Abstract:
A suspension system is disclosed utilizing oil addition and subtraction to actuate an accumulator to control position and stiffness in an Emulsion Shock/Oleo Pneumatic strut/Air spring strut. The strut maintains ride height for a wide variation in sprung mass and adjusts for the expansion/compression of the gas due to variations in temperature. The strut provides spring and damping characteristics.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 62/277,160, filed Jan. 11, 2016, the disclosure of which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    This invention relates in general to load leveling suspensions. In particular, this invention relates to a fluid sprung, load leveling strut having a compensation unit that can adjust for factors affecting vehicle ride height. 
         [0003]    Load leveling suspensions are known that compensate for vehicle ride height by providing for the addition of fluid, such as oil or air, to directly extend an inner strut member relative to an outer strut member. The compensating fluid may be added manually or in response to a sensed unlevel condition. Some leveling suspensions rely on conventional coil or leaf springs to support the majority of vehicle weight and utilize a load leveling component for additional load compensation. Certain types of leveling suspensions, such as disclosed in U.S. Pat. No. 3,582,106 to Keijzer, utilize a pumped hydraulic oil as the compensation fluid to extend the inner and outer members. This design provides a separate pneumatic bladder chamber that compresses or expands in response to the increased sprung load and suspension articulations. 
         [0004]    Current load leveling suspensions, however, are not tunable over a wide range of vehicle types or operating conditions. Thus, it would be desirable to provide a load leveling strut that can be tuned for different vehicles or changing load conditions. 
       SUMMARY OF THE INVENTION 
       [0005]    This invention relates to a fluid sprung, load leveling strut having a compensation unit that can adjust for factors affecting vehicle ride height. 
         [0006]    A load leveling strut comprises a main strut body and a compensation unit. The main strut body includes a strut rod telescopically received within a sleeve. The strut rod and sleeve define a volume that contains a first compressible fluid. The compensation unit defines first, second, and third fluid chambers. The first chamber is in fluid communication with the volume defined by the strut rod and sleeve. The first chamber contains the first compressible fluid retained by a first piston. The second chamber has a stop ring that defines a second chamber volume and is configured to accept a volume of an incompressible fluid. The stop ring limits movement of the first piston in one direction. The third chamber has a second piston and a closed end defining a third chamber volume that contains a second compressible fluid. The second chamber alters a vehicle ride height in response to the volume of the incompressible fluid in the second chamber. 
         [0007]    Various aspects of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1A  is an elevational view of an exemplary vehicle having a load leveling strut in accordance with the invention. 
           [0009]      FIG. 1B  is a close up view of the load leveling strut of  FIG. 1A . 
           [0010]      FIG. 2A  is a perspective view of an embodiment of a load leveling strut. 
           [0011]      FIG. 2B  is a perspective view, in cross section, of the load leveling strut of  FIG. 2A . 
           [0012]      FIG. 3  is an enlarged, sectional view of an upper portion of the load leveling strut of  FIG. 2B . 
           [0013]      FIG. 4  is an exploded view of the upper portion of the load leveling strut of  FIG. 3 . 
           [0014]      FIG. 5  is an enlarged exploded view of a compensation unit of the load leveling strut of  FIG. 3 . 
           [0015]      FIG. 6  is an exploded, perspective view of a piston/shaft and damper assembly of the load leveling strut of  FIG. 2B . 
           [0016]      FIG. 7  is a comparative plot of stiffness over a deflection range of a first embodiment of an Emulsion Shock and a Dual Spring rate Coil-over shock assembly. 
           [0017]      FIG. 8  is a comparative plot of stiffness over a deflection range for the first embodiment Emulsion Shock, the Dual Spring Rate Coil-over shock and a second embodiment of an Emulsion shock. 
           [0018]      FIG. 9  is a comparative plot of stiffness over a deflection range another embodiment of an Emulsion shock and the Dual Spring rate Coil. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0019]    Referring now to the drawings, there is illustrated in  FIG. 1A  a vehicle, shown generally at  10 , having a front suspension  12  and a rear suspension  14 . The rear suspension  14  is shown in an enlarged view of  FIG. 1B  and includes a trailing arm  16  that is pivotally connected to the vehicle  10 . The trailing arm  16  including drive axles or wheel hubs and halfshaft assemblies generally illustrate rear unsprung mass of the vehicle. A similar condition exists at the front suspension  12 . The unsprung mass generally is weight that is not supported by the suspension. The remainder of the vehicle  10  that is supported by the suspension is considered sprung mass. Though illustrated as an independent rear suspension, a conventional solid axle suspension is also within the scope of the invention. Additionally, the invention is equally applicable to the front suspension  12 . The rear suspension  14  includes a load leveling strut  18  connected between the trailing arm  16  and a portion of the vehicle  10 , such as a frame, body, space-frame, or other position representing the sprung mass. 
         [0020]    Referring now to  FIGS. 2A, 2B and 3 , the load leveling strut  18  includes a main strut body  20  and a compensation unit  22 . The main strut body  22  includes a sleeve  24  and a strut rod  26  that is telescopically received within the sleeve  24 . The sleeve includes a first mounting point  28  and the strut rod  26  includes a second mounting point  30  that permit a pivotal attachment of the strut  18  between the sprung and unsprung masses. The sleeve  24  includes a seal and bushing assembly  32  that seals against a portion of the diameter of the strut rod  26  and permits movement of the strut rod  26  within the sleeve  24 . A fluid diffuser  34  seals the opposite end of the sleeve  24  from the seal and bushing assembly  32  and is attached to the first mounting point  28 . The fluid diffuser  34  includes a plurality of fluid ports  36  in fluid communication with a channel  38  that permit fluid flow between the sleeve  24  and the compensation unit  22 . The strut rod  26  terminates in a damping plunger  40 . The damping plunger  40  includes a plurality of fluid damping ports or orifices  42  that permit fluid to flow through as the strut rod  26  moves within the sleeve  24 . The damping ports  42  provide a fluid shearing effect to create an appropriate damping force. 
         [0021]    The compensation unit  22  includes a cylindrical outer body  44  terminating in a sealed end  46  on one end and a compensation diffuser  48  on the other end. The compensation diffuser  48  includes a plurality of fluid ports  50  connected together by a fluid channel  52 , similar to the fluid diffuser  34 . The compensation diffuser  48  and the fluid diffuser  34  are coupled for fluid communication therebetween by a bridge  54 . The bridge  54  includes one or more fluid channels  56  in communication with the channels  38  and  52  and also the plurality of fluid ports  36  and  50 . The compensation unit  22  includes an oil inlet port  58  extending through a stop ring  60 . The stop ring  60  divides the interior of the compensation unit  22  into three chambers. While the load leveling strut  18  is illustrated as having a separate accumulator arrangement the design is not limited to a separate reservoir/accumulator. This system can be configured into a single strut housing. 
         [0022]    A first chamber defines a spring chamber  62  that provides a load resistance as a function of the volume of a compressible fluid, such as a compressed gas or a mixture of gas and oil. In one embodiment, the spring chamber  62  is filled with a mixture of Nitrogen gas and oil to form an emulsion. In another embodiment, the spring chamber  62  may be filled with a gas, such as air, Nitrogen, an inert gas or other compressible fluid medium to form an Air Spring strut. These suspensions do not require a mechanical spring, such as coil or leaf springs commonly found in most wheeled vehicle applications. The spring chamber  62  is in fluid communication with the interior of the sleeve  24 , defining a strut spring chamber  64 . The chambers  62  and  64  are charged to a specific pressure and oil level to provide a “spring force” for a desired stiffness and ride characteristics. 
         [0023]    The strut rod  26 , as shown in  FIG. 6 , terminates in a piston end  66  (which includes the area connecting the damper plunger  40  to the rod) having a diameter, D that provides a force differential between the mounting points  28  and  30 . The force differential is adequate to provide the “spring” force to suspend the vehicle. The spring chamber  62  of the compensation unit  22  terminates in a spring chamber piston  68 . The piston  68  and the strut rod piston end  66  define the variable volume of the spring chambers  62  and  64  that reacts against the applied load to support the vehicle weight. To change the amount of “spring” progression, the compressible fluid is added or subtracted to the chambers  62  and  64  during initial set up. To change the amount of spring force, the gas component of the compressible fluid is increased or decreased appropriately. Damping in the strut is done by the oil/nitrogen mixture traveling through the orifices  42  of the damping plunger  40 . Alternatively, damping can be accomplished through other orifices, such as the fluid ports  36  and  50 , and/or bridge channels  56 . 
         [0024]    A second chamber defines a load leveling chamber  70 . The piston  68 , which is moveable within the spring chamber  62  separates the first and second chambers  62  and  70 . Oil, or another generally incompressible fluid, may be introduced or withdrawn from the load leveling chamber  70 , in response to a sensed out of level condition of the vehicle or a force or pressure differential in the strut  18 . When no oil is in the load leveling chamber  70 , the piston  68  rests against one portion of the stop ring  60 . In this condition, the strut  18  reacts in a generally conventional manner, similar to other types of fluid or air spring struts. When the strut rod  26  is compressed due to an increased load, oil is added to the load leveling chamber  70 . This additional oil causes the piston  68  to travel towards the compensation diffuser  48 , compressing the volume within the chambers  62  and  64 , thus increasing the pressure therein. When the internal pressure increases, more spring force is created, bringing the suspended vehicle back to the desired ride height. 
         [0025]    A third chamber of the compensation unit  22  is a ride characteristic chamber  72 . The ride characteristic chamber  72  is charged with a compressible fluid, such as Nitrogen, though any suitable gas, such as another inert gas, may be used. The ride characteristic chamber  72  is defined by the sealed end  46  on one side and a second piston  74 , located against the stop ring  60 , in a static, unloaded or empty condition. When the strut  18  is subjected to a loaded state, oil in the load leveling chamber  70  provides a hydraulic link between the spring chamber  62 ,  64  and the ride characteristic chamber  72 . By varying the amount of pressure in the ride characteristic chamber  72 , a tunable ride characteristic and spring rate progression during the loaded state can be achieved. In one embodiment, the pressure in the ride characteristic chamber  72  is a fixed pre-charged pressure. In an alternative embodiment, the pressure in the ride characteristic chamber  72  may be varied during operation. Adjusting the pressure in ride characteristic chamber  72  changes or tunes the spring progression throughout the various positions of the strut rod  26 . The size and pressure of ride characteristic chamber  72  is another factor that affects the spring characteristics in the strut  18 , particularly during a loaded state. 
         [0026]    During operation, as the strut  18  is loaded, the emulsion fluid in chambers  62 ,  64  compresses due to the Nitrogen content and the distance between the mounting points  28  and  30  decreases. The ratio of Nitrogen gas to oil is one tunable parameter that may be adjusted in conjunction with the volume defined by the sleeve interior bore dimension and the strut diameter D. The sleeve and strut sizes are typically determined by the structural and fatigue considerations of the system and the available design envelope. Compression of the fluid causes the ride height to be reduced proportionally to the weight. As the volume of Nitrogen is increased in the emulsion fluid, the stiffness curve becomes shallower. As the volume of Nitrogen is decreased, the stiffness curve becomes steeper. The ride characteristic chamber  72  is charged to provide a desired, secondary reaction spring rate responding to oil added to the load leveling chamber  70 . To raise the ride height, oil is added (by way of a pump or other oil pressure source) to the load leveling chamber  70 . Conversely, oil may be removed back to a reservoir to lower the ride height. The piston  68  compresses the emulsion fluid in chambers  62 ,  64  causing an increase in pressure in the chamber and the strut  26  to extend, thus raising the vehicle. The piston  74  deflects proportionally based on the Nitrogen pressure in ride characteristic chamber  72 . 
         [0027]    As the vehicle suspension articulates in response to the terrain, the strut rod  26  compresses the emulsion fluid. Typically, the ride characteristic chamber  72  is pressurized to a level that adjusts the movement of the strut  18  in the upper load range. For example, as shown in  FIG. 9 , a “knee” or change in slope occurs at approximately 9 inches of deflection and 3000 lbs. of force. This knee represents the initiation point of the influence of the ride characteristic chamber response to overall strut performance. Thus, by varying the Nitrogen charge pressure in conjunction with the gas/oil ratio of the emulsion fluid, the response of the strut  18  may be tailored to different response over the load/deflection curve. 
         [0028]    In another embodiment of a strut system using a plurality of load leveling struts  18 , two struts  18  may be fluidly interconnected by the oil inlet ports  58 . In addition, an oil pump may be coupled to the interconnected struts to supply leveling oil for one or both struts  18 . In applications involving a solid axle, for example, the interconnected struts  18  have the advantage that a compressed strut may be able to supply oil from the compressed strut load leveling chamber  70  to an extended strut load leveling chamber  70 . This condition may result in a beneficial balancing of forces when a vehicle traverses a ditch or other undulation that compresses one strut but permit extension of the other strut across the same axle. 
         [0029]    Referring now to  FIG. 7 , there is a comparative plot of stiffness of a stiffness for a standard strut having an emulsion-based support fluid (“Emulsion Shock”) versus a Dual Spring rate Coil-over strut assembly, showing load (Lbs.) over a deflection range (inches). As shown in  FIG. 7 , the stiffness of the Emulsion Shock can be adjusted to simulate a conventional coil-over shock arrangement. As can be seen from the plot of the Emulsion Shock, there is an increase in stiffness toward the end of travel. In addition, the Emulsion Shock stiffness curve is characteristic of a second or higher degree polynomial, rather than the linear segments of the dual rate coil-over shock. This increased stiffness is beneficial when the vehicle is in a loaded condition. 
         [0030]    Referring now to  FIG. 8 , there is illustrated a comparative plot of stiffness over a deflection range for the Emulsion Shock, the Dual Spring Rate Coil-over shocks and the load leveling strut  18  having the compensation unit  22 . The compensation unit  22  of the load leveling strut  18  permits the ability to tune the response characteristics of the strut  18 . Depending on adjustment of the tuning parameters, the response of the strut can simulate the stiffness characteristics of the dual rate coil-over shock, the Emulsion Shock, a combination of both curves or other response functions of load and deflection. The plot for the load leveling strut  18  of  FIG. 8  represents the compensation unit  22  having the load leveling function detuned throughout the stroke range of the strut rod  26 . In the detuned state, the load leveling chamber  70  is discharged of oil. Thus, the load leveling strut  18  is configured to respond similarly to the Emulsion Shock. 
         [0031]    Referring now to  FIG. 9 , a comparative graph, similar to  FIG. 8 , shows the stiffness of the load leveling strut  18  with the compensation unit  22  operating with an oil charge to provide a load leveling function.  FIG. 9  compares the effectiveness of the load leveling feature over the Emulsion Shock stiffness and the Dual Spring rate Coil against stiffness. By adding oil to the middle chamber in the accumulator, the stiffness plot is shifted. This provides increased stiffness in the middle of the travel to maintain ride height and increase the stiffness at the end of the travel for bottom out control. During testing, when a load was added to the vehicle, the coil-over shock compressed 2 inches. The coil-over shock was configured for a 500 lb/in spring rate. In order to maintain the original ride height, an additional 1000 lbs of stiffness is needed. With the addition of oil to the compensation unit  22 , the deflection of the strut  18  is compensated for the additional weight and ride height, and the increased stiffness though out the travel helps control the increase in sprung mass. 
         [0032]    The principle and mode of operation of this invention have been explained and illustrated in its preferred embodiment. However, it must be understood that this invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope.