Abstract:
A suspension system includes an air spring and a shock absorber disposed between the sprung and unsprung portions of a vehicle. A vehicle height sensor sends signals to a control system which adjusts the height of the vehicle by increasing or decreasing the air pressure within the spring. This same air pressure is provided to the shock absorber in order to increase the damping rate for high loads and decrease the damping rate for low loads. The air pressure to the shock absorber is provided to a valve assembly which controls fluid flow between the working chamber of the shock absorber and a reserve chamber.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a hydraulic damper or shock absorber adapted for use in a suspension system such as the suspension systems used for automotive vehicles. More particular, the present invention relates to a hydraulic damper or shock absorber for use in a suspension system which incorporates pneumatic controls which select between a firm damping and a soft damping characteristic for the shock absorber based upon the loading of the vehicle. 
     BACKGROUND OF THE INVENTION 
     In recent years, substantial interest has grown in motor vehicles having suspension systems which can offer improved comfort and road handling for the vehicle. The improvements for these suspension systems can be achieved by utilization of an “intelligent” suspension system. An “intelligent” suspension is capable of controlling the suspension forces generated by the hydraulic dampers or shock absorbers provided at each corner of the motor vehicle in response to one or more operating characteristics of the vehicle. 
     In general, vehicle suspension systems are provided to filter or isolate the vehicle body from road surface irregularities as well as to control body and wheel motion. In addition, it may be desirable that the suspension system maintain an average vehicle attitude to promote improved vehicle stability during maneuvering. The conventional non-intelligent suspension system includes a spring and a damping device in parallel which is located between the sprung mass (vehicle body) and the unsprung mass (the wheel and suspension systems). 
     Hydraulic actuators, such as shock absorbers and/or struts, are used in conjunction with the conventional non-intelligent or passive suspension systems to absorb unwanted vibrations which occur during driving. To absorb these unwanted vibrations, the conventional hydraulic actuators often include a piston which is located within a pressure tube and which is connected to the body of the automobile through a piston rod. The pressure tube is connected to the vehicle&#39;s suspension system. Because the piston is able to limit the flow of damping fluid within the working chamber of the pressure tube when the actuator is telescopically displaced, the actuator is able to produce a damping force which counteracts the vibration which would otherwise be directly transmitted from the suspension system to the vehicle body. The greater the degree to which the flow of damping fluid within the working chamber is restricted by the piston, the greater the damping forces which are generated by the actuator. 
     In order to maintain a vehicle&#39;s attitude for multiple loading conditions, it is often desirable to have a leveling system associated with the vehicle. This vehicle leveling system can be associated with the hydraulic damper, it can be associated with the vehicle&#39;s springs, or it may be separate from both the hydraulic dampers and the springs. These leveling systems are used to change the relationship between the vehicle&#39;s suspension system and the vehicle body. The leveling systems are used to compensate for weight changes associated with the vehicle. The weight changes can be the result of changes in static loading or changes in dynamic loading. Static loading is simply the load which is supported by the suspension system which is due to the weight associated with the passengers of the vehicle, the weight of the cargo in the vehicle, and the like. In contrast, dynamic loading involves the loading which normally varies according to different types of road conditions. 
     When changing the height of the vehicle in response to the vehicle&#39;s weight, it is also desirable to adjust the damping characteristics of the vehicle&#39;s hydraulic dampers. A relatively low weighted vehicle typically requires a softer or lower damping characteristic than a relatively highly weighted vehicle. The continued development of suspension systems have been directed towards methods of adjusting the damping characteristics of the hydraulic dampers in response to the leveling system which reacts to the vehicle&#39;s weight. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a suspension system that is self-adjusting in response to the loading of the vehicle. The system incorporates pneumatic controls which act as a leveling system while simultaneously adjusting the damping characteristics of the vehicle&#39;s hydraulic damper or shock absorbers. The present invention includes a valve associated with each shock absorber which opens or closes a bypass passage between the working chamber of the shock absorber and the reserve chamber of the shock absorber. The opening and closing of the bypass passage by the valve is controlled by the air pressure being supplied to the leveling system for the vehicle. 
     Other advantages and objects of the present invention will become apparent to those skilled in the art from the subsequent detailed description, appended claims and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings which illustrate the best mode presently contemplated for carrying out the present invention: 
         FIG. 1  is a schematic perspective of an automobile incorporating a load dependent suspension system which includes the air pressure proportional damping system in accordance with the present invention; 
         FIG. 2  is a schematic representation of the pneumatic control system for the load dependant suspension system in accordance with the present invention; 
         FIG. 3  is a vehicle cross-sectional view of the air pressure proportional damper in accordance of the present invention; and 
         FIG. 4  is an enlarged cross-sectional view of the control valve for the air pressure proportional damper shown in  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings in which like reference numerals designate like or corresponding parts throughout the several views, there is shown in  FIG. 1  a vehicle incorporating a load dependant suspension system in accordance with the present invention which is indicated generally by the reference numeral  10 . While the present invention is illustrated in the drawings as being associated with an automotive vehicle, it is within the scope of the present invention to incorporate the load dependant suspension system of the present invention in other types of vehicles. In addition, the term “shock absorber” as used herein refers to shock absorbers in the general sense of the phrase and includes MacPherson struts. 
     Referring now to  FIGS. 1 and 2 , vehicle  10  includes a body  12 , a rear suspension assembly  14  and a front suspension assembly  16 . Rear suspension assembly  14  includes a transversely extending rear axle assembly adapted to operatively support the vehicle&#39;s rear wheels  18 . Rear suspension assembly  14  is operatively connected to body  12  by means of a pair of shock absorbers  20  as well as by a pair of air springs  22 . Front suspension system  16  includes a transversely extending front axle assembly adapted to operatively support the vehicle&#39;s front wheels  24 . Front suspension system  16  is operatively connected to body  12  by means of a pair of shock absorbers  26  and by another pair of air springs  22 . Shock absorbers  20  and  26  serve to dampen the relative motion of the unsprung portion (front suspension assembly  16  and rear suspension assembly  14 ) and the sprung portion (body  12 ) of vehicle  10 . It should be understood that reference is being made within this detailed description to the terms “air shock” and “air pressure proportional damper”. It should be understood that the “air” referred to may be substituted with other gas or liquids without deviating from the present invention. 
     Referring to  FIGS. 1 and 2 , vehicle  10  includes a control system  30  which is in communication with a height sensor  32  located at each corner of vehicle  10 . Each height sensor  32  monitors the height of body  12  in relation to suspension assemblies  14  and  16 . Control system  30  also includes a pneumatic pressure line  34  connecting each air spring  22  with a compressor  36  controlled by control system  30 . Each pressure line  34  includes a connecting pressure line  38  which connects each pressure line  34  with a respective shock absorber  20  or a respective shock absorber  26 . When one or more of height sensors  32  indicates that the position of vehicle body  12  is lower than a specified amount, control system  30  activates compressor  36  to supply pressurized air to the air spring  22  adjacent to the specific height sensor  32 . The pressurized air extends the individual air spring  22  to raise vehicle body  12  back to its specified height. Connecting line  38  supplies pressurized air to the adjacent shock absorber  20  or  26  to adjust the damping characteristics of the adjacent shock absorber  20  or  26  as will be detailed below. When one or more of height sensors  32  indicates that the position of vehicle body  12  is higher than a specific amount, control system  30  releases air pressure from the air spring  22  adjacent to the specific height sensor  32 . The release of pressurized air lowers vehicle body  12  back to the specified height. Connecting line  38  releases pressurized air from the adjacent shock absorber  20  or  26  to adjust the damping characteristics of the adjacent shock absorber  20  or  26  as will be described below. 
     While control system  30  is shown controlling each shock absorber  20  and  26  individually, it is within the scope of the present invention to simultaneously control both shock absorbers  20  and to simultaneously control both shock absorbers  26 . Also, it is within the scope of the present invention to simultaneously control all four shock absorbers  20  and  26  if desired. 
     Referring now to  FIGS. 3 and 4 , shock absorber  20  is shown in greater detail. While  FIGS. 3 and 4  illustrate shock absorber  20 , it is to be understood that shock absorber  26  also includes the air pressure proportional damping system in accordance with the present invention. 
     Shock absorber  20  is a dual tube shock absorber which comprises an elongated pressure cylinder  40  defining a damping fluid containing working chamber  42 . A slidably movably piston assembly  44  divides chamber  42  into a lower working chamber  46  and an upper working chamber  48 . 
     Shock absorber  20  further comprises a base valve  50  located within the lower end of pressure cylinder  40  which permits the flow of damping fluid between lower working chamber  46  and an annular reserve chamber  52  defined by a reserve tube  54 . 
     Referring to the upper end of shock absorber  20 , a rod guide and seal assembly  56  seats within an upper end cap  58  of pressure cylinder  40  and reserve tube  54 . Rod guide and seal assembly  56  limits radial movement of an axially extending piston rod  60  and provides a fluid seal to prevent fluid from leaking from either upper working chamber  48  or from reserve chamber  52  during reciprocation of piston rod  60 . Further, rod guide and seal assembly  56  seals shock absorber  20  from the introduction of dirt, dust or other contaminants into the fluidic portions of shock absorber  20 . 
     A variable valve assembly  100  fluidly communicates with upper working chamber  48  through a fluid tube  102  and a fluid passage  104  extending through rod guide and seal assembly  56 . Variable valve assembly  100  comprises a valve housing  110 , an inner valve body  112 , an upper valve body  114 , a plunger seat  116 , a plunger housing  118 , a plunger assembly  120 , a nipple housing assembly  122 , and a closing ring  124 . Valve housing  110  is a cup shaped housing which extends through an aperture  126  extending through reserve tube  54 . Housing  110  defines an internal chamber  128  which is in communication with reserve chamber  52  through an aperture  130 . 
     Inner valve body  112  is disposed within aperture  130  and it defines a fluid passage  132  within which is disposed fluid tube  102 . For reasons of clarity, variable valve assembly  100  has been rotated  900  in  FIG. 4 . Fluid passage  132  is an L-shaped passage which receives fluid tube  102  through a radial portion and communicates with passage  142 . Inner valve body  112  also defines an axial passage  134  disposed adjacent to passage  132 . Passage  134  also provide communication between internal chamber  128  and reserve chamber  52 . 
     Upper valve body  114  is a cylindrical shaped body which defines a central fluid passage  136  and an axially extending fluid passage  138 . Plunger seat  116  is located within a recessed area  140  of upper valve body  114 . Upper valve body  114  is disposed within the bottom area of internal chamber  128  and is positioned such that plunger seat  116  sealingly engages inner valve body  112  such that fluid passage  132  fluidically communicates with central fluid passage  136  through a passage  142  extending through plunger seat  116 . 
     Plunger housing  118  is disposed within internal chamber  128  adjacent to upper valve body  114  and engages a recessed area  144  of upper valve body  114  to defines a fluid chamber  146 . An O-ring  148  seals the interface between plunger housing  118  and valve housing  110 . Plunger assembly  120  is slidingly disposed within an aperture  150  extending through plunger housing  118 . An O-ring  152  seals the interface between plunger assembly  120  and plunger housing  118 . Plunger assembly  120  comprises a plunger  154  and a plunger head  156 . Plunger  154  has an enlarged end portion  158  which is disposed within passage  136  and which engages plunger seat  116  to control fluid flow through passage  142  of plunger seat  116 . Thus, when enlarged end portion  158  of plunger  154  is spaced from plunger seat  116 , fluid flow from upper working chamber  48  through passage  104 , through tube  102 , through passage  132 , through passage  142  and passage  136  into chamber  146  is permitted. Fluid then flows from chamber  146  to reserve chamber  52  through passages  138  and  134 . This places upper working chamber  48  in fluid communication with reserve chamber  52 . When enlarged end portion  158  is urged against plunger seat  116 , fluid flow through passage  142  is prohibited and upper working chamber  48  is not in open communication with reserve chamber  52 . Plunger head  156  is secured to the end of plunger  154  opposite to enlarged end portion  158 . 
     Nipple housing assembly  122  is disposed within internal chamber  128  adjacent to plunger housing  118  and with plunger housing  118  defines a first pressure chamber  160 . Nipple housing assembly  122  comprises a nipple housing  162 , a disc seal assembly  164  and a nipple assembly  166 . Disc seal assembly  164  is sealingly attached to nipple housing  162  and with nipple housing  162  it defines a second pressure chamber  170 . Nipple assembly  166  is sealingly disposed within an aperture  172  defined by nipple housing  162 . Nipple assembly  166  defines a fluid passage  174  which is in communication with second pressure chamber  170  through a control orifice  176 . 
     Thus, when connecting line  38  is sealingly attached to nipple assembly  166 , the pressurized fluid within the adjacent air spring  22  is in communication with second pressure chamber  170 . The pressurized fluid within second pressurized chamber  170  deflects disc seal assembly  164  to urge it against plunger head  156  and urge end portion  158  of plunger  154  against plunger seat  116 . The amount of pressure within air spring  22  will determine the load urging end portion  158  against plunger seat  116  and this will in turn determine the fluid pressure within upper working chamber  48  required to unseat end portion  158  from plunger seat  116  and allow fluid flow between upper working chamber  48  and reserve chamber  52 . 
     When the vehicle is in an unladen or low loaded condition, the air pressure within one or more of air springs  22  is reduced by control system  30 . The reduction of air pressure within air spring  22  simultaneously reduced the air pressure in a respective pressure line  38  and thus a respective second pressure chamber  170 . The reduction of pressure within chamber  170  releases pressure exerted by disc seal assembly  164  against plunger head  156  of plunger  154 . This allows end portion  158  of plunger  154  to move away from seat  116  easier to allow fluid flow between upper working chamber  48  and reserve chamber  52 . On a rebound stroke of shock absorber  20 , in an unladen condition, fluid within upper working chamber  48  is compressed causing fluid to flow through piston assembly  44  and eventually through valve assembly  100 . This dual flow path for fluid within upper working chamber  48  provides a relatively soft or low damping force to be generated when the pressure within air spring  22  is relatively low. 
     When the vehicle is in a laden or highly loaded condition, the air pressure within one or more of air springs  22  is increased by control system  30 . The increase of air pressure within air spring  22  simultaneously increases the air pressure in a respective pressure line  38  and thus a respective second pressure chamber  170 . The increase of pressure within chamber  170  increases pressure exerted by disc seal assembly  164  against plunger head  156  of plunger  154 . This, in turn, urges end portion  158  of plunger  154  against seat  116  to restrict fluid flow between upper working chamber  48  and reserve chamber  52 . On a rebound stroke of shock absorber  20 , in a laden condition, fluid within upper working chamber  48  is compressed causing fluid to flow through piston assembly  44 . Fluid pressure will increase within upper working chamber  48  as well as within fluid passage  104  and fluid tube  102 . This pressurized fluid will react against end portion  158  of plunger  154  and once the fluid pressure is sufficient to unseat end portion  158  from seat  116 , fluid will then flow through valve assembly. The initial single flow path for fluid within upper working chamber  48  (only through piston assembly  44 ) provides a relatively firm or high damping force to be generated. The degree of damping will be controlled by the force being exerted by air pressure from spring  22  against plunger  154  which is biased against seat  116 . 
     Shock absorber  20  and variable valve assembly also incorporate a fail safe function. When there is a problem with the air pressure supply, for instance if connection line  38  leaks, there will be little or no air pressure acting on disc seal assembly  164  and on plunger  154 . Consequently, pressurized oil coming from passage  132  and  142  will encounter no resistance from plunger  154  and plunger  154  will be pushed against an upper plunger seat  180 , formed by upper valve body  114 . As a result, oil will not flow through passages  136  to fluid chamber  146  and the damping force created by shock absorber  20  will increase to a level that is higher or equal to the highly loaded situation or what is called its fail safe function. 
     While the above detailed description describes the preferred embodiment of the present invention, it should be understood that the present invention is susceptible to modification, variation and alteration without deviating from the scope and fair meaning of the subjoined claims.