GB2270050A

GB2270050A - Suspension control system for a vehicle

Info

Publication number: GB2270050A
Application number: GB9316850A
Authority: GB
Inventors: Atsushi Mine
Original assignee: Fuji Jukogyo KK; Fuji Heavy Industries Ltd
Current assignee: Subaru Corp
Priority date: 1992-08-31
Filing date: 1993-08-13
Publication date: 1994-03-02
Anticipated expiration: 2013-08-13
Also published as: GB9316850D0; DE4329161C2; GB2270050B; DE4329161A1

Abstract

A road surface sensor for detecting roughness of a road surface is provided under the front side of a vehicle body. At intermediate speed, the road surface sensor is displaced forwardly of the vehicle body by an angular displacement apparatus. At high speed, the road surface sensor is further angularly displaced forwardly by an angle variation apparatus to a maximum displaced state to move the road surface detecting position forwardly. A delay time is calculated as required, and an attenuation force switching signal is outputted to the front and rear wheel suspensions, and a timing for at least the front wheel to arrive at the road surface detecting position is always brought substantially into coincidence with the timing for switching the attenuation force of the front wheel suspension by considering the delay time of a control system. Thus, the road surface sensor is displaced to optimize detection of a road surface and switch suspension characteristics at an optimum timing. <IMAGE>

Description

2270050

DESCRIPTION

SUSPENSION CONTROL SYSTEM FOR A VEHICLE This invention relates to a suspension control system for a vehicle provided at each wheel for controlling the switching of suspension characteristics in response to the roughness of a road surface. More particularly, the invention concerns a suspension control system for reliably switching an attenuation force against a delay of a control system in a whole travel area.

In general, a suspension system is interposed between a vehicle body and a vehicle wheel with a spring and a shock absorber for absorbing an impact from a road surface by the spring and attenuating continuous vibration of its recoiling by the shock absorber, thereby moderating the impacts and the like. If the attenuation force of the shock absorber is large, rolling of the vehicle body is suppressed to improve stability of the vehicle attitude, but the shock absorber reacts sensitively with the roughness of the road surface, and hence a stiff riding feel is attained. On the contrary. if the attenuation force is small, a vibration input from the road surface decreases, and a soft riding comfort is obtained. Thus, recently, a semiactive suspension system has been proposed in which an attenuation force variable apparatus is added to a shock absorber to control the attenuation force of suspension characteristics in -2response to a road surf ace state of good and bad roads, a travel state of braking, starting, turning, etc., to allow steering stability and a compatible riding feel- In a control system for switching suspension characteristics against the roughness of a road surface, a road surface sensor of an ultrasonic type for detecting a rouglu.,ess of a road surface is provided at a front side of a vehicle body. In this case, the road surface senso-r is desirably disposed as near as possible to a front wheel so as to decrease a detecting error due to pitching of a vehicle body and to so displace as to detect a road surface.

On the other hand, in the case where the road surface sensor is held fixedly, a period of time when a vehicle wheel actually reaches a road surface detecting position to be detected by the road surface sensor varies in accordance with a vehicle speed. Further, a sensor system, a control system, and an actuator system respectively have intrinsic delay times. In the case where the delay time of the whole control system is considered, when the vehicle travels at a predetermined speed or faster, there is no timing margin for road surface information detected by the road surface sensor to be used for controlling the switching of suspension characteristics to cause no optimum timing of controlling to switch. Therefore it is always required to so control -3as to bring a timing f or the vehicle wheel to arrive at a road surf ace detecting position into coincidence with a timing for switching the suspension characteristics by considering the delay time of the whole control system in the-whole travel area ofthe vehicle.

Heretofore, regarding a control system for switching suspension characteristics against a roughness of a road surf ace, there is prior art as disclosed, for example, in Japanese Patent Laid-Open Publication No. 18282511991. In the prior art, a road roughness sensor is provided at a lower front end of a vehicle body, and suspension characteristics are switched based on an output of the senscr.

In this prior art, the road surface roughness sensor is fixedly provided at a vehicle body to always detect a road surface separately at a predetermined distance forwardly of its front wheel. Therefore, it cannot control the switching of suspension characteristics at an optimum timing due to the time delay of the whole control system during high speed.

If the attenuation force of the shock absorber is large in the suspension, vibration can be rapidly attenuated to decrease change in the attitude of the vehicle to improve a steering stability. On the other hand, if the attenuation force is small, the vibration is -4continued to improve a riding f eel. Thus, recently,, an attenuation f orce variable apparatus has been added to a shock absorber to control the attenuation force of suspension characteristics in response to a road surface state of good and bad roads, a travel state of braking, starting, turning, etc., to propose a steering stability and a riding feel to be compatible has been presented.

In a stable attitude control f or changing suspension characteristics against a roughness of a road surf ace, a road surf ace sensor of an ultrasonic type f or detecting a roughness of a road surface is provided at a front side of a vehicle body. In this case. the road surface sensor is desirably disposed as near as a front wheel so as to decrease a detecting error due to pitching of a vehicle body and to so displace as to detect a road surf ace. In the control system, the signal from the road surface sensor is inputted, processed in the control system, and actuated for the actuator of the attenuation force variable apparatus of the suspension.

Therefore, a sensor system, a control system, and an actuator system respectively have delay times. In the case where the sensor mounted position near the front wheel and the delay time of the whole control system are considered, there is no timing margin f or road surface inf ormation detected by the road surface sensor to be used for -5 controlling to switch the suspension characteristics to cause no optimum timing of controlling to switch. Thus. it is required to so control as to bring a timing f or the vehicle wheel to arrive at a road surface detecting position into coincidence with a timing f or switching the suspension characteristics by considering the delay time of the whole control system in the wide vehicle speed range of the vehicle. When four-wheeled suspensions are simultaneously controlled, it cannot be applied in the case where the roughness of the road surface occurs in a short period. Thus, it is necessary to control the suspensions in coincidence with the timing for the front and rear wheels to arrive at the rough road surface.

Heretofore. regarding a control system for switching suspension characteristics against a roughness of a road surface, there is prior art as disclosed, for example, in Japanese Patent Laid-Open Publication No. 18282511991.

Accordingly, an object of this invention is to provide a suspension control system for a vehicle which suitably displaces and angularly displaces a road surface sensor thereby to optimize detection of a road surface and always switch suspension characteristics against a delay of a whole control system at an optimum timing in a whole travel area.

Another object of this invention is to provide a suspension control system f or a vehicle in which a road surface sensor is suitably displaced and angularly displaced to a vehicle body to optimize detection of a road surf ace and suspension characteristics are always switched at an optimum timing against a delay of a whole control system in an entire travel area.

Yet another object of this invention is to provide a suspension control system for a vehicle in which a road surface sensor is suitably displaced to optimize detection of a road surface and suspension characteristics are always switched at the optimum timing against a delay of a whole control system in an entire travel area.

Still another object of this invention is to provide a suspension control system for a vehicle in which suspension characteristics are controlled to be changed by a road surface sensor to a sensor mounted position and a delay time of a whole control system in a wide vehicle speed range.

Still another object of the invention is to provide a suspension control system for a vehicle which can control change of suspension characteristics in accordance with a road surface sensor in a wide vehicle speed range against a sensor mounting position and a delay time of a whole control system and accurately control front and rear wheel suspensions.

In order to achieve the above first object, this invention provides a suspension control system for a vehicle having a vehicle body and a plurality of vehicle wheels, a suspension interposed between said body and said wheel, a vehicle speed sensor mounted on said vehicle for detecting a speed of said wheel and for generating a vehicle speed signal, a shock absorber with a spring and a variable attenuation system, and an actuator provided in said shock absorber for controlling an attenuation force.

the system comprising a road surface sensor mounted under a front side of said vehicle body for detecting a roughness of a road surface in front of said wheel and for producing a road surface condition signal, a displacement apparatus connected to said road surface sensor for forwardly and rearwardly moving said road surface sensor, an angular displacement apparatus engaged with said displacement apparatus for rotatably changing an angle against said road surface, and control means responsive to said vehicle speed signal and said road surface condition signal for processing and outputting an actuating signal selectively to said displacement apparatus and said angular displacement apparatus without delay and for generating an adjusted attenuation signal so as to enable an optimum control of said suspension and a stable attitude control of said vehicle in any driving condition.

With the above suspension control system, the road surface-is accurately detected by the road surface sensor, and an attenuation force of the suspension is controlled to be switched in accordance with road surface information from the road surface sensor. When travelling at low speed, the road surface sensor is fixed to a shortest position. A delay time against a delay of the control system is calculated in this state, and an attenuation force switching signal is output to an actuator after the delay time is elapsed. When the vehicle travels at a higher speed and its front wheels reach road surface detecting positions faster, the road surface sensor itself is displaced forwardly by the displacement apparatus. Or, when the road surface sensor itself is angularly displaced forwardly from the state directing directly thereunder by the angular displacement apparatus, the road surface detecting position is separated forwardly of the vehicle body. Thus, the delay time of the whole control system can be always attained. The delay time is calculated similarly in this sensor actuating state as required to output an attenuation force switching signal to the actuator, thereby always bringing the timing for at least the front wheel to reach the road surface detecting position substantially into coincidence with the timing for switching the attenuation force of the front wheel suspension by -9considering the delay time of the control system. Thus. a vehicle attitude can be reliably stabilized in the whole travel area.

In order to achieve another object, this invention provides a suspension control system for a vehicle in which an actuation controller for a road surface sensor is hung from a front side of a vehicle body to be operated by an electric signal from a control unit to project forwardly from a position of a shortest front-and-rear distance thereby sequentially displace a road surface detecting position.

With the arrangement described above, the road surface sensor is mounted by the sensor actuation controller to always accurately detect the road surface forwardly of the front wheels, and attenuation force of the suspension is controlled to be switched in accordance with road surface information of the road surface sensor. Thus, the timing for at least the front wheel to arrive at the road surface detecting position is always brought into coincidence with the timing for switching the attenuation force of the front wheel suspension by considering the delay time of the control system, thereby reliably stabilizing an attitude of the vehicle in a whole travel area.

In order to achieve yet another object, this invention provides a suspension control system for a -10vehicle having a vehicle body and a plurality of vehicle wheels,:a suspension interposed between said body and said wheel, a vehicle speed sensor mounted on said vehicle for detecting a speed of said wheel and for generating a vehicle speed signal, a shock absorber with a spring and a variable attenuation system, and an actuator provided in said shock absorber for controlling an attenuation force, the system comprising a road surface sensor mounted under a front side of said vehicle body for detecting a roughness of a road surface in front of said wheel and for producing a road surface condition signal, a displacement apparatus connected to said road surface sensor for forwardly and rearwardly moving said road surface sensor, and control means responsive to said vehicle speed signal and said road surface condition signal for processing and outputting a stepped displacing signal to said displacement apparatus without delay and for generating an adjusted attenuation force switching signal so as to adjust the delay time by a period of time f or at least the front wheel to reach the road surf ace detecting position in response to its vehicle speed and the delay time of a whole control system to output the attenuation f orce switching signal to the actuator.

With the above suspension control system, the road surface is accurately detected by the road surface sensor, and an attenuation force of the suspension is controlled to be switched in accordance with road surf ace inf ormation from the road surface sensor. When travelling at low speed, the road surface sensor is fixed to a shortest position. A delay time is calculated by subtracting the delay time of a whole control system from a period of time for the front wheel to reach a road surface detecting position in response to the vehicle speed in this state, and an attenuation f orce switching signal is output to an actuator after the delay time is elapsed. When the vehicle travels at a higher speed and its front wheels reach road surf ace detecting positions f aster, the road surf ace sensor itself is projected stepwisely forwardly of the vehicle body to be separated forwardly of the vehicle body. Thus, the delay time of the whole control system can be always attained. The delay time is calculated similarly in this sensor actuating state as required to output an attenuation force switching signal to the actuator, thereby always bringing the timing for at least the front wheel to reach the road surface detecting position substantially into coincidence with the timing for switching the attenuation force of the front wheel suspension by considering the delay time of the control system. Thus, a vehicle attitude can be reliably stabilized in the whole travel area.

-12In order to achieve still another object, this invention provides a suspension control system for a vehicle having a vehicle body and a plurality of vehicle wheels, a suspension interposed between said body and said wheel, a vehicle speed sensor mounted on said vehicle for detecting a speed of said wheel and for generating a vehicle speed signal, a shock absorber with a spring and a variable attenuation system, and an actuator provided in said shock absorber for controlling an attenuation force, the system comprising a road surface sensor mounted under a front side of said vehicle body for detecting a roughness of a road surface in front of said wheel as to be displaced forwardly from the vicinity of the front wheel to change a road surface detecting position and a control unit for processing signals from the road surface sensor and a travel state to actuate the actuator and a sensor displacing apparatus.

With the arrangement as described above, at low speed with a time margin for a delay time of the whole control system, the road surface sensor is fixed to the vicinity of zhe front wheel, the delay time is adjusted by the control unit to output an attenuation force variable signal responsive to the roughness of the road surface to the actuator. Thus, in the case where the wheels reach a projection and a recess, it actuates attenuation so as to -13suitably change suspension characteristics to stably control an attitude of the vehicle. At the time of intermediate and high speeds, the road surf ace sensor is sequentially displaced forwardly to early detect the road surface to output the attenuation force variable signal to the actuator. In this manner, in the case where the wheels reach the projection and the recess, the suspension characteristics can be changed similarly without time delay. Thus, the road surface near the wheels can be accurately detected by the road surf ace sensor, and the suspension characteristics can be changed without time delay in a wide vehicle speed range.

In order to achieve still another object, this invention provides a suspension control system for a vehicle having a vehicle body and a plurality of vehicle wheels, a suspension interposed between said body and said wheel, a vehicle speed sensor mounted on said vehicle for detecting a speed of said wheel and for generating a vehicle speed signal, a shock absorber with a spring and a variable attenuation system, and an actuator provided in said shock absorber for controlling an attenuation force, the system comprising a road surface sensor mounted under a front side of said vehicle body to move from the vicinity of the front wheel forwardly to change a road surface detecting position for detecting a roughness of a road surface in front of said wheel and for producing a road surf ace condition signal, and control means responsive to said vehicle speed signal and said road surf ace condition signal for adjusting a delay time or a sensor displaced amount against said actuator of said front wheel suspension to output an attenuation f orce variable signal responsive to a roughness of a road surf ace and adjusting a delay time against said actuator of said rear wheel suspension to output an attenuating f orce variable signal responsive to a roughness of the road surface.

With the above suspension control system. the delay time or the sensor displaced amount is adjusted by the control unit to the actuator of the front wheel suspension to sequentially move the road surf ace sensor forwardly of the vehicle body to early detect the road surface. and an attenuation force variable signal responsive to the roughness of the road surface is outputted, thereby controlling the delay time of the whole control system in a wide vehicle speed range. The delay time considered for a wheel base by the control unit is delayed to the actuator of the rear wheel suspension, and the attenuation force variable signals responsive to the roughnesses of the road surface are respectively outputted. Thus, even if the front wheels are transferred to next rough surface, the suspension actuates the attenuation to suitable change the -is- suspension characteristics similarly to those of the case of the front wheels if the rear wheels reach the rough surface, thereby reliably stably controlling the attitude of the vehicle.

By way of example only, specific embodiments of the present invention will now be described, with reference to the accompanying drawings, in which:Fig. 1 is a general structural view of an embodiment of a susDension control system for a vehicle according to this invention; Fig. 2 is a sectional view showing an attenuation force variable shock absorber; Fig. 3 is a graph indicating attenuating force characteristics of the suspension; Fig. 4 is a flow chart showing con.&'-.rol of changing suspension characteristics in response to the rough state of a road surface; Fig. 5 is graphs indicating a delay time, a sensor displacement amount and a sensor inclined angle adjusted state; Fig. 6 is a schematic view showing a rough state of a road surface; Fig. 7 is an explanatory view showing a sensor mounted state; Fig. 8 is a structural view of an overall of another embodiment of a suspension control system for a vehicle according to this invention; Fig. 9 is a graph indicating attenuation force characteristics in response to the rough state of a road surface; Fig. 10 is a graph indicating attenuation force characteristics of a suspension; Fig. 11 is a schematic view showing a rough state of a road surface; Fig. 12 is a graph showing attenuating force characteristics of a suspension; Fig. 13 is a flow chart indicating a control of changing suspension characteristics in response to a rough state of a road surface; Fig. 14 is a graph showing an adjusted state of a delay time and a sensor travel amount; Fig. 15 is a flow chart indicating a control of changing suspension characteristics in response to a rough state of a road surface; and Fig. 16 is a graph showing an adjusted state of a delay time and a sensor travel amount.

The embodiments of this invention will be explained with reference to accompanying drawings. Referring first to Fig. 1, a suspension control system for a vehicle will be described. Numeral 1 indicates a vehicle body. Suspensions 5 and 51 are respectively interposed between wheel axles 4 of a front wheel 2 and a rear wheel 3 and the vehicle body 1. The front wheel suspension 5 is provided in parallel with an attenuation force variable shock absorber 20 with a spring 6 between the vehicle body 1 and the wheel axle 4, and an electric motor 7 is provided as an actuator for controlling the switching of an attenuation force at -17the upper end of the shock absorber 20. The rear wheel suspension 51 is similarly constituted to the front wheel suspension 5, wherein the same components are denoted by the same numerals with "dash", and the description of the operation will be omitted.

A road surface sensor 10 for detecting a roughness of a road surface is mounted at a displacement apparatus 11 having a motor 12 of an actuator and an angular displacement apparatus 15 directly forwardly of the front wheel 2 of the vehicle body 1. Thus, the road surf ace sensor 10 is displaced forwardly by the displacement apparatus 11, or inclined forwardly by the angular displacement apparatus 15 to be able to displace its road surface detecting position. Further, a vehicle speed sensor 13 f or detecting a travel state of the vehicle is provided. Signals from the road surface sensor 10 and the vehicle speed sensor 13 are inputted to a control unit 14. The motors 7 and 71 of the front and rear wheel suspensions 5 and 5 1, the displacement apparatus 11 and the angular displacement apparatus 15 are actuated in accordance with the output signal of the control unit 14.

The control unit 14 selects an attenuation force switching signal responsive to road surface information, and further controls an output timing of the attenuation force switching signal against a delay of the control -18system and the road surface detecting position. Its control rule will be described below. If the vehicle speed is designated by V, the delay time of the whole control system by At. the shortest front-and-rear distance between the sensor and a center of a tire by Lo, a sensor horizontal displacement amount of the sensor by AL1, and a horizontal displacement amount angularly displaced, i.e., a sensor inclined displacement amount by AL2, the whole length to the road surface detecting position in front of the tire is obtained by Lo + AL1 + AL2, the time f rom the time of detecting the road surf ace to arrival at the time is obtained by (Lo + AL1 + AL2)/V. A margin time including the delay time AT to be adjusted when the road surf ace inf ormation is used for controlling is obtained by (Lo + AL1 + AL2)1V - At.

Specifications in the case where the road surface sensor 10 is inclined in front of the vehicle body are defined as shown in Fig. 7. That is, the sensor mounting height is designated by Ho, the sensor inclined angle by 0, the height of the roughness E of the road surf ace D is by AH, and the sensor detecting distance by In. In this case, at the time of directing the road surface sensor 10 directly downward of 0 = 0, the height of the roughness E of the road surface D is obtained by AH = Ho Ln. In the case of 0 > 0, AL2 = Ln-sin 0 and AH = Ho Ln.cos 0 are attained. In this case, the upward direction of the roughness E is positive, and the forward distance is positive. Therefore, at the time of a low speed capable of calculating the delay time, the delay time AT is calculated to be controlled. At the time of an intermediate speed and a high speed, the road surface sensor 10 itself is horizontally displaced and further angularly displaced to so control as to displace the road surface detecting position forwardly of the vehicle body. Thus, the delay time At of the whole control system can be always attained, and the timing f or arriving at least the front wheel 2 at the road surface detecting position can be brought substantially into coincidence with the timing for switching the attenuation force of the front wheel suspension 5 in the whole travel area.

Then, when the vehicle speed V is equal to or lower than a set vehicle speed Vsi (Lo/At) capable of calculating the delay time, it is assumed to be AL1 = 0 = 0, and the delay time At is calculated by AT = Lo/V - At, and the height AH of the roughness of the road surface is calculated by AH = Ho - Ln to be controlled. At the time of an intermediate speed and a high speed equal to or faster than the set vehicle speed Vsl, a set vehicle speed Vs2 capable of controlling when the sensor is displaced most forwardly is set. When the vehicle speed V is equal to or lower than the set vehicle speed Vs2, it is assumed to be AT = 0 = 0, and the sensor horizontal displacement amount AL1 is calculated by cLl = V.At -.Lo, and the height AH of the roughness of the road surface is similarly calculated by AH = Ho - Ln to be controlled.

Further, when the vehicle speed V is equal to or faster than the set vehicle speed Vs2, AL = ALmax (ALmax indicates a sensor maximum displacement amount) is set, and the sensor inclined angle A is sequentially increased with margin in response to the acceleration of the vehicle speed V. Then,, the sensor inclined displacement AL2 amount is calculated by AL2 = Ln.sin 0. Further,, the delay time AT is calculated by AT = (Lo + AImax + AL2) /V - At. The height AH of the roughness of the road surface is calculated by AR = Ho - Ln.cos 0 to be controlled.

Referring to Fig. 2, an embodiment of an attenuation force variable shock absorber 20 will be described in detail. in the shock absorber 20. a rod 22 with a piston 23 at the side of the vehicle body 1 is movably inserted into a cylinder 21 at the side of the vehicle axle 4. The cylinder 21 is partitioned by the piston 23 into an upper chamber 24 and a lower chamber 25, and oil 0 is f illed in the chambers 24 and 25. The piston 23 is provided with a main passage 26 and a main valve 26a of an extension side and with a main passage 27 and a main valve 27a of a compression side. When the rod 22 rises to be extended, the one main valve 26a is opened, and the oil 0 flows from the upper chamber 24 to the lower chamber 25 through the main passage 26. When the rod 23, on the contrary, falls to be compressed, the other main valve 27a is opened, and the oil 0 flows from the lower chamber 25 to the upper chamber 24 through the main passage 27. In this case, diameters of orifices of the main passages 26 and 27 are set to small values, thereby generating equal hard attenuating forces at both the extension and compression sides.

An attenuation force variable apparatus 30 is provided in the rod 22. The attenuation force variable apparatus 30 is provided with a communication hole 31 at the center of the rod 22 f or communicating at its lower end with the lower chamber 25. The communication hole 31 communicates a subpassage 32 at the extension side with a subvalve 32a, a subpassage 33 at the compression side with a subvalve 33a and with the upper chamber 24 through a subpassage 34 at both the extension and compression sides. A shutter 35 from the motor 7 is rotatably inserted into the communication hole 31 through a connecting rod 36, and three types of holes 38, 39 and 40 are formed at three positions angularly displaced at predeterminedangle on the circumference of the shutter 35.

When the shutter 35 is angularly displaced at a predetermined angle by the motor 7 to communicate only the hole 38 with the subpassage 32, in the case where the rod 22 falls to be compressed, the subvalve 32a is closed. In the case where the rod 22 rises to be extended. the subvalve 32a is opened, the oil 0 in the upper chamber 24 flows to the subpassage 32 to increase the diameter of the orifice, thereby obtaining first mode attenuating force characteristics which are soft at the extension side and hard at the compression side as illustrated in Fig. 3. Then, when the other hole 39 communicates with the subpassage 33 by the motor 7,, the subvalve 33a is also opened to increase the diameter of the orifice only in the case where the rod 22, on the contrary, falls to be compressed. Thus, second mode attenuating force characteristics which are hard at the extension side and soft at the compression side are obtained as illustrated in Fig. 3. Furthert when the other hole 40 communicates with the subpassage 34 by the motor 7, the oil 0 always flows to the subpassage 34 to increase the diameter of the orifice, and hence third mode attenuating force characteristics which are slightly soft at both the extension and compression sides are obtained as illustrated in Fig. 3. Thus, three types of the modes of the attenuating force characteristics can be attained by the motor 7.

Then, the operation of this embodiment will be described by referring to a flow chart of Fig. 4. When the vehicle travels, the vehicle speed V is read at step SI. The output Ln of the road surface sensor 10 is read at step S2. Then, the vehicle speed V is compared -with the set vehicle speed Vsi at step S3 to check a travel state. In this case, as practical values, Lo = 0.5m and At = 0.03 sec. are, for example. employed. Then, Vs1 = 60 km/hr is obtained.

Then. at the time of a low speed lower than the set vehicle speed Vsi, the flow advances to step S4, the road surface sensor 10 is fixed to a shortest distance in the state directed directly down by AL1 = 0 = 0, and the delay time AT is calculated at step S4. Then, the delay time AT is calculated by subtracting the delay time At of the whole control system from the time Lo/V when the front wheel 2 reaches the road surface detecting position (Lo) in response to the vehicle speed V to be adjusted in a decreasing function manner with respect to the vehicle speed V as shown by delay time characteristics in Fig. 5(a). Thus, in the case where the vehicle speed V is low and the front wheel 2 reaches relatively slowly to the road surface detecting position of the road surface sensor 10, the delay time AT is also increased correspondingly.

Then, at step SS, the height A H of the roughness of the road surf ace is calculated. At step S6, time hysteresis data Ah of the height AH of the road surface is formed. At step S7, road surface height information Ah (AT) necessary to change the attenuation force this time is calculated in dependency an the time hysteresis data Ah and the calculating period of a microcomputer. At step S8, attenuating force characteristics adapted for the road surface height information Ah is determined, and the attenuating force switching signal is simultaneously outputted to the motors 7, 7 of the shock absorbers 20. 201 of the front and rear wheel suspensions 5.. 51 after the delay time AT has elapsed., Then, in the case where the above-described vehicle speed V is low, the attenuation force switching signal is slowly outputted at a longer delay time AT, thereby switching the attenuation force variable apparatus 30 of the front wheel suspension 5 to a suitable attenuation force at the optimum timing substantially coincident with the case where at least the front wheels 2 reach the road surface detecting position.

AS shown in Fig. 6, when the road surface sensor 10 detects a projection A, the attenuation force switching signal of the second mode of Fig. 3 is outputted to the motors 7. 7', and the attenuation force variable apparatus 30 of the front wheel suspension 5 is switched to the -25characteristics. Thus, in the case where the front wheels 2 actually travel on the protrusion A to move above the protrusion A, the attenuation force variable apparatus 30 actuates the attenuation which is soft at the compression side and hard at the extension side. Then, in the case where the rear wheels 3 travel the protrusion A, since the rear wheel suspensions 51 are already switched to the same characteristics, the attenuation force variable apparatus 30 similarly actuates the attenuation to suppress the upward movement of the vehicle body 1.

On the other hand, when the road surface sensor 10 detects a recess B, the attenuation force switching signal of the f irst mode of Fig. 3 is outputted to the motors 7, 71 this time. In the case where the front wheels 2 and the rear wheels 3 actually travel the recess B tc move downwardly, the attenuation force variable apparatus 30 of the front and rear wheel suspensions 5, 5 1 actuates the attenuation which is soft at the extension side and hard at the compression side to suppress the downward movement of the vehicle body 1. Thus, the vehicle body 1 of the vehicle is reliably controlled to hold an attitude which moves up and down less than the protrusion A and the recess B of the road surface.

Then, if the vehicle speed V is accelerated equal to or faster than the set vehicle speed Vsl, the flow advances -26from the step S3 to step S9 of the flow chart of Fig. 4. At step S9-, it is compared with the set vehicle speed Vs2 controllable in the case where the sensor is moved mostly forwardly. In this case, practical values are set to Lo = 0.5m. At = 0.03 sec. and ALmax = 0.33m. Then, Vs2= 100 km/hr is attained.

At the time of an intermediate speed lower than the set vehicle speed Vs2, the flow advances to step S10. At step S10, AT = 0 is set fixedly. In this case, the sensor horizontal displacement amount AL1 is calculated by subtracting the sensor front-and-rear shortest distance Lo from the distance v-At advancing in response to the vehicle speed V and the delay time AT of the whole control system as shown in Fig. 5 (b) - At step S11, the height AH of the roughness of the road surface is calculated similarly to the above. At step S12, the displacement signal is outputted to the displacement apparatus 11. The road surface sensor 10 itself is moved in the state directed directly downwardly,, and the road surface detecting position is moved forwardlv of the front wheel 2 at the sensorhorizontal displacement amount ALl.

In the case where the front wheel 2 quickly reaches the road surface detecting position as the vehicle speed V is accelerated, the road surface position is so controlled by the movement of the road surface sensor 10 itself in -27response thereto as to be separately forwardly of the vehicle'body, thereby always obtaining the delay time 4t of. the whole control system. Thus, even if the attenuating force characteristics adapted for the height AH of the roughness of the road surface is determined and then the attenuation force switching signal is outputted, similarly to the above, to the motors 7, 71 of the shock absorbers 20, 201 of the front and rear wheel suspensions 5, 51, the attenuation force variable apparatus 30 of the front wheel suspension 5 is switched to a suitable attenuation force at the optimum timing substantially coincident with the arrival of at least the front wheels 2 at the road surface detecting position. Theref ore, even at the time of the intermediate speed, in the case where the f ront wheels 2 and the rear wheels 3 reach the projection A and the recess B of the road surface, the front and rear wheel suspensions 5, 51 actuate the attenuation to stably control the attitude of the vehicle.

Further, at the time of the high speed equal to or faster than the abovedescribed set vehicle speed Vs2, the f low advances from step S9 to step S13. In this vehicle speed range, sensor inclined angles 0 are, for example, respectively set at the vehicle speeds V to 0 = 30 degrees in the case of Vs2:! V < Vs3 (120 km/hr). 0 40 degrees in the case of Vs3 5 V < Vs4 (140 km/hr), 0 50 degrees in -28the case of Vs4 z V < VsS (150 km/hr) and 0 = 55 degrees in the case of VsS 5 V < Vs6 (180 km/hr) like the sensor inclined angle characteristics in Fig. 5(c). Then, at the time of the set vehicle speed Vs3 or less,, the flow advances to step S14, and the road surface sensor 10 itself is inclined further at 30 degrees forwardly from the state directed directly downwardly in the state held at the sensor maximum displacement amount ALmax. Thus, the road surface detecting position is moved with margin further forwardly from the position horizontally moved to the maximum limit in accordance with the angular change of the road surface sensor 10 itself. Even if the vehicle speed V is further accelerated, the delay time At of the whole control system is attained.

Then, the flow advances to step S15, and the sensor inclined displacement amount AL2 of this case is calculated. At step S16, similarly to the time of the low speed, the delay time AT is calculated by subtracting the delay time AT of the whole control system from the time (Lo + ALmax + AL2)/V for the front wheels 2 to reach the position of the whole length of this case in response the vehicle speed V, and the height AH of the roughness of the road surface is calculated by the sensor inclined angle 0. Then, at step S17, time hysteresis data AT(n) of the delay time AT is formed. At step S18, time hysteresis data Ah of -29the height AH of the road surf ace is f ormed. At step S19 road surface height information Ah (AT) necessary to change the attenuation force this time is calculated in dependency on the time hysteresis data AT(n), the Ah and the calculating period of the microcomputer. At step S20,, attenuating force characteristics adapted for the road surf ace height inf ormation Ah (AT) are determined, and the attenuation force switching signal is outputted af ter the delay time AT is elapsed.

As described above. at high speed, the road surface sensor 10 is directed forwardly, the road surface information is obtained in the sensor inclined state, and controlled to be outputted at the delay time thereby for the attenuation force variable apparatus 30 of the front wheel suspension 5 to be switched to a suitable attenuation force similarly at the optimum timing substantially coincident with the arrival of at least the front wheels 2 at the road surface detecting position. In the case where the vehicle speed is equal to or faster than the set vehicle speed Vs3, the flow advances from step S13 to S21 and the following stepst and is similarly controlled. Then, even at high speed, in the case where the front wheels 2 and the rear wheels 3 reach the projection A and the recess B of the road surface, the front and rear wheel suspensions 5, 51 actuate -30the attenuation to reliably stably control the attitude of the vehicle.

In the case where the road surface sensor 10 detects a flat road surface, the attenuation force variable apparatus 30 is controlled to the characteristics of the third mode which is slightly soft at both the extension and compression sides. thereby improving the riding feel.

The embodiments of this invention have been described, and the horizontal displacement and the angular displacement of the road surface sensor may be controlled arbitrarily in combination. This invention has been also described with respect to the semiactive suspension system, but may also be applied to an active suspension system, a vehicle behavior characteristic changing means.

As described above, according to this invention, the road surface sensor is provided at the vehicle body and so constituted under the control of switching suspension characteristics in response to the rough state of the road surface as to always detect the road surface as near as the vehicle axle by the road surface sensor. Theref ore, the road surf ace can be accurately detected in the state of less influence of pitching of the vehicle, and the control accuracy is also improved. Since the road surf ace sensor itself is displaced or angularly displaced against the delay of the control system to move the road surface detecting position forwardly, thereby always obtaining the delay time of the control system. The delay time is calculated in this state as required to so control as to output the attenuation force switching signal, the suspension characteristics can be always switched at the optimum timing against the delay of the control system, and the attitude of the vehicle can be reliably stabilized in the whole travel area.

At intermediate speed., the road surface sensor is displaced, and at high speed, the road surface sensor is angularly displaced. Accordingly, projection of the road surface sensor is decreased to reliably displace the road surface detecting position to a high speed range. Since the road surface sensor is angularly displaced by a predetermined displacement amount, the operation is reliably achieved. Since the road surface sensor is projected forwardly of the vehicle body only at the time of the intermediate and high speeds and the projection is relatively small in this case, the sensor does not disturb or damage the vehicle at the time of turning at an acute angle of an extremely low speed. The road surface sensor need or may not affect or influence the design of the vehicle.

Fig. 8 shows a suspension control system for a vehicle according to another embodiment of this invention.

Referring first to Fig. 8, a suspension control system for a vehicle will be described. Numeral 1 indicates a vehicle body. Suspensions 5 and 51 are respectively interposed between wheel axles 4 of a front wheel 2 and a rear wheel 3 and the vehicle body 1. The front wheel suspension 5 is provided in parallel with an attenuation force variable shock absorber 20 with a spring 6 between the vehicle body 1 and the wheel axle 4, and an electric motor 7 is provided as an actuator for controlling to switch an attenuation force at its upper end of the shock absorber 20. the rear wheel suspension 51 is similarly constituted to the front wheel suspension 5, wherein the same components are denotes by the same numerals with "dash"., and the description of the operation will be omitted.

A road surface sensor 10 for detecting a roughness of a road surface is mounted at a sensor actuation apparatus 60 to change a road surface detecting position. Further, a vehicle speed sensor 13 for detecting a travel state of the vehicle is provided. Signals from the road surface sensor 10 and the vehicle speed sensor 13 are inputted to a control unit 14. The motors 7 and 71 of the front and rear wheel suspensions 5 and 5', the sensor actuation apparatus 60 is actuated in accordance with the output signal of the control unit 14.

The control unit 14 selects an attenuation force -33switching signal responsive to road surf ace inf ormation, and further controls an output timing of the attenuation force switching signal against the delay of a control system and a road surface detecting position. That is, if the vehicle speed is designated by V, the delay time of the whole control system by At, the shortest front-and-rear distance between the sensor and a center of a tire by Lo, a sensor displacement amount of the sensor by AL, a delay time to be adjusted when the road surface roughness information is used for controlling by AT, and the following equation is satisfied.

(Lo + AL)V = At + AT Then, when the vehicle speed V is low equal to or lower than a set vehicle speed Vs (Lo/At). the delay time AT is determined in a sensor fixed state of AL = 0 by AT = Lo/V At, and the attenuation force switching signal is outputted to front and rear wheel suspensions 5, 51. When the vehicle speed V is intermediate and high equal to or faster than the set vehicle speed Vs and impossible to calculate the delay time, AT = 0 is satisf ied. Then, the sensor travel amount AL is determined by AL = V-At = Lo, and a travel signal is outputted to the sensor actuation apparatus 60.

Referring to Figs. 9 to 11, an operation of yet another embodiment of this invention is shown. When the -34vehicle travels, the vehicle speed V is read at step S1. A sensor ppsition of AL = 0 is f ixed to a shortest distance at step S2. At step S3, the vehicle speed V is compared with the set vehicle speed VsO (Lo/At) at step S3 to check a travel state. In this case, as practical values, Lo = 0.5m and At = 0.03 sec. are, for example, employed. Then, vsl = 60 km/hr is obtained.

Then, at the time of a low speed lower than the set vehicle speed VsO, the flow advances to step S4, the road surface sensor 10 is fixed to a shortest distance in the state directed directly down by AL1 = 0 = 0, and the delay time AT is calculated at step S4. Then, the delay time AT is calculated by subtracting the delay time At of the whole control system from the time Lo/V when the front wheel 2 reaches the road surface detecting position (Lo) in response to the vehicle speed V to be adjusted in a decreasing function manner with respect to the vehicle speed V as shown by delay time characteristics in Fig. 10(a). Thus, in the case where the vehicle speed V is low and the front wheel 2 reaches relatively slowly to the road surface detecting position of the road surface sensor 10, the delay time AT is also increased correspondingly.

Then, at step S6, the height A H of the roughness of the road surface is calculated. At Step S7, time hysteresis -35data Ah of the height AH of the road surface is formed. At step S8, road surface height information Ah (AT) necessary to change the attenuation force this time is calculated in dependency on the time hysteresis data Ah and the calculating period of a microcomputer. At step S9, attenuating force characteristics adapted for the road surface height information Ah is determined. and the attenuating force switching signal is simultaneously outputted to the motors 7, 7 of the shock absorbers 20, 201 of the front and rear wheel suspensions 5, 51 af ter the delay time AT is elapsed. Then, in the case where the above-described vehicle speed V is low, the attenuation force switching signal is slowly outputted at a longer delay time AT, thereby switching the attenuation force variable apparatus 30 of the front wheel suspension 5 to a suitable attenuation force at the optimum timing substantially coincident with the case where at least the front wheels 2 reach the road surface detecting position.

As shown in Fig. 11, when the road surf ace sensor 10 detects a projection A, the attenuation force switching signal of the second mode of Fig. 3 is outputted to the motors 7, 71, and the attenuation force variable apparatus 30 of the front wheel suspension 5 is switched to the characteristics. Thus, in the case where the front wheels 2 actually travel on the protrusion A to move above the protrusion A, the attenuation force variable apparatus 30 actuates-. the attenuation which is soft at the compression side and hard at the extension side. Then, in the case where the rear wheels 3 travel the protrusion A, since the rear wheel suspensions 51 are already switched to the same characteristics, the attenuation force variable apparatus 30 similarly actuates the attenuation to suppress the upward movement of the vehicle body 1.

On the other hand, when the road surface sensor 10 detects a recess B, the attenuation force switching signal of the f irst mode of Fig - 3 is outputted to the motors 7, 71 this time. In the case where the front wheels 2 and the rear wheels 3 actually travel the recess B to move downwardly, the attenuation force variable apparatus 30 of the front and rear wheel suspensions 5, 51 actuates the attenuation which is soft at the extension side and hard at the compression side to suppress the downward movement of the vehicle body 1. Thus,, the vehicle body 1 of the vehicle is reliably controlled to hold an attitude which moves up and down less than the protrusion A and the recess B of the road surface.

Then, at the time of intermediate and high speeds equal to or faster than the set vehicle speed VsO, the flow advances from the step S3 to step S10 of the flow chart of Fig. 9. In terms of cL = Ll, a road surf ace detecting -37position is set like a curve bl of sensor travel characteristic of Fig. 10(b), and the travel signal is outputted. Then, the road surface sensor 10 itself projects forwardly of the vehicle body by the displacement apparatus 11, and the road surface detecting position is displaced forwardly at a distance corresponding to the sensor travel amount Ll. Thus, as the vehicle speed V is accelerated, the front wheel 2 rapidly reaches the road surface detecting position, the road surface detecting position is separated forwardly of the vehicle body with margin. Thus, the delay time At of the whole control system is obtained again similarly to the above-described operation. and the delay time At can be calculated.

At the time of an intermediate speed lower than the set vehicle speed Vs2, the flow advances to step S10. At step S10, AT = 0 is set f ixedly. In this case, the sensor horizontal displacement amount AL1 is calculated by subtracting the sensor front-and-rear shortest distance Lo from the distance V.At advancing in response to the vehicle speed V and the delay time AT of the whole control system as shown in Fig. 6(b) - At step S11, the height AH of the roughness of the road surface is calculated similarly to the above. At step S12, the displacement signal is outputted to the displacement apparatus 11. The road surface sensor 10 itself is moved in the state -38directed directly downwardly, and the road surface detecting position is moved forwardly of the front wheel 2 at the sensor horizontal displacement amount ALl.

When the vehicle speed V is accelerated to the set vehicle speed Vsl or more, the flow advances to steps S11 to S13 of a f low chart of Fig. 9, and the sensor travel amount &L is increased to L2, and similarly controlled. In this case, practical values are set to Lo = 0. Sm, At = 0. 03 sec. and the maximum sensor travel amount is set, for example,. to AL = 0. 5m, and then the controllable maximum vehicle speed becomes 120 km/hr to be sufficiently practical.

In the case where the road surface sensor 10 detects a flat road surface. the attenuation force variable apparatus 30 are controlled to the characteristics of the third mode which is slightly soft at both the extension and compression sides, thereby improving the riding feel.

As the embodiment of this invention,, the semiactive suspension system has been described, and this invention may also be applied to an active suspension system, vehicle behavior characteristics changing means.

As described above, according to this invention, the road surface sensor is provided at the.vehicle body and so constituted under the control of switching suspension characteristics in response to the rough state of the road -39surface as to always detect the road surface as near as the vehicle axle by the road surface sensor. Theref ore, the road surf ace can be accurately detected in the state of less influence of pitching of the vehicle, and the control accuracy is also improved. Since the road surf ace sensor itself is displaced or angularly displaced against the delay of the control system to move the road surface detecting position forwardly, thereby always obtaining the delay time of the control system. The delay time is calculated in this state as required to so control as to output the attenuation force switching signal, the suspension characteristics can be always switched at the optimum timing against the delay of the control system, and the attitude of the vehicle can be reliably stabilized in the whole travel area. Further, the projection of the road surface sensor may be decreased, and the delay time can be easily controlled.

Since the road surface sensor is adapted to be displaced in f ront-and-rear direction by the displacement apparatus, the structure is simple with high practicability. The road surface sensor is projected forwardly of the vehicle body gradually as the vehicle is accelerated, and hence the sensor does not disturb or damage the vehicle at the time of turning at an acute angle at an extremely low speed. The road surface sensor may not affect influence to the -4odesign of the vehicle.

Figg. 12 to 14 show still another embodiment of this invention. When the vehicle travels, the vehicle speed V is read at step S1. At step S2, the vehicle speed V is compared with Lo/At to check a travel state. In this case. as practical values, Lo = 0.5m and At = 0.03 sec. are, for example, employed. Then, Lo/At = 60 km/hr is obtained. Then, at the time of a low speed lower than the km/hr, the flow advances to step S3. At step S3, in terms of AL = 0, the sensor position is fixed to a shortest distance, and the delay time ATf against the front wheel suspension 5 is adjusted in response to the vehicle speed V in accordance with the above-described equation. The delay time ATf of this case is indicated by a solid line in Fig. 5(a) to the vehicle speed V, and adjusted in a decreasing function manner to a predetermined vehicle speed Lo/At. At step S4 road surface roughness information by the road surface sensor 10 is read. At step S6, an attenuation force variable signal adapted for the roughness information is simultaneously outputted to motors 7, 71 of shock absorbers 20, 201 of front and rear wheel suspensions 5, 5r at the timing when the delay time AT is elapsed.

The delay time ATr against the rear wheel suspension 51 is adjusted in response to the vehicle speed V in accordance with the above-described equation. The delay -41time 4Tr of this case is adjusted in a smoothly decreasing function manner as shown by a broken line in Fig. 5 (a) to the vehicle speed V. Therefore. the delay time &Tr is always delayed to be largely set to the delay time &Tf. Then,, the flow advances to step S4. At step S4,, road surface roughness information of the road surface sensor 10 is read. At step SS, the attenuation force variable signal adapted for the roughness information is outputted to the motor 7 of the shock absorber 20 of the front wheel suspension 5 at the timing when the delay time ATf is elapsed. The similar attenuation force variable signal is delayed by the delay time ATr, and outputted to the motor 71 of the shock absorber 201 of the rear wheel suspension 5 As shown in Fig. 6, when the road surface sensor 10 at the front side of the vehicle body 1 detects a projection Af the attenuation force variable signal of the second mode of Fig. 3 is outputted. That is. when the front wheels 2 first reaches the projection A, the attenuation force variable signal is outputted to the motor 7 of the front wheel suspension 5, and the attenuation force variable apparatus 30 can actuate the characteristics of the second mode. Then, in the case where the front wheels 2 actually travel on the protrusion A to move above the protrusion Af the attenuation force variable apparatus 30 actuates the attenuation which is soft at the compression side and hard at the extension side. Then, in the case where the rear wheels 3 travel the protrusion Ap the rear wheel suspensions 51 can be already actuated in the same characteristics. Thus, even if the front wheels 2 are transferred to next rough surface, the attenuation is actuated similarly by the rear wheel suspension 51 irrespective of the transfer, thereby reliably suppressing the upward movement of the vehicle body 1.

On the other hand, when the road surface sensor 10 detects a recess B, the attenuation force variable signal of the first mode of Fig. 3 is outputted to the motors 7 at the timing of the delay time ATf, then outputted to the motor 71 at the timing of the delay time ATr delayed. Thus,, in the case where the f ront wheels 2 and the rear wheels 3 sequentially travel the recess B to displace down. the attenuation force variable apparatuses 30 of the front and rear wheel suspensions 5, 5 actuate the attenuation which is soft at the extension side and hard at the compression side in thecharacteristics of the first mode to reliably suppress the downward displacement of the vehicle body 1. Thus, the vehicle body 1 of the vehicle is so controlled as to hold an attitude of less up-and-down displacements against the projection A and the recess B of the road surface.

Then, if the vehicle speed V is accelerated equal to or faster than the above-described 60 km/hr, the flow advances from the step S2 to step S6 of the f low chart of Fig. 18. The delay time ATf is f ixed to the f ront wheel suspension 5 in terms of ATf = 0. The sensor displaced amount AL is adjusted in response to the vehicle speed V in accordance with the abovedescribed equation. The sensor displaced amount AL of this case becomes as shown in Fig. 5(b) to the vehicle speed V, and adjusted in an increasing function manner after a predetermined vehicle speed Lo/At.

In this case, the road surface sensor 10 is sequentially moved forwardly at a distance corresponding to the delay time At of the whole control system f rom the position of a shortest front-and-rear distance near the front wheel 2 by the displacement apparatus 11 and the road surface is early detected. Thus. the road surface roughness information is obtained early by the road surface sensor 10, thereby absorbing the delay of the whole control system. In this case, practical values are set to Lo = 0.5m, At = 0.03 sec. and the maximum sensor displaced amount AL is, for example set to AL = 0.5m. Then, controllable maximum vehicle speed becomes 120 km/hr to be sufficiently practical. on the other hand, the delay time 4Tf is similarly adjusted in this case to the rear wheel suspension 51 and determined.

The flow then advances to steps S4 and SS of the flow chart of f ig. 4. Then, the attenuation force variable signal adapted for the roughness information of the road surface is immediately outputted to the front wheel suspension 5. The attenuation force variable signal is delayed by the delay time 4Tr and outputted to the rear wheel suspension 51. Then, in the case where the f ront wheels 2 and the rear wheels 3 sequentially reach and travel the projection A and the recess B of the road surface. the front and rear wheel suspensions 5, 51 similarly actuate the attenuation to change the suspension characteristics, thereby stably controlling the attitude of the vehicle.

In the case where the road surface sensor 10 detects a flat road surface, the attenuation force variable apparatus 30 is controlled to the characteristics of the third mode which is slightly soft at both the extension and compression sides, thereby improving the riding feel.

The embodiments of this invention have been described, and this invention is not limited to the particular embodiments.

As described above, according to this invention, the road surface sensor is provided at the vehicle body and so constituted under the control of the attitude of the vehicle for changing suspension characteristics in response -45to the rough state of the road surface as to always detect the road surf ace as near as the vehicle axle by the road surface sensor. Therefore, the road surface can be accurately detected in the state of less influence of pitching of the vehicle. and the control accuracy is also improved. The delay time is adjusted or the sensor displaced amount is adjusted to the sensor mounted position and the delay time of the whole control system in the front wheel suspension to control to input the attenuation force variable signal, and hence the characteristics of the suspension can be suitably changed in a wide vehicle speed range. At the time of intermediate and high speeds, the road surface sensor is controlled to be sequentially traveled forwardly so as to absorb the delay time, and hence the suspension characteristics in the respective traveling states can be suitably changed. Thus, the performance of changing the suspension characteristic of the wide vehicle speed range can be sufficiently obtained, and easily controlled.

Since the road surface sensor is constituted to move in front-and-rear direction by the displacement apparatus, its structure is simple and practicability is high. Since the road surface sensor projects forwardly of the vehicle body only at the time of inte=nediate and high speeds, it is not disturbed or damaged at the time of turning at an -46extremely low speed. The road surface sensor does not affect influence to the design of the vehicle.

Referring to Figs. 20 and 21, still another embodiment of the invention will be described.

When the vehicle speed V is accelerated equal to or faster than the abovedescribed 60 km/hr, the flow advances from the step S2 to step S6 of the flow chart of Fig. 4. The delay time 4Tf is fixed to the front wheel suspension 5 in terms of ATf = 0. The sensor displaced amount &L is adjusted in response to the vehicle speed V in accordance with the abovedescribed equation. The sensor displaced amount 4L of this case becomes as shown in Fig. 5(b) to the vehicle speed V, and adjusted in an increasing function manner after a predetermined vehicle speed Lo/4t.

In this case, the road surface sensor 10 is sequentially moved forwardly at a distance corresponding to the delay time At of the whole control system f rom the position of a shortest front-and-rear distance near the front wheel 2 by the displacement apparatus 11 and the road surface is early detected. Thus, the road surface roughness information is early obtained by the road surface sensor 10, thereby absorbing the delay of the whole control system. In this case, practical values are set to Lo = 0.5m, 4t = 0.03 sec. and the maximum sensor displaced amount 4L is, for example set to 4L = 0.5m. Then, -47controllable maximum vehicle speed becomes 120 km/hr to be sufficiently practical. On the other hand, the delay time ATf is similarly adjusted in this case to the rear wheel suspension 51 and determined.

The flow then advances to steps S4 and SS of the flow chart of Fig. 4. Then, the attenuation force variable signal adapted for the roughness information of the road surface is immediately outputted to the front wheel suspension 5. The attenuation force variable signal is delayed by the delay time &Tr and outputted to the rear wheel suspension 51. Then,, in the case where the f ront wheels 2 and the rear wheels 3 sequentially reach and travel the projection A and the recess B of the road surface, the front and rear wheel suspensions 5, 51 similarly actuate the attenuation to change the suspension characteristics, thereby stably controlling the attitude of the vehicle.

As described above, according to this invention, the road surface sensor is provided at the vehicle body and so constituted under the control of the attitude of the vehicle for changing suspension characteristics in response to the rough state of the road surface as to always detect the road surf ace as near as the vehicle axle by the road surface sensor. Therefore, the road surface can be accurately detected in the state of less influence of pitching of the vehicle, and the control accuracy is also improved. The delay time is adjusted or the sensor displaced amount is adjusted to the sensor mounted position and the delay time of the whole control system in the front wheel suspension to control to input the attenuation force variable signal, and hence the characteristics of the suspension can be suitably changed in a wide vehicle speed range.

Since the rear wheel suspension is so controlled as to input the attenuation force variable signal by delaying at the delay time considered f or the wheel base in a whole vehicle speed range, the suspension characteristics can be reliably changed next to the front wheel on the same roughness surface. The rear wheel suspension is separately controlled thereby to process the case where the roughnesses occur in a short period, thereby providing high utility.

Claims

1. A suspension control system for a vehicle having a vehicle body and a plurality of vehicle wheels, a suspension interposed between said body and said wheels, a vehicle speed sensor mounted on said vehicle for detecting a speed of said wheel and for generating a vehicle speed signal, a shock absorber with a spring and a variable attenuation systemr and an actuator provided in said shock absorber for controlling an attenuation force, the system comprising:

a road surface sensor mounted under a front side of said vehicle body for detecting a roughness of a road surface in front of said wheel and for producing a road surface condition signal; a displacement apparatus connected to said road surface sensor for forwardly and rearwardly moving said road surface sensor; an angular displacement apparatus engaged with said displacement apparatus for rotatably changing an angle against said road surface; and control means responsive to said vehicle speed signal and said road surface condition signal for processing and outputting an actuating signal selectively to said displacement apparatus and said angular displacement apparatus without delay and for generating an adjusted attenuation signal so as to enable an optimum control of said suspension and a stable attitude control of said vehicle in any driving condition.

2. A suspension control system according to claim 1, wherein; said control means produces said actuating signal -so- to direct said road surface sensor in a substantially perpendicular direction against said road surface in a shortest length of said displacement apparatus and said attenuation signal to adjust a delay time in dependency on a predetermined whole delay time when said vehicle speed is low; said control means produces said actuating signal to direct said road surface sensor in a substantially perpendicular direction against said road surface and to substantially horizontally and forwardly move said road surface sensor and said attenuation signal without delay in dependency on said vehicle speed and said predetermined whole delay time when said vehicle speed is intermediate; and said control means produces said actuating signal to direct said road surface sensor in an inclined angle against said road surface in a longest length of said displacement apparatus and said attenuation signal to adjust said delay time in dependency on said predetermined whole delay time at each said inclined angle when said vehicle speed is high.

3. A suspension control system according to claim 1 or claim 2, wherein said delay time is adjusted to a decreasing function of said vehicle speed; and said length and inclined angle of said road surface sensor is determined in an increasing function of said vehicle speed.

4. A suspension control system for a vehicle in which an actuation controller for a road surface sensor is hung from a front side of a vehicle body to be operated by an electric signal from a control unit to project forwardly from a position of a shortest front-and-rear distance thereby sequentially displace W51a road surface detecting position.

:

5. A suspension control system for a vehicle having a vehicle body and a plurality of vehicle wheels, a suspension interposed between said body and said wheel, a vehicle speed sensor mounted on said vehicle for detecting a speed of said wheel and for generating a vehicle speed signal, a shock absorber with a spring and a variable attenuation system, and an actuator provided in said shock absorber for controlling an attenuation force. the system comprising a road surface sensor mounted under a front side of said vehicle body for detecting a roughness of a road surface in front of said wheel and for producing a road surface condition signal; a displacement apparatus connected to said road surface sensor for forwardly and rearwardly moving said road surface sensor; and control means responsive to said vehicle speed signal and said road surface condition signal for processing and outputting a stepped displacing signal to said displacement apparatus without delay and for generating an adjusted attenuation force switching signal so as to adjust the delay time by a period of time for at least the front wheel to reach the road surface detecting position in response to its vehicle speed and the delay time of a whole control system to output the attenuation force switching signal to the actuator.

6. A suspension control system for a vehicle having a vehicle body and a plurality of vehicle wheels, a suspension interposed between said body and said wheel, a vehicle speed sensor mounted on said vehicle for detecting a speed of said wheel and for -52generating a vehicle speed signal. a shock absorber with..a spring and a variable attenuation system, and an actuator provided in said shock absorber for controlling an attenuation force, the system comprising:

a road surface sensor mounted under a front side of said vehicle body for detecting a roughness of a road surface in front of said wheel as to be displaced forwardly from the vicinity of the front wheel to change a road surface detecting position and a control unit for processing signals from the road surface sensor and a travel state to actuate the actuator and a sensor displacing apparatus.

7. A suspension control system for a vehicle having a vehicle body and a plurality of vehicle wheels, a suspension interposed between said body and said wheel, a vehicle speed sensor mounted on said vehicle for detecting a speed of said wheel and for generating a vehicle speed signal, a shock absorber with a spring and a variable attenuation system. and an actuator provided in said shock absorber for controlling an attenuation force, the system comprising:

a road surface sensor mounted under a front side of said vehicle body to move from the vicinity of the front wheel forwardly to change a road surface detecting position for detecting a roughness of a road surface in front of said wheel and for producing a road surface condition signal; and control means responsive to said vehicle speed signal and said road surface condition signal for adjusting a delay time or a sensor displaced amount against said actuator of said front wheel suspension to output an attenuation force variable signal -53responsive to a roughness of a road surface and adjusting a delay time against said actuator of said rear wheel suspension to output an attenuating force variable signal responsive to a roughness of the road surface.

8. A suspension control system for a vehicle, substantially as herein described, with reference to, and as illustrated in, the accompanying drawings.

9. A vehicle comprising a suspension control system as claimed in any of the preceding claims.

z