Automotive suspension system with variable damping characteristics

Abstract

In order to ensure riding comfort and driving stability in an automotive suspension system, the nature of the effect of the damping force generated by the suspension system is observed. When the damping characteristics of the suspension system are too hard, resulting in amplification of vibrations in the suspension system, the damping characteristics are softened to ensure satisfactory riding comfort. Therefore, according to the present invention, an automotive suspension system has variable damping characteristics which depend on the nature of the damping force produced in response to bounding and/or rebounding motion of the vehicle so as to optimize damping characteristics to achieve both riding comfort and driving stability. In the preferred embodiment, a suspension control system uses the vibration frequency of a sprung mass and the relative speed between the sprung mass and an unsprung mass as control parameters representing the nature of damping force.

What is claimed is: 
     
       1. A suspension control system for an automotive vehicle comprising: a vehicular suspension system with damping characteristics variable at least between a first harder suspension mode and a second softer suspension mode;   a first sensor means for monitoring vertical displacement of a vehicle body within a gravity field and producing a first sensor signal indicative of the vertical speed of said vehicle body;   a second sensor means for monitoring relative distance between the vehicle body and a vehicular wheel assembly and producing a second sensor signal indicative of the relative speed between said vehicle body and said wheel assembly;   a controller responsive to said first and second sensor signals for predicting the effect of damping characteristics of the suspension system .[.from.]. between a first condition in which said damping characteristics of the suspension system act to amplify vehicle body vibrations and a second condition in which damping characteristics of the suspension system act to absorb vehicle body vibrations, said controller causing said vehicular suspension system to assume said second softer suspension mode when said first condition is predicted and to assume said first harder suspension mode when said second condition is predicted; .Iadd.and   means responsive to said second sensor signal for selectively enabling and disabling operation of said controller for varying damping characteristics depending upon a predetermined magnitude of relative speed. .Iaddend.   
     
     
       2. The suspension control system as set forth in claim 1, wherein said first sensor means comprises a sensor adapted to detect acceleration of the vehicle body and .[.producing.]. .Iadd.produce .Iaddend.an acceleration indicative signal. 
     
     
       3. The suspension control system as set forth in claim 2, wherein said second sensor means comprises a sensor adapted to monitor relative displacement between said vehicle body and said wheel assembly, an integrator for integrating the relative displacement indicative output of said sensor and an arithmetic means for deriving said relative speed based on said integrated value by differentiating said integrated value. 
     
     
       4. The suspension control system as set forth in claim 3, wherein said suspension system comprises a hydraulic shock absorber with damping characteristics variable at least between said first mode and said second mode. 
     
     
       5. The suspension control system as set forth in claim 4, wherein said hydraulic shock absorber has upper and lower fluid chambers filled with a working fluid and of variable volumes according to a piston stroke, said shock absorber being provided with a flow control valve which is operable in either one of a first mode position, in which it restricts the rate of flow of working fluid between said upper and lower fluid chambers to a minimum rate, and a second mode position in which it allows fluid flow between said chambers at a maximum rate. 
     
     
       6. The suspension control system as set forth in claim 3, wherein said suspension system comprises a stabilizer with stiffness variable at least between said flow mode and said second mode. 
     
     
       7. The suspension control system as set forth in claim 3, wherein said suspension system comprises a pneumatic spring means exerting a pneumatic damping force variable at least between said first mode and said second mode. 
     
     
       8. In an automotive suspension system with damping characteristics variable at least between a first harder suspension mode and a second softer suspension mode, a process for suppressing vibration of a vehicle body comprising the steps of: detecting the vertical speed of said vehicle body .Iadd.using a first sensor and producing a first sensor signal indicative of said vertical speed.Iaddend.;   detecting the relative speed between said vehicle body and a vehicular wheel assembly .Iadd.using a second sensor and producing a second sensor signal indicative of relative speed;   using a controller for .Iaddend.predicting the effect of damping force produced by said suspension system based on said vehicle body speed and said relative speed .[.from.]. between a first condition in which damping characteristics act to amplify vehicle body vibrations, and a second condition in which damping characteristics of the suspension system act to absorb vehicle body vibrations; .[.and.].   causing said vehicular suspension system to assume said second softer suspension mode when said first condition is detected, and to assume said first harder suspension mode when said second condition is detected.Iadd.; and   responsive to said second sensor signal, selectively enabling and disabling operation of said controller for varying damping characteristics depending upon a predetermined magnitude of relative speed.Iaddend..   
     
     
       9. The method as set forth in claim 8, wherein said first condition is .Iadd.also .Iaddend.predicted when said vehicle body speed indicative value and said relative speed indicative value indicate action in the same direction and said second condition is predicted when said vehicle body speed indicative value and said relative speed indicative value indicate action in opposite directions. 
     
     
       10. The method as set forth in claim 9, wherein said actuating step is performed by adjusting the damping characteristics of a shock abosrber in the suspension system between a soft mode and a hard mode. 
     
     
       11. A suspension control system for an automotive vehicle comprising: a vehicular suspension system with damping characteristics variable at least between a first harder suspension mode and a second softer suspension mode;   a first sensor means for monitoring vertical displacement direction and speed of a vehicle body within a gravity field and producing a first sensor signal indicative of the direction of motion of the vehicle body in bounding and rebounding directions, and further indicative of the vertical speed of said vehicle body;   a second sensor means for monitoring relative direction of relative motion, and relative speed of motion between the vehicle body and a vehicular wheel assembly and producing a second sensor signal indicative of the direction of relative motion between the vehicle body and the vehicular wheel in bounding or rebounding directions, .Iadd.relative displacement between the vehicle body and the wheel assembly .Iaddend.and the relative speed of motion between said vehicle body and said wheel assembly;   a controller responsive to said first and second sensor signals for predicting the effect of damping characteristics of the suspension system depending on the direction of motion of said vehicle body and the direction of relative motion of said vehicle body and said vehicular wheels .[.from.]. between a first condition in which said damping characteristics of the suspension system act to .[.absorb.]. .Iadd.amplify .Iaddend.vehicle body vibrations and a second condition in which said damping characteristics of the suspension system act to absorb vehicle body vibrations, said controller causing said vehicular suspension system to assume said second softer suspension mode when said first condition is predicted and to assume said first harder suspension mode when said second condition is predicted.Iadd.; and   means responsive to said second sensor signal for selectively enabling and disabling operation of said controller for varying damping characteristics depending upon a predetermined magnitude of relative displacement.Iaddend..   
     
     
       12. In an automotive suspension system with damping characteristics variable at least between a first harder suspension mode and a second softer suspension mode, a process for suppressing vibration of a vehicle body comprising the steps of: detecting direction and speed of vertical motion of said vehicle body and producing a first signal indicative of the direction and speed of said vertical motion;   detecting direction of relative motion and speed of relative motion between said vehicle body and a vehicular wheel assembly and producing a second signal indicative of the direction of relative motion and speed of relative motion between said vehicle body and said vehicular wheel assembly;   .Iadd.using a controller for .Iaddend.predicting the effect of damping force produced by said suspension system based on said vehicle body speed and said relative speed by comparing the direction of said detected vertical motion of said vehicle body and the direction of said relative motion between said vehicle body and said vehicular wheel .[.from.]. between a first condition in which damping characteristics act to amplifying vehicle body vibrations and a second condition in which damping characteristics of the suspension system act to absorb vehicle body vibrations; and   causing said vehicular suspension system to assume said second softer suspension mode when said first condition is detected, and to assume said first harder suspension mode when said second condition is detected.Iadd.; and   responsive to said second signal, selectively enabling and disabling operation of said controller for varying damping characteristics depending upon a predetermined magnitude of relative displacement.Iaddend.. .Iadd.13. A suspension control system as set forth in claim 1 wherein said means for selectively enabling and disabling operation of said controller disables said operation of said controller when said relative speed is in a predetermined range having a limit defined by said predetermined magnitude. .Iaddend. .Iadd.14. A suspension control system as set forth in claim 1, wherein said controller derives a product of said vertical speed of said vehicle body and said relative speed and checks the polarity of said product for predicting said second softer suspension mode when the   
     
     
        polarity of said product is negative. .Iaddend. .Iadd.15.  A suspension control system as set forth in claim 1 wherein said suspension system includes a variable damping characteristics shock absorber with a rotary valve having at least two mutually different path area orifices for selective alignment with a fluid flow path for adjusting damping characteristics at least between said first harder suspension mode and said second softer suspension mode and wherein said controller causes said vehicular suspension system to assume said second softer suspension mode by driving said rotary valve to align one of said orifices having a greater path area when said first condition is predicted and to assume said first harder suspension mode by driving said rotary valve to align the other orifice having a smaller path area when said second condition is predicted. .Iaddend. .Iadd.16. A suspension control system as set forth in claim 1 wherein said second sensor means comprises a sensor for detecting relative distance between said vehicle body and said vehicular wheel assembly and means for differentiating the relative displacement. .Iaddend. .Iadd.17. A suspension control system as set forth in claim 1 wherein said second sensor means signal also represents relative displacement between said vehicle body and said wheel assembly and said means for enabling and disabling operation of said controller also enables or disables operation of said controller based upon a predetermined magnitude of relative displacement. .Iaddend. .Iadd.18. A suspension control system as set forth in claim 11 wherein said means for selectively enabling and disabling operation of said controller disables operation of said controller when said relative displacement is in a predetermined range having a limit defined by said predetermined magnitude. .Iaddend. 
     
     
        .Iadd.19.  A suspension control system as set forth in claim 18 wherein said means for selectively enabling and disabling operation of said controller disables operation of said controller when said relative displacement is within said range and said relative speed is in a predetermined range. .Iaddend. .Iadd.20. A suspension control system as set forth in claim 11 wherein said means for selectively enabling and disabling operation of said controller derives a reference value on the basis of said second sensor signal and periodically updates said reference value, derives a difference between an instantaneous relative displacement indicated by said second sensor signal and said reference value, compares said difference with said predetermined magnitude of relative distance and disables operation of said controller when said difference is less than said predetermined magnitude of relative displacement. .Iaddend. .Iadd.21. A suspension control system as set forth in claim 20 wherein said reference value is indicative of a relative distance between the vehicle body and the vehicular wheels at a neutral vehicular height position. .Iaddend. .Iadd.22. A suspension control system as set forth in claim 21 wherein said reference value is an average of a number of values of relative displacement determined based on said second sensor signal. .Iaddend. .Iadd.23. A suspension control system as set forth in claim 11 wherein said first sensor means comprises an acceleration sensor and an integrator for integrating the monitored vertical acceleration. .Iaddend. 
     
     
        .Iadd.24.  A suspension control system as set forth in claim 11, wherein said controller derives a product of said vertical speed of said vehicle body and said relative speed and checks the polarity of said product for predicting said second softer suspension mode when the polarity of said product is negative. .Iaddend. .Iadd.25. A suspension control system as set forth in claim 11 wherein said suspension system includes a variable damping characteristics shock absorber with a rotary valve having at least two mutually different path area orifices for selective alignment with a fluid flow path for adjusting damping characteristics at least between said first harder suspension mode and said second softer suspension mode and wherein said controller causes said vehicular suspension system to assume said second softer suspension mode by driving said rotary valve to align one of said orifices having a greater path area when said first condition is predicted and to assume said first harder suspension mode by driving said rotary valve to align the other orifice having a smaller path area when said second condition is predicted. .Iaddend. .Iadd.26. A suspension control system as set forth in claim 1 wherein said first sensor means comprises an acceleration sensor and an integrator for integrating the monitored vertical acceleration. .Iaddend.