Abstract:
A shock absorber has a first pressure tube and a second pressure tube. A first piston is disposed within the first pressure tube and a second piston is disposed within the second pressure tube. Movement of the first and second pistons within their respective pressure tubes control both damping characteristics for the shock absorber and stiffness for the shock absorber. Valving in the pistons and/or external valving associated with each pressure tube generates both the damping characteristics and the stiffness.

Description:
FIELD 
       [0001]    The present disclosure relates generally to hydraulic dampers or shock absorbers for use in a suspension system such as a suspension system used for automotive vehicles. More particularly, the present disclosure relates to a hydraulic damper or shock absorber which includes four working chambers. 
       BACKGROUND 
       [0002]    This section provides background information related to the present disclosure which is not necessarily prior art. 
         [0003]    Shock absorbers are used in conjunction with automotive suspension systems to absorb unwanted vibrations which occur during driving. To absorb the unwanted vibrations, shock absorbers are generally connected between the sprung portion (body) and the unsprung portion (suspension) of the automobile. A piston is located within a pressure tube of the shock absorber and the pressure tube is connected to one of the sprung portion and the unsprung portion of the vehicle. The piston is connected to the other of the sprung portion and unsprung portion of the automobile through a piston rod which extends through the pressure tube. The piston divides the pressure tube into an upper working chamber and a lower working chamber both of which are filled with hydraulic fluid. Because the piston is able, through valving, to limit the flow of the hydraulic fluid between the upper and the lower working chambers when the shock absorber is compressed or extended, the shock absorber is able to produce a damping force which counteracts the vibration which would otherwise be transmitted from the unsprung portion to the sprung portion of the vehicle. In a dual-tube shock absorber, a fluid reservoir or reserve chamber is defined between the pressure tube and a reserve tube. A base valve is located between the lower working chamber and the reserve chamber to also produce a damping force which counteracts the vibrations which would otherwise be transmitted from the unsprung portion of the vehicle to the sprung portion of the automobile. 
         [0004]    As described above, for a dual-tube shock absorber, the valving on the piston limits the flow of damping fluid between the upper and lower working chambers when the shock absorber is extended to produce a damping load. The valving on the base valve limits the flow of damping fluid between the lower working chamber and the reserve chamber when the shock absorber is compressed to produce a damping load. For a mono-tube shock absorber, the valving on the piston limits the flow of damping fluid between the upper and lower working chambers when the shock absorber is extended or compressed to produce a damping load. During driving, the suspension system moves in jounce (compression) and rebound (extension). During jounce movements, the shock absorber is compressed causing damping fluid to move through the base valve in a dual-tube shock absorber or through the piston valve in a mono-tube shock absorber. A damping valve located on the base valve or the piston controls the flow of damping fluid and thus the damping force created. During rebound movements, the shock absorber is extended causing damping fluid to move through the piston in both the dual-tube shock absorber and the mono-tube shock absorber. A damping valve located on the piston controls the flow of damping fluid and thus the damping force created. 
         [0005]    In a dual-tube shock absorber, the piston and the base valve normally include a plurality of compression passages and a plurality of extension passages. During jounce movements in a dual-tube shock absorber, the damping valve or the base valve opens the compression passages in the base valve to control fluid flow and produce a damping load. A check valve on the piston opens the compression passages in the piston to replace damping fluid in the upper working chamber but this check valve may or may not contribute to the damping load. The damping valve on the piston closes the extension passages of the piston and a check valve on the base valve closes the extension passages of the base valve during a compression movement. During rebound movements in a dual-tube shock absorber, the damping valve on the piston opens the extension passages in the piston to control fluid flow and produce a damping load. A check valve on the base valve opens the extension passages in the base valve to replace damping fluid in the lower working chamber but this check valve may or may not contribute to the damping load. 
         [0006]    In a mono-tube shock absorber, the piston normally includes a plurality of compression passages and a plurality of extension passages. The shock absorber will also include means for compensating for the rod volume flow of fluid as is well known in the art. During jounce movements in a mono-tube shock absorber, the compression damping valve on the piston opens the compression passages in the piston to control fluid flow and produce a damping load. The extension damping valve on the piston closes the extension passages of the piston during a jounce movement. During rebound movements in a mono-tube shock absorber, the extension damping valve on the piston opens the extension passages in the piston to control fluid flow and produce a damping load. The compression damping valve on the piston closes the compression passages of the piston during a rebound movement. 
       SUMMARY 
       [0007]    This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
         [0008]    The present disclosure relates to a hydraulic damper or shock absorber which includes four working chambers. A conventional hydraulic or shock absorber typically includes an upper working chamber and a lower working chamber defined by a pressure tube which are separated by a piston assembly. Movement of the piston assembly in the pressure tube causes fluid to be transferred between the upper and lower working chambers. Valving located within the piston assembly and/or exterior to the pressure tube restricts flow of the fluid between the upper and lower working chambers to create damping characteristics for the hydraulic damper or shock absorber. The present disclosure includes a second pressure tube which defines a second upper working chamber and a second lower working chamber which are separated by a second piston assembly. Movement of the second piston assembly in the second pressure tube causes fluid to be transferred between the second upper and second lower working chambers. Valving located within the second piston assembly and/or exterior to the second pressure tube restricts flow of the fluid between the second upper and second lower working chambers to create damping characteristics for the hydraulic damper or shock absorber. The damping characteristics generated by fluid flow between the upper and lower working chambers can be tuned separately from the damping characteristics generated by fluid flow between the second upper and second lower working chambers. 
         [0009]    Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
         [0010]    DRAWINGS 
         [0011]    The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
         [0012]      FIG. 1  illustrates an automotive vehicle which incorporates shock absorbers in accordance with the present disclosure; 
         [0013]      FIG. 2  is a cross-sectional side view of one of the shock absorbers illustrated in  FIG. 1 ; 
         [0014]      FIG. 3  is an enlarged cross-sectional side view of one of the piston assemblies from the shock absorber illustrated in  FIG. 2 ; 
         [0015]      FIG. 4  is a cross-sectional side view of a shock absorber in accordance with another embodiment of the present disclosure; and 
         [0016]      FIG. 5  is a cross-sectional side view of a shock absorber in accordance with another embodiment of the present disclosure. 
     
    
       [0017]    Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
       DETAILED DESCRIPTION 
       [0018]    Example embodiments will now be described more fully with reference to the accompanying drawings. 
         [0019]    The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. Referring now to the drawings in which like reference numerals designate like components throughout the several views, there is shown in  FIG. 1  a vehicle incorporating a suspension system having shock absorbers in accordance with the present disclosure, and which is designated by the reference numeral  10 . 
         [0020]    Vehicle  10  includes a rear suspension  12 , a front suspension  14  and a body  16 . Rear suspension  12  has a transversely extending rear axle assembly (not shown) adapted to operatively support a pair of rear wheels  18 . The rear axle is attached to body  16  by means of a pair of shock absorbers  20  and by a pair of springs  22 . Similarly, front suspension  14  includes a transversely extending front axle assembly (not shown) to operatively support a pair of front wheels  24 . The front axle assembly is attached to body  16  by means of a pair of shock absorbers  26  and by a pair of springs  28 . Shock absorbers  20  and  26  serve to dampen the relative motion of the unsprung portion (i.e., front and rear suspensions  12 ,  14 ) with respect to the sprung portion (i.e., body  16 ) of vehicle  10 . While vehicle  10  has been depicted as a passenger car having front and rear axle assemblies, shock absorbers  20  and  26  may be used with other types of vehicles or in other types of applications including, but not limited to, vehicles incorporating non-independent front and/or non-independent rear suspensions, vehicles incorporating independent front and/or independent rear suspensions or other suspension systems known in the art. Further, the term “shock absorber” as used herein is meant to refer to dampers in general and thus will include McPherson struts and other damper designs known in the art. 
         [0021]    Referring now to  FIG. 2 , shock absorber  26  is shown in greater detail. While  FIG. 2  illustrates only shock absorber  26 , it is to be understood that shock absorber  20  also includes the dual pressure tube design described below for shock absorber  26 . Shock absorber  20  only differs from shock absorber  26  in the manner in which it is adapted to be connected to the sprung and unsprung masses of vehicle  10 . Shock absorber  26  comprises a first pressure tube  30 , a first piston assembly  32 , a piston rod  34 , a second pressure tube  36 , a second piston assembly  38  and a compensation piston  40 . 
         [0022]    First pressure tube  30  defines a first fluid chamber  44 . First piston assembly  32  is slidably disposed within first pressure tube  30  and divides first fluid chamber  44  into a first upper working chamber  46  and a first lower working chamber  48 . A seal is disposed between first piston assembly  32  and first pressure tube  30  to permit sliding movement of first piston assembly  32  with respect to first pressure tube  30  without generating undue frictional forces as well as sealing first upper working chamber  46  from first lower working chamber  48 . Piston rod  34  is attached to first piston assembly  32  and extends through first upper working chamber  46  and through a first rod guide assembly  50  which closes one end of first pressure tube  30  and one end of second pressure tube  36 . A sealing system seals the interface between first rod guide assembly  50  and piston rod  34 . The end of piston rod  34  opposite to first piston assembly  32  is adapted to be secured to one of the sprung mass and unsprung mass of vehicle  10 . Because piston rod  34  extends only through first upper working chamber  46  and not first lower working chamber  48 , extension and compression movements of first piston assembly  32  with respect to first pressure tube  30  causes a difference in the amount of fluid displaced in first upper working chamber  46  and the amount of fluid displaced in first lower working chamber  48 . The difference in the amount of fluid displaced is known as the “rod volume” and compensation for this difference of fluid flow causes movement of compensation piston  40  within first pressure tube  30  as is well known in the art. A compressed fluid is typically disposed between compensation piston  40  and the end of first pressure tube  30 . The end of first pressure tube  30  opposite to first rod guide assembly  50  is adapted to be secured to the other of the sprung mass and the unsprung mass of vehicle  10 . 
         [0023]    Second pressure tube  36  defines a second fluid chamber  54 . Second piston assembly  38  is slidably disposed within second pressure tube  36  and divides second fluid chamber  54  into a second upper working chamber  56  and a second lower working chamber  58 . A seal is disposed between second piston assembly  38  and second pressure tube  36  to permit sliding movement of second piston assembly  38  with respect to second pressure tube  36  without generating undue frictional forces as well as sealing second upper working chamber  56  from second lower working chamber  58 . Piston rod  34  is attached to second piston assembly  38  and extends through second upper working chamber  56 , second lower working chamber  58  and through a second rod guide assembly  60  which closes the other end of second pressure tube  36 . A sealing system seals the interface between second rod guide assembly  60  and piston rod  34 . 
         [0024]    A fluid port  62  is in communication with second lower working chamber  58  and a fluid port  64  is in communication with second upper working chamber  56 . A hydraulic system  66 , which may include at least one accumulator, is in communication with fluid port  62  and fluid port  64 . Damping characteristics are determined by first piston assembly  32  and can also be determined by second piston assembly  38 . Stiffness for shock absorber  26  is determined by hydraulic system  66 . 
         [0025]    Referring to  FIG. 3 , each piston assembly  32 ,  38  comprises a piston  70 , a compression valve assembly  72  and an extension valve assembly  74 . A nut  76  is assembled to piston rod  34  to secure compression valve assembly  72 , piston  70  and extension valve assembly  74  of first piston assembly  32  to piston rod  34 . Compression valve assembly  72 , piston  70  and extension valve assembly  74  of second piston assembly  38  are secured to piston rod  34  using nuts, welding or other methods known in the art. Each piston  70  defines a plurality of compression passages  78  and a plurality of extension passages  80 . 
         [0026]    Each compression valve assembly  72  comprises one or more valve discs  82 , an interface disc  84 , one or more preload discs  86 , one or more spacer discs  88  and a retainer  90 . Retainer  90  is attached to piston rod  34  by threading engagement, welding, engagement with a shoulder on piston rod  34  or by any other method known in the art. The one or more spacer discs  88  directly abut retainer  90 . Each extension valve assembly  74  comprises the one or more valve discs  82 , the interface disc  84 , the one or more preload discs  86 , the one or more spacer discs  88  and a retainer  90 . In extension valve assembly  74  associated with first piston assembly  32 , nut  76  operates as retainer  90 . Retainer  90  is attached to piston rod  34  by threading engagement, welding, engagement with a shoulder on piston rod  34  or by any other method known in the art for second piston assembly  38 . The one or more spacer discs  88  directly abut retainer  90 . The one or more preload discs  86  directly abut the one or more spacer discs  88 . The interface disc  84  directly abuts the one or more preload discs  86 . The one or more valve discs  82  directly abut both interface disc  84  and piston  70 . The one or more preload discs  86  generate a biasing load due to deflection of the one or more preload discs  86  to bias the one or more valve discs  82  into engagement with piston  70  by reacting through interface disc  84 . 
         [0027]    During a compression stroke, fluid in first and second lower working chambers  48  and  58  are pressurized causing fluid pressure to react against each compression valve assembly  72  associated with first piston assembly  32  and second piston assembly  38 . Fluid pressure will react against each of the one or more valve discs  82  of each compression valve assembly  72  until the generated load exceeds the preload of each of the one or more preload discs  86 . When the generated load exceeds the preload, each of the one or more valve discs  82  will totally separate from each piston  70  to open both of the plurality of compression passages  78  by bending each of the one or more preload discs  86 . 
         [0028]    During a rebound stroke, fluid in upper working chambers  46  and  56  are pressurized causing fluid pressure to react against each extension valve assembly  74  associated with first piston assembly  32  and second piston assembly  38 . Fluid pressure will react against each of the one or more valve discs  82  of each extension valve assembly  74  until the generated load exceeds the preload of each of the one or more preload discs  86 . When the generated load exceeds the preload, each of the one or more valve discs  82  will totally separate from each piston  70  to open each of the plurality of compression passages  78  by bending each of the one or more preload discs  86 . 
         [0029]    During both compression and rebound strokes, stiffness for shock absorber  26  is determined by hydraulic system  66  which receives fluid from upper working chamber  56  and from lower working chamber  58  and transfers fluid to upper working chamber  56  and to lower working chamber  58 . 
         [0030]    Shock absorber  26  can be utilized a suspension system where one set of upper and lower working chambers (the upper set in  FIG. 2 ) is used to generate damping forces in rebound and compression and the other set of upper and lower working chambers (the lower set in  FIG. 2 ) is used to generate stiffness in rebound and compression independently. Thus, shock absorber  26  can partially or completely replace the spring in a suspension system with a tuneable stiffness generated from the shock absorber. 
         [0031]    Referring now to  FIG. 4 , a shock absorber  126  in accordance with another embodiment of the present disclosure is illustrated. Shock absorber  126  comprises a first pressure tube  130 , a first piston  132 , a piston rod  134 , a second pressure tube  136 , a second piston  138 , a first external valving system  140  and a second external valving system  142 . 
         [0032]    First pressure tube  130  defines a first fluid chamber  144 . First piston  132  is slidably disposed within first pressure tube  130  and divides first fluid chamber  144  into a first upper working chamber  146  and a first lower working chamber  148 . A seal is disposed between first piston  132  and first pressure tube  130  to permit sliding movement of first piston  132  with respect to first pressure tube  130  without generating undue frictional forces as well as sealing first upper working chamber  146  from first lower working chamber  148 . Piston rod  134  is attached to first piston  132  and extends through first upper working chamber  146  and through a first rod guide assembly  150  which closes one end of first pressure tube  130  and one end of second pressure tube  136 . A sealing system seals the interface between first rod guide assembly  150  and piston rod  134 . The end of piston rod  134  opposite to first piston  132  is adapted to be secured to one of the sprung mass and unsprung mass of vehicle  10 . Because piston rod  134  extends only through first upper working chamber  146  and not first lower working chamber  148 , extension and compression movements of first piston  132  with respect to first pressure tube  130  causes a difference in the amount of fluid displaced in first upper working chamber  146  and the amount of fluid displaced in first lower working chamber  148 . The difference in the amount of fluid displaced is known as the “rod volume” and compensation for this difference of fluid flow is accommodated for by external valving system  140 . The end of first pressure tube  130  opposite to first rod guide assembly is adapted to be secured to the other of the sprung mass and unsprung mass of vehicle  10 . 
         [0033]    Second pressure tube  136  defines a second fluid chamber  154 . Second piston  138  is slidably disposed within second pressure tube  136  and divides second fluid chamber  154  into a second upper working chamber  156  and a second lower working chamber  158 . A seal is disposed between second piston  138  and second pressure tube  136  to permit sliding movement of second piston  138  with respect to second pressure tube  136  without generating undue frictional forces as well as sealing second upper working chamber  156  from second lower working chamber  158 . Piston rod  134  is attached to second piston  138  and extends through second upper working chamber  156 , second lower working chamber  158  and through a second rod guide assembly  160  which closes the other end of second pressure tube  136 . A sealing system seals the interface between second rod guide assembly  160  and piston rod  134 . 
         [0034]    During a compression stroke, fluid in first and second lower working chambers  148  and  158  are pressurized causing fluid to flow into first external valving system  140  and second external valving system  142 . First and second external valving systems  140  and  142  include the necessary valving systems to generate the damping loads for shock absorber  26 , the stiffness for shock absorber  26  as well as compensate for any rod volume of fluid generated. 
         [0035]    During a rebound stroke, fluid in first and second upper working chambers  146  and  156  are pressurized causing fluid to flow into first external valving system  140  and second external valving system  142 . First and second external valving systems  140  and  142  include the necessary valving systems, accumulators and other hydraulic components to generate the damping loads for shock absorber  26 , the stiffness for shock absorber  26  as well as compensate for any rod volume of fluid generated. 
         [0036]    Referring now to  FIG. 5 , a shock absorber  226  in accordance with another embodiment of the present disclosure is illustrated. Shock absorber  226  comprises a first pressure tube  230 , a first piston  232 , a piston rod  234 , a second pressure tube  236 , a second piston  238 , a first external valving system  240  and a second external valving system  242 . 
         [0037]    First pressure tube  230  defines a first fluid chamber  244 . First piston  232  is slidably disposed within first pressure tube  230  and divides first fluid chamber  244  into a first upper working chamber  246  and a first lower working chamber  248 . A seal is disposed between first piston  232  and first pressure tube  230  to permit sliding movement of first piston  232  with respect to first pressure tube  230  without generating undue frictional forces as well as sealing first upper working chamber  246  from first lower working chamber  248 . Piston rod  234  is attached to first piston  232  and extends through first upper working chamber  246  and through second piston  238  which closes one end of first pressure tube  230  and is attached to a first rod guide assembly  250  which closes one end of second pressure tube  236 . A sealing system seals the interface between second piston  238  and piston rod  234 . The end of piston rod  234  opposite to first piston  232  is adapted to be secured to one of the sprung mass and unsprung mass of vehicle  10 . Because piston rod  234  extends only through first upper working chamber  246  and not first lower working chamber  248 , extension and compression movements of first piston  232  with respect to first pressure tube  230  causes a difference in the amount of fluid displaced in first upper working chamber  246  and the amount of fluid displaced in first lower working chamber  248 . The difference in the amount of fluid displaced is known as the “rod volume” and compensation for this difference of fluid flow is accommodated for by external valving system  240 . The end of first pressure tube  230  opposite to second piston  238  is adapted to be secured to the other of the sprung mass and unsprung mass of vehicle  10 . 
         [0038]    Second pressure tube  236  defines a second fluid chamber  254 . Second piston  238  is slidably disposed within second pressure tube  236  and divides second fluid chamber  254  into a second upper working chamber  256  and a second lower working chamber  258 . A seal is disposed between second piston  238  and second pressure tube  236  to permit sliding movement of second piston  238  with respect to second pressure tube  236  without generating undue frictional forces as well as sealing second upper working chamber  256  from second lower working chamber  258 . Piston rod  234  slidingly engages second piston  238  and extends through second upper working chamber  256 , second lower working chamber  258  and is attached to rod guide assembly  250  which closes the one end of second pressure tube  236 . A sealing system seals the interface between second rod guide assembly  250  and piston rod  234 . The opposite end of second pressure tube  236  is closed by a sealing system  262  which seals the interface between second pressure tube  236  and first pressure tube  230 . A coil spring  264  extends between second pressure tube  236  and a lower spring retainer  266  engaging an end cap  268  which closes the end of first pressure tube  230 . An intermediate tube  270  defines an intermediate chamber that places first upper working chamber  246  in direct fluid communication with external valve system  240 . 
         [0039]    During a compression stroke, fluid in first lower working chambers  248  and second upper chamber  256  are pressurized causing fluid to flow into first external valving system  240  and second external valving system  242 . First and second external valving systems  240  and  242  include the necessary valving systems, accumulators or other hydraulic components to generate the damping loads for shock absorber  26 , the stiffness for shock absorber  26  as well as compensate for any rod volume of fluid generated. 
         [0040]    During a rebound stroke, fluid in first upper working chambers  246  and second lower working chamber  258  are pressurized causing fluid to flow into first external valving system  240  and second external valving system  242 . First and second external valving systems  240  and  242  include the necessary valving systems, accumulators or other hydraulic components to generate the damping loads for shock absorber  26 , the stiffness for shock absorber  26  as well as compensate for any rod volume of fluid generated. 
         [0041]    The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.