JPH03284408A - Suspension device for vehicle - Google Patents

Abstract

PURPOSE:To prevent deterioration in running stability when an exhaust valve is fixed in such a state that it is opened, by exhausting the fluid in each cylinder so as to lower the entire car height when the exhaust valve belongs to a front wheel side, and by having the control for lowering the entire car height regulated, when the exhaust valve belongs to a rear wheel side. CONSTITUTION:In each fluid cylinder 3 arranged between a car body 1 and a front wheel 2F, or a rear wheel 2R, the fluid from a hydraulic pump 8 is supplied to and exhausted from a liquid pressure chamber 3c partitioned by a piston 3b, under the control of a flow control valve 9. A suspension characteristic can be changed by controlling the supply and exhaustion by a controller 19, independently according to the activity of a vehicle. When a failure is detected by a failure detection means 81, the control for lowering the entire can height by exhausting the fluid in each cylinder, is carried out, and the control for lowering the entire car height is thus permitted only when an exhaust valve in the flow control valve 9 correspondent to the cylinder 3 in a front wheel side is fixed in such a state that it is opened.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a suspension system for a vehicle in which suspension characteristics can be changed by controlling the supply and discharge of fluid to and from cylinders, and in particular, the present invention relates to a suspension system for a vehicle in which suspension characteristics can be changed by controlling the supply and discharge of fluid to and from cylinders. This is related to safety measures.

(Prior Art) Conventionally, as a suspension device for a vehicle, a plurality of cylinders are provided between a sprung mass and an unsprung mass for each wheel, as disclosed in, for example, Japanese Unexamined Patent Publication No. 63-130418. A so-called active control suspension system (ACS system) is equipped with a plurality of gas springs connected to each cylinder, and is capable of changing suspension characteristics by independently controlling the supply and discharge of fluid to each cylinder. ) is known.

In such an AC5 device, if equipment such as switching valves or detection sensors in the control system that controls the supply and discharge of fluid to and from the cylinders malfunctions, the fluid in each cylinder is discharged and the vehicle height of each wheel is reduced. Generally, all vehicle heights are lowered to the lowest position so that they are all equal, and control is then stopped in that state.

(Issues to be solved by the invention l!i) However, there is a problem in uniformly lowering the entire vehicle height in the event of equipment failure. In other words, if the discharge valve that discharges the fluid in the cylinder is stuck open and the discharge valve is on the front wheel side, the steering wheel will be difficult to operate due to the sideways tilt of the vehicle body, so it is necessary to immediately lower the entire vehicle height. However, if the exhaust valve is located on the rear wheel side, not only is there no need to immediately lower the entire vehicle height, but there is also a risk that running stability may be impaired due to the sudden lowering of the vehicle height.

In particular, it is a problem that the vehicle height is lowered while the vehicle is turning or braking, when the vehicle is likely to fall into an unstable state.

The present invention has been made in view of these points, and its purpose is to provide a suspension system for a vehicle that can take appropriate fail-safe measures depending on the location where a malfunctioning exhaust valve is used. It is something.

(Means for solving the problem) In order to achieve the above object, the invention described in claim (1):
In a vehicle suspension system, fluid supply and discharge is possible in a vehicle suspension system that allows suspension characteristics to be changed by independently controlling fluid supply and discharge to multiple cylinders provided between the sprung and unsprung portions of each wheel. A failure detection means for detecting a failure in each device of the control system; a control means for draining fluid in each cylinder to lower the overall vehicle height when a failure is detected by the detection means; A configuration comprising a control correction means that allows the control to lower the exhaust valve when the exhaust valve corresponding to the cylinder on the front wheel side is stuck open and restricts it when the exhaust valve corresponding to the cylinder on the rear wheel side is stuck open and stuck. That is.

Here, in the control correction means, when the exhaust valve corresponding to the cylinder on the rear wheel side is stuck open, the period for regulating the control to lower the overall vehicle height by the control means is the invention according to claim (2). In the case of , the vehicle is at least turning, and in the case of the invention described in claim (3), the vehicle is at least braking.

(Function) With the above configuration, in the present invention, when the discharge valve is stuck open and the discharge valve is on the front wheel side, the fluid in each cylinder is discharged under the control of the control means, The overall vehicle height is lowered, which prevents the steering wheel from becoming heavier due to the lateral tilt of the vehicle body. On the other hand, when the malfunctioning exhaust valve is the one on the rear wheel side, the control correcting means restricts the control to lower the overall vehicle height by the control means, which reduces driving stability due to sudden changes in vehicle height. This means that this can be prevented.

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

In FIG. 1, 1 is a vehicle body, 2F is a front wheel, and 2R is a rear wheel, and a fluid cylinder 3 is disposed between the vehicle body 1 on sprung and the front wheel 2F or rear wheel 2R on unsprung. There is. In the fluid cylinder 3, a hydraulic chamber 3c is defined by a piston 3b fitted into a cylinder body 3a. The upper end of the rod 3d connected to the piston 3b is connected to the vehicle body 1, and the cylinder body 3a is connected to the wheels 2F and 2, respectively.
Connected to R.

A gas spring 5 is connected to the hydraulic pressure chamber 3c of each of the fluid cylinders 3 through a communication path 4. Each gas spring 5 is divided into a gas chamber 5r and a hydraulic chamber 5g by a diaphragm 5e, and the hydraulic chamber 5g communicates with the hydraulic chamber 3c of the fluid cylinder 3.

Reference numeral 8 denotes a hydraulic pump, and 9.9 denotes a flow rate control valve interposed in a hydraulic passage 10 serving as a high-pressure line that communicates the hydraulic pump 8 and each fluid cylinder 3.
has a function of supplying and discharging fluid (oil) to each fluid cylinder 3 and adjusting the internal pressure (pressure of the hydraulic pressure chamber 3C).

Further, 12 is a main pressure sensor that detects the oil discharge pressure of the hydraulic pump 8 (more specifically, the pressure of oil stored in accumulators 22g and 22b, which will be described later), and 13 is a main pressure sensor that detects the hydraulic pressure in the hydraulic chamber 3c of each fluid cylinder 3. 14 is the vehicle height (cylinder stroke amount) of the corresponding wheels 2F and 2H.
15 is a vertical acceleration sensor that detects the vertical acceleration of the vehicle (spring speed of wheels 2F and 2H); 16 is a lateral acceleration sensor that detects the lateral acceleration of the vehicle;
17 is a steering angle sensor that detects the steering angle of the front wheel 2F, which is a steered wheel, and 18 is a vehicle speed sensor that detects the vehicle speed. The detection signals of these sensors are each input to a controller 19 having a CPU, etc. inside, and the suspension is adjusted. Used for variable control of characteristics.

Next, a hydraulic circuit for controlling supply and discharge of fluid to and from the fluid cylinder 3 is shown in FIG. In the figure, a hydraulic pump 8 is a variable displacement swash plate piston pump, and a hydraulic pump 21 for a power steering device is driven by a drive source 20.
are connected in two series. The hydraulic passage 10 connected to the hydraulic pump 8 includes three accumulators 22a, 22.
a and 22a are connected to each other at the same location, and
At the connection point, the hydraulic pressure passage 10 is branched into a front wheel side passage 10F and a rear wheel side passage 10R. Furthermore, the front wheel side passage 10F is a left front wheel side passage 10PL and a right front wheel side passage 10FR.
The passages 10FL and 10PR are communicated with the hydraulic pressure chambers 3C of the fluid cylinders 3FL and 3FR of the corresponding wheels. On the other hand, one accumulator 22b is connected to the rear wheel passage 10R, and on the downstream side, the left rear wheel passage 10RL and the right rear wheel passage 10R.
The passages 10RL and 10RH are communicated with the hydraulic pressure chambers 3C of the corresponding wheel fluid cylinders 3RL and 3RR.

Each of the above fluid cylinders 3FL, 3PR, 3RL,
Gas springs 5FL, 5PR, 5RL connected to 3RR
, 5RR are each specifically provided with a plurality of pieces (four pieces in the figure), and these gas springs 5a, 5b, 5c,
5d are connected in parallel to the hydraulic pressure chambers 3c of the corresponding fluid cylinders 3 via the communication passages 4. Further, each of the gas springs 5a to 5d is provided with an orifice 25 interposed at the branching part of the communication path 4, and the damping effect at each orifice 25 and the buffering effect of the gas sealed in the gas chamber 5f are It has come to demonstrate both. A damping force switching valve 26 for adjusting the passage area of the communication path 4 is interposed in the communication path 4 between the first gas spring 5a and the second gas spring 5b. , has two positions: an open position where the communicating passage 4 is opened and a constricted position where the passage area is significantly narrowed.

Furthermore, an unload valve 27 and a flow control valve 28 are connected to the hydraulic passage 10 on the upstream side of the accumulator 22a. The unload valve 27 transfers the pressure oil discharged from the hydraulic pump 8 to the swash plate operating cylinder 8a of the hydraulic pump 8.
It has an introduction position where the oil is introduced to reduce the oil discharge amount of the hydraulic pump 8, and a discharge position where the pressure oil in the cylinder 8a is discharged, and the oil discharge pressure of the hydraulic pump 8 is set to a predetermined upper limit oil discharge pressure ( 160±10 kgf/cd) or higher, the hydraulic pump switches from the discharge position to the introduction position, and maintains this state until it falls below a predetermined lower limit discharge pressure (120±10 kgf/cd). It has a function to maintain and control the oil discharge pressure of No. 8 within a predetermined range (120 to 160 kgf/cd).

The flow rate control valve 28 has an introduction position where pressure oil from the hydraulic pump 8 is introduced into the swash plate operating cylinder 8a of the hydraulic pump 8 via the unload valve 27, and an introduction position where the pressure oil in the cylinder 8a is unloaded. and a discharge position for discharging from the valve 27 to the reserve tank 29, and when the oil discharge pressure of the hydraulic pump 8 is maintained within a predetermined range by the unload valve 27, the throttle 30 arrangement part of the hydraulic pressure passage 10 It has a function of keeping the differential pressure between the upstream and downstream sides constant and controlling the oil discharge amount of the hydraulic pump 8 to keep it constant. Therefore, each fluid cylinder 3
Oil is supplied to the accumulator 22a.

This is done by storing oil at 22b (this oil pressure is called main pressure).

On the other hand, on the downstream side of the accumulator 22a of the hydraulic passage 10, there are four flow control valves 9, 9, corresponding to the four wheels of the vehicle. ...
is provided. Hereinafter, since the configuration of the parts corresponding to each wheel is the same, only the left front wheel side will be explained, and the explanation of the others will be omitted. That is, the flow rate control valve 9 is an inflow valve 35 interposed in the left front wheel side passage 10FL of the hydraulic pressure passage 10.
And oil is stored in the reserve tank 29 from the left front wheel side passage 10FL.
and a discharge valve 37 interposed in a low pressure line 36 for discharging water. The inflow valve 35 and the discharge valve 37 both have two positions, an open position and a closed position, and incorporate a differential pressure valve that maintains the hydraulic pressure at a predetermined value in the open position.

Further, a pilot pressure responsive check valve 38 is interposed in the left front wheel side passage 10PL between the inflow valve 35 and the fluid cylinder 3FL. The check valve 38 receives the hydraulic pressure (that is, the main pressure) in the hydraulic pressure passage 10 upstream of the inflow valve 35 of the flow rate control valve 9 as a pilot pressure through a pilot line 39, and this pilot pressure
It is provided to close when the pressure is below kgr/c-. In other words, pressure oil is supplied to the fluid cylinder 3 only when the main pressure is 40 kgr/cj or more.
It becomes possible to drain the oil inside.

In addition, in FIG. 2, 41 is the accumulator 2 of the hydraulic pressure passage 10.
This is a fail-safe valve installed in the communication path 42 that communicates the downstream side of the accumulators 2a and the low-pressure line 36, and is switched to the open position in the event of a failure, returning the stored oil in the accumulators 22a and 22b to the reserve tank 29, and maintaining the high pressure state. It has a function to release the . Reference numeral 43 denotes a throttle provided in the pilot line 39, which has the function of delaying the closing of the check valve 38 when the fail-safe valve 41 is opened. Reference numeral 44 denotes a relief valve that opens when the oil pressure in the hydraulic pressure chamber 3C of each of the front wheel side fluid cylinders 3FL and 3PR increases abnormally, and returns the oil to the low pressure line 36. Reference numeral 45 is a turn accumulator connected to the low pressure line 36, which performs a pressure accumulating action when oil is discharged from the fluid cylinder 3.

Next, variable control of the suspension characteristics by the controller 19, that is, fluid supply and discharge control for each fluid cylinder 3 will be explained based on FIG.

The figure basically shows a control system A that controls the vehicle height to the target vehicle height (cylinder stroke amount to the target amount) based on the detection signal of the vehicle height sensor 14 of each wheel, and three vertical acceleration sensors. Control system B aims to reduce the vertical vibration of the vehicle based on the detection signal of 15, and equalizes the support load between the left and right wheels on the front wheel side and the rear wheel side, respectively, based on the detection signal of the hydraulic pressure sensor 13 of each wheel. It has a control system C that aims to achieve

In the control system A, 40 is the output XFI of the left and right front wheels 2F of the vehicle height sensor 14? , XPL is summed up, and the output XRR of the left and right rear wheels 2R side.

This is a bounce component calculation unit that totals the XRL and calculates the bounce component of the vehicle. Further, 41 is a pitch component calculation unit that calculates the pitch component of the vehicle by subtracting the total value of the outputs XRR and XRL on the left and right rear wheels 2R side from the total value of the outputs XFR and XPL on the left and right front wheels 2F side; 42 is a roll component calculation unit that calculates a roll component of the vehicle by adding the difference XPRXPL between the outputs of the left and right front wheels 2F and the difference XRR-XRL between the outputs of the left and right rear wheels 2R.

Reference numeral 43 inputs the bounce component of the vehicle calculated by the bounce component calculation unit 40 and applies the flow rate control valve 9 of each wheel in bounce control based on the following PD sub-control proportional-derivative control) formula % formula %. This is a bounce control unit that calculates a control amount. Also, 4
4 is a pitch control unit which inputs the pitch component of the vehicle calculated by the pitch component calculation unit 41 and calculates the control amount of each flow rate control valve 9 in pitch control based on the proportional-differential control equation similar to the above; In 45, the roll component of the vehicle calculated by the roll component calculation unit 42 and the target roll angle T ROL of the vehicle are shown.
A roll control unit that inputs L and calculates the control amount of each flow rate control valve 9 in roll control so that the vehicle height is inclined to the target roll angle T ROLL based on a proportional-differential control equation similar to the above. It is.

In order to control the vehicle height to the target vehicle height, each of the control units 4
After inverting each control amount calculated in steps 3 to 45 for each wheel (reversing in the opposite direction to the positive/negative direction of the signal input to the vehicle height sensor 14), the bounce, pitch, and roll control amounts for each wheel are calculated. Add the corresponding control amount QF of the proportional flow rate control valve 9
R, QFL, QRR, QRL.

In the control system B, 50 is a bounce component calculation unit that calculates the bounce component of the vehicle by summing the outputs GFR, GFL, and GR of the three vertical acceleration sensors 15;
Pitch component calculating section that calculates the pitch component of the vehicle by subtracting the output GR of the rear wheel 2R from the sum of half values of the outputs GFR and GPL of the left and right front wheels 2F among the vertical acceleration sensors 15. , 52 is a roll component calculation unit that calculates the roll component of the vehicle by subtracting the output GPL of the left front wheel 2F from the output GFR of the right front wheel 2F.

In addition, 53 inputs the bounce component of the vehicle calculated by the bounce component calculation unit 50 and calculates the flow rate of each wheel in bounce control based on the following lPD control (integral-proportional-derivative control) formula 1 (%). This is a bounce control section that calculates a control amount for the control valve 9. Also, 5
Reference numeral 4 denotes a pitch control unit which inputs the pitch component of the vehicle calculated by the pitch component calculation unit 51 and calculates the control amount of each flow rate control valve 9 in pitch control based on the same integral-proportional one-integrated control equation as above. , Similarly, 55 inputs the roll component of the vehicle calculated by the roll component calculation section 52 and calculates the same integral -
This is a roll control unit that calculates the control amount of each flow rate control valve 9 in roll control based on a proportional one-to-one control formula.

Then, the vertical vibration of the vehicle is divided into bounce component, pitch component,
In order to suppress the roll component, each control amount calculated by each of the control units 53 to 55 is reversed for each wheel in the same manner as above, and then the bounce, pitch, and roll control amounts for each wheel are added, Control amount QPR, Q of the corresponding flow control valve 9
PL, QRR, QRL. In addition, each control unit 53 to 5
The control amount for each wheel calculated in step 5 is weighted by the coefficient k (k-1
, 08> is corrected to a large value.

Further, in the control system C, reference numeral 60 denotes a warb control section, which inputs the hydraulic pressure PPR and PPL signals of the two hydraulic pressure sensors 13 on the front wheel side, and calculates the total hydraulic pressure on the front wheel side. Hydraulic pressure difference between left and right wheels (P FR-P PL
) (load transfer ratio), and a rear wheel side load transfer ratio calculation section 60b that calculates a similar load transfer ratio on the rear wheel side. Then, after multiplying the load transfer ratio on the rear wheel side by a predetermined value by a coefficient Wr, this is subtracted from the load transfer ratio on the front wheel side, and the result is multiplied by a predetermined value by a coefficient wA and weighted on the front wheel side. In order to equalize the control amounts between the left and right wheels, the corresponding control amounts QPR, QPL, QRR,
QRL.

In addition, in FIG. 3, various switching controls are performed in the control system in order to improve the responsiveness of fluid supply and discharge control to each fluid cylinder 3 when the vehicle turns.

That is, in the control system, the steering angular velocity θH is multiplied by the vehicle speed V, and a value S1 obtained by subtracting the reference value G1 from the result θH−■ is input to the turning determination unit 65. Also, the value S obtained by subtracting the reference value G2 from the current lateral acceleration Gs of the vehicle
2 is input to the turning determination section 65. Then, the turning determination section 6
In step 5, if human power S+ or S2≧0, it is determined that the vehicle is turning, and the suspension characteristic hardening signal Sa is
In order to improve the followability of fluid supply and discharge control for each fluid cylinder 3, the damping force switching valve 26 is switched to the throttle position, and each of the proportionality constants Ki (l so 81 to B
S, PI~PS, Rl~R5) are each set to a large value K Ha
rd and stores the target roll angle TR011 in advance. Map G■ap (Gs) (becomes a large value as the lateral acceleration Gs increases, and at a predetermined value Gsl, TR0II-O, Gs
The map is set to a value corresponding to the lateral acceleration Gs at that time.

On the other hand, when the inputs S1 and S2 are 0, the turning determination unit 65 determines that the vehicle is traveling straight, outputs the suspension characteristic softening signal sb, switches the damping force switching valve 26 to the open position, and switches the damping force switching valve 26 to the open position. Set the constant to 1 to each normal value KSoft
and the target roll angle TR0II-0.

In addition, in the control systems A to C as described above, in order to prevent the control from being performed more frequently than necessary, the control amounts QFR, QPL, QRR, and QR of the proportional flow rate control valve 9 are controlled.
A dead zone area is provided in which no control is performed when L is less than a predetermined value.

The controller 19 has a fail-safe control system for responding to a failure of each device in the fluid supply/discharge control system, in addition to the control systems A-D for variable control of suspension characteristics. As shown in FIG. 1, a failure detection means 8 detects a failure of each device of the fluid supply/discharge control system based on detection signals from various sensors 12 to 18.
1, a first failure mode in which the fluid in each fluid cylinder 3 is discharged and the total vehicle height is lowered according to the degree of failure detected by the detection means 81, and a first failure mode in which the current vehicle height is maintained and control is stopped. It has a fail control means 82 that executes either the second failure mode or the third failure mode in which only a warning (activation of an alarm device such as a warning lamp or a warning buzzer) is performed and control is continued.

Here, among the failures of each device of the fluid supply/discharge control system, the inflow valve 35 or the discharge valve 37 of the flow control valve 9 is stuck open, that is, the fluid (working fluid) Detection of a failure when the fluid in the fluid cylinder 3 is supplied or when the fluid in the fluid cylinder 3 is exhausted is performed as follows.

First, the total strokes of the rebound and bump of each wheel are each 80 degrees, and with the neutral position as a reference,
The rebound side is indicated by a "+" value, and the bump side is indicated by a "-" value. In other words, the vehicle height sensor 14 is a sensor that detects this rebound bump, but the output value of the vehicle height sensor 14 varies from -80 degrees to +8 degrees in wheel stroke amount.
C) corresponds to the range of + soda.

Based on this premise, when the following three conditions (1) to (2) are satisfied in total, it is determined that the inflow valve 35 has failed (stuck in the open state). That is, ■ the amount of rebound is at least a predetermined value (for example, 60 mm), ■ the pressure inside the fluid cylinder 3 detected by the cylinder pressure sensor 13 is at least a predetermined value (for example, 100 kgf/cd), and ■ the above (■). The pressure state remains constant for a predetermined time (e.g. 300m5e)
c) Continuation of the above. In this way, when a failure of the inflow valve 35 is detected, not only is a warning issued, but the fail-safe valve 41 is opened to release the pressure on the accumulators 22a and 22b, and
A failure mode is executed in which all flow control valves 9 (inflow valves 35 and discharge valves 37) are fully opened, the fluid in each fluid cylinder 3 is discharged, and the entire vehicle height is lowered to the lowest position (until it hits the bump stopper). Ru.

Furthermore, detection when the discharge valve 37 of the flow rate control valve 9 is stuck open means that the pressure inside the fluid cylinder 3 should increase when it bumps, contrary to the case of the inflow valve 35 described above. The basic focus will be on That is, the condition for determining that the discharge valve 37 is malfunctioning is when the following three conditions (1) to (2) are satisfied in total.

■ The amount of bumping is greater than a predetermined value (for example, 30 m); ■ The pressure inside the fluid cylinder 3 is a predetermined value (for example, 30 kg).
f/d) or less, ■ The pressure state of
c) Continued. The response when this discharge valve 37 fails is the same as the response when the inflow valve 35 fails (failure control), as well as issuing a warning and discharging the fluid in each fluid cylinder 3 to lower the overall vehicle height to the minimum. lower to position.

The control for determining failure of the inflow valve 35 and the discharge valve 37 will be explained with reference to the flowchart shown in FIG.

First, in step S1, flag A or flag B is set to "1".
Determine whether or not. Flag A is set to "1" when a failure of the inflow valve 35 is detected, and flag B is set to "1".
is set to "1" when a failure of the discharge valve 37 is detected. When the determination in step S1 is YES,
Control is terminated to prohibit active control.

When the determination in step S1 is No, the system is initialized in step S2. At this time, failsafe valve 41 is closed. Subsequently, in step S3, detection signals from the various sensors 12 to 18 are read.

After that, as determined in steps 84 to S6, the inflow valve 3
5 failure (sticking in open state) is determined (confirm the above-mentioned determination conditions ① to ②). Then, when all the failure determination conditions are satisfied (all determinations from steps 84 to S6 are YES),
), the flag A is set to "1" in step S7, and then the above-mentioned fail control t(
At the same time as issuing a warning, control is performed to discharge the fluid in each fluid cylinder 3 and lower the entire vehicle height to the lowest position, and the control ends in this state.

On the other hand, when the inflow valve 35 is not out of order (steps 54 to S
6), step 59~
Based on the determination of Sll, the failure of the discharge valve 37 is determined (
Confirmation of the above-mentioned judgment conditions ■ to ■). Then, when all the failure determination conditions are satisfied (when all the determinations in steps S9 to Sll are YES), it is determined in step S12 whether or not the failed inflow valve 35 is for the rear wheels, and the determination is confirmed. If YES, it is determined in step 313 whether the vehicle is turning, that is, whether the lateral acceleration (lateral G) is greater than or equal to a predetermined value of 60. When the determination in step 813 is No, it is further determined in step S14 whether or not the vehicle is being braked, that is, whether the brake switch is ON. The determination in either step S13 or S14 is Y.
In the case of ES, that is, when the vehicle is turning or braking, the process returns to step 512. Step 512 or S1
If the determination in step 4 is No, that is, if the failed valve is for the front wheels instead of the rear wheels, or if the vehicle is neither turning nor braking, the process proceeds to step S15.
After setting the flag B to "1" in step S16, control is performed in the event of a fail, and thereafter, the control is terminated.

Through the above series of steps 812 to S16, when a failure occurs in which the exhaust valve 37 on the rear wheel side is stuck open, the control correction means suspends and regulates the control to lower the overall vehicle height while the vehicle is turning or braking. 83 are configured.

On the other hand, when the discharge valve 37 is not out of order (steps 89 to S
ll is No), step S1
7, the above-mentioned active control shown in FIG. 3 is performed, and then the process returns.

Therefore, in this type of control, if the discharge valve 37 fails while being stuck in the open state, the failed discharge valve 3
When 7 is for the front wheels, fail control is performed, that is, the fluid (working fluid) in the fluid cylinder 3 is discharged, and the overall vehicle height is lowered, resulting in a lateral tilt on the vehicle body side. This prevents the steering wheel from becoming too heavy to operate.

On the other hand, if the malfunctioning exhaust valve is on the rear wheel side,
Since the above-mentioned fail control is restricted while the vehicle is turning or braking, it is possible to prevent the running condition from becoming unstable due to a sudden drop in vehicle height while the vehicle is turning or braking. , driving stability can be improved.

FIG. 5 is a flowchart showing a modification of control for failure determination of the inflow valve 35 and the discharge valve 37. This modification differs from the embodiment only in the determination of failure (sticking in the open state) of the inflow valve 35 and the discharge valve 37.

That is, failure determination of the inflow valve 35 (steps 824 to 5)
27) is determined to be a failure when all of the following four conditions (1) to (2) are satisfied. However, HO is the standard vehicle height without bump or rebound, H(1) and H(t-Δt) are the current and previous vehicle heights, and P(t) and p(t-Δt) are the current and previous fluid heights. The pressure inside the cylinder 3 is shown respectively.

■ It is the time of rebound, that is, H(t) −H
O >0; ■ There has been a further rebound from the state in ■ above, that is, H(t) −H(t−Δt)>0; ■ The pressure inside the fluid cylinder 3 has increased. , that is, P (t) −P (−Δt)〉0, ■ The pressure increase state in (■) above lasts for a predetermined time (for example, 300 m
5ec) or more.

In addition, the failure of the discharge valve 37 is determined based on the fact that, contrary to the case of the inflow valve 35, the pressure inside the fluid cylinder 3 should increase when it bumps, and the failure determination ( The conditions for steps S30 to S833) are when all of the following four conditions (1) to (2) are satisfied.

■ It is a bump time, that is, H(t) − HO < 0. ■ It is a bump further from the state of ■ above, that is, H (t) − H (t − Δt) < 0. ■ The pressure inside the fluid cylinder 3 is decreasing, that is, P (t) - P (t - Δt) < 0, and ■ The pressure decrease state in (■) above continues for a predetermined period of time (for example, 300 m).
5ec) or more.

(Effects of the Invention) As described above, according to the vehicle suspension device of the present invention, when the discharge valve that is stuck in the open state is on the front wheel side, the fluid in each cylinder is discharged to lower the overall vehicle height. control to prevent the steering wheel from becoming too heavy due to a side lean.Also, when the vehicle is on the rear wheel side, control that lowers the overall vehicle height is regulated to stabilize driving due to sudden changes in vehicle height. It is possible to prevent a decline in sexual performance. Therefore, fail-safe measures can be taken appropriately depending on the type of discharge valve that has failed.

In particular, the regulation of control when the rear wheel side exhaust valve breaks down has been changed.
It is effective if done during turning and braking, when the vehicle is likely to fall into an unstable state.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention, in which Fig. 1 is a general schematic diagram, Fig. 2 is a hydraulic circuit diagram, Fig. 3 is a control block diagram showing variable control of suspension characteristics, and Fig. 4 is an inlet valve and discharge valve. FIG. 3 is a flowchart showing control of valve failure determination. FIG. 5 is a diagram corresponding to FIG. 4 showing a modified example. 3 (3PL, 3PR, 3RL, 3RR)...
・Fluid cylinder 37...Discharge valve 81...Failure detection means 82...Fail control means 83...Control correction means 3 (3FL, 3FR, 3RL, 3RR)...
・Fluid cylinder 37...Discharge valve 81...Failure detection means 82...Fail control means 83...Control correction means

Claims (3)

[Claims] (1) In a vehicle suspension system that allows suspension characteristics to be changed by independently controlling the supply and discharge of fluid to a plurality of cylinders provided between the sprung mass and the unsprung mass for each wheel, a failure detection means for detecting a failure of each device in the fluid supply/discharge control system; a control means for discharging fluid in each cylinder to lower the overall vehicle height when a failure is detected by the detection means; A control correction means that allows control for lowering the overall vehicle height when an exhaust valve corresponding to a front wheel cylinder is stuck open and restricts it when an exhaust valve corresponding to a rear wheel cylinder is stuck open. A vehicle suspension device comprising: (2) Claim (1), wherein the control correction means restricts the control means to lower the overall vehicle height at least during turning when the exhaust valve corresponding to the cylinder on the rear wheel side is stuck open. Suspension equipment for the vehicle described. (3) Claim (1) wherein the control correction means restricts the control to lower the overall vehicle height at least during braking when the exhaust valve corresponding to the cylinder on the rear wheel side is stuck open. Suspension equipment for the vehicle described.