.5 or less, and mode 7 is the value of each control gain in a sharp turning state where the lateral acceleration Gh acting on the vehicle exceeds 0.5. The values are shown respectively.

Further, in Table 1, Qmax indicates the maximum control flow rate supplied to the proportional flow rate positive control valve 10 of each wheel, and Pmax indicates the maximum pressure within the hydraulic pressure chamber 3c of the fluid cylinder 3. , from each hydraulic pressure chamber 3c to the accumulator 2
2 is set so that the hydraulic oil does not flow backward, and Pmin indicates the lowest pressure in the hydraulic pressure chamber 3c of each fluid cylinder 3, and Pmin is set so that the pressure in each hydraulic pressure chamber 3c does not decrease excessively. The setting is made so that the gas spring 5 will not be fully extended and damaged.

[0048] In Table 1, except for mode 4, the larger the mode number, the more suspension control is set to be performed with emphasis on steering stability. Also,
In Table 1, L indicates liters/minute.

Next, the first gas spring 5 constituting the gas spring unit 4 connected to each of the fluid cylinders 3FL, 3FR, 3RL, and 3RR, which is a characteristic part of the present invention.
To specifically explain the structure of the second gas spring 6, as shown in FIG. 6, the first gas spring 5 is of a free piston type, and the second gas spring 6 is of a metal bellows type. That is, a free piston 5d that is slidable with respect to the main body 5a is installed inside the main body 5a of the first gas spring 5, and the free piston 5d allows each fluid cylinder 3FL, 3FR, 3RL, It is defined into a hydraulic pressure chamber 5b communicating with each hydraulic pressure chamber 3c of the 3RR via a branch passage 7a, and a gas chamber 5c filled with a predetermined gas.

Note that a seal member 5e is attached to the circumferential surface of the free piston 5d, and this seal member 5e
This reliably prevents liquid leakage from the hydraulic pressure chamber 5b side to the gas chamber 5c side, or conversely from the gas chamber 5c side to the hydraulic pressure chamber 5b side. In addition, the hydraulic pressure chamber 5
A damping valve 25a provided with the above-mentioned orifice 25 is interposed in the upper part of b.

On the other hand, inside the main body 6a of the second gas spring 6 is a retractable metal bellows 6 filled with a predetermined gas.
d constitutes a gas chamber 6c, and a hydraulic pressure chamber 6b whose periphery communicates with the hydraulic pressure chambers 3c of each fluid cylinder 3FL, 3FR, 3RL, and 3RR via a branch passage 7a.
It is said that

As shown in the figure, the volume of the second gas spring 6 of the metal bellows type is set smaller than that of the first gas spring 5 of the free piston type. As shown, the internal pressure of the gas chamber 6c in the second gas spring 6, that is, the dynamic spring constant of the second gas spring 6, is greater than the gas chamber 5b partitioned by the free piston 5d, as shown by the solid line b in the figure. , i.e., the internal pressure of the first gas spring 5
is set higher than the dynamic spring constant of.

Note that the first gas spring 5 having a different dynamic spring constant
When the second gas spring 6 and the second gas spring 6 are combined in series, the overall dynamic spring constant of the gas spring unit 4 decreases, as shown by the solid line c in FIG. 7, thereby improving riding comfort. become. Furthermore, in the figure, a line indicated by a dotted line e indicates the hydraulic pressure value when the vehicle is stopped.

According to the above configuration, the gas spring unit 4
The second gas spring 6 constituting the metal bellows type gas spring 6 is of a free piston 5d like the first gas spring 5 of the free piston type.
There is no reduction in responsiveness to high-frequency vibrations due to sliding resistance, and the metal bellows 6d responds extremely well to high-frequency micro-vibrations, thereby reducing transmission of high-frequency micro-vibrations to the vehicle body. will be effectively suppressed.

By the way, in the second gas spring 6 of the metal bellows type, it is difficult to set a large amount of displacement of the metal bellows 6d due to its structure. In order to suppress amplitude vibrations, the second gas spring 6 as a whole has to be enlarged, but according to this embodiment, the second gas spring 6 of the metal bellows type and the free piston are The second gas spring 5 of the free piston type is used in combination with the first gas spring 5 of the formula, and for vibrations with a relatively large amplitude, the second gas spring 5 of the free piston type responds with good response, and the vibrations are transferred to the vehicle body side. Transmission will be suppressed. In this way, the gas spring unit 5
Since the second gas spring 6 of the metal bellows type and the first gas spring 5 of the free piston type are used together, the entire gas spring unit 4 can be constructed from only metal bellows type gas springs. High frequency vibrations can be effectively suppressed without increasing the size.

In particular, vibrations with relatively large amplitudes are effectively absorbed by the free piston type first gas spring 5, which has a larger volume than the metal bellows type second gas spring 6. High-frequency microvibrations with small amplitudes can be adequately dealt with by the metal bellows-type second gas spring 6 whose volume is set smaller than that of the first gas spring 5, and as a result, the gas spring unit 4
The entire structure can be made more compact.

Furthermore, as shown in FIG. 7, the second gas spring 6
Since the dynamic spring constant a of the first gas spring 5 is set higher than the dynamic spring constant b of the first gas spring 5, the dynamic spring constant of the second gas spring 6 will rapidly increase with the displacement of the metal bellows 6d. As a result, the vibration damping effect of the metal bellows-type second gas spring 6 is reduced, thereby making it possible to suppress the roll speed when the vehicle body 1 rolls. This means that transmission of vibrations with large amplitudes to the vehicle body 1 is suppressed. In particular, a damping force is generated by the sliding resistance of the free piston 5d in the first gas spring 5, so that vibrations can be effectively damped.

In this embodiment, the gas spring unit 4 is composed of two gas springs, the first gas spring 5 and the second gas spring 6. It goes without saying that the number of first gas springs 5 to second gas springs 6 can be increased to a number suitable for each vehicle.

[0059]

As described above, in any of the first to third inventions, at least one of the gas springs is a metal bellows type gas spring with excellent responsiveness to high frequency vibrations, and this metal bellows type gas spring As a result, the transmission of high-frequency minute vibrations to the vehicle body is effectively suppressed, and the free piston type gas spring also suppresses the transmission of relatively large amplitude vibrations to the vehicle body. In this way, since the metal bellows type and the free piston type are used together as the gas spring, unlike when the gas spring is configured only with the metal bellows type, the size of the gas spring as a whole does not increase. Furthermore, high frequency vibrations can be effectively suppressed.

In particular, according to the second invention, vibrations with a relatively large amplitude can be effectively absorbed by the free piston type gas spring whose volume is set larger than that of the metal bellows, and vibrations with a small amplitude can be absorbed effectively. High-frequency micro-vibrations can be adequately dealt with by metal bellows-type gas springs, which have a smaller volume than free-piston-type gas springs, and this allows the entire gas spring to be configured more compactly. .

Furthermore, in the third invention, since the internal pressure of the gas chamber constituted by the metal bellows is set higher than the internal pressure of the gas chamber partitioned by the free piston, the metal The dynamic spring constant of the bellows increases rapidly, and the vibration damping effect of the metal bellows gas spring decreases.
The roll speed when the vehicle body rolls can be suppressed, and the free piston type gas spring suppresses the transmission of relatively large amplitude vibrations to the vehicle body. In particular, since a damping force is generated by the sliding resistance of the free piston, vibrations can be effectively damped.

[Brief explanation of drawings]

FIG. 1 is an overall schematic diagram of a vehicle including a vehicle suspension device according to the present invention.

[Fig. 2] Hydraulic circuit diagram of the suspension device.

FIG. 3 is a control block diagram of a fluid control amount calculation circuit provided in the control unit.

FIG. 4 is a control block diagram of a fluid control amount calculation circuit provided in the control unit.

FIG. 5 is a control block diagram of a fluid control amount calculation circuit provided in the control unit.

FIG. 6 is an enlarged sectional view showing the configuration of a first gas spring and a second gas spring that constitute the gas spring unit.

FIG. 7 is a characteristic diagram of a first gas spring, a second gas spring, and dynamic spring constants when these are combined.

[Explanation of symbols]

1
Vehicle body 2FL, 2FR
Wheel 3 (3
FL, 3FR, 3RL, 3RR) Fluid cylinder 3c

Hydraulic chamber 4
gas spring unit 5
First gas spring 5a

Gas spring body 5b
Hydraulic pressure chamber 5
c.
gas chamber 5d
free piston

Claims (3)

[Claims] 1. A suspension device for a vehicle that varies suspension characteristics by supplying and discharging fluid to and from fluid cylinders provided between each wheel and a vehicle body, wherein the fluid in the fluid cylinder is At least two gas springs are provided, each consisting of a hydraulic chamber communicating with the pressure chamber and a gas chamber partitioned from the hydraulic pressure chamber and filled with gas, and at least one of these gas springs,
It is a metal bellows type with a metal bellows with gas sealed inside to form a gas chamber, and the other gas spring is a free piston type with a slidable free piston that partitions the hydraulic pressure chamber and the gas chamber. A vehicle suspension device characterized by: 2. A suspension device for a vehicle that varies suspension characteristics by supplying and discharging fluid to and from fluid cylinders provided between each wheel and a vehicle body, wherein the suspension characteristics of the fluid cylinder are At least two gas springs are provided, each consisting of a hydraulic chamber communicating with the pressure chamber and a gas chamber partitioned from the hydraulic pressure chamber and filled with gas, and at least one of the gas springs has a gas chamber inside. It is a metal bellows type with a metal bellows enclosed therein to constitute a gas chamber, and the other gas spring is a free piston type with a slidable free piston that partitions the hydraulic pressure chamber and the gas chamber. A suspension device for a vehicle, wherein the volume of the metal bellows is set smaller than the volume of the free piston. 3. A suspension device for a vehicle in which suspension characteristics are varied by supplying and discharging fluid to and from fluid cylinders provided between each wheel and a vehicle body, wherein the suspension characteristics of the fluid cylinder are At least two gas springs are provided, each consisting of a hydraulic chamber communicating with the pressure chamber and a gas chamber partitioned from the hydraulic pressure chamber and filled with gas, and at least one of the gas springs has a gas chamber inside. It is a metal bellows type with a metal bellows enclosed therein to constitute a gas chamber, and the other gas spring is a free piston type with a slidable free piston that partitions the hydraulic pressure chamber and the gas chamber. A suspension device for a vehicle, wherein the internal pressure of the gas chamber in the metal bellows type gas spring is set higher than the internal pressure of the gas chamber in the free piston type gas spring.