Abstract:
An anti-roll suspension system for a motor vehicle includes a plurality of double-acting cylinders coupling the unsprung and sprung portions of the vehicle. The upper fluid chamber of each cylinder is exclusively connected to the lower fluid chamber of the laterally opposite cylinder to create a fluid circuit having first and second portions which hydraulically link the cylinders. When the vehicle is subjected to a centrifugal force, the position of the sprung portion rotates relative to the position of the unsprung portion of the vehicle. This relative rotation is resisted by the tendency to substantially equalize the forces acting on pistons of the first and second cylinders, thereby reducing the tendency of the sprung portion of the vehicle to roll. An alternate embodiment includes a valve which is operable in either of a recirculating mode and cross-flow mode. When the vehicle is subjected to a centrifugal force which exceeds a predetermined value, the valve is actuated to establish the cross-flow mode and enable fluid to flow between the laterally opposite cylinders. The valve is otherwise maintained in its recirculating mode whereby fluid is circulated between the upper and lower fluid chambers of each individual cylinder.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates generally to vehicle suspension systems and more particularly to a hydraulic anti-roll suspension system for a motor vehicle. 
     2. Discussion 
     Traditional vehicle suspension systems include resilient devices, such as coil springs, leaf springs and torsion bars, to flexibly support a portion of a vehicle and enable all of the wheels to maintain contract with the ground when traversing uneven terrain. Segregating the vehicle into unsprung and sprung portions in this manner is also useful for preventing severe impulsive forces from being transmitted to the vehicle occupants. It is known that as a vehicle travels around a corner, centrifugal forces acting on the vehicle tend to cause the sprung portion of the vehicle to roll. In severe instances, the effects of roll could cause instability and impede the ability of the driver to control the vehicle. Although the effects of roll are more pronounced with vehicles having a comparatively high center of gravity, such as vans or trucks, every vehicle is effected by roll. 
     To combat the effects of roll, anti-roll suspension systems have been developed. Their use, however, has not been widespread, as they have generally proved to be relatively expensive, complex, or inconvenient to manufacture, install or service. For instance, many of these systems require the use of a fluid power source, such as a hydraulic pump, which increases the load on the vehicle&#39;s power source and reduces fuel economy. Furthermore, most anti-roll suspension systems are not easily integrated into vehicles having conventional suspension system components. Consequently, there remains a need for a simplified anti-roll suspension system which is inexpensive and easily integrated into a vehicle equipped with otherwise conventional suspension system components. 
     SUMMARY OF THE INVENTION 
     It is a general object of the present invention to provide an effective and inexpensive anti-roll suspension system comprised of a pair of double-acting cylinders which are coupled between a sprung portion and an unsprung portion of a vehicle and which are interconnected by a fluid circuit. 
     It is another object of the present invention to provide an anti-roll suspension system that controls the roll angle of the sprung portion of the vehicle while the vehicle is cornering without decreasing passenger comfort during normal highway conditions. 
     It is a further object of the present invention to provide an anti-roll suspension system that is easily integrated into a vehicle having conventional suspension components. 
     In accordance with the present invention, an anti-roll suspension system for a motor vehicle is provided which includes a pair of double-acting cylinders coupling the unsprung and sprung portions of the vehicle. The upper fluid chamber of each cylinder is exclusively connected to the lower fluid chamber of the laterally opposite cylinder to create a fluid circuit having first and second portions which hydraulically interconnect the cylinders. When the vehicle is maneuvered around a corner, the position of the sprung portion rotates relative to the position of the unsprung portion of the vehicle. This relative rotation is resisted by the tendency to substantially equalize the forces acting on the cylinder pistons, thereby reducing the tendency of the sprung portion of the vehicle to roll. As such, anti-roll capabilities are provided without the need for costly fluid pumps which reduce the fuel economy of the vehicle. 
     In an alternate embodiment, a valve is included which is operable in either of a recirculating mode and a cross-flow mode. When the vehicle is subjected to a centrifugal force which exceeds a predetermined value, the valve is actuated to establish the cross-flow mode and enable fluid to flow between the laterally opposite cylinders. The valve is otherwise maintained in its recirculating mode whereby fluid is circulated between the upper and lower fluid chambers of each individual cylinder. Configuration of the suspension system in this manner controls roll during cornering maneuvers while preventing vertically directed forces encountered by an individual wheel during normal driving conditions from being transmitted to the laterally opposite wheel. 
     Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from a reading of the subsequent description of the preferred embodiment and the appended claims, taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In order to appreciate the manner in which the advantages and objects of the invention are obtained, a more particular description of the invention will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. Understanding that these drawings only depict preferred embodiments of the present invention and are not therefore to be considered limiting in scope, the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which: 
     FIG. 1 is a perspective view of an exemplary front wheel suspension system into which the present invention is incorporated; 
     FIG. 2 is a diagrammatical view of the anti-roll suspension system of the present invention incorporated into the front end of an exemplary motor vehicle having suspension components linking the unsprung and sprung portions of the vehicle together; 
     FIG. 3 is an enlarged diagrammatical view of the anti-roll system shown in FIG. 2; 
     FIG. 4 is a partial diagrammatical view of an anti-roll suspension system according to an alternate embodiment of the present invention showing a valve disposed in the fluid circuit for normally preventing the flow of fluid to laterally opposite cylinders; 
     FIG. 5 is a view of an inertia-sensitive valve suitable for use in the anti-roll suspension system of FIG. 4; and 
     FIG. 6 is a diagrammatical view of an electrically-actuated valve suitable for use in the anti-roll system of FIG.  4 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In general, the present invention is directed toward a hydraulic anti-roll suspension system interconnected between the spring and unsprung portions of a motor vehicle. The hydraulic anti-roll suspension system is adapted to work in conjunction with conventional front and rear suspension systems. Thus, the present invention may be utilized in a wide variety of vehicular suspension systems and is not intended to be limited to the particular application described herein. Moreover, certain terminology is used in the following detailed description for convenience only and is not intended to be limiting. 
     Turning now to the drawings, FIG. 1 shows an independent front wheel suspension system generally indicated at  10 , of the type having upper and lower control arms and a strut assembly at each wheel which are suspended from the vehicle frame. Reference will be made to a vehicle frame in the present disclosure, yet those skilled in the art will recognize that many current vehicles do not have a frame as such but instead have regions of the body which act as an integrated frame structure. With this in mind, frame  12  is shown to partially include a pair of longitudinal side rails  14  and a crossbeam  16 . Suspension system  10  includes a lower control arm  18  and an upper control arm  20  which are both pivotally attached to frame  12 . A strut assembly having a helical coil spring  22  and a strut damper  24  is retained between an intermediate portion of lower control arm  18  and frame  12  to support the weight of the vehicle body and any loads which are transmitted through lower control arm  18 . Upper control arm  20  is connected to lower control arm  18  by a steering knuckle  26 . A hub and rotor assembly  28  is rotatably attached to a spindle portion (not shown) of steering knuckle  26  such that a wheel and tire (also not shown) may be mounted thereon. A stabilizer bar  30  is shown to include an elongated central segment  32  which extends laterally across the vehicle and a pair of arm segments  34  which extend longitudinally along the vehicle at each end of central segment  32 . Central segment  32  is rotatably attached to frame rails  14  by a pair of to mounting brackets  36 . A distal end  38  of each arm segment  34  is pivotably connected to a corresponding lower control arm  18  by an end link  40 . 
     Referring to FIG. 2, an anti-roll suspension system  42  is diagrammatically depicted in operative association with components of suspension system  10 . Anti-roll suspension system  42  is arranged to couple the “sprung” portion of the vehicle to its “unsprung” portion. The sprung portion includes, among other things, frame  12  and the body (not shown) of the vehicle. As shown, the unsprung portion includes, among other things, lower control arms  18 , spindles  28  and wheels  44 . As is conventional, lower control arms  18  link the sprung portion to the unsprung portion. Each lower control arm  18  pivots about a pivot point  46  in response to a vertically directed force from its respective wheel  44 , such as when the vehicle is operated over uneven terrain. As noted, suspension system  10  is installed between the sprung and unsprung portions so as to support the vehicle in each “corner” and dampens the relative movement of each wheel  44 . 
     Anti-roll system  42  is shown in FIGS. 2 and 3 to include a pair of double-acting cylinders  48   a  and  48   b,  each being located in a laterally opposite corner from the other. Cylinder  48   a  includes a housing  52   a,  a piston  54   a  and a rod  56   a.    
     Housing  52   a  and piston  54   a  combine to form an upper fluid chamber  58   a  and a lower fluid chamber  60   a  which vary in volume according to the position of piston  54   a.    
     Similarly, cylinder  48   b  includes a housing  52   b,  a piston  54   b  and a rod  56   b,  with upper chamber  58   b  and lower fluid chamber  60   b  defined therein. Housings  52   a  and  52   b  are fixed to frame  12 . Rods  56   a  and  56   b  couple lower control arms  18  to corresponding pistons  54   a  and  54   b  such that relative movement between the sprung and unsprung portions of the vehicle causes a corresponding vertical movement of pistons  54   a  and  54   b.  As seen, upper fluid chamber  58   a  of cylinder  48   a  is connected through a first fluid conduit  62  to lower fluid chamber  60   b  of cylinder  48   b.  Likewise, upper fluid chamber  58   b  of cylinder  48   b  is connected through a second fluid conduit  64  to lower fluid chamber  60   a  of cylinder  48   a.  Connection of cylinders  48   a  and  48   b  in this manner establishes a closed-loop fluid circuit  66  therebetween. It should be noted that fluid circuit  66  is the sole means for interconnecting cylinders  48   a  and  48   b  and that no interconnections between first and second conduits  62  and  64  are utilized. 
     When the vehicle, equipped with anti-roll system  42  of the present invention, is maneuvered around a corner, the sprung portion of the vehicle will rotate in a first direction relative to the unsprung portion, thereby tending to extend rod  56   a  from cylinder  48   a  and retract rod  56   b  from cylinder  48   b.  The extension of rod  56   a  from cylinder  48   a  will cause its piston  54   a  to push fluid from lower fluid chamber  30   a  in cylinder  28   a  into second fluid conduit  64 . This, in turn, causes fluid to enter upper fluid chamber  58   b  of cylinder  48   b,  which tends to push its piston  54   b  down. Movement of piston  54   b  in cylinder  48   b  in this direction causes fluid to flow out of lower chamber  60   b  in cylinder  48   b  and into first fluid conduit  62  which, in turn, tends to push fluid into upper chamber  58   a  of cylinder  48   a.  This transfer of fluid between the laterally opposite cylinders  48   a  and  48   b  tends to level the sprung portion of the vehicle. Fluid in fluid circuit  66  will continue to distribute itself in this manner until the forces exerted on pistons  54   a,    54   b  by the fluid in their associated upper and lower fluid chambers reaches a substantial equilibrium. The natural tendency of the system to reach equilibrium eliminates the need for costly pumps which would increase the load on the engine and reduce fuel economy. 
     Preferably, anti-roll system  42  is tuned to the vehicle to optimize its performance. Tuning effectively varies the response of anti-roll system  42 , eliminating the sudden shifting of the sprung portion as well as preventing the individual motions of one wheel  44  from being copied to the laterally opposite wheel  44 . Tuning is accomplished through a tuning apparatus  68  which causes the equilibrium forces to vary as a function of the displacement of the individual pistons wherein the equilibrium forces increase as piston displacement increases. 
     As shown in FIGS. 2 and 3, tuning apparatus  68  includes compression springs  70   a  and  70   b.  Compression springs  70   a,    70   b  are concentrically disposed about rods  56   a,    56   b  and are located in corresponding lower fluid chambers  60   a,    60   b  of cylinders  48   a  and  48   b.  Tuning through this method is highly desirable due to the flexibility associated with the use of compression springs. For example, a change in the tuning rate can easily be achieved by changing the spring rate or the length of one or both of compression spring  70   a,    70   b.  However, other turning methods can also be effectively employed to tune the response of anti-roll system  42 , either singly or in combination. For example, expandable bladders (not shown) could be incorporated into first and second conduits  62  and  64 , respectively. These expandable bladders would function as fluid-powered “springs” and would provide tuning characteristics similar to those provided by the compression springs  70 . Another type of tuning apparatus  68  is a resilient member (not shown) coupled to at least one side of each piston. The resilient member would deform or expand in response to changes in the fluid pressure in the upper and lower chambers of cylinders  48   a,    48   b.  A further tuning apparatus  68  would be the use of a compressible fluid, either wholly or in partly in combination with an incompressible fluid, which would provide the desired tuning rate though compression of the compressible fluid during movement of the pistons. Moreover, the tuning can be different for each lateral side of anti-roll system  42 , if so desired. 
     Referring now to FIG. 4, a partial diagrammatical view of an anti-roll system  42 ′ according to an alternate embodiment of the present invention is shown. Anti-roll system  42 ′ is similar to anti-roll system  42  but also includes a valve  80  which is placed in fluid circuit  66  and arranged to define a pair of first conduits  62   a  and  62   b  as well as a pair of second conduits  64   a  and  64   b.  Preferably, valve  80  has a valve element  82  that is moveable between a first position and a second position for respectively defining a “recirculate” mode and a “cross-flow” mode of operation for anti-roll system  42 ′. With valve element  82  in its first position, fluid flow is permitted between conduits  62   a  and  64   a  and between conduits  62   b  and  64   b  to provide recirculation paths between the upper and lower chambers of each of cylinders  48   a  and  48   b.  Furthermore, location of valve element  82  in its first position prevents fluid communication between conduits  62   a  and  62   b  as well as between  64   a  and  64   b,  thereby establishing the recirculate mode wherein fluid communication between cylinders  48   a  and  48   b  is interrupted. In this manner, anti-roll system  42 ′ is effectively disabled. 
     In contrast, with valve element  82  in its second position, fluid flow is permitted between first conduits  62   a  and  62   b  as well as between second conduits  64   a  and  64   b  while fluid communication between conduits  62   a  and  64   a  and between conduits  62   b  and  64   b  is prevented. Thus, with valve element  82  in its second position, anti-roll system  42 ′ operates in its cross-flow mode and is effectively activated. Valve element  82  is normally located in its first position and is only shifted to its second position when the vehicle is subjected to a centrifugal force exceeding a predetermined threshold value. With anti-roll system  42  disabled, suspension system  10  provides all damping of movement between the sprung and unsprung portions of the vehicle. In contrast, activation of anti-roll system causes it to work in conjunction with suspension system  10  to control roll conditions. 
     Referring to FIG. 5, valve  80  is shown as a mechanically-actuated valve  82  which relies on a pendulum-type movement of an inertia-sensitive actuator  84  to open and close flow paths in a valve element  86 . Valve element  86  is shown located in its centered position whereat the recirculate mode of valve  82  is established. However, valve element  86  is movable in either direction (based on the direction of roll) from its centered position to an actuated position whereat the cross-flow mode of valve  82  is established. Thus, use of mechanically-actuated valve  82  in anti-roll system  42 ′ facilitates automatic shifting between the recirculate and cross-flow modes in response to centrifugal forces exerted on inertia-sensitive actuator  84 . Alternatively, as shown in FIG. 6, valve  80  can be an electrically-actuated two-position servo-valve  88  whose control is based upon the dynamic condition of the vehicle as determined based on input signals from various sensors located throughout the vehicle. These sensors could include lateral accelerometers, steering wheel position sensors and/or vehicle speed sensors. A solenoid  90  of electronically controlled servo-valve  88  is coupled to an electronic control module  92  through leads  94 . As shown, controller  92  receives input signals from the various onboard sensors  96 . Solenoid  90  is operable in a power-off mode to locate a movable valve element  98  in a first position (shown) so as to establish the recirculate mode. However, when sensors  96  detect vehicle dynamics indicative of an excessive roll condition, solenoid  92  receives electrical power from controller  92  and causes valve element  98  to move from its first position to a second position, thereby establishing the cross-flow mode of operation. 
     Configuration of anti-roll systems  42 ′ in the manner described above provides anti-roll capabilities when the vehicle is subjected to centrifugal forces, but prevents the impulsive forces encountered by an individual wheel from being transmitted to the laterally opposite wheel during normal highway driving. 
     While the invention has been described in the specification and illustrated in the drawings with reference to several embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention as defined in the claims. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiments illustrated by the drawings and described in the specification as the best mode presently contemplated for carrying out this invention, but that the invention will include any embodiments falling within the description of the appended claims.