JPS63106129A - Vehicle suspension device - Google Patents

Abstract

PURPOSE:To obtain an optimum characteristic in accordance with a drive condition of a vehicle with the use of a device for controlling the suspension characteristic by means of a hydraulic cylinder, by providing a means for detecting the drive condition of the vehicle, and by changing the roll rigidities of front and rear wheels in accordance with a signal from the detecting means. CONSTITUTION:A desired flow rate is determined in accordance with a variation in pressure in a cylinder 2FR or the like for each wheel, and hydraulic oil is fed and discharged in accordance with the desired flow rate. In this arrangement, signals from pressure sensors for wheels are synthesized to detect a vehicle body input mode such as a bound, pitch, roll or warp mode, and control is made in the direction in which the detected mode is restrained. Further, in a rolling condition, a desired warp moment is set to give a predetermined roll rigidity. In this phase, the roll rigidity ratio is changed in accordance with a braking force upon braking. Thereby, it is possible to obtain a characteristic suitable for the drive condition.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a suspension device for a vehicle.

(Prior art and its problems) Some vehicle suspension devices are European (EPC)
As seen in the specification identified in Application Publication No. 0 114 757, the suspension is constructed by installing a liquid cylinder between the vehicle body and each wheel, and supplying and discharging a working liquid to and from the liquid cylinder. A so-called active suspension whose characteristics are variably controlled is known.

Incidentally, one of the characteristics required of a vehicle suspension device is roll stiffness, and the determining factors of this roll stiffness include suspension geometry and spring characteristics.

For example, increasing the spring constant of the suspension and decreasing the roll angle is effective in improving the maneuverability and stability of the vehicle. However, on the other hand, there is a problem in that the riding comfort is impaired.

For this reason, while providing desirable spring constants for the front and rear wheels from the viewpoint of riding comfort, a stabilizer is attached to set the reciprocal magnitude of the suspension roll rigidity of each of the front and rear wheels. That is, the stabilizer functions as an auxiliary spring for the suspension device, increasing the spring constant of the suspension only during rolling.

By the way, the relative size of the front wheel suspension roll stiffness and the rear wheel suspension roll stiffness, that is, the roll stiffness ratio between the front wheels and the rear wheels, has a large effect on the running performance of the vehicle. To explain, when the suspension roll rigidity of the front wheels is increased, the tendency for understeer increases and the roll angle tends to decrease. On the other hand, when the suspension roll rigidity of the rear wheels is increased, angesteer tends to be weakened. For this reason, in conventional suspension devices, a constant roll stiffness ratio is currently set depending on the vehicle type.

However, when looking at the relationship between the roll stiffness ratio and the vehicle driving condition, for example, when driving in a straight line at high speed, the suspension roll stiffness on the front wheel side is relatively strengthened, increasing the tendency of understeer and improving straight line stability. Furthermore, during acceleration, it is preferable to relatively weaken the suspension roll rigidity on the drive wheel side to improve the ground contact of the drive wheels.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a suspension device for a vehicle that can meet the above requirements.

(Means and effects for solving the problems) The present invention focuses on the fact that when using the above-mentioned active suspension, suspension characteristics can be freely controlled. A roll stiffness ratio changing means for changing the roll stiffness ratio between the front wheels and the rear wheels is added.

In this way, by adding a function to the active suspension that changes the roll stiffness ratio according to the driving condition, it is possible to set the roll stiffness ratio that is suitable for the driving condition, which improves the vehicle's running performance. It is possible to pursue this at a more advanced level.

(Example) Embodiments of the present invention will be described below based on the drawings.

First Embodiment In FIG. 1, reference numeral 1 denotes a suspension device, and in the following description of the elements included in this suspension device 1, when the elements are collectively referred to, they will be identified by numbers, and when they are distinguished for each wheel, rFRJ (right for front wheels),
They shall be identified by adding the codes rFI, J (for left rear wheel), rRRJ (for right rear wheel), and rRLJ (for left rear wheel).

The suspension device l includes cylinders 2FR12FL and 2RR12 installed between the vehicle body and each wheel (not shown).
RL, each cylinder 2 is slidably inserted into the cylinder 2, and a cylinder liquid chamber 6 is defined by a piston 4 integrated with a piston rod 3, as is known. .Each cylinder liquid chamber 6 has gas springs 8FR18FL, 8
RR18RL and oil path 10FR1IOFL, l0RR11
0RL, and each oil passage IO has an orifice 1.
2FR112FL, 12RR, and 12RL are provided. Each of the gas springs 8 has the same configuration and has a gas chamber 16 and a liquid chamber 18 defined by a diaphragm 14 as a movable partition, and this liquid chamber 18 is connected to the oil passage lO.
is communicated with. A cylinder 2 like this, a gas spring 8
and a unit 20 consisting of a combination of the orifice 12
has a basic function as a suspension with the buffering action of the gas spring 8 and the damping action of the orifice 12. The characteristics of this suspension unit 20 are the elastic modulus (spring coefficient) of the gas spring 8 and the orifice 1.
It is uniformly determined by the aperture resistance of 2.

On the other hand, an external pipe 22 is connected to the cylinder 2,
Through the supply and discharge passage formed by this external piping 22,
Oil is supplied and discharged into the cylinder 2, that is, into the cylinder liquid chamber 6.

To explain the hydraulic circuit for this cylinder 2,
In FIG. 1, reference numeral 30 denotes a pump driven by the engine, and the hydraulic fluid pumped up from the reservoir tank 32 by the pump 30 is supplied to each circumferential cylinder 2 through a supply passage 33. There is. That is, the upstream side of the supply passage 33 is a common passage 34, and this common passage 34 is branched into a front wheel passage 35 and a rear wheel passage 36,
The front wheel passage 35 is branched into a right front wheel passage 38FR and a left front wheel passage 38FL, and the rear wheel passage 36 is branched into a right rear wheel passage 40RR and a left rear wheel passage 40RL. Width passage 38FR138FL, 40RR1
40RL is a supply/discharge passage 22F leading to each circumferential cylinder 2
It is connected to R122FL and 22RR122RL, respectively. The common passage 34 is provided with a switching valve 42, a check valve 44, and an accumulator 46 in this order from the upstream side, and the accumulator 46 has the same configuration as the gas spring 8 and functions as a pressure accumulator. has been done. On the other hand, a flow rate control valve 48 is interposed between each width passage 38, 40 and the supply/discharge passage 22, and the amount of hydraulic fluid passing per unit time, that is, the flow rate of the hydraulic fluid. It is supposed to be adjusted.

On the other hand, the reflux passage 50 is connected to the reservoir tank 3 via the reflux passage 52 for each wheel and the common reflux passage 54 from each flow rate control valve 48.
2, and a switching valve reflux passage 56 from the switching valve 42 is connected to this common reflux passage 54.

Next, the operation of the above hydraulic circuit will be explained. First, when the flow control valve 48 is closed, the suspension unit 20 exhibits characteristics based on the throttle resistance of the orifice 12 and the elastic modulus of the gas spring 8. That is, the amount of change in the load applied to the cylinder 2 is ΔF, the amount of displacement of the piston 4 is ΔX, and it is defined by the throttle resistance of the fist 12 and the elastic modulus of the gas spring 8. Therefore, the suspension unit 20 is closed as a system. This forms a so-called passive system.

On the other hand, when the flow rate control valve 48 is opened, for example, when hydraulic fluid is supplied into the cylinder 2 while the piston rod 3 is being displaced in the direction of shortening, the supplied hydraulic fluid causes the piston to As a result of suppressing the shortening movement of the rod 3, the dynamic spring constant K changes in the direction of increasing. In other words, by supplying and discharging the hydraulic fluid in the cylinder 2, the throttle resistance of the orifice 12 and the gas spring 8 are reduced.
The same effect as when the elastic modulus of is made variable is obtained. Therefore, the suspension unit 20 opened as a system is
A so-called active system is formed.

The flow rate control valve 48 is actuated by a control signal from a control unit 60 composed of a microcomputer. In order to generate this control signal, the control unit 60 includes a brake sensor 61 that detects brake pressure.
A braking signal from a brake signal and a signal from a pressure sensor 62 that picks up the pressure inside each cylinder 2 are input, and the pressure signal from this pressure sensor 62 is sent to a bypass filter 64 (differential After being filtered by a type of filter), the signal is input to the control circuit 66. The control unit 60 also includes a pressure sensor 6 provided in the common passage 34.
When the pressure signal from 8 is input and the pressure in the hydraulic circuit becomes equal to or higher than a predetermined pressure, the switching valve 42 is switched to transfer the hydraulic fluid pumped up by the pump 30 to the recirculation passage 56 .
54 and return to the reservoir tank 32. On the other hand, when the pressure in the hydraulic circuit becomes lower than a predetermined pressure, the switching valve 42 is switched to allow the hydraulic fluid pumped up by the pump 30 to flow into the supply passage 33, thereby reducing the pressure in the hydraulic circuit to a predetermined level. It is designed to maintain pressure.

Next, an overview of active control will be explained. First, the basic control model involves determining a target flow rate according to changes in the oil pressure in the cylinder 2 for each wheel, and supplying and discharging hydraulic fluid to and from each cylinder 2 based on this target flow rate. It has become. In addition to this basic model, the four vehicle body input modes of bounce, pitch, roll, and warp are detected by combining the signals from the pressure sensors 62 for each width.
Control is performed to suppress these vehicle body input modes. In addition, adding a warp moment to the car body while the car body is rolling will also add roll rigidity, so
Among the above vehicle body input modes, the target warp moment is determined based on the detected roll moment value, and a warp moment is applied according to the roll angle. The roll stiffness ratio is changed in accordance with the braking force by determining a target weaving moment in accordance with the braking force based on the braking signal.

If such a control system is represented by a block diagram, the circuit shown in FIG.
) KW, where GB(S) is bound, G
P(S) is pitch.

GR(S) is for roll, and KW is for warp. Further, R- is a transfer characteristic of the weaving moment target value calculation circuit.

The above-mentioned transfer function GB(S) etc. are obtained as follows. In the following explanation, in order to make it easier to understand, the explanation will be based on basic control of only one wheel, which is the basic unit of this control. Therefore, in the following explanation, the above transfer functions GB(S), GP(S), etc. will be collectively referred to as G(S), and the transfer function G(S) will be derived based on the basic model omitting the above mode analysis. That's it.

First, the transfer characteristics of each element in the control system are expressed by the following relational expression.

ΔP=ΔF/A...(1) Here, the amount of change in load A for ΔF cylinder 2: the amount of change in the fluid pressure in piston 4's pressure receiving area ΔP cylinder 2 ΔPN = ΔP −Δ PC fist ・ ・
(2) Here, ΔPC: Amount of pressure change ΔPN of the liquid spring 8
Amount of change in throttle pressure difference at the niorifice 12 QN = ΔPN /KN ... (3) Here, KN
Restriction resistance QN of the niorifice 12 Flow rate of the oil passing through the niorifice 12 ΔVC=QN/S (4) Here, ΔVC: Volume change amount of the fluid spring 8 ΔPC=KC
:・Δvc @--(5) Here, KCC wave fluid 8
Elastic modulus Δe=Ke・ΔF (6) Here, Ke: Sensor characteristic of pressure sensor 62 Δe: Output of pressure sensor 62 Δ 1=G(S) ・ Δ e Fist ・ ・
(7) Here, the control current ΔVL corresponding to the target flow rate of the flow rate control valve 48 output from the Δi secondary control circuit 66 = Q↑/S・Fist・(9) Here, ΔvL The oil liquid in the Niji cylinder 2 The amount of change ΔV=Δ
VC-ΔVL * * * (10) Here, ΔV Volume change amount of cylinder 2 (cylinder liquid chamber 6) ΔX = ΔV/A @ (11) Here, ΔX: Displacement amount of piston 4 Next, the above When the target characteristic in the control system, that is, the frequency characteristic of the dynamic spring constant, is set as shown in FIG. 3, the target characteristic is expressed by the following equation.

... (12) Here, S Nira plus operator T: time constant If the above equation (12) is replaced, By the way, the body posture change amount ΔVC of the fluid spring 8 is expressed as the above (1
) ~ (5), ΔVc = QN / S = ΔPN / (KN ・
S) = (ΔP-ΔPG)/(KN-3) = (ΔP-KCΔVC)/(KN@S)=
(ΔF/A-KC-ΔVc)/(KN 115
).

Also, the amount of change ΔVL of the oil in the cylinder 2 is.

From the above formulas (6) to (9), It is expressed as

Further, the amount of change ΔX of the piston 4 is the above (10) to (1
From formula 5), Δx = ΔV/A = (ΔVC-ΔVL) / A Therefore, if this formula (18) is replaced by R, ΔF
A (KG +KN s) (1+TV S) S
・ψ・(17) This equation (17) and the above (13) which shows the control target
In comparison with the formula (17), KI=A”
・KC−・・(I8) K2=A −KN ・ ・ ・ (19)T
=N-TV --@ (20)
Substituting these formulas (1 day) to (20) into formula (139), ΔF NA (KG +KV @5) (1+TV
-3)...(21)

Therefore, from the above equations (17) and (21), (1+TV @S,) -AKV Ke (KG +KN @S)G
(S)/S, resulting in the characteristics shown in FIG. That is, by providing the above equation (22) or the transfer function G (S) shown in FIG. 4, the dynamic spring characteristic shown in FIG. 3 is equivalent to a bypass filter. In other words, the suspension device 1 for each wheel has a dynamic spring constant K that is variable according to the frequency, and the suspension device f responds to the frequency by simply picking up the load acting on the suspension device 1. Further, as shown in FIG. 3, the suspension device 1 is an active suspension device in the low frequency range, so it is possible to realize a large dynamic spring constant K (hard) in the low frequency range. , changes in vehicle body posture, such as roll and pitch, which are problematic in this area, can be suppressed to a small level. For comparison, in FIG. 3, the characteristics of only passive control are shown by broken lines. In other words, in the high frequency range, the flow control valve 48 is closed and a passive system is formed, so the dynamic spring constant of the base passive system is kept low (for example, the spring constant of the gas spring 8 is made small). It is said that it is possible to improve ride comfort in the high frequency range under a soft suspension. Furthermore, since the flow control valve 48 is not required to have responsiveness in a high frequency range,
It has the advantage of being simple. Further, when there is a failure in the hydraulic circuit, by closing the flow control valve 48, the basic functions of the suspension are maintained in an active system, so safety against failure is not compromised.

For the basic model described above, detection of the vehicle body input mode is performed as follows.

(Left below) (1) Bound Bound is a movement mode in the vertical direction of the vehicle body, so the movement directions of all four wheels are the same. From this, detection of bounds is based on the following formula.

ΔeB = ΔeFR + ΔeFL + ΔeRR + ΔeRL Temple (23) where, Δe: Bound detection value Δe corresponding to the amount of pressure change in bound mode FR: Output Δe of the right front wheel pressure sensor 62FR FL: Output ΔeRR of the left front wheel pressure sensor 62FL: Output Δe RL of pressure width sensor 62RR for right rear wheel: Output of pressure sensor 62RL for left rear wheel (2) Pitch Pitch is a motion mode in which the direction of motion of the front part of the vehicle body and the direction of motion of the rear part of the vehicle body are in opposite phases. (movement of forward balling or front balling), and from this, pitch detection is based on the following equation.

ΔeP = (ΔeFR+ΔeFL) −(Δe RR
+ Δe RL) * * e (22) Here, Δe
P: Pitch detection value corresponding to the amount of pressure change in pitch mode (3) Roll Roll is a motion mode in which the direction of motion of the right side of the vehicle body and the direction of motion of the left side of the vehicle body are in opposite phases (centered on an axis extending in the longitudinal direction of the vehicle body). Therefore, the detection of the roll is based on the following equation.

ΔeR= (ΔeFR−ΔeFL)+(Δe RR−
Δe RL) a e e (25) Here, Δ
eR: Roll detection value corresponding to pressure change it in roll mode (4) The torsional moment acting on the warped vehicle body causes the front right wheel (FR) and rear left wheel (RL) to have components in the same direction, and other combinations ( FL, RR) is in the opposite direction. From this, warp detection is based on the following equation.

Δe W = (Δe FR−Δe FL) −(Δe
RR-Δe RL) * * * (2B) Here, ΔeW: Warp detection value corresponding to the amount of pressure change in warp mode The target flow rate Δi day, ΔiP, etc. in each mode obtained in this way is -F Each flow control valve 48FR, FL, RR, RL is distributed in the same manner as in the mode analysis described above.
Target flow rate Δi FR1Δi FL, Δ1RR1ΔiR
Converted to L.

That is, the bound target flow rate ΔiB is
The pitch target flow rate ΔiP is distributed under the opposite sign between the front wheels and the rear wheels, and the roll target flow rate Δi
R is distributed between the right wheel and the left wheel under opposite signs, and the warp target flow rate Δi- is distributed under opposite signs for each combination of wheels located diagonally on the vehicle body. If this is shown from the side of the target flow rates Δ1ER1ΔiFL and Δ1RR1ΔiRL of each wheel, it is expressed by the following equation.

Δi FR=ΔiB+ΔiP+ΔiR+ΔiW...(
27) Δ1FL=(ΔiB+Δ1P) −(ΔiR+ΔiW) ...(28) Δ1RR=(ΔiB−ΔiP) +(ΔiR−ΔiW) φ...(29) Δ1B=(ΔiB−Δ1P) −(ΔiR−ΔiW) ・(30) That is, with this, control in the direction of suppressing the moment of each mode is added to the basic model according to the vehicle body input mode. Further, when the vehicle body is rolling, a target warb moment is set, and as a result, a predetermined roll stiffness ratio is provided. At that time, when braking is applied, this braking force is reflected in the target warp moment, and as shown in Figure 5, the suspension roll rigidity on the rear wheel side is relatively strengthened according to the braking force. As a result, the ground contact load on the rear wheel side increases, and the tendency for understeer becomes stronger. This prevents the occurrence of spin due to braking during cornering, making it possible to safely stop the vehicle.

Although the present invention has been described in detail above, the present invention is not limited thereto and includes the following modifications.

(1) Even if the steering angle and vehicle speed are detected, and the higher the speed when driving straight, the stiffness of the suspension roll on the front wheel side is relatively strengthened to strengthen the tendency of understeer, thereby increasing straight-line stability. Also, when making a large turn at low speed, the suspension roll stiffness on the rear wheel side may be relatively increased to increase the tendency for oversteer.

(2) The acceleration state of the heavy vehicle may be detected, and when the heavy vehicle is in the acceleration state, the suspension roll rigidity on the drive wheel side may be weakened to improve the ground contact of the drive wheels.

(Effects of the Invention) As explained above, according to the present invention, it is possible to further develop the feature of active suspension, which is the ability to freely control dynamic spring characteristics, into roll stiffness ratio control, and to control the vehicle driving condition. Since the roll stiffness ratio can be arbitrarily set according to the vehicle operating condition, it is possible to provide a roll stiffness ratio suitable for the driving condition of the vehicle.

[Brief explanation of the drawing]

Fig. 1 is an overall system diagram in the embodiment, Fig. 2 is a block diagram in the embodiment, Fig. 3 is a target dynamic spring characteristic diagram in the embodiment, Fig. 4 is a characteristic diagram of the transfer function in the embodiment, and Fig. 5 is a diagram of the characteristic of the transfer function in the embodiment. The figure is a diagram showing changes in suspension roll stiffness on the rear wheel side with respect to brake pressure. 1: Suspension device 2 Niji cylinder 8: Gas spring 30: Pump 46: Accumulator 48: Flow rate adjustment valve 60: Control unit 62: Load sensor 64: Bypass filter (differential filter) 66: Control circuit 68: Pressure sensor Fig. 5 Brake IE f (@wave number) f (shoulder beam k)

Claims (1)

[Claims] (1) A suspension system for a vehicle that variably controls the characteristics of the suspension of each wheel by supplying and discharging working fluid to and from a fluid cylinder installed between the vehicle body and each wheel. a driving state detecting means for detecting the driving state of the vehicle; and a roll stiffness ratio changing means for receiving a signal from the driving state detecting means and changing a roll stiffness ratio between the front wheels and the rear wheels according to the driving state of the vehicle. A vehicle suspension device characterized by: