Abstract:
A suspension system for carrying a compressed gas fuels in vehicle. The suspensions arms and springs are configured to maximize the space between the wheels while providing a high degree of suspension stiffness to maintain proper wheel alignment during cornering, braking and in rough terrain. The suspension arms have two broadly-spaced attachment points to the chassis that provides structural rigidity to the rear suspension subassembly.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    This application claims priority to U.S. Provisional Application No. 60/332,836 filed on Nov. 6, 2001, the contents of which are incorporated by reference herein. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to a method and system for the onboard storage of a large volume of high-pressure hydrogen or natural gas on vehicles powered by either internal combustion engines or fuel cells. Particularly, this invention relates to a rear suspension subassembly having improved structural rigidity, that is designed to straddle a large diameter high-pressure storage tank with high volumetric efficiency.  
           [0004]    2. Description of the Relation Art  
           [0005]    Hydrogen powered Fuel Cell Vehicles (FCV) and natural gas powered vehicles are solution to problems of air quality and dependency on petroleum fuel. Fuel cells produce electricity by combining hydrogen with oxygen from air to produce electrical power and give off only water vapor. Natural gas fueled internal combustion engine vehicles produce exhaust emissions that are a fraction of diesel or gasoline fueled counterparts. The onboard vehicle storage of hydrogen gas or natural gas poses challenges in the areas of relatively low energy density, system cost, crashworthiness, and vehicle packaging. Gaseous fuels (e.g., hydrogen and natural gas), stored at high pressure, carry a fraction (between ⅓ rd  and ⅛ th ) of the energy density compared to gasoline or diesel fuels. To have an acceptable driving range, significant container volume is needed. Furthermore high-pressure tanks are most efficiently built as cylinders, with large diameter cylinders offering high volumetric efficiencies and manufacturing cost advantages needed for practical and affordable gaseous fuel vehicles. Large cylinders however pose a problem for vehicle packaging, impacting vehicle interior space (passenger, trunk or truckbed), undercarriage clearance and/or room for suspension assemblies that provide handling and ride acceptable to drivers. To support crashworthiness the storage tank needs to be placed as far as possible from the back of the vehicle for structural protection. In designing a suspension system that straddles a large diameter tank full consideration of the functions of the suspension system must be taken into account. The purpose of the suspension system is to (1) support the weight of the vehicle, (2) cushion bumps and holes on the road, (3) maintain traction between the tires and the road and (4) hold the wheels in alignment.  
           [0006]    The suspension assembly includes springs, dampers, linkages and tires that control the way in which a vehicle moves and reacts to roadway disturbances and directional changes.  
           [0007]    The angular and vertical movements of the wheels provide directional control compensating for (or utilize) body roll to improve cornering and respond to roadway irregularities in order to smooth out the ride and maintain adhesion. Wheels are connected to the sprung mass (car body) through linkages and are therefore affected by the rolling and pitching movements that occur about the suspensions system&#39;s reaction centers. It is critical that the suspension linkages be designed to allow the wheels to meet the dynamic requirements of various combinations of events. However, the designer is constrained by mechanical conflicts between structural members, and fuel storage containers that also must fit into the vehicle.  
           [0008]    A large-volume gaseous fuel tank, mounted between the rear wheels provides suspension design and structural difficulties. As a result, the rear suspension may not be sufficiently stiff to keep the rear wheels aligned, which leads to the vehicle&#39;s lateral instability, particularly when it is driven on rough terrain. To minimize the lateral instability, the rear suspension has to be designed to exhibit enhanced stiffness or rigidity to minimize the negative effect produced by the road irregularities on the wheels.  
           [0009]    U.S. Pat. Nos. 5,924,734 and 6,086,103 disclose a rear suspension flanking a fuel tank assembly and attached to the front portion of the vehicle by means of front ends of opposite trailing (control) arms in front of the fuel tank assembly. Accordingly, the rear suspension has only two reaction points aligned with one another and spaced frontward from the wheel axis. This structure may not be rigid enough to provide stiffness sufficient to keep the rear wheels aligned. Misalignment of the rear wheels leading to the lateral instability of the car renders the ride both unpleasant and unsafe. In addition stabilizing arms aligned with the principal axis of the storage tank and the wheel occupy valuable space in the undercarriage that reduces the overall tank length and thus the volume of gaseous fuel that can be carried onboard.  
           [0010]    It is desirable to increase stiffness of a rear suspension while providing for a large open space between the wheels, unencumbered by stiffening arms in order to house a longer tank and thus a large volume of compressed gas fuel.  
         SUMMARY OF THE INVENTION  
         [0011]    This objective of this invention is to provide a system consisting of a rear suspension subassembly shaped to extend around the fuel tank and operatively attached to the front and rear portions of the vehicle so that the front and rear portions of the vehicle provide structural rigidity for the suspension assembly, allowing the longest possible tank to be nestled between the rear wheels.  
           [0012]    There are two embodiments in the inventive suspension assembly (1) a semi-trailing design consisting of arms mounted to a forward crossmember that extend past the centerline of wheel assemblies to have their free ends connected by a stabilizing lateral link and (2) a wishbone design with arms that straddle the tank and attach to both a forward and aft crossmember. The two advantages of either embodiment of the inventive suspension subassembly is its improved rigidity for enhanced handling and maximizing the space between the rear wheels for a larger storage volume tank.  
           [0013]    Wrapping the rear suspension subassembly around a single fuel tank allows the inventive assembly to efficiently carry a large volume of gas while minimizing the loss of space within the passenger compartment or trunk. The single large diameter fuel tank is the most cost, weight and volumetric efficient storage container for high-pressure gas. Attaching the tank to body of the vehicle as far away as reasonable from the rear bumper and surrounding it by the rear suspension affords high crashworthiness protection in case of a rear or side impact collision.  
           [0014]    It is, therefore, an object of the present invention to provide a rear suspension subassembly with improved rigidity so as to hold the rear wheels of the vehicle in alignment under severe road conditions  
           [0015]    Still another object of the invention is to provide a rear suspension assembly, which has a minimum structure between the wheel centerline to enable carrying a single large-diameter, long overall length gaseous storage tank, configured to maximize fuel volume.  
           [0016]    Yet a further object of the invention is to provide an arrangement that allows for the onboard storage of a large volume tank while minimizing intrusion into the trunk compartment or passenger space and yet provide sufficient undercarriage ground clearance.  
           [0017]    Yet a further object of this invention is to provide an arrangement that positions a large diameter, high-pressure gaseous fuel tank as far as possible from the rear of the vehicle for crashworthiness protection. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which:  
         [0019]    [0019]FIG. 1A is an isometric view of the trailing arm design inventive assembly including a rear suspension subassembly and a fuel tank;  
         [0020]    [0020]FIG. 2A is an isometric view of the wishbone design inventive assembly including a rear suspension subassembly and fuel tank;  
         [0021]    [0021]FIGS. 1B and 2B are bottom isometric views of the inventive assembly corresponding to FIGS. 1A and 2A, respectively;  
         [0022]    [0022]FIG. 3 is a bottom plan view of the inventive assembly;  
         [0023]    [0023]FIG. 4 is a side view of the inventive assembly, and  
         [0024]    [0024]FIG. 5 is an elevated, partially broken front view of the inventive assembly in combination with a wheel assembly. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0025]    A preferred embodiment of the present invention will be described herein below with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail.  
         [0026]    Referring to FIGS. 1-5, a rear-suspension assembly for the chassis  10  (FIGS. 1A, 1B,  2 A and  2 B) of a vehicle powered by a combustion engine or a fuel cell is configured to conform to a contour of a single, lightweight, all-composite gaseous storage tank  12 . The inventive configuration of the inventive suspension assembly designs, i.e., a trailing arm design, as illustrated in FIGS. 1A-1B, and a wishbone design, as seen in FIGS. 2A-2B, allows both front  14  and rear  16  (FIG. 2) portions of the vehicle to contribute to the overall rigidity of the suspension, particularly to a rear suspension subassembly  18 . As a consequence of enhanced rigidity, the rear suspension subassembly  18  exhibits the improved ability of keeping the rear wheel assemblies  20  (FIG. 5) aligned even on rough terrain.  
         [0027]    For the trailing arm design, as seen in FIG. 1A, the rear suspension subassembly  18  has two crossmembers  22  and  54  (FIGS. 1-4), attached to a chassis frame  11  (FIG. 1A). While numerous types of fasteners  52  (FIG. 3) can be used for coupling the crossmembers to the chassis, elastomeric bushings decoupling the suspension from the chassis to reduce noise and harshness transmitted to the passengers are preferred. The crossmember  22  serves as a support for a pair of angled control arms  24  (FIG. 1B) and crossmember  54  serves as a support for a pair of lateral links  30 . Preferably, the control arms each have a longitudinal or trailing portion  40 , which generally extends parallel to a longitudinal axis A-A of the vehicle and past the centerline C-C of the wheel assemblies (FIG. 5), and by a transverse portion  42 , which extends along the crossmember. Accordingly, the control arms each generally have an L-shape.  
         [0028]    The control arms of the present invention, as shown in FIGS. 1A-1B, are semi-trailing arms. As known, the semi-trailing arms angle inboard and toward the rear portion  16  of the vehicle while being pivotally mounted on the crossmember  22 . Accordingly, each hinge axis B-B (FIG. 1A) extends at an angle to the vehicle longitudinal axis A-A (centerline) differing from a right angle. With semi-trailing arm suspensions the wheels  20  (FIG. 5) is free to bounce independently.  
         [0029]    Note that although the rear wheel subassembly, as disclosed above, is the semi-trailing arm type, a trailing arm type suspension subassembly can be used as well within the broadest scope of the present invention. The difference between the two designs is that the axis of the trailing arm is at a right angle to the vehicle centerline. The advantage posed by the semi-trailing system is that the angle offset enhances vehicle control during cornering.  
         [0030]    Referring to FIGS. 2A-2B, in the wishbone design, the suspension arm  24  has a U-shape and is formed in a structure similar to the breastbone in a bird (“the wishbone”). The U-shaped arms each may be formed by welding together two (2) J-shape halves or by being provided with a unitary U-shaped body. In particular, the suspension arms  24  include two fulcrums hinged about axes D-D, which extend parallel to the longitudinal axis A-A of the vehicle chassis, and attach to a forward  72  and aft  74  crossmember at pivotal attachment points  78  and  80 . The wheels are free to bounce independently. The hinge point of the wishbone design enables the tire to change its contact area with the road depending on wheel vertical movement thus enhancing vehicle control during cornering. The forward  78  and aft  80  attachment points of the arms to the forward  72  and aft  74  crossmembers provides the rigidity needed for vehicle handling and control.  
         [0031]    Returning to FIGS. 1A-1B, in a semi-trailing design, the transverse portions  42  each are pivotally mounted on the crossmember  22  by means of multiple hinges  28 . As better shown in FIG. 1A, each hinge  28  has a rubber bushing with a brass or bronze insert and a large bolt which allows the arms, in accordance with the basic principle of the semi-trailing suspension, to pivot somewhat relative to the crossmember. To have the hinge axes B-B inclined with respect to the longitudinal axis A-A, the crossmember  22  has a bearing surface, which faces the transverse portions  42 , with a rearwardly concave cross-section. Other modifications of the shape of the crossmember  22  and the semi-trailing arms  24  are, of course, possible without, however, compromising the principle of the operation of the semi-trailing arm suspension assembly.  
         [0032]    The trailing or longitudinal portions  40  of the semi-trailing arms  24  or wishbone structure each support a spring and shock-absorber unit  46  (FIG. 1B, 2B and  4 ) attached to the chassis. One of possible modifications of a unit mount  48 , as shown in FIG. 5, may be similar to the hinges  28 . In a preferred embodiment of the present invention, a MacPherson strut (combined spring/shock absorber) is selected to maximize the useful space offered by the inventive assembly. Particularly, a coil spring  56  (FIGS. 1B, 2B and  5 ) resides in the open space between the wheel assembly  20  and the gaseous storage tank  12  and terminates above the tire  58 . As is with other components of the present invention, the MacPherson strut can be replaced with a system of separate shock absorbers and springs. However, the separate spring/shock system occupies added space between the wheels reducing the length of the gaseous storage tank and hence its volume.  
         [0033]    Referring to FIG. 5, to attach the semi-trailing arms  24  to the wheel assemblies  20 , the longitudinal portions  40  of the arms are rigidly connected to a wheel mount  60 , which, in turn, is rigidly connected to a spindle  52  of the wheel assemblies  20 .  
         [0034]    One of the main advantages of the inventive semi-trailing suspension subassembly  18 , the improved stiffness, is obtained by a connecting structure including at least one lateral stabilizing link  30  coupled to free ends  62  of the longitudinal portions  40  of the arms. As a result, each semi-trailing arm  24  has a front point of attachment—the connection between the transverse portions  42  and the crossmember  22 , and a rear point of attachment, which is a ball joint  32  coupling the longitudinal portion and the lateral stabilizing link  30 . Thus, each of the control arms has two attachment points which are broadly spaced apart from the centerline C-C of the wheel assembly in opposite directions along the longitudinal axis A-A. The broad spacing and structure of the rear suspension subassembly is more stable, than, for example, a two-point, narrowly spaced apart attachment, structure of the discussed prior art patents. Accordingly, the increased stiffness of the inventive rear suspension subassembly  18  substantially minimizes lateral motion of the rear wheel assemblies even on rough terrain. The stabilizing link  30  is attached to the crossmember  54  extending between longitudinal rails  26  of the chassis frame through a hinge  90 . More than one lateral link can be provided to even further increase the lateral stability of the suspension. The lateral stabilizing link functions to allow vertical motion of the wheel assemblies while limiting lateral movement. In addition, the inventive suspension subassembly  18  has an anti roll bar  36 , a central portion of which is suspended on mounts  38  located on the underside of the crossmember. 22 , as shown in FIG. 2. As better illustrated in FIG. 5, opposite bent portions of the anti roll bar  36  are articulately attached to the trailing or longitudinal portions  40  by joints  50 . The locations of the joints  50  are offset from the hinges  28  and are spaced from the free ends  62  of the arms  24 . The anti-roll bar reduces body roll, which happens when the vehicle leans toward the outside of the turn, and thus provides for the better handling of the vehicle.  
         [0035]    In the wishbone embodiment, improved wheel control is obtained by connecting to two crossmembers one forward and the other aft of the space created for the storage tank. The wishbone fulcrum arms are attached to the crossmembers with a bushing hinge joint parallel to axis A-A. This arrangement stiffens lateral stability of each wheel, while allowing for wheel camber angle with the vertical motion of the wheel thus enhancing vehicle control in cornering. The wishbone arm arrangement with its two attachment points spaced from the centerline C-C of the wheel is more stable, than, for example, a two-point attachment structure of the discussed prior art patents.  
         [0036]    Additionally, unlike the prior art wherein the stabilizing arm and its attachment frame occupy valuable space between the wheels, the wishbone and trailing arm with lateral link straddles the tank space thus allowing for a longer length and thus larger volume tank to be placed onboard.  
         [0037]    The inventive rear suspensions including the crossmember  22 , the semi-trailing arms  24  and the lateral stabilizing or stabilizer links  30 , in the trailing arm design, or the crossmembers  72  and  74  and U-shaped arm  24  in the wishbone design, is shaped and dimensioned to substantially conform to the contour of the storage tank  12  and to wrap around it. While the location of the tank axis can be slightly displaced frontwards or rearwards from the centerline of the wheels, the configuration and dimension of the inventive subassembly makes it possible to have the tank axis and the centerline C-C of the wheel assemblies extend coplanar in a vertical plane. The single gaseous storage tank  12  intended to contain a large volume of high-pressure hydrogen or natural gas onboard the front-wheel-vehicle is suspended to the car body to help de-couple load transfer in the event of a rear or side end collision. To maintain the unsprung weight of the inventive subassembly  18  low and to minimize the space occupied by the semi-trailing arms  24  and, thus, to maximize the size of the storage tank  12 , the arms could be formed from high strength steel tubing. Other materials may include, for example, aluminum and magnesium.  
         [0038]    To mount the gaseous storage tank  12 , the vehicle has a protrusion  66  (FIG. 4) stamped into a floor pan of the vehicle and receiving a smaller portion of the tank. Multiple U-shaped straps  34  extending around a lower half portion of the tank circumference extend substantially vertically towards the floor of the vehicle and engage in recesses formed in the floor. The straps can be formed with horizontal top portions  44  which have a plurality of openings traversed by fasteners. The rear wheel subassembly  18  is dimensioned so that when the tank is nestled therein, the loss of space in the passenger compartment and the trunk is minimized. All necessary tank valving and safety devices are housed within the tank boss for safety protection. The circumference of the gaseous storage tank is distributed between the trunk and undercarriage space under the floor.  
         [0039]    As shown in the drawings and disclosed above, the crossmember  22  is spaced frontward from the centerline C-C of the wheel assemblies. Numerous designs have been considered such as the reversed structure, in which the crossmember is spaced rearward from the wheel centerline C-C. However, the preferred forward location of the crossmember, as discussed above, is optimal because it is mounted in small space in the underchassis under the rear seat. If the crossmember is moved to the rear of the automobile, it would be located in the space normally occupied by the spare tire. Furthermore, the reversed location of the crossmember would not allow the gaseous tank to be mounted further forward because the tank would move into the passenger space affecting, thus, the rear seat. Thus, the rear subassembly, as shown and described, optimizes the location of the gaseous storage tank and provides it with an improved collision protection.  
         [0040]    The foregoing is considered as illustrative of the principles of the invention. Accordingly all suitable modifications and equivalents may be resorted to, falling within the scope of the invention considered in light of the appended claims.