Abstract:
An automatic damper for an automobile automatic damper system which provides a compression valve operable to vary compressive damping characteristics of a damper, as well as a rebound valve operable to vary rebound damping characteristics of the damper. Use of the invention in cooperation with presently available electronic control modules and sensing algorithms provides a damper with either discrete valves or continuously variable valves for independently setting the rebound and compression damping characteristics of the damper.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to hydraulic dampers, and more particularly to a new and improved semi-active damper with an externally mounted valve assembly for selectively varying stiffness of the damper in compression and separately selectively varying stiffness of the damper in rebound. 
     2. Description of Related Art 
     Dampers are used in conjunction with automotive suspension systems to absorb unwanted vibrations which occur while driving a vehicle. In order to absorb unwanted vibrations, dampers are generally connected between the body and the suspension of an automobile. A piston is located within the damper which is connected to the body of the automobile through a piston rod. Furthermore, the damper body is connected to the suspension of the automobile. Because the piston is able to limit the flow of damping fluid within the working chamber of the damper as the damper is compressed extended, the damper is able to produce a damping force which counteracts suspension system vibration which wold otherwise be transmitted from the suspension to the body. By further restricting the flow of damping fluid within the working chamber of a damper, greater damping forces are generated by the damper. 
     In determining the optimal amount of damping that a damper should provide, three vehicle performance characteristics are often considered: ride comfort, vehicle handling and road holding ability. Ride comfort is typically a function of the spring constant of the vehicle&#39;s main springs, as well as the spring constant of the occupant&#39;s seat, the vehicle&#39;s tires the suspension geometry, and the damper. Vehicle handling is related to changes in the vehicle&#39;s attitude (i.e., pitch, yaw, and roll). To achieve optimum vehicle handling, relatively large damping forces are required to avoid excessively rapid variation in the vehicle&#39;s attitude during acceleration, deceleration, and cornering. Road holding ability is generally dependent on the amount of contact between the vehicle tires and the ground. In order to optimize a vehicle&#39;s road holding ability, large damping forces are required as a vehicle passes over irregular surfaces in order to prevent loss of contact between the wheels and ground for an excessive period of time. 
     Because different driving characteristics require differing amounts of damping force from the damper in order to optimize its performance, it is often desirable to have a damper which can be adjusted to increase or decrease the requisite damping forces. One method for selectively changing a damper&#39;s damping characteristics is described in U.S. Pat. No. 4,890,858. This reference discloses a rotary valve for use in controlling a damper. The damper comprises a first valve member which is disposed within the pressure cylinder for establishing a plurality of flow passages. Furthermore, the damper comprises a second valve member also disposed within the pressure cylinder for establishing a second plurality of flow passages. In addition, the damper includes an actuator for providing an accelerating and decelerating force to the second valve member. Finally, control means for controlling displacement of the second valve member are also disclosed. 
     Because dampers which provide adjustable damping generally use a single valve to control the flow of damping fluid during both compression and rebound, a sensor is generally required to determine whether the damper is in compression or rebound. Not only does this provide a degree of difficultly in terms of sensor placement, there are also disadvantages with respect to the electronics which are required to generate an output indicative of whether the damper is in compression or rebound from the output of the sensor. Accordingly, these systems tend to be somewhat expensive. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a damper which includes a pressure cylinder and a piston which is reciprocally mounted in the cylinder so as to define a compression chamber and rebound chamber. The compression and rebound chambers are operable to store damping fluid and the piston is movable for reciprocally varying the volumes of the compression and rebound chambers. The damper further includes a valve for controlling the flow of fluid between the compression and rebound chambers, as well as a reservoir for receiving damping fluid. A compression transfer tube is provided which allows fluid communication between the compression chamber and the reservoir. The damper further includes a compression valve in communication with the transfer tube as well as a base valve in the pressure cylinder in communication with the pressure chamber and the reservoir. Finally, the damper includes a reservoir fluid aperture in the reservoir for establishing fluid flow from the reservoir to the rebound chamber. 
     Accordingly, the primary object of the present invention is to provide a semiactive damper for use in an automatic damping system of a vehicle which can be controlled by individually dedicated or shared electronic control modules. In this regard, a related object of the present invention is to provide a simplified and lower cost semiactively adjustable damper in which adaptive external valves allow for independent adjustable setting of the damper damping in rebound and compression. 
     A further object of the present invention is to provide a semi-active damper in which a pair of separate dedicated valving systems are utilized to soften damper damping in rebound and compression, which simplifies the damper while still providing an automatic damper system in which the rate of damping fluid flow between upper and lower portions of a working chamber may be controlled with a relatively high degree of accuracy. A related object of the present invention is to provide a semi-active damping system in which detection of rebound-compression transitions for each damper are not required which eliminates the need for a position sensor to sense the transition, yet still allows for achievement of separately tailored compression and rebound characteristics. 
     Further objects, features and advantages of this invention are to provide a damper which can be easily and readily adjusted automatically and semi-actively to optimize damping characteristics, with separate discrete or continuously variable external valves achieving separate damping settings in rebound and compression, and which has a long service life and is rugged, durable, reliable, of simplified design and of relatively economical manufacture and assembly. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Various advantages of the present invention will become apparent to those skilled in the art upon reading the following detailed description, appended claims, and accompanying drawings in which: 
     FIG. 1 is an illustration of an automobile using a plurality of semi-active fluid dampers according to the teachings of a preferred embodiment of the present invention; 
     FIG. 2 is a schematic representation of the damper utilized in FIG. 1 using the automatic, or semi-active, damping system according to the teachings of the preferred embodiment of the present invention; 
     FIG. 3 is a center line sectional and side elevational view of the damper shown in FIG. 2, showing the compression and rebound valves in closed positions; and 
     FIG. 4 is a view corresponding to that shown in FIG. 3 depicting the compression and rebound valves in open positions. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The following description of the preferred embodiment of the present invention is merely exemplary in nature and is in no way intended to limit the invention or its application or uses. 
     Referring now to FIG. 1, a plurality of four dampers  10  according to the preferred embodiment of the present invention are shown. Each damper  10  is depicted in operative association with a diagrammatic representation of a conventional automobile  12 . Automobile  12  provides a rear suspension system  14  having a transversely extending rear axle assembly (not shown) adapted to operatively support the vehicle&#39;s rear wheels  16 . The rear axle assembly is operatively connected to the automobile  12  by means of a pair of dampers  10  as well as by helical coil springs  18 . Similarly, automobile  12  has a front suspension system  20  including a transversely extending front axle assembly (not shown) which operatively supports the front wheels  22 . The front axle assembly is operatively connected to the automobile  12  by means of a second pair of dampers  10  and by the helical coil springs  24 . The dampers  10  serve to damp the relative movement of the unsprung portion (i.e., the front and rear suspension systems  20  and  14 ) and the sprung portion (i.e., the body  26 ) of the automobile  12 . While the automobile  12  has been depicted as a passenger car, the damper  10  may be used with other types of automotive vehicles or in other types of vehicles or system applications. Furthermore the term “damper” as used herein will refer to dampers in general and will include shock absorbers and McPherson struts. 
     In order to automatically adjust the dampers  10  of this invention, an electronic control module  28  is electrically connected to the dampers. As depicted in FIG. 1, each damper  10  is provided with a dedicated electronic control module  28 . Each control module  28  is used for controlling operation of each damper  10  in order to provide appropriate damping characteristics during compression and rebound resulting from movement of the body  26  of the automobile  12 . While the present invention is being illustrated with dedicated control modules  28 , it is within the scope of the present invention to utilize a single control module communicating with each damper  10 . Various techniques are known in the art for implementing electronic control modules in conjunction with dampers in order to regulate damping characteristics of a damper through variation of fluid flow valves in the damper. 
     As a general rule, it is desirable to have soft damping when the frequency of movement of the body  26  of the automobile  12  in the vicinity of damper  10  is less than a first specified frequency as well as when it is above a specified frequency. It is also generally desirable to have firm damping only when the acceleration of body  26  of automobile  12  in the range of the damper  10  exceeds a preselected value even when the frequency of the acceleration is between the first and second specified frequencies. Furthermore, it is generally desirable to separately adjust between soft and firm damping for the rebound mode and for the compression mode, which means the transition between rebound and compression modes must be detected in order to selectively switch parameters in order to achieve the desired optimal rebound and compression performance stiffness parameters during each mode. By designing a damper which has separate valving for the rebound mode and the compression mode, the electronic control module  28  can be used to generate an electronic control signal for separately and concurrently setting desirable compression and rebound damping characteristic of the damper  10  to which it is connected. 
     Referring to FIG. 2, to retain the damper  10  to an automotive vehicle  12 , the damper  10  includes an upper end fitting  30  and a lower end fitting  32 . The upper end fitting  30  extends through an upper cap portion  34  and is connected to a vehicle body structure, such as a shock tower (not shown). Similarly, the lower end fitting  32  is connected to the damper  10  adjacent a lower cap portion  36  so as to secure the damper  10  to one of the suspension systems  14  and  20 . As will be appreciated by those skilled in the art, other suitable means may be used to secure the damper, or dampers,  10  to the automotive vehicle  12 . 
     As shown in FIG. 2, the damper  10  of this invention comprises an elongated tubular pressure cylinder  38  defining a damping fluid-containing working chamber  40 , and disposed within the chamber  40  is a reciprocal piston  42 . The reciprocal piston  42  is secured to one end of an axially extending piston post  44  which is in turn secured to one end of an axially extending piston rod  46 . Alternatively, the piston  42  can be secured directly to one end of piston rod  46 . Preferably, the piston  42  carries an annular TEFLON™ sleeve  48  which is trapped on the outer circumference of the piston to permit movement of the piston with respect to the pressure cylinder  38  without generating undue frictional forces. Additionally, the piston  42  is further provided with a bi-directional flow valve  43  which allows regulated flow of damping fluid from one side of the piston to the other, or alternatively, is provided with at least a pair of uni-directional flow valves arranged on piston  42  for opposite-directional fluid flow therethrough. Further variations of piston valves are presently known in the art which include spring biased valves with valve seats which provide fluid flow in a regulated manner above a threshold pressure, or alternatively, metering pins and orifices which variably regulate fluid flow depending on exerted pressure therethrough. A further explanation of the construction and operation of pistons and piston valves is disclosed in U.S. Pat. No. 4,113,072, which is hereby incorporated by reference. 
     A base valve  50  is located within the lower end of the pressure cylinder  38  and is used to control the flow of damping fluid between the working chamber  40  and an annular fluid reservoir  52 . The annular fluid reservoir  52  is defined as the space between the outer periphery of a compression transfer tube  54 , a circumferential interface ring  56 , and a rebound transfer tube  58  and the inner periphery of a reservoir tube  60  forming the exterior surface of the damper  10 . Preferably, the operation of base valve  50  is similar to the operation of the base valve shown in U.S. Pat. No. 3,757,910, which is hereby incorporated by reference. However, other types of base valves may be used. 
     In addition to receiving the upper and lower cap portions  34  and  36 , reservoir tube  60  of damper  10  may support a spring base flange  62  such that flange  62  is received circumferentially about tube  60  where it is welded. Additionally, a support collar  64  is received circumferentially about the piston rod  46  where it exits through upper cap portion  34  such that the collar  64  is retained atop the upper cap portion  34 . The spring base flange  62  receives a bottom end of a helical coil spring  18  (as depicted in FIG. 1) which is circumferentially carried about the top end of the damper  10 . Likewise, a spring cap (not shown) is received on the top of spring  18  such that a hole in the cap mates with a collar  68  formed on piston rod  46  and abuts with a corresponding shoulder  70  onto which it is trapped by threading a nut (not shown) onto threaded end  66 . The spring cap is first loaded onto the threaded end  66  before loading end  66  into a receiving hole formed in vehicle body shock tower (not shown), such that a nut is threaded onto end  66  which traps the shock tower and spring cap to the end of the piston rod  46 . Vehicle loads produced between the vehicle shock tower on the piston rod  46  react against loads imparted by lower end fitting  32  which is affixed to a vehicle wheel such that compression therebetween counteracts forces produced by a coil spring  18 . In its assembly configuration, the spring acts in a compressive mode to space apart base flange  62  from the spring cap on the end of the piston rod  46 . Finally, the apertures  72  and  74  are provided through reservoir tube  60 , on opposite sides, such that each receives a compression valve  76  and a rebound valve  78 , respectively. The compression valve  76  and rebound valve  78  fluidly communicate with a circumferential interface ring  56  against which they are sealingly retained. Preferably, each aperture  72  and  74  is circumferentially welded to a valve housing of each valve  76  and  78 . 
     Reciprocating motion of the piston  42  and the piston rod  46  within the pressure cylinder  38  is axially guided by sliding contact of annular TEFLON sleeve  48  within the pressure cylinder  28  at one end, and by sliding and sealing reciprocation of the piston rod  46  through a rod guide  80  which is supported by the upper cap portion  34  to seal the top end of the damper  10 , and slidably seal the piston rod as it exits therethrough. Various configurations for rod guides which incorporate single and multiple circumferential seals are well known in the art for sealing and seating the ends of dampers. 
     Reciprocation of the piston  42  within the work chamber  40  formed inside pressure cylinder  38  partitions the work chamber to define a variable volume compression chamber  82  and a variable volume rebound chamber  84 . Damping fluid is provided in both the compression chamber  82  and the rebound chamber  84 . 
     A rebound transfer volume  86  is formed between the exterior surface of the pressure cylinder  38  and the interior surface of the rebound transfer tube  58 , and is further defined at either end by the rod guide  80  and the circumferential interface ring  56 , respectively, with which they seal. A rebound connection opening  88  is formed in the pressure cylinder  38  proximate the rod guide  80  which provides damping fluid flow between the rebound transfer volume  86  and the rebound chamber  84 . If desired, opening  88  can be formed in rod guide  80 . Additionally, the rebound transfer volume  86  communicates through rebound transfer tube  58  with rebound valve  78 . 
     A compression transfer volume  90  is formed between the exterior surface of the pressure cylinder  38  and the interior surface of the compression transfer tube  54 , and is further defined at either end by base valve  50  and circumferential inner face ring  56 , respectively, with which they seal. A compression connection opening  92  is formed in the pressure cylinder  38  proximate the base valve  50  which provides damping fluid flow between the compression transfer volume  90  and the compression chamber  82 . Additionally, the compression transfer volume  90  communicates through the compression transfer tube  54  with the compression valve  76 . 
     The base valve  50  mates within the pressure cylinder  38  at one end as a decreased diameter shoulder  94  on the valve  50  is received within pressure cylinder  38  where it substantially circumferentially seals therebetween, and an annular face  96  on the valve  50  seats against both ends of pressure cylinder  38  and compression transfer tube  54  such that a seal is formed therebetween which cooperates in defining the compression transfer volume  90 . Preferably, the base valve  50  is circumferentially welded to the end of the compression transfer tube  54 . Preferably, the base valve  50  is provided with a fluid aperture  98  which controllably regulates a bidirectional fluid flow between the compression chamber  82  and the fluid reservoir  52 . Various other forms of base valves are presently known in the art for providing bidirectional flow in the bottom of a damper. 
     As shown in FIG. 3, the compression valve  76  and rebound valve  78  sealingly fasten to the reservoir tube  60  such that they extend through apertures  72  and  74 , respectively, and abut and seal in fluid communication with fluid ports provided in circumferential interface ring  56 . The compression valve  76  has a solenoid  102  in electrical communication through a flex cable  104  with the accompanying electronic control module  28  which selectively electrically sends signals to engage and disengage the solenoid which opens and closes the compression valve  76 . By electrically activating the solenoid  102 , the compression valve  76  is opened which provides a flow of damping fluid from the compression transfer volume  90  into the annular fluid reservoir  52  in response to compressive motion of piston  42  toward the compression chamber  82 . Likewise, the rebound valve  78  has a solenoid  106  in electrical communication through a flex cable  108  with the same electronic control module  28  which selectively electrically activates and deactivates the solenoid to close and open, respectively, the rebound valve  78 . As a consequence, when rebound valve  78  is opened by activating solenoid  106 , fluid flows from rebound transfer volume  86  into a compression transfer volume  90  in response to rebound motion of the piston  42  towards the rebound chamber  78 . 
     It is to be understood that opening of the compression valve  76  and the rebound valve  78  through activation of the solenoid  102  and activation of the solenoid  106 , respectively, produces supplemental fluid flow between the compression chamber  82  and the reservoir  52 , and between the rebound chamber and the compression chamber. Primary fluid flow between the compression chamber  82  and the rebound chamber  84  is provided by damping fluid which flows through the piston aperture  43 . By closing the compression valve  76 , the stiffness of the damper  10  during compression is increased. Likewise, by closing the rebound valve  78 , the rebound stiffness of the damper  10  is decreased. Through either discrete fluctuation of the valve  76  and  78 , or continuously variable actuation of such valves, fluid flow between the compression chamber  82  and rebound chamber  84  can be tailored to provide adjustable stiffness of the damper  10  in an independent manner for both pressure cycles and rebound cycles. 
     In the case of fluid flow from the compression chamber  82  through the compression valve  76  and into the rebound chamber  84 , it is to be understood that the damping fluid travels a circuitous path. Damping fluid compressed in the compression chamber  82  is passed through the base valve  50  which empties into the fluid reservoir  52 . Concurrently, damping fluid in compression chamber  82  exits through the compression connection opening  92  into the compression transfer volume  90  where it passes through the compression valve  76 , while in an open position, into the reservoir  52 . Further transfer of fluid from the reservoir  52  is provided through a reservoir fluid aperture  110  (FIG. 1) which is formed in the rod guide  80  for transferring fluid from the reservoir  52  into the rebound chamber  84 . Furthermore, the rebound chamber  84  communicates with the rebound transfer volume through the rebound connection opening  88  such that fluid compressed in the rebound chamber is transferred through rebound transfer volume  86  through the rebound valve  78 , when in an open position, and into the annular fluid reservoir  52  which further transfers fluid through the compression connection opening  92  into the compression volume  82 . 
     As shown in FIGS. 3 and 4, the solenoid  102  has an axially extendable and retractable core  112 . The core  112  is formed from a ball  114  biased by a spring  116  and a sealing plate  118 . When deactuated, the core  112  moves towards a seat  120  sealing off fluid flow through the center bore of seat  120  with the ball  114  in a first stage. Fluid flow continues through the seat  120  due to a plurality of bleed holes  121  circumferentially spaced around the central bore of the seat  120 . In a second stage, the sealing plate  118  seals against the seat  120  to seal off the bleed holes  121  extending through the seat  120 . The two stage sealing described above reduces the water-hammer effect of closing compression valve  76 . A check valve  122  prevents back flow from reservoir  52  to compression transfer volume  90 . 
     As shown in FIG. 4, compression valve  76  is depicted with reference arrows showing flow of damper fluid through the valve while it is in an open position. Fluid is delivered from the compression transfer volume  90  through the compression valve  76  and into the fluid reservoir  52  via flow ports in the circumferential interface ring  56  which is mated with a valve collar  129  to the assembly of solenoid  102  to form the compression valve  76 . Fluid leaving the compression transfer volume  90  enters a radial port  124  which opens into a circumferential upstream well  128  in the collar  129  where damping fluid is passed through a bleed disc  126  into a circumferential downstream well  130  to transfer through the center bore of seat  120  while solenoid  102  is energized. The upstream well  128  and the downstream well  130  are integrally formed within the collar  129 . Likewise, the bleed disc  126  is seated in the ring between the upstream and downstream wells. The seat  120  is carried in a receiving bore  136  interjacent the upstream well  128 , and fluid flows through a central aperture  138  in the bleed disc  126  where it is delivered to the center bore of seat  120 . Upon energizing the solenoid  102 , fluid flows past check valve  122  into a spring port  132  which supports the check valve  122 , where damping fluid is further delivered through an exit port  134  into the reservoir  52 . 
     As further shown in FIGS. 3 and 4, the solenoid  106  is energized such that a core  140  having an end mounted plunger ball  142  is retracted from a flow orifice  144  and a plunger seat  146  through which flow is provided, thus opening the rebound valve  78 . The rebound valve  78  is provided in sealing abutment against flow passages provided in the circumferential interface ring  56  by welding the solenoid  106  outer housing circumferentially to aperture  74 . As a result, a flowpath is provided from the rebound transfer volume  86  through the interface ring  56 , into and through the rebound valve  78 , back through the interface ring  56 , and out through the compression transfer volume  90 . More particularly, damping fluid flows from rebound transfer volume  86  into a first radial port  148  formed in the interface ring  56  which empties into a circumferential upstream well  152 , through a bleed disc  150  and into a circumferential downstream well  154  where it passes through a central aperture  158  in the bleed disc  150  for transfer through orifice  144 . The circumferential upstream and downstream wells  152  and  154  are provided in a valve collar  157  carried in the rebound valve  78  which seats and abuts with the interface ring  56  on one side, and abuts with the solenoid  106  on the other side, and further provides a receiving bore  160  for carrying plunger seat  146  therein. Furthermore, a flow exit port  162  is provided downstream of the plunger seat  146  through which damping fluid exits from flow orifice  144  and enters a second radial port  156  provided in the interface ring  156  for exit to the compression transfer volume  90 . As depicted in FIG. 4, the solenoid  106  is activated in a retracted position which provides fluid flow through the rebound valve  78 . By de-energizing the solenoid  106 , the rebound valve  78  is activated, axially extending core  140  and the plunger ball  142  to seal with the plunger seat  146  and stop flow through the orifice  144 , thereby effectively shutting off the rebound valve  78 . 
     In operation, the solenoid  102  can be energized to open the compression valve  76  in order to provide a bypass flow of damping fluid over flow provided through the base valve  50 , as well as the flow apertures  98  provided in the piston  42 . By energizing the solenoid  102  and opening the compression valve  76 , the flow of damping fluid in the compression chamber  82  is provided into the reservoir  52 , via the various flow paths described above. By providing by-passing fluid flow in addition to fluid flow of the piston  42  and the base valve  50 , compressive damping of the damper  10  can be varied. In operation, the solenoid  106  is de-energized to close rebound valve  78 , and is energized to open the rebound valve  78 . When opened, a by-pass flow is created for damping fluid in addition to fluid valves, or ports, provided in the piston  42 . This by-pass flow is regulated by the bleed disc  150 , valving or slots formed in the disc. In operation, while the rebound valve  78  is open, hydraulic fluid volume passing through the rebound valve, at low pressure after leaving the rebound valve, will partly fill the compression chamber  82 , via the compression transfer volume  90 . The damping fluid flows through the compression connection chamber  82 , via the compression transfer volume  90 . The damping fluid flows through the compression connection opening  92  which further meters transfer of the fluid between the compression transfer volume  90  and the compression chamber  82 . Each of the preceding occurs during the rebound phase of the piston  42  in the damper  10 . Furthermore, the check valve  122  in the compression valve  76  prevents damping fluid flow from being sucked into the compression chamber  82  through the compression valve  76  while the piston  42  is in rebound. Furthermore, remaining damping fluid necessary for filling the compression chamber  82  is provided through the intake of the base valve  50  as the piston  42  is moved upward toward a rebound position. 
     While it is apparent that the preferred embodiment illustrated above is well-calculated to fulfill the objects stated, it will be appreciated that the present invention is capable of modification, variation and change without departing from the scope of the invention. For example, from the discussion above, application of discrete valve concepts have been incorporated in the compression valves  76  and rebound valve  78  of the preferred embodiment. However, modifications are generally known in the art for providing variable flow orifices, such as metering pins having varying diameters which axially cooperate with flow orifices to provide annular flow paths, such that tailored flow delivery can be produced through each vale provide a continuously variable valve for both the compression and rebound phases of a damper  10 . Furthermore, construction of a rebound transfer tube  58  which is concentric over pressure cylinder  38  can be substituted with a transfer tube of various other design currently utilized with normal external valve damper systems currently available on the market. Likewise, the disc valving provided through bleed discs  126  and  150  can be replaced by spring valving systems which regulate fluid flow, by increased dimensions of the valve. 
     In addition, various methods may be used for sensing accelerations or velocities of a vehicle suspension which dictate settings for tailoring damping characteristic in compression and rebound. For example, accelerometers can be provided atop each damper  10  which monitor shock conditions resulting from pitch, yaw, and roll, as well as interaction with various bumps and obstacles, such sensed signal being further processed by the electronic control module  28  and compared to determine the desired compression and rebound damping characteristics for the damper  10 . As a result, compression valve  76  and rebound valve  78  are actuated accordingly. In accordance, the scope of the invention is to be measured against the scope of the following claims.