Abstract:
A vibration damping system for absorbing shock loads includes a hydraulic damper containing a piston slidably reciprocating within an oil filled chamber and dividing the chamber into a pair of subchambers. A hydraulic motor is in fluid communication with and located between the subchambers and is controlled by a field responsive fluid, such as an electrorheological (ER) actuated device. The hydraulic motor transforms fluid motion into rotating motion by a pair of meshing gears. The ER device is a flow cell and is connected to a shaft of one or both of the meshing gears. The magnitude of an electric field applied to the ER fluid controls the flow rate of the hydraulic fluid passing through the hydraulic motor by controlling the resistive force to the rotary motion of the gears. A plurality of check valves controls the direction of flow of the hydraulic fluid between the hydraulic motor and the subchambers.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The invention relates to vibration damping devices and systems which develop a controllable, user-adjustable damping-force when applied between two moving members, for applications such as automobile suspensions, industrial machinery, or other equipment. More particularly, the invention relates to a hydraulic damping system which uses a field responsive fluid such as an electrorheological (ER) fluid as the medium for controlling the damping performance of the device. 
     2. Background Information 
     In automotive vehicles and in other types of equipment which are subjected to vibration and shocks, various devices and systems are used to dampen, or lessen, the effect of the vibration. In automotive vehicles, vibrations are caused by traveling over road protrusions or depressions and are transmitted from the road surface, through the suspension, to the vehicle body. Vibration damping devices placed between the vehicle suspension and body are commonly used to damp these vibrations to maintain control of the vehicle and provide a smoother ride for occupants of the vehicle. 
     Typical automobile dampers are axially-sliding, oil-filled, hydraulic devices that produce a velocity dependant resistive, or damping force as they are compressed or extended. The damping force is generated via viscous/turbulent dissipation mechanisms associated with the flow of the hydraulic fluid through valves and passageways inside the damper. 
     Although such conventional devices have proven satisfactory for most applications, attempts to further refine ride-quality, while maintaining vehicle control, have identified a need for a damper with adjustable damping performance. In conventional hydraulic dampers, this tuneability is achieved by modifying the geometry of the flow-path. For example, an external motor may be connected to mechanisms within the damper such that motion of the motor alters the size of a metering orifice and/or the preload on a valve. In typical applications, an on-board computer monitors body and suspension motions to calculate an optimum damping performance and issues a control signal so that the damper is adjusted to the desired state. 
     A more recent development has evolved in which an electrorheological (ER), or field-responsive fluid is used within the chamber of the damper. One or more electrodes are provided within the device such that an applied voltage effects an increase in the ER fluid&#39;s viscosity. Since the fluid&#39;s viscosity varies in proportion with the intensity of the applied voltage, adjustability of damping performance is achieved by altering the physical properties of the fluid in the damper rather than the geometry of the flow path. In practice, this allows for a damper which can respond to a control signal more quickly than a conventional adjustable damper. U.S. Pat. Nos. 5,180,145; 5,316,112 and 5,366,048 are examples of such devices. 
     For certain applications, it has been found desirable to combine the known, durable construction of a conventional hydraulic damper with the adjustability and fast response of an ER damper. In such hybrid units, the damping energy is dissipated by viscous/turbulent dissipation mechanisms associated with the flow of the hydraulic fluid inside the damper. ER fluid is used in a separate control element to alter the characteristics of the flow path through which the hydraulic oil circulates. With proper design and placement of the control element, many of the ER damper&#39;s desirable properties can be maintained. Some examples of controllable hybrid dampers using an ER control fluid are shown in U.S. Pat. Nos. 5,161,653 and 5,752,891. 
     Although these prior art, hybrid dampers provide satisfactory solutions for certain applications, they possess several shortcomings. For example, U.S. Pat. No. 5,161,653, which is believed to be the closest prior art to that of the subject invention, discloses a hybrid ER/hydraulic fluid damper. However, the ER control element of this damper does not permit an increase in damping force during the course of a stroke beyond that which is achieved at time that the control element is energized. This means that in order to effect a maximum force response, the control element must be energized precisely at the end of a stroke when there is no flow. Consequently, if the system is not fast enough to react to an event, damping performance is compromised until the direction of the stroke is reversed. Therefore, it is desirable to provide a hybrid ER/hydraulic fluid damper in which the damping force can be controlled independently of other operating parameters such as stoke direction, velocity, frequency, or amplitude. 
     SUMMARY OF THE INVENTION 
     Objectives of the invention include providing an improved damping device and system using a field responsive fluid, such as an electrorheological and/or magnetorheological fluid, preferably of the type suitable for a vehicle suspension system, which solves the aforementioned problems of prior art hybrid ER/hydraulic dampers by providing a system that is fast enough to react to various forces exerted on the vehicle or equipment and which requires a relatively small amount of ER fluid and which does not subject such fluid to a harsh environment as in those dampers wherein the ER fluid is the main fluid contained within the piston chamber. 
     A further objective of the invention is to provide such a damping system which is able to independently change the magnitude of the damping force during the course of the stroke and in which the response time is in the millisecond time-frame, thereby enabling control of individual wheel motions in an automobile or similar vehicle. 
     A still further objective of the invention is to provide such a damping system which is significantly less costly than an electromechanical valve system that can respond in a similar time period, and in which a field responsive fluid cell containing the ER fluid is placed outside of the path of the main hydraulic fluid and can be serviced and/or replaced easily without affecting the integrity of the main body of the hydraulic damper. 
     A further objective of the invention is to provide such a damping system which has relatively few moving parts which are exposed to the ER fluid, and which requires a minimum amount of field responsive fluid and is therefore less expensive to construct and maintain. 
     Another objective of the invention is to provide such a damping system which is similar in many respects to conventional hydraulic dampers as to size and means of attachment to the vehicle thereby enabling the damping system to be utilized in existing spaces intended for conventional type hydraulic dampers yet is able to provide the desired versatilities of dampers required to contain the ER fluid as the replacement for the heretofore hydraulic fluid. 
     A further objective of the invention is to provide such a damping system which is of a rugged, compact, relatively lightweight simple design and which achieves the stated objectives in a simple and efficient manner. 
     These objectives and advantages are obtained by the improved vibration damping system of the present invention, the general nature of which may be stated as including a hydraulic damper including a housing forming an internal hydraulic fluid chamber and a damping member slidably reciprocating within said chamber and dividing said chamber into a pair of subchambers, said damping member being adapted to be connected to a first support structure; connection means on the housing for connecting said housing to a second support structure spaced from said first support structure; a hydraulic motor in fluid communication with the hydraulic damper for controlling the movement of hydraulic fluid between the subchambers upon movement of the damping member within the fluid chamber; a fluid line providing the fluid communication between the hydraulic motor and the fluid subchambers, said motor being mounted in said fluid line which said hydraulic fluid flows through said motor; and a flow cell adapted to contain a field responsive fluid operatively connected to the hydraulic motor for controlling the amount of damping of the vibration damper by controlling the hydraulic motor by regulating the amount of pressure required to pass a fixed amount of hydraulic oil through said hydraulic motor. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred embodiments of the invention, illustrative of the best modes in which applicants have contemplated applying the principles, are set forth in the following description and are shown in the drawings and are particularly and distinctly pointed out and set forth in the appended claims. 
     FIG. 1 is a side elevational view of the damping system of the present invention; 
     FIG. 2 is an enlarged fragmentary sectional view taken on line  2 — 2 , FIG. 1; 
     FIG. 3 is a diagrammatic view of FIG. 1 showing the movement of the hydraulic fluid as the piston is moving toward the right end of the cylinder; 
     FIG. 4 is a diagrammatic view similar to FIG. 3 showing the movement of the hydraulic fluid as the piston is moving toward the left end of the cylinder; 
     FIG. 5 is an enlarged fragmentary sectional view taken on line  5 — 5 , FIG. 1; 
     FIG. 6 is an enlarged fragmentary sectional view similar to FIG. 5 showing the hydraulic motor connected to two ER flow cells; and 
     FIG. 7 is a diagrammatic elevational view similar to FIG. 1, showing a second embodiment of the subject damping system. 
     Similar numerals refer to similar parts throughout the drawings. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The improved vibration damping system of the present invention is indicated generally at  1 , and is shown particularly in FIGS. 1-6. Damping system  1  includes as its main components a usual hydraulic damper indicated generally at  2 , consisting of an outer cylindrical housing or cylinder  3  which has an internal fluid chamber  4  which contains a usual hydraulic fluid such as oil. A damping member indicated generally at  6 , is slidably reciprocally mounted within chamber  4  and includes a usual piston  7  and a piston rod  8 . Piston  7  divides chamber  4  into a pair of subchambers  4 A and  4 B which vary in size as the piston slides within chamber  4 . Piston rod  8  will be connected to a support structure  5  such as one part of a vehicle, as by a threaded end  10  (FIG.  1 ), with housing  3  having an attachment device such as a bushing  11 , secured thereto for mounting the housing on another spaced component  5 A of the vehicle so that as the two spaced components move with respect to each other piston  7  will slide within housing  3 . These components are well known in the art and can have other arrangements than that shown in the drawings without affecting the concept of the invention. 
     In accordance with the invention, a hydraulic motor indicated generally at  15 , is located externally of housing  3  and is in fluid communication with subchambers  4 A and  4 B by a plurality of fluid lines  17 ,  18  and  19 . As shown in FIGS. 3 and 4, fluid lines  17  and  18  extend between and are in fluid communication with subchambers  4 A and  4 B, with fluid line  19  extending between hydraulic motor  15  and each of the fluid lines  17  and  18 . One-way check valves  20  and  21  are located at the fluid openings of subchambers  4 A and  4 B respectively, which communicate with fluid line  18  (FIGS.  3  and  4 ). A second pair of similar one-way check valves  22  and  23  are located at the fluid openings with chambers  4 A and  4 B respectively and fluid line  17 . The function of these one-way check valves is best shown in FIGS. 3 and 4 and is described in further detail below. 
     In further accordance with the invention, a flow-cell indicated generally at  25 , is operatively connected with hydraulic motor  15 , two types of which are shown in detail in FIGS. 5 and 6. 
     Hydraulic motor  15  (FIG. 2) is of a usual construction and includes a housing  26  formed with an internal fluid reservoir  27  in which is rotatably mounted a pair of gears  30  and  31  by a pair of shafts  32  and  33 , respectively. The operation of gears  30  and  31  in hydraulic motor  15 , is well known wherein it develops a flow through the motor by carrying fluid around the teeth  34  and the walls of reservoir  27 . The fluid flows into to fill the space and is carried around the outside of the gears as the gears mesh, and is forced out of the outlet  36 . In the particular embodiment shown in FIG. 2, the inlet port is indicated at  35  with the outlet port being indicated at  36 . The incoming hydraulic fluid is shown at A and the outgoing fluid shown at B which will be the flow pattern for the embodiment shown in FIGS. 3 and 4. 
     Flow cell  25  is shown in FIG. 5 as a couette cell. Cell  25  has an outer housing  40  which forms an internal chamber or reservoir  41 , which contains a supply of a field responsive fluid  42 , such as an electrorheological and/or magnetorheological fluid, hereinafter referred to as an ER fluid. A cylinder or other type of vane member  44  is rotatably mounted within chamber  41  by shaft  32  of hydraulic motor  15 . A positive electrode  46  communicates with ER fluid  42  and a ground electrode  47  communicates with shaft  32  or vane  44 . 
     The operation of the improved hydraulic damping system is shown diagrammatically in FIGS. 3 and 4. FIG. 3 shows the movement of piston  7  in the right-hand direction as shown by arrow A. Piston  7  forces the hydraulic oil into fluid line  18  through one-way check valve  20  as indicated by arrow B, with check valve  22  preventing the flow of fluid from subchamber  4 A into line  17 . The fluid flows through fluid line  18  and into hydraulic motor  15  through inlet port  35  as shown in FIG. 2, and is prevented from flowing into subchamber  4 B by one-way check valve  20 . Thus, as piston  7  moves to the right, the hydraulic fluid contained in subchamber  4 A flows through a portion of fluid line  18  and into hydraulic motor  15  where it flows through fluid reservoir  27  and around the gear teeth and out through outlet  36  as shown by arrow D, and through fluid line  19  and into a portion of fluid line  17  where it flows into subchamber  4 B through one-way check valve  23 . This return fluid is prevented from entering subchamber  4 A by one-way check valve  22 . 
     In accordance with one of the main features of the invention as shown in FIGS. 2 and 5, the passing of the hydraulic fluid through hydraulic motor  15 , causes the rotation of shaft  22  which in turn rotates cylinder or vane  44  within flow cell  25 . Depending upon the amount of voltage or electric field applied to ER fluid  42 , it will control the rotation of vane  44  and correspondingly of shaft  32  and attached gear  31 . The speed of rotation of gear  31  in turn controls the rotation of gear  30  and thus the velocity of the hydraulic fluid passing through hydraulic motor  15 . This will change the pressure drop across the hydraulic motor and enhance the damping force by controlling the speed of cylinder  7  sliding within the hydraulic housing or cylinder  3 . 
     FIG. 4 shows the operation of system  1  when piston  7  moves in the direction of arrow D or towards the left end of fluid chamber  4 . In this situation, check valve  21  opens permitting the fluid to flow as shown by arrow E into a portion of fluid line  18  and correspondingly into line  19  but is prevented from flowing into subchamber  4 A by check valve  20  being closed. Thus, the fluid flows through hydraulic motor  15  in the same direction as that described above with respect to FIG. 5, that is through inlet port  35  and out through outlet port  36  where it then moves into subchamber  4 A through open check valve  22  as shown by arrows F. Again, the strength of the electrical field applied to the ER fluid  42  will control the speed of  25  piston  7  by controlling the rotation of shaft  32  and gear  31 . Likewise, the hydraulic fluid flowing through line  17  is prevented from flowing into subchamber  4 B by one-way check valve  23 . 
     Thus, hydraulic damper  2  functions much like any conventional tube type damper wherein the piston rod is axially movable within the damper body and a force which is applied to the piston rod, such as shown by arrow G (FIG. 3) begins to move the piston  7  to the right of housing  3 . Since the flow of the hydraulic fluid through hydraulic motor  15  requires mechanical work by the fluid, a pressure difference is created between the two ends of the piston which acts on the face of the piston to create a resistive (damping) force that acts in a direction opposite to the force that initiated the damper motion. The magnitude of this force is determined by many designed parameters including the physical dimensions of the damper components, hydraulic motor characteristics, material properties of the hydraulic oil (e.g. viscosity) and the resistive force generated by the ER fluid in flow cell  25 . 
     It is the field responsive fluid characteristics that gives rise to the adjustability of the damper. When there is no electric field applied, the ER fluid can generate moderately low stresses and thus the damping force or given motion is at its minimum. When the electrical or magnetic field is applied, the fluid becomes significantly more viscous and/or develops a large static and dynamic yield stress. This extra stress manifests itself in larger resistive forces to the motion of the hydraulic motor, and thus it increases the pressure drop and consequently damping force. 
     FIG. 6 shows a modified hydraulic motor/flow cell combination wherein shaft  33  of hydraulic motor  15  is connected to a second flow cell  50 , which preferably is similar to flow cell  25  discussed above, but not required. Thus, this arrangement enables larger resistive forces to be applied to the flow of hydraulic fluid through motor  15  by providing a positive breaking action to the rotation of both gears  30  and  31  instead of just to gear  31  discussed above in the embodiment of FIG.  5 . The configuration of FIG. 6 may be incorporated into the arrangement shown in FIGS. 1,  3  and  4  or can be incorporated into a modified damping system indicated generally at  52  and shown in FIG.  7 . 
     Embodiment  52  includes the same hydraulic damper  2  as that described above but includes a first fluid line  53  which connects subchambers  4 A with motor  15  and a second fluid line  54  which connects motor  15  to subchamber  4 B. Thus, as piston  7  moves in a certain direction such as shown by arrow  1 , it will force the fluid from chamber  4 A into fluid line  53  and through hydraulic motor  15  and back into subchamber  4 B through fluid line  54 . The reverse is true when piston  7  moves in the opposite direction in the direction of arrow J. Again, the velocity of the hydraulic fluid flowing through motor  15  is controlled by the strength of the electric field applied to one or more flow cells  25 . 
     One of the important features which distinguishes the present invention over that of U.S. Pat. No. 5,161,653 is that any time during the movement of piston  7  the flow rate can be increased or decreased by varying the electric field applied to the ER fluid of cells  25 . In the damper of U.S. Pat. No. 5,161,653, it is impossible to increase the damping force during the course of a stroke beyond that which is achieved by the valve position at switching time. This means that if the system is not fast enough to react to an event, damping performance may be compromised until the direction of the stroke is reversed. 
     Accordingly, the improved vibration damping system is simplified, provides an effective, safe, inexpensive, and efficient device which achieves all the enumerated objectives, provides for eliminating difficulties encountered with prior devices, and solves problems and obtains new results in the art. 
     In the foregoing description, certain terms have been used for brevity, clearness and understanding; but no unnecessary limitations are to be implied therefrom beyond the requirement of the prior art, because such terms are used for descriptive purposes and are intended to be broadly construed. 
     Moreover, the description and illustration of the invention is by way of example, and the scope of the invention is not limited to the exact details shown or described. 
     Having now described the features, discoveries and principles of the invention, the manner in which the improved vibration damping system is construed and used, the characteristics of the construction, and the advantageous, new and useful results obtained; the new and useful structures, devices, elements, arrangements, parts, combinations and method steps, are set forth in the appended claims.