JPS63106132A - Vehicle suspension device - Google Patents

Abstract

PURPOSE:To prevent hydraulic oil from being abnormally discharged, by providing a flow control valve for feeding and discharging hydraulic oil to and from a cylinder between a vehicle body and a wheel, and by providing a shut-off valve disposed in a passage between the cylinder and the flow control valve. CONSTITUTION:A flow control valve 48 adapted to be controlled by a control unit 60 is connected to a cylinder 2 laid between a vehicle body A and a wheel B, and a shut-off valve 49 is disposed in a supply and discharge passage 22 between the flow control valve 48 and the cylinder 2. This shut-off valve 49 is opened when an ignition switch 67 is turned on. Accordingly, when a hydraulic circuit upstream of the shut-off valve 49 is damaged or when the control unit 60 for the flow control valve 45 fails, the shut-off valve 49 is closed, thereby it is possible to prevent hydraulic oil in the cylinder 2 from being abnormally discharged.

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 suspension systems for vehicles include European (EPC)
As seen in the specification identified in Application Publication No. 0 114 757, suspension characteristics are controlled by supplying and discharging a working fluid to and from a fluid cylinder installed between the vehicle body and the wheels. A so-called active suspension is known.

That is, to explain this type of device in principle, for example, when the cylinder is operating in the contraction direction and a working liquid is supplied to the cylinder, the supplied working liquid causes the cylinder to move. As a result of suppressing shortening movement,
This results in the same effect as when the suspension device is set to a hard setting. In other words, according to this system, by supplying and discharging the working fluid to and from the fluid cylinders installed between the vehicle body and the wheels, it is possible to control the suspension characteristics in a flexible manner.

However, in such an active suspension, the supply and discharge of the working fluid to and from the liquid cylinder is controlled via a flow control valve such as a spool valve. There is a problem that the blocking performance is poor. For this reason, when the vehicle is parked for a long time, the working fluid in the fluid cylinder gradually leaks out, resulting in the inconvenience of lowering the vehicle height.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a suspension device for a vehicle that prevents leakage of working fluid in a liquid cylinder caused by poor passage blocking performance, which is a characteristic of a flow control valve. It is in.

(Means and effects for solving the problem) The present invention controls suspension characteristics by supplying and discharging working fluid to and from a fluid cylinder installed between the vehicle body and the wheels via a flow control valve. In a suspension system for a vehicle, that is, a so-called active suspension, an on-off valve for opening and closing the supply/discharge passage is provided in the supply/discharge passage connecting the liquid cylinder and the flow rate control valve.

With this configuration, when the vehicle is parked, it is possible to close the on-off valve to prevent leakage of the working fluid from the fluid cylinder. Moreover, the above-mentioned on-off valve can provide fail-safety in the event of a system failure.

In other words, when the hydraulic circuit on the upstream side of the on-off valve is destroyed or the control unit 7 of the flow control valve malfunctions,
Immediately closing the on-off valve prevents abnormal discharge of the working fluid in the liquid cylinder.

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

In FIGS. 1 and 2, l is a suspension device,
In the following description of the elements included in this suspension device l, when the elements are collectively referred to, they will be identified by numbers,
When distinguishing between each wheel, the codes "FR" (for the right front wheel), rFLJ (for the left rear wheel), rRR" (for the right rear wheel), and rRLJ (for the left rear wheel) are added for identification. shall be.

The suspension device 1 includes cylinders 2FR, 2FL, and 2RR12RL installed between a vehicle body A and each wheel B, and each cylinder 2 is slidably inserted into the cylinder 2, as is known. A cylinder liquid chamber 6 is defined by a piston 4 integrated with a piston rod 3. Each cylinder liquid chamber 6 has gas springs 8FR18FL, 8RR18
It communicates with RL via oil passages 10FR1IOFL and 10RR1IORL, and each oil passage 10 has an orifice 12FR,
12FL, 12RR, and 12RL are provided. Each of the gas springs 8 has the same configuration and has a gas chamber 16 defined by a diaphragm 14 as a movable partition wall and a liquid chamber 18, and the liquid chamber 18 is communicated with the oil passage 10. There is. The unit 20 consisting of such a combination of the cylinder 2, the gas spring 8, and the orifice 12 has a basic function as a suspension due to the buffering action of the gas spring 8 and the damping action of the orifice 12.

The characteristics of this suspension unit 20 are uniformly determined by the elastic modulus (spring coefficient) of the gas spring 8 and the throttle resistance of the orifice 12.

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,
Reference numeral 30 in the figure is a pump driven by the engine, and the hydraulic fluid pumped up from the reservoir tank 32 by this pump 30 is supplied to each circumferential cylinder 2 through a supply passage 33. 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 a right rear wheel passage. Branched into 40RR and left rear wheel passage 40RL,
Each of these circumferential passages 38FR138FL, 40RR140
RL is a supply/discharge passage 22FR1 leading to each circumferential cylinder 2;
22FL, 22RR, and 22RL, 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, between each width passage 38, 40 and the above-mentioned supply/discharge passage 22, a flow control valve 48 consisting of a spool valve is interposed, so that the amount of hydraulic fluid passing per unit spool, i.e. It is said to be used to adjust the flow rate of hydraulic fluid. An on-off valve 49 is interposed in each of the supply/discharge passages 22, and this on-off valve 49 is normally used as an rA on-off valve, and is opened when the ignition switch 67 is turned on, as will be described later. It has become.

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 this common recirculation passage 54 is connected to a switching valve volume flow passage 56 from the switching valve 42 .

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 defined by ΔF, the amount of displacement of the piston 4 is defined by ΔX, the throttling resistance of the rewiring device 12, and the elastic modulus of the gas spring 8. Therefore, the suspension unit 20, which is closed as a system, is defined as follows. This forms a so-called passive control 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 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 that obtained by making the elastic modulus of
A so-called active control 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 is connected to a pressure sensor 62 that picks up the pressure inside each cylinder 2. The pressure signal from the pressure sensor 62 is filtered by a bypass filter 64 (a type of differential filter) in the control unit 60, and then input to the control circuit 66. . In addition, the control unit 60
When the supply pressure signal from the pressure sensor 68 provided in the common passage 34 is input to the pump 3, and the supply pressure of the hydraulic fluid exceeds a predetermined pressure, the switching valve 42 is switched to switch the pump 3
The hydraulic fluid pumped up by the
The water is refluxed to the reservoir tank 32 through the . On the other hand, when the supply pressure of the first hydraulic pressure 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 increasing the supply pressure of the hydraulic fluid. is maintained at a predetermined pressure. In this embodiment, if the hydraulic fluid supply pressure drops below the predetermined pressure for some reason,
A flow rate control correction means is provided to change the control characteristics of the flow rate control valve 48 in accordance with this supply pressure.

A control circuit 56 that generates a control signal for the flow rate control valve 48
The control system is represented by the block diagram shown in FIG. 2, where the transfer function H(S) is
S) is obtained as follows.

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

ΔP=ΔF/A...(1) Here, ΔF Load change amount A for Niji cylinder 2: Pressure receiving area of piston 4 ΔP Fluid pressure change amount in Niji cylinder 2 ΔPN = ΔP-ΔPC...(2) Here , △PC: Amount of pressure change in liquid spring 8 △Amount of change in throttle pressure difference at PN niorifice 12 QN = ΔPN /KN ... - (3) Here, KN
Squeezing resistance QN of the niorifice 12 Flow rate of oil passing through the niorifice 12 ΔVC=QN/S @Φ−(4) Here, ΔvC: Volume change amount of the fluid spring 8 ΔPC=KC
・ΔVC@Mockery・(5) Here, KC: Elastic modulus of fluid spring 8 Δe=Ke・ΔF ...(8) Here, Ke: Sensor characteristic of pressure sensor 62 Δe: Output of pressure sensor 62 Δ1= H(S)-Δ6 1111@(7) Here, Δi
: Control current ΔvL of the flow rate control valve 48 output from the control circuit 66 = QT/S...φ (8) Here, ΔvL Amount of change in oil in the cylinder 2 ΔV=
ΔVc −ΔVL e * m (10) Here, Δ
Volume change amount Δx of the V-niji cylinder 2 (cylinder liquid chamber 6); Δv/A 11... (11) Here, ΔX: Displacement amount of the piston 4 In the method, the target characteristic in the control system, and the dynamic spring constant When the frequency characteristic of is set as shown in FIG. 4, the target characteristic is expressed by the following equation.

...(12) Here, if we replace the above equation (12) with the S nira plus operator T sub-time constant, then the volume change amount ΔVc of the fluid spring 8 is expressed as the above (1
) to (5), ΔVc = QN /S = ΔPN / (KN ・S) =
(ΔP-ΔPG)/(KN @S)= (ΔP-K
CΔVC)/(KN-5)= (ΔF/A -KC・Δ
VC)/(KN-5).

In addition, the amount of change ΔVL of the oil in the cylinder 2 is the above (6
) to (8), it is expressed as follows.

Further, the amount of change ΔX of the piston 4 is the above (10) to (1
5) From the formula, ΔX=Δv/A=(ΔvC−ΔvL)/A...(16
) Therefore, by replacing equation (16), ΔF
A2 (KC1KN S) (1+TV S)
S...φ(17). Equation (17) and the above (13) showing the control target
In comparison with formula (17), Kl = A2・K
C... (18) K2=A2・KN... (19) T=N-
TV, --(20), these (18
)~(20) into equation (13), ΔF NA2 (KO+KV @5) (1+TV @
S)...(21) becomes.

Therefore, from the above equations (17) and (21), (1
+TV・5) -AKV Ke (KG +KN @S)H(S)/5
(l-2)·S, resulting in the characteristics shown in FIG. That is, the above (2
By using the control circuit 66 having the transfer function H(S) shown in equation 2) or in FIG. 5, such a transfer function H(S) is equivalent to a bypass filter.

From this, the dynamic spring constant K of the suspension device M1 is made variable according to the frequency, and the suspension device I can be made to respond to the frequency simply by picking up the load acting on the suspension device I. Furthermore, in this embodiment, as shown in FIG. 3, since it is an active suspension device in the low frequency range, it is possible to realize a large dynamic spring constant K in the low frequency range. Changes in vehicle body posture, such as roll and pitch, which are problematic in this area, can be reduced.

For comparison, in FIG. 4, 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 possible to improve ride comfort in the high frequency range under a soft suspension. Further, since the flow control valve 48 is not required to have responsiveness in a high frequency range, it has the advantage that it can be simple.

On the other hand, when the ignition switch 2 Ciro 7 is turned OFF, the on-off valve 49 interposed between the flow control valve 48 and the cylinder 2 is closed, and the supply/discharge passage 22 communicating with each cylinder 2 is closed. Be cut off. Therefore, while parking,
The hydraulic fluid in the cylinder 2 does not leak, and the vehicle height is prevented from lowering due to this.

6 and 7 show other embodiments of the present invention, and the same elements as those in the first embodiment are given the same reference numerals and their explanations are omitted, and the characteristic parts thereof will be described below. I will only add an explanation for this.

FIG. 6 shows a second embodiment of the present invention. In this embodiment, the supply pressure of hydraulic fluid is introduced into the normally closed on-off valve 49, and the valve opens and closes when this supply pressure exceeds a predetermined pressure. It looks like this. That is, the supply pressure of hydraulic fluid is introduced into the on-off valve 49 via the pilot passage 70, and the predetermined pressure is the maximum value of the oil pressure in the cylinder. Therefore, if the supply pressure of the hydraulic fluid drops below the predetermined pressure for some reason, such as malfunction of the pump 30, the on-off valve 49 is closed and the hydraulic fluid in the cylinder 2 is reduced. Backflow is prevented. Of course,
The suspension device 1 after the on-off valve 49 is closed,
It will function as a passive suspension.

FIG. 7 shows a third embodiment of the present invention, in which the normally closed on-off valve 49 is opened in response to a signal from a control unit 60. Also,
The hydraulic circuit includes a supply bypass passage 72 that bypasses the flow control valve 48 and connects the supply/discharge passage 22 and the supply passage 38 (40), and a supply bypass passage 72 that connects the supply/discharge passage 22 and the recirculation passage 54. The supply bypass passage 72 and the return bypass passage 74 are provided with check valves 76 and 78, respectively.

A check valve 76 provided in the supply bypass passage 72
The supply bypass passage 74 is opened when the pressure on the supply/discharge passage 22 side becomes negative, and the check valve 78 provided in the return bypass passage 74 has an upper limit of the oil pressure on the supply/discharge passage 22 side. When the value is exceeded, this rapid flow bypass passage 74
It is said that it will open.

The opening signal for the on-off valve 49 generated by the control unit 60 is first generated by selective operation of the active-passive switching manual switch, and when active is selected, the signal from the control unit 60 is generated. Second, when an abnormality occurs in the control unit 60, the signal from the control unit 6o is stopped and the on-off valve 49 is closed. ing.

Therefore, in this embodiment, the suspension system 521 functions as an active suspension or a passive suspension depending on the driver's selection. When an abnormality occurs in the control unit 60, the on-off valve 49 is immediately closed and the suspension is switched to passive suspension, thereby providing fail-safety. In addition, the supply bypass passage 742,
Since check valves 76 and 78 are provided in each of the return bypass passages 74, it is possible to prevent an abnormal rise in the oil pressure in the cylinder 2 or the generation of negative pressure in the cylinder 2, thereby preventing damage to the cylinder 2. This can be prevented.

Although the present invention has been described in detail above, the present invention is not limited thereto, and for example, the present invention can be applied to a device without the gas spring 8.

(Effects of the Invention) As is clear from the above description, according to the present invention, by providing an on-off valve between a liquid cylinder and a hydraulic circuit for an active suspension, it is possible to avoid poor passage blocking performance. The characteristics of the flow control valve are compensated by this on-off valve, and it is possible not only to eliminate the inconvenience caused by the characteristics of the flow control valve, but also to provide fail-safe against the occurrence of an abnormality in the active suspension.

[Brief explanation of the drawing]

Figures 1 to 5 show a 5Sl embodiment of the present invention. Figure 1 is an overall system diagram, Figure 2 is a partial system diagram, Figure 3 is a block diagram, and Figure 4 is a target motion spring. FIG. 5 is a characteristic diagram of the transfer function, and FIG. 6 shows a second embodiment of the present invention, and is a partial system diagram corresponding to FIG. 2. FIG. 7 shows a third embodiment of the present invention, and is a partial system diagram corresponding to FIG. 2. 1: Suspension device 2 Niji cylinder 8: Gas spring 30: Pump 46: Accumulator 48: Flow rate adjustment valve 60: Control unit 62: Pressure sensor 64: Bypass filter (differential filter) 66: Control circuit 68: Pressure sensor

Claims (1)

[Claims] (1) A suspension system for a vehicle that controls suspension characteristics by supplying and discharging working fluid to and from a fluid cylinder installed between a vehicle body and a wheel via a flow control valve, wherein the fluid cylinder A suspension device for a vehicle, characterized in that an on-off valve is provided in a supply/discharge passage connecting the flow control valve and the flow control valve.