Abstract:
A vehicle drive arrangement for a vehicle of the type having differential power transmission arrangement that converts the rotatory motion of the rotatory power shaft to rotatory motion of first and second drive shafts disposed substantially orthogonal the rotatory power shaft. Primary leaf springs are each coupled at their respective centers to respective drive shafts by pivotal arrangements. The first and second primary springs may include helical springs that are used in place of, or in combination with, the primary leaf springs. Secondary leaf springs may be splayed and therefore need not be arranged parallel to the primary leaf springs. Control over vehicle kinematics is enhanced by configuring the resilience of a fulcrum bumper using resilient, rheological, or active systems. An active system will control vehicle height while stationary to facilitate loading and unloading of the vehicle.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    This patent application claims priority to U.S. patent application Ser. No. 12/308,481, filed Sep. 13, 2010, which claims the benefit of International Application Ser. No. PCT/US2007/014290 filed on Jun. 18, 2007, which claims the benefit U.S. Provisional Patent Application Ser. No. 60/814,518, filed on Jun. 16, 2006; U.S. Provisional Patent Application Ser. No. 60/900,796 filed on Feb. 7, 2007; U.S. Provisional Patent Application Ser. No. 60/921,881 filed on Apr. 3, 2007, each of which are incorporated herein by reference in their entireties. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    This invention relates generally to suspension systems for vehicles, and more particularly, to a leaf suspension arrangement that is useable with independent and semi-independent suspension systems. 
       DESCRIPTION OF THE RELATED ART 
       [0003]    Leaf spring systems have for many years been used for the suspension of wheeled vehicles. The central element of a leaf spring suspension system for a vehicle is termed a “semi-elliptical” spring configured as an arc-shaped length of spring steel having a rectangular cross-section. At the center of the arc is provided an arrangement for coupling to the axle of the vehicle. At the ends are provided coupler holes for attaching the spring to the vehicle body. For heavy vehicles, leaf springs are stacked on one another to form layers of springs of different lengths. Leaf springs are still used in heavy commercial vehicles and railway carriages. In the case of very heavy vehicles, leaf springs provide the advantage of spreading the load over a larger region of the vehicle&#39;s chassis. A coil spring, on the other hand, will transfer the load to a single point. 
         [0004]    The well-known Hotchkiss drive, the name of which derives from the French automobile firm of Hotchkiss, employs a solid axle that is coupled at its ends to the centers of respective semi-elliptical leaf springs. There are a number of problems with this form of drive arrangement. First, this drive system is characterized by high unsprung mass. Additionally, the use of a solid axle results in coupled left/right wheel motion. During heavy cornering and fast acceleration, this known system suffers from vertical deflection and wind-up. 
         [0005]    One prior art effort to address the problems associated with the Hotchkiss system employs a parallel leaf spring arrangement at each end of a solid axle. This known arrangement affords increased axle control, in the form of reduced power hop. Other advantages of this known arrangement include roll under steer, auto load leveling and the gross vehicle weight, and no frame changes are required to convert from a Hotchkiss system. However, the known parallel leaf spring arrangement employs a solid axle, and therefore does not provide the benefits of independent suspension. In addition, this known arrangement is plagued with the disadvantage of high unsprung mass. 
         [0006]    A de Dion tube vehicle suspension arrangement is a form of semi-independent suspension and constitutes an improvement over the Hotchkiss drive. In this type of suspension, universal joints are employed at the wheel hubs and the differential, and there is additionally provided a solid tubular beam that maintains the opposing wheels in parallel. The de Dion tube is not directly connected to the chassis and is not intended to flex. 
         [0007]    The benefits of a de Dion suspension include a reduction in the unsprung weight compared to the Hotchkiss drive. This is achieved by coupling the differential to the chassis. In addition, there are no camber changes during suspension unloading. Since the camber of both wheels is set at zero degrees, the traction from wide tires is improved, and wheel hop under high power operations is reduced compared to an independent suspension. However, the de Dion tube adds unsprung weight. 
         [0008]    It is, therefore, an object of this invention to provide a vehicle suspension arrangement that provides the benefits of independent suspension while using leaf spring technology. 
         [0009]    It is another object of this invention to provide a vehicle suspension arrangement that employs leaf spring technology and yet affords reduced unsprung mass for reduced inertial effects and improved vehicle handling response. 
         [0010]    It is also an object of this invention to provide a vehicle suspension arrangement that employs leaf spring technology and affords reduced suspension inertia. 
         [0011]    It is a further object of this invention to provide a vehicle suspension arrangement that employs leaf spring technology and affords reduced noise, vibration, and harshness (NVH). 
         [0012]    It is additionally an object of this invention to provide a vehicle suspension arrangement that employs leaf spring technology and affords reduced lateral wheel shake. 
         [0013]    It is yet a further object of this invention to provide a vehicle suspension arrangement that employs leaf spring technology and affords reduced side view wind-up at the axle bracket. 
         [0014]    It is also another object of this invention to provide a vehicle suspension arrangement that employs leaf spring technology and affords reduced forward and rearward movement. 
         [0015]    It is yet an additional object of this invention to provide a vehicle suspension arrangement that employs leaf spring technology and affords a semi-independent suspension effect during asymmetric wheel travel. 
         [0016]    It is yet an additional object of this invention to provide a vehicle suspension arrangement that employs leaf spring technology in combination with a coil spring element. 
       SUMMARY OF THE INVENTION 
       [0017]    These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. 
         [0018]    The foregoing and other objects are achieved by this invention which provides a vehicle drive arrangement for a vehicle of the type having a chassis extending longitudinally, and a rotary power shaft extending longitudinally along the chassis. The rotary power shaft is coupled at a rearward end thereof to a differential power transmission arrangement that converts the rotary motion of the rotatory power shaft to rotatory motion of first and second drive shafts disposed substantially orthogonal the rotary power shaft. Each of the first and second drive shafts has a respective longitudinal axis. In accordance with the invention, there are provided a differential coupling arrangement for fixedly coupling the differential arrangement to the chassis, and first and second universal coupling arrangements for coupling respective ones of the first and second drive shafts to the differential arrangement, whereby the first and second drive shafts are transaxially displaceable. First and second spring elements are coupled to respective ones of the first and second drive shafts at respective ends distal from the first and second universal coupling arrangements, and to the chassis. In addition, first and second secondary leaf springs are coupled at respective first ends thereof to the first and second drive shafts at respective ends distal from the first and second universal coupling arrangements, and at respective second ends thereof to the chassis. There is additionally provided a beam having first and second ends. The beam is coupled at the first and second ends to respective ones of the first and second drive shafts at respective ends distal from the first and second universal coupling arrangements. 
         [0019]    In one embodiment of the invention, each of the first and second ends of the beam are coupled to the first and second drive shafts at a determined transaxial distance. 
         [0020]    In a highly advantageous embodiment, the first and second spring elements are respective first and second primary leaf springs. Each of the first and second primary leaf springs is coupled at a respective first end thereof to the chassis and at substantially the center thereof to a respective one of the first and second drive shafts. The first and second secondary leaf springs are arranged, in this embodiment, to be substantially parallel to the respective first and second primary leaf springs. 
         [0021]    A beam coupler arrangement is provided for coupling the beam to the chassis. The beam coupler arrangement includes a pivotable beam coupler element pivotally coupled to the beam. A first beam coupler arm is coupled at one end thereof to the pivotable beam coupler element, and at a distal end thereof substantially in the direction of the longitudinal axis of the first drive shaft, to the chassis. There is additionally provided a second beam coupler arm coupled at one end thereof to the pivotable beam coupler element, and at a distal end thereof substantially in the direction of the longitudinal axis of the second drive shaft, to the chassis. 
         [0022]    In a practicable embodiment of the invention, the first and second secondary leaf springs are disposed below the respective first and second primary leaf springs. In other embodiments, however, the first and second secondary leaf springs are disposed above the respective first and second primary leaf springs. In some of such other embodiments, the first and second secondary leaf springs are arranged to extend through the chassis. 
         [0023]    In a highly advantageous embodiment of the invention, there are further provided first and second displaceable pivot coupling arrangements for coupling the respective second ends of the first and second secondary leaf springs to the chassis. The displaceable pivot coupling arrangements facilitate adjustment of the effective spring rate of the secondary leaf springs. 
         [0024]    In other embodiments, there are provided first and second displaceable fulcrum arrangements, also for facilitating the varying of the respective spring rates of the first and second secondary leaf springs. 
         [0025]    In accordance with a further aspect of the invention, there is provided a vehicle drive arrangement for a vehicle of the type having a chassis extending longitudinally, and a rotatory power shaft extending longitudinally along the chassis. The rotary power shaft is coupled at a rearward end thereof to a differential power transmission arrangement that converts the rotary motion of the rotatory power shaft to rotary motion of first and second drive shafts disposed substantially orthogonal the rotary power shaft. Each of the first and second drive shafts has a respective longitudinal axis. In accordance with the invention, there are provided a differential coupling arrangement for fixedly coupling the differential arrangement to the chassis, and first and second universal coupling arrangements for coupling respective ones of the first and second drive shafts to the differential arrangement, whereby the first and second drive shafts are transaxially displaceable. First and second primary leaf springs are each coupled at respective first and second ends thereof to the chassis and at substantially the center thereof to respective ones of the first and second drive shafts at respective ends of the drive shafts distal from the first and second universal coupling arrangements. In addition, first and second secondary leaf springs are coupled at respective first ends thereof to the first and second drive shafts at respective ends distal from the first and second universal coupling arrangements, and at respective second ends thereof to the chassis. There is additionally provided a beam having first and second ends. The beam is coupled at the first and second ends to respective ones of the first and second drive shafts at respective ends distal from the first and second universal coupling arrangements. 
         [0026]    In a highly advantageous embodiment of the invention, there is provided a vehicle suspension arrangement for a vehicle having a chassis and a drive axle. The vehicle suspension arrangement is provided with a primary leaf spring having a substantially longitudinal configuration and first and second ends for coupling to the chassis of the vehicle. A secondary leaf spring has a substantially longitudinal configuration, a first end for coupling to the chassis, and a second end. A coupling element is provided for coupling to the drive axle. In addition, a first pivot joint for pivotally coupling to substantially the center of said primary leaf spring intermediate of its first and second ends for coupling to said coupling element. Finally, a second pivot joint for pivotally coupling the second end of said secondary leaf spring to said coupling element. 
         [0027]    In one embodiment, there is further provided a primary leaf coupler for securing said first pivot joint to substantially the center of said primary leaf spring. The first pivot joint is formed of first and second pivot portions, the first pivot portion being fixedly coupled to said primary leaf coupler, and the second pivot portion being fixedly coupled to the coupling element. The first and second pivot portion being configured to be pivotally coupled to each other. 
         [0028]    In a still further embodiment, the first pivot joint is configured to enable limited pivotal motion between said primary leaf spring and said coupling element. The pivotal motion in this embodiment therefore is directed longitudinally in see-saw like relation to said primary leaf spring. 
         [0029]    In accordance with a further apparatus aspect of the invention, there is provided a vehicle suspension arrangement for a vehicle having a chassis and a drive axle. The vehicle suspension arrangement is provided with a primary spring having a substantially helical configuration, the primary spring having a first end for coupling to the chassis of the vehicle, and a second end for coupling to an axle of the vehicle. A secondary leaf spring that has a substantially longitudinal configuration is further provided. The secondary leaf spring has a first end for coupling to the chassis, and a second end. Additionally, a coupling element couples the second ends of the secondary leaf spring to the drive axle. 
         [0030]    In one embodiment of the vehicle suspension arrangement, the coupling element includes a pivot joint for pivotally coupling the second end of said secondary leaf spring to the drive axle. 
         [0031]    In a still further embodiment of the invention, there is provided a further primary spring having respective first and second ends thereof coupled to the chassis. The further primary spring is coupled at substantially the center thereof to the drive shaft and to the second en of said primary spring. In a highly advantageous embodiment, the further primary spring is a flat locating plate. The flat locating plate is, in some embodiments, a single plate-main leaf spring. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0032]    Comprehension of the invention is facilitated by reading the following detailed description, in conjunction with the annexed drawing, in which: 
           [0033]      FIG. 1  is a perspective representation of a specific illustrative embodiment of the invention; 
           [0034]      FIG. 2  is a side plan view of the embodiment of  FIG. 1 ; 
           [0035]      FIG. 3  is a perspective representation of a further specific illustrative embodiment of the invention; 
           [0036]      FIGS. 4   a  and  4   b  are respective side plan and partially cross-sectional front plan simplified schematic illustrations of a rotary joint arrangement constructed in accordance with the principles of the invention; 
           [0037]      FIGS. 5   a  and  5   b  are simplified representations of a suspension system constructed in accordance with the principles of the invention ( FIG. 5   a ) and a prior art suspension arrangement ( FIG. 5   b ), both in a simulated static acceleration condition; 
           [0038]      FIGS. 6   a  and  6   b  are simplified representations of the suspension system constructed in accordance with the principles of the invention of  FIG. 5   a  and a prior art suspension arrangement of  FIG. 5   b , both in a simulated static braking condition; 
           [0039]      FIG. 7  is a simplified schematic representation of a side view of a suspension system constructed in accordance with the principles of the invention with a 1 st  stage leaf spring, and further showing the wheel center path, with a fulcrum arranged to communicate with the  2   nd  stage lower leaf; 
           [0040]      FIG. 8  is a simplified schematic representation of a side view of a suspension system constructed in accordance with the principles of the invention with a 1 st  stage consisting of a substantially equivalent coil spring, or air spring, with the fulcrum of the 2 nd  stage lower leaf removed; 
           [0041]      FIG. 9  is a simplified schematic representation of a side view of a suspension system constructed in accordance with the principles of the invention with a 1 st  stage consisting of a coil spring or air spring, with an optional fulcrum, arranged to communicate with the secondary stage lower leaf, and further showing an optional locating spring plate in the 1 st  stage; 
           [0042]      FIG. 10  is a simplified schematic representation of a clip bracket that can be used to push or pull the main spring or the secondary stage; 
           [0043]      FIGS. 11   a ,  11   b , and  11   c  are simplified schematic side view representations of a height control arrangement constructed in accordance with the invention that is useful in the loading and unloading of a stationary vehicle,  FIG. 11   a  showing a simplified system control arrangement in block and line form; 
           [0044]      FIG. 12  is a simplified schematic top plan representation of a splayed suspension arrangement constructed in accordance with the invention wherein secondary leaf springs are shown to be mounted at angles with respect to the primary leaf springs; 
           [0045]      FIG. 13  is a simplified schematic perspective representation of a variable position fulcrum bumper constructed in accordance with the invention that may be active or passive to rotate in a controlled manner to create a variation in the stiffness of the secondary spring rate; 
           [0046]      FIG. 14  is a simplified schematic plan representation of the variable position fulcrum bumper of  FIG. 13 ; and 
           [0047]      FIG. 15  is a simplified schematic representation of the variable position fulcrum bumper of  FIG. 14  that is useful to illustrate the variation in vehicle height that is achievable, particularly when the vehicle (not shown) is stationary. 
       
    
    
     DETAILED DESCRIPTION 
       [0048]      FIG. 1  is a perspective representation of a specific illustrative embodiment of the invention. As shown in this figure, a vehicle suspension system  100  has a chassis that is generally designated as chassis  110 . The chassis has a pair of substantially parallel chassis rails  112   a  and  112   b  that are coupled to one another by cross-braces  116  and  118 . 
         [0049]    A differential drive arrangement  120  is fixedly coupled to the chassis and converts the rotary motion of a drive shaft  122  to substantially orthogonal rotary motion at half shafts  125   a  and  125   b . Each half shaft has an associated pair of universal joints (not specifically designated) that are arranged to be proximal and distal with respect to the differential drive arrangement Thus, the half shafts, each of which has an associated longitudinal axis (not shown), accommodate transaxial motion, particularly by operation of the proximal universal joints. 
         [0050]    Half shafts  125   a  and  125   b  are shown to be coupled at their distal ends to respective leaf springs  130   a  and  130   b . Referring to leaf spring  130   a , for example, the leaf spring is, in this specific illustrative embodiment of the invention, pivotally coupled at its forward end to a bracket  132   a . At its rearward end, leaf spring  130   a  is pivotally coupled to a link  134   a . As shown in this figure, there is additionally provided a half leaf spring  136   a  that is also, in this specific illustrative embodiment of the invention, coupled at its forward end to bracket  132   a . At its rearward end, half leaf spring  136   a  is coupled to the distal end of half shaft  125   a . Half leaf spring  136   a  is shown in this specific illustrative embodiment of the invention, to engage a fulcrum  133   a.    
         [0051]    There is additionally provided a transverse beam  140  that is coupled to cross-brace  116  by a damper  142  and to cross-brace  118  by a further damper  144 . Transverse beam  140  has installed thereon a pivoting member  150  to which are attached link elements  152  and  154 . The link elements are attached, via brackets (not specifically designated), to cross-brace  118 . 
         [0052]      FIG. 2  is a side plan view of the embodiment of  FIG. 1  of vehicle suspension system  100 . Elements of structure that have previously been discussed are similarly designated. As shown in this figure, leaf spring  130   a  and half leaf spring  136   a  are each coupled at their respective forward ends to bracket  132   a . Leaf spring  130   a  is pivotally coupled at a pivot  160 , and half leaf spring  136   a  is pivotally coupled at a pivot  162 , at bracket  132   a . In this specific illustrative embodiment of the invention, pivots  160  and  162  are fixed on bracket  132   a , which is fixed in relation to chassis rail  112   a . In other embodiments, and as will be described below, there is provided a mechanism (not shown in this figure) that displaces bracket  132   a , and in some embodiments, only pivot  162 , in relation to chassis rail  112   a . Such displacement of the pivots enables advantageous adjustment of the combined spring rate of leaf spring  130   a  and half leaf spring  136   a . Additionally, such displacement is useful to adjust the height of the vehicle (not shown) while stopped, illustratively to facilitate loading and unloading of cargo and passengers (not shown). 
         [0053]      FIG. 3  is a perspective representation of a further specific illustrative embodiment of the invention. Elements of structure that have previously been discussed are similarly designated. As shown in this figure, a vehicle suspension system  170  has a leaf spring  171  and a half leaf spring  172 . In contrast to the embodiment of  FIGS. 1 and 2 , leaf spring  171  is arranged to be coupled to the underside of half shaft  125   b . Half leaf spring  172  is coupled above half shaft  125   b.    
         [0054]    Leaf spring  171  is, in this specific illustrative embodiment of the invention, coupled to a bracket  175 . Half leaf spring  172  is coupled to chassis rail  177  at a bracket  180 . Bracket  180  is shown to be disposed within chassis rail  177 . It is particularly noteworthy that in this embodiment half leaf spring  172  is arranged to extend through chassis rail  177  at a fulcrum point  182 . The arrangement of this embodiment advantageously reduces the extent to which the leaf suspension system is visible when installed on a vehicle. 
         [0055]      FIGS. 4   a  and  4   b  are respective side plan and partially cross-sectional front plan simplified schematic illustrations of a rotary joint arrangement  200  constructed in accordance with the principles of the invention. Elements of structure that bear analogous correspondence to elements of structure that have previously been discussed are similarly designated in this figure. Referring to  FIG. 4   a , it is seen that there is provided a leaf spring  130   a  that, in this specific illustrative embodiment of the invention, is pivotally coupled at its forward and rear ends, as previously described. There is additionally provided a half leaf spring  210  that is also, in this specific illustrative embodiment of the invention, pivotally coupled at a pivot mount  212  at its end distal to a further pivotal mounting  213  at a coupling member  214 . The coupling member is itself coupled to axle shaft  215 . Half leaf spring  210  is shown in this specific illustrative embodiment of the invention to engage a fulcrum  216 . 
         [0056]      FIG. 4   a  further illustrates a pivot link mounting arrangement  220  wherein leaf spring  130   a  is securely clamped between clamping member  222  and  224 , as will be described below in relation to  FIG. 4   b . Referring once again to  FIG. 4   a , clamping member  224  is coupled to a pivot joint  226  that is itself engaged with coupling  214 . This arrangement permits a further degree of motion that reduce system internal loading on the pivot joint arrangement and leaf spring elements. 
         [0057]      FIG. 4   b  is a partially cross-sectional front plan simplified schematic illustrations of rotary joint arrangement  200  constructed in accordance with the principles of the invention. Elements of structure that bear analogous correspondence to elements of structure that have previously been discussed are similarly designated in this figure. It is seen in this figure that leaf spring  130   a  (shown cross-sectionally) is securely clamped between clamping members  222  and  224  by operation of bolts  230 . 
         [0058]    Pivot joint  226  is shown in  FIG. 4   b  to be formed of two pivot sections,  214   a  and  224   a . More specifically, pivot section  214   a  is coupled to coupling  214  (not specifically designated in this figure), and pivot section  224   a  is coupled to clamping member  224 . The pivot sections in this specific illustrative embodiment of the invention, are pivotally engaged in this embodiment of the invention in a hinge-like manner. Therefore, in this embodiment, the pivotal motion is directed longitudinally in see-saw like fashion of leaf spring  130   a.    
         [0059]      FIGS. 5   a  and  5   b  are simplified representations of a suspension system  200  constructed in accordance with the principles of the invention ( FIG. 5   a ) and a prior art suspension arrangement  300  ( FIG. 5   b ), illustratively a conventional parallel leaf suspension, both represented in computer-simulated static acceleration conditions. Elements of structure that have previously been discussed are similarly designated in this figure.  FIGS. 5   a  and  5   b  are situated next to one another for sake of facilitating comparison of the effect of acceleration. It is seen that the prior art embodiment of  FIG. 5   b  does not comprise the structural equivalent of half leaf spring  210  shown in  FIG. 5   a.    
         [0060]    As can be seen in  FIG. 5   a , leaf spring  130   a  remains essentially without distortion during simulated vehicle acceleration as the vehicle (not shown) travels in the direction shown by arrow  201 . Prior art suspension arrangement  300 , on the other hand, shows during the simulated vehicle acceleration in the direction of arrow  301   a  distortion in leaf spring  302  wherein region  313  of leaf spring  302  is distorted downward and region  314  is distorted upward. This condition, which is commonly referred to as “side view windup,” results in the unacceptable condition of power hop during acceleration, as well as a disadvantageous reduction in axle control. 
         [0061]      FIGS. 6   a  and  6   b  are simplified representations of suspension system  200  of  FIG. 5   a  and prior art suspension arrangement  300  of  FIG. 5   b , both in computer-simulated static braking conditions. Elements of structure that have previously been discussed are similarly designated in this figure. As shown in  FIG. 6   a , leaf spring  130   a  remains substantially in its base line configuration during simulated acceleration in the direction of arrow  201 .  FIG. 6   b , on the other hand, shows leaf spring  302  to undergo significant side view windup. Region  313  of leaf spring  302  is distorted upward significantly, while region  314  is distorted downward. When leaf spring  302  is wound up as shown in this simulation, its spring rate is changed significantly, as well as other suspension parameters, resulting in reduced control, particularly when braking is performed on an uneven or bumpy surface (not shown). 
         [0062]      FIG. 7  is a simplified schematic representation of a side view of a suspension system  400  constructed in accordance with the principles of the invention with a 1 st  stage leaf spring  410 , and further showing the path of the center of axle  411 , as indicated by curved arrow  412  with a fulcrum  414  arranged to communicate with 2 nd  stage lower leaf spring  416 . The embodiment of the invention represented in this figure is pivotally coupled to 1 st  stage leaf spring  410  at a pivot coupling  414 . 
         [0063]      FIG. 8  is a simplified schematic representation of a side view of a suspension system  430  constructed in accordance with the principles of the invention. Elements of structure that previously have been discussed are similarly designated in this figure. In this figure, there is illustrated a 1 st  stage consisting of a coil spring  435 , which may, in certain embodiments be a conventional air spring (not shown). In still further embodiments of the invention, coil spring  435  may constitute a combination of a coil spring and an air spring. Coil spring  435  is substantially equivalent in function to 1 st  stage leaf spring  410  of the embodiment of  FIG. 7 . However, as will be noted below, the use of a coil spring results in a variation in the path of the axle. 
         [0064]    Fulcrum  414  of the 2 nd  stage lower leaf has been removed, but is nevertheless illustrated in phantom representation to show that its use is optional in this specific illustrative embodiment of the invention. Its use will depend on the geometric needs of the vehicle (not shown). 
         [0065]    In this embodiment, the path of center of axle  411  is indicated by curved arrow  437 . Curved arrow  412 , which represents the path of the center axle in the embodiment of  FIG. 7 , is shown in this figure for comparison purposes. 
         [0066]    A significant aspect of this specific illustrative embodiment of the invention is that lower leaf spring  440  is configured as a lower link subcomponent that allows a measure of compliance. It is not a rigid link. 
         [0067]      FIG. 9  is a simplified schematic representation of a side view of a suspension system  450  constructed in accordance with the principles of the invention with a 1 st  stage consisting of a substantially equivalent coil spring  455 , which in some embodiments of the invention may be an air spring or a combination of a coil spring and an air spring. Coil spring  455  provides vertical load support in place of 1 st  stage leaf spring  410  shown in  FIG. 7 . However, in this specific illustrative embodiment of the invention, added control is achieved by the use of an optional single plate main leaf spring  457  as part of the 1 st  stage with coil spring  455 . A lower leaf  460  of the 2 nd  stage is employed for additional control. In this embodiment, lower leaf  460  permits a measure of compliance and is not a rigid link. 
         [0068]    Again, Fulcrum  414  of the 2 nd  stage lower leaf has been removed, but is illustrated in phantom representation to show that its use is optional in this specific illustrative embodiment of the invention. Its use will depend on the geometric needs of the vehicle (not shown). 
         [0069]    In this specific illustrative embodiment of the invention, the center of axle  411  travels along a path that conforms to curved arrow  462 , as seen in the present side view. 
         [0070]      FIG. 10  is a simplified schematic representation of a clip bracket  500  that can be used to push or pull a stack of spring plates  502 . Spring plates  502  may be the main spring or the secondary stage in the practice of the invention. In operation, clip bracket  500  is urged upward and downward in the direction of arrows  504  and  506 , respectively. Spring plates  502  are contained between rubber bushings  510  and  512 , to prevent damage to the spring plates. The operation of clip bracket  500  will be described below in relation to  FIGS. 11   a ,  11   b , and  11   c.    
         [0071]      FIGS. 11   a ,  11   b , and  11   c  are simplified schematic side view representations of a height control arrangement  520  constructed in accordance with the principles of the invention that is useful in the loading and unloading of a stationary vehicle,  FIG. 11   a  showing a simplified system control arrangement in block and line form. Elements of structure that have previously been discussed are similarly designated in these figures. 
         [0072]    As shown in  FIG. 11   a , a primary leaf spring  130   a  is coupled at its ends to a chassis rail (not specifically designated) as described in relation to  FIGS. 1 and 2 , above. Leaf spring  130   a  and secondary spring  502 , which may be the equivalent of half leaf spring  136   a  described above, are coupled to the axle (not specifically designated in this figure). Moreover, although clip bracket  500  is shown in this specific illustrative embodiment of the invention, to operate on the secondary spring system, other embodiments can employ clip bracket  500  on the primary spring, i.e., primary leaf spring  130   a . The principle is to provide a way literally push or pull on the spring assembly in a local area to force a temporary camber change This translates into a change in the height “Z” of the vehicle (see,  FIG. 15  and its corresponding description below) that can be selectively employed in response to the operation of a height control system that is generally designated as  530  in the figure. 
         [0073]    Height control system  532  includes a height control system  532  that receives vehicle height information from a height sensor  534 . A desired vehicle height is entered by a user (not shown) at user input  536 . In a simple embodiment of the invention, user input  536  may constitute a simple pair of switches (not shown) that enable the user to raise or lower the vehicle height as desired. In other embodiments, user input  536  may constitute a programable arrangement (not shown) wherein several vehicle heights and other conditions can be preprogramed. In response to the data received at user input  536  and the corresponding height data received from height sensor  534 , height control system  532  operates an electrical or hydraulic system (not shown) that exerts a force on clip bracket  500  whereby the clip bracket is urged upward or downward, as the case may be, in the direction of arrows  504  and  506 , respectively, relative to the chassis rail. In this embodiment of the invention, clip bracket  500  can only exert force on secondary spring  502  statically and must be withdrawn to a baseline condition when the vehicle is in use to prevent damage to the spring. More specifically, the compression surface of the spring should not be loaded during dynamic or fatigue loading, and secondary spring  502  should therefore be employed only statically, such as for loading and unloading the vehicle. For this reason, this specific illustrative embodiment of the invention is provided with a vehicle interface  538  that, among other functions, disables the operation of height control system  532  when vehicle motion is detected. 
         [0074]    If the vehicle is lightly loaded, a height sensor  534  provides vehicle height data that indicates that clip bracket  500  must pull on secondary spring  502  such that vehicle trim position is lowered. This allows the vehicle to be loaded more easily by the user. In some embodiments of the invention, when the vehicle is shifted to the “drive” position, vehicle interface  538  instructs height control system  532  to restore the height of the vehicle to a predetermined baseline position to avoid creating a rise in the operational stress applied to secondary spring  502 . 
         [0075]    Referring to  FIG. 11   b , it is noted that as the clip bracket (not specifically designated in this figure) is urged upward in the direction of arrow  504 , the vehicle height is reduced from the baseline of Z to Z′, where Z′ 502  upward, a downward force  542  is applied at the distal end of secondary spring  502 . 
         [0076]    In  FIG. 11   c , the clip bracket (not specifically designated in this figure) is urged downward in the direction of arrow  506 , the vehicle height is increased from the baseline of Z to Z″, where Z″&gt;Z. As the clip bracket urges secondary spring  502  upward, an upward force  544  is applied at the distal end of secondary spring  502 . 
         [0077]      FIG. 12  is a simplified schematic top plan representation of a splayed suspension arrangement  560  constructed in accordance with the invention wherein secondary leaf springs  562   a  and  562   b  are shown to be mounted at angles with respect to respective ones of primary leaf springs  130   a  and  130   b . Elements of structure that have previously been discussed are similarly designated in this figure. The secondary leaf springs are not parallel to the respective primary leaf springs, as is the case in the embodiments of  FIGS. 1 and 2 . In a practical embodiment of the invention, angles of deviation for the secondary leaf springs will be on the order of 5°-10°. Of course, the present invention is not limited to this angular range, which can be determined in response to finite element and kinematic analyses as will be discussed below. 
         [0078]    Further in relation to the embodiment of  FIG. 12 , it is noted that the addition of secondary leaf springs  562   a  and  562   b , which are mounted in the system at an angle relative to primary leaf springs  130   a  and  130   b , enhances axle control, as the present non-parallel arrangement emulates a rigid 4-link rear axle system (not shown). 
         [0079]    However, a key difference is that in the present system leaf springs  562   a  and  562   b  function as springs, not just rigid links. This significant difference allows for compliance that will affect all aspects of the dynamic and kinematic response, including axle wind-up and roll response. The angularly disposed secondary springs of this embodiment of the invention will increase roll stiffness significantly. The resulting stresses that are applied by this arrangement to the mounting plate (not specifically designated) can be balanced on a case-by-case basis using standard analytical systems, such as finite element analysis (“FEA”). Additionally, kinematic analysis performed using commercially available software, such as the ADAMS software, will on a case-by-case basis identify exact values for the vehicle response to roll inputs. Wheel sideslip and axle steer control are thereby improved. 
         [0080]      FIG. 13  is a simplified schematic perspective representation of a variable position fulcrum bumper  570  constructed in accordance with the invention that may be active or passive to rotate in a controlled manner to create a variation in the stiffness of the secondary spring rate. By allowing the fulcrum bumper (whether passive or active) to rotate in a controlled manner about the ground point on the frame bracket, a change in secondary plate stiffness is produced. Essentially, the bumper ground point at chassis rail  112   b  is rotated such that the point of contact on the secondary spring is moved. The resulting stiffness and kinematic effects are significantly affected. The specific value of the amounts of stiffness and kinematic effects is determined on a case-by-case basis with the use of kinematic modeling. Additionally, the resulting change in spring rate thereby calculated. 
         [0081]    In the practice of this aspect of the invention, an electric motor (not shown) is mounted to the frame bracket (not specifically designated) and is actuated to cause the desired rotation after a signal sent from a height transducer identifies how much rotation is needed. A simplified height analysis system is described in relation to  FIG. 11   a . The displaceable fulcrum bumper herein described can be used in combination with a bumper having a variable stiffness, whereby numerous combinations of final stiffness and kinematic path result. In some embodiments of the invention, variable position fulcrum bumper  570  comprises a rheological material that changes viscosity or stiffness in response to the application of electrical energy. The stiffness of variable position fulcrum bumper  570  is the focus. By activating the fulcrum bumper to become more (or less) rigid, a desired change in supporting spring stiffness is effected and, correspondingly, the geometric and kinematic attributes of the suspension system are affected. 
         [0082]    The fulcrum bumper is not limited to be used in combination with a rheological material, and can employ an air spring or other mechanical means to effect the engagement of the secondary stage leaf. Although in this embodiment of the invention there would be no “active” vehicle retrim, the system could “passively” allow for the rate change, which as a result of the linked kinematic geometry effect, would affect vehicle dynamic behavior in roll, acceleration, braking, or cornering motions. Once vehicle attitude is effected via suspension displacement activity, the secondary plate contact with the fulcrum bumper would initiate reaction forces. A variable rate bumper made of rubber, urethane, like material that can be voided or otherwise manufactured to cause a nonlinear compression effect that will influence the secondary plate deflection character while under load, albeit to a lesser degree than an active system. 
         [0083]      FIG. 14  is a simplified schematic plan representation of the variable position fulcrum bumper of  FIG. 13 , that has been magnified to facilitate the illustration of certain details of its operation. It is seen in this figure that variable position fulcrum bumper  570  is installed on a carrier  575  that is configured to pivot about a pivot coupling  580  to which is also coupled primary leaf spring  130   a . The carrier is coupled to half leaf spring  136   a  at pivot coupling  582 . An electric drive arrangement  590  (shown schematically) is actuatable, illustratively in response to the system described in connection with  FIG. 11   a , to cause carrier  575  to be rotated about pivot coupling  580  in the direction of arrow  596 . Electric drive arrangement  590  is coupled to carrier  575  by a drive coupler  592  that, in this specific illustrative embodiment of the invention, is urged in the directions of two-headed arrow  593 . The actuation of the carrier by electric drive arrangement  590  causes variable position fulcrum bumper  570  to change the point at which it communicates with half leaf spring  136   a  over a range c, whereby half leaf spring  136   a  is displaced to position  136   a ′, and primary leaf spring  130   a  is displaced to position  130   a′.    
         [0084]      FIG. 15  is a simplified schematic representation of the variable position fulcrum bumper of  FIG. 14  that is useful to illustrate the variation in vehicle height that is achievable, particularly when the vehicle (not shown) is stationary. Elements of structure that have previously been discussed are similarly designated in this figure. As shown in this figure, variable position fulcrum bumper  570  causes, as previously noted, half leaf spring  136   a  is displaced to position  136   a ′. This displacement is responsive to a displacement of z′ at the point identified by line  600 . The height displacement of the vehicle corresponds substantially to the displacement z′ multiplied by the mechanical advantage nx/x, or n. In a typical vehicle, the value of n may be on the order of 6, and therefore the height of the vehicle will be lowered by approximately 6 z′. 
         [0085]    Although the invention has been described in terms of specific embodiments and applications, persons skilled in the art may, in light of this teaching, generate additional embodiments without exceeding the scope or departing from the spirit of the invention herein claimed. Accordingly, it is to be understood that the drawing and description in this disclosure are proffered to facilitate comprehension of the invention, and should not be construed to limit the scope thereof. 
         [0086]    Having thus described the invention,