Abstract:
The present disclosure provides a suspension system for a vehicle that includes a primary load bearing system and a secondary load bearing system. The primary load bearing system is disposed between a frame and an axle of the vehicle, and is continually loaded. The secondary load bearing system is also disposed between the frame and the axle of the vehicle, but the secondary load bearing system is operable between a loaded condition and an unloaded condition. During the loaded condition, the secondary load bearing system is contacted by an engaging member attached to the frame such that a load carried by the vehicle is supported by the primary load bearing system and the secondary load bearing system. During the unloaded condition, the secondary load bearing system is isolated from the frame and the axle.

Description:
FIELD 
     The present disclosure relates to suspension system for a vehicle including a leaf spring. 
     BACKGROUND 
     This section provides background information related to the present disclosure which is not necessarily prior art. 
     Suspension systems connect a vehicle to its wheels. Suspension systems serve a dual purpose. The system contributes to the vehicle&#39;s roadholding/handling and braking for good active safety and driving pleasure, and keeping vehicle occupants comfortable and reasonably well isolated from road noise, bumps, and vibrations. These goals are generally at odds, so the tuning of suspensions involves finding the right compromise. It is important for the suspension to keep the road wheel in contact with the road surface as much as possible because all of the forces acting on the vehicle do so through the contact patches of the tires. 
     One type of suspension system is a leaf spring suspension system. Leaf spring suspension systems are beneficial when the vehicle is carrying an increased load. Unfortunately, when leaf spring suspension systems are loaded 100 percent of the time, higher friction in the system results, which causes a feeling of stiffness and roughness while driving. Accordingly, while providing for good roadholding/handling and braking, leaf spring suspension systems may not be optimal for isolating road noise, bumps, and vibrations from the vehicle&#39;s occupants. 
     SUMMARY 
     The present disclosure provides a suspension system for a vehicle that includes a primary load bearing system and a secondary load bearing system. The primary load bearing system is disposed between a frame and an axle of the vehicle, and is continually loaded. The secondary load bearing system is also disposed between the frame and the axle of the vehicle, but the secondary load bearing system is operable between a loaded condition and an unloaded condition. During the loaded condition, the secondary load bearing system is contacted by an engaging member attached to the frame such that a load carried by the vehicle is supported by the primary load bearing system and the secondary load bearing system. During the unloaded condition, the secondary load bearing system is isolated from the frame and the axle. 
     Further areas of applicability of the present disclosure will become apparent from the detailed description, drawings and claims provided hereinafter. It should be understood that the detailed description, including disclosed embodiments and drawings, are merely exemplary in nature, intended for purposes of illustration only, and are not intended to limit the scope of the invention, its application, or use. Thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. 
    
    
     
       DRAWINGS 
         FIG. 1  is a perspective view of a suspension system according to a principle of the present disclosure; 
         FIG. 2  is a schematic side view of a suspension system according to a principle of the present disclosure where a secondary load carrying system is in an unloaded condition; and 
         FIG. 3  is a schematic side view of the suspension system illustrated in  FIG. 2  where the secondary load carrying system is in a loaded condition. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure is directed to a suspension system that provides good roadhandling, while also being operable to isolate vibrations, road noise, and bumps from the vehicle&#39;s occupants. To accomplish this, the suspension system according to the present disclosure can include a primary load bearing system that is always loaded (i.e., supports the normal weight of the vehicle), as well as a secondary load bearing system that is only engaged when the vehicle is subjected to increased loads or increased jounce. The secondary load bearing system can be a leaf spring suspension system that is tunable in a variety of ways such that, when the secondary load bearing system is engaged, the overall suspension system still achieves good roadhandling, while also being operable to isolate vibrations, road noise, and bumps from the vehicle&#39;s occupants. 
       FIGS. 1-3  illustrate a suspension system  10  according to a principle of the present disclosure. Suspension system  10  is generally for a vehicle such as a truck, but is equally applicable to all types of vehicles. Suspension system  10  connects axle  12  to a frame  14  of the vehicle. While the purpose of suspension system  10  of the vehicle is to allow the wheels (not shown) to move vertically with respect to frame  14 , it is undesirable to allow them to move forward and backwards (longitudinally), or side to side (laterally). Suspension system  10 , therefore, can further include a track bar  16  to prevent lateral movement. 
     Track bar  16  runs sideways in the same plane as axle  12 , including a first end  18  connected at one end  20  of axle  12  and a second end  22  connected to frame  14  on the opposite side of the vehicle. Track bar  16  can be attached on either end  18  or  22  pivotably to permit track bar  16  to swivel upwards and downwards only, so that axle  12  is allowed to move in the vertical plane only. As track bar  16  does not effectively locate axle  12  longitudinally, suspension system  10  can also include link arms  24  that stabilize axle  12  in the longitudinal direction. 
     Suspension system  10  can also include a stabilizer bar  26 . Stabilizer bar  26  (also known as an anti-roll bar) is used along with shock absorbers or struts (not shown) to give the moving vehicle additional stability. Stabilizer bar  26  can be a metal rod that spans the entire axle  12  and effectively joins each side of suspension system  10  together. When suspension system  10  at one wheel moves up and down, stabilizer bar  26  transfers movement to the other wheel. This creates a more level ride and reduces vehicle sway. In particular, it combats the roll of the vehicle on suspension system  10  as the vehicle corners. 
     As noted above, suspension system  10  can include link arms  24  that stabilize the axle in the longitudinal direction. In general, a pair of link arms  24  is used on both sides of the vehicle (one link arm connecting a top of axle  12  to frame  14 , and a second link arm connecting a bottom of axle  12  to frame  14 ). According to the present disclosure, however, one of the link arms  24  that connects axle  12  to frame  14  can be replaced by leaf spring assemblies  28  that act as secondary load carrying members. 
     More particularly, suspension system  10  can include primary load carrying members  30  ( FIGS. 2 and 3 ). Primary load carrying members  30  can be coil springs that are loaded 100 percent of the time by the weight of the vehicle. If the vehicle carries a larger load or experiences a large amount of jounce, however, leaf spring assemblies  28  can be engaged to provide additional load carrying capability. 
     Leaf spring assemblies  28  include a plurality of slender arc-shaped leaves  30  of spring steel, or other composite material, that include a rectangular cross-section. One of the leaves  30  can include a first eyelet  32  that couples to a first bushing  34  formed on bracket  35  attached to frame  14 , as well as a second eyelet  36  that couples to a second bushing  38  formed on a bracket  37  attached to axle  12 . Alternatively, eyelets  32  and  36  can be separately formed and welded to one of lengths  30  of leaf spring assembly  28 . Eyelets  32  and  36  and bushings  34  and  38  allow leaf spring assemblies  28  to pivot relative to axle  12  and frame  14 , as required during use of the vehicle. Leaf spring assemblies  28 , therefore, can also act in a manner similar to link arms  24 . 
     The number of leaves  30  of spring steel is variable. For very heavy vehicles, leaf spring assemblies  28  can be made from several leaves  30  stacked on top of each other in several layers. Often but not required by the present disclosure, leaves  30  will have progressively shorter lengths to vary flex of each leaf  30  when loaded. 
     Connecting the plurality of lengths  30  of spring steel is a clamp  40 . A distance between clamp  40  and first bushing  34  that connects leaves  30  to frame  14  can be described as a forward length L 1 , while a distance between clamp  40  and second bushing  38  that connects lengths  30  to axle  12  can be described as an aft length L 2 . Forward length L 1  and aft length L 2  can be unequal, which enables a position of clamp  40  to determine the effective link strength for suspension kinematics while controlling the motion of axle  12  as the vehicle moves up and down with respect to the ground and the wheels of the vehicle. Regardless, it should be understood that a position of clamp  40  can be modified to tune the kinematics of suspension system  10 . 
     As noted above, leaf spring assemblies  28  act as secondary load carrying members. To engage leaf spring assemblies  28 , a fulcrum bracket  42  is fixed to frame  14 . As frame  14  moves toward axle  12  (or axle  12  moves toward frame  14 ) during carrying of increased loads or increased jounce, fulcrum bracket  42  can contact with clamp  40 . Upon contact between fulcrum bracket  42  and clamp  40 , lengths  30  of leaf spring assemblies  28  will begin to add rate (i.e., pounds/inch or N/mm) and load carrying capacity to suspension system  10 . 
     Fulcrum bracket  42  can include a bumper  44  that dampens the contact between fulcrum bracket  42  and clamp  40 , as well as reduces noise and vibration between fulcrum bracket  42  and clamp  40  during contact thereof. Bumper  44  can be formed of an elastomeric or rubber material, or any other material having damping and noise-reducing properties known to one skilled in the art. Further, bumper  44  should be water- and environmentally-resistant so that bumper  44  lasts throughout the useful life of suspension system  10 . 
     Moreover, bumper  44  can be tuned or modified as required by the desired rate change of suspension system  10  and soften engagement of leaf spring assemblies  28 . Although bumper  44  is illustrated as being attached to fulcrum bracket  42 , one skilled in the art would readily acknowledge and appreciate that bumper  44  can be attached to clamp  40  without departing from the scope of the present disclosure. Lastly, it should be understood that fulcrum bracket  42  is not required to contact clamp  40  for operation of leaf spring assemblies  28  to be effective. In contrast, fulcrum bracket  42  can be adapted for direct contact with lengths  30  formed of spring steel without departing from the scope of the present disclosure. 
     A position of fulcrum bracket  42 , relative to bushings  34  and  38  and eyelets  32  and  36 , affects the load carried by bushings  34  and  38  and eyelets  32  and  36  and the corresponding brackets  35  and  37  attached to frame  14  and axle  12 , respectively. Adjusting a position of fulcrum bracket  42 , therefore, can control both the kinematics of axle  12  and loads on leaf spring assemblies  28 , bushings  34  and  38 , and eyelets  32  and  36 . 
     Utilizing fulcrum bracket  42  to engage leaf spring assemblies  28  negates the need to directly clamp leaf spring assemblies  28  to frame  14  and axle  12 . Rather, utilizing fulcrum bracket  42  to engage leaf spring assemblies  28  allows leaf spring assemblies  28  to be engaged only when a vehicle is carrying increased loads or experiences increased jounce. Such a design provides for only part time use of leaf spring assemblies  28  load carrying capacity. Accordingly, overall suspension system friction is reduced at lower loads (i.e., when leaf spring assemblies  28  are not engaged), which allows for improved vehicle ride at the lower loads. 
     In addition, suspension system  10  including leaf spring assemblies  28  as secondary load carrying members provides many tunable elements to suspension system  10 . A position of fulcrum bracket  42 , whether it be positioned forward or aft along leaf spring assemblies  28 , or positioned at different vertical distances relative to leaf spring assemblies  28 , can adjust the loads at which leaf spring assemblies  28  will be engaged. Other factors that affect tuning of suspension system  10  include the forward L 1  and aft L 2  lengths of leaves  30 . This is affected by positioning clamp  40  at various positions along leaves  30 . The number and lengths of leaves  30  also affects kinematics and load-carrying capabilities of leaf spring assemblies  28 . By carefully selecting the characteristics of each element of suspension system  10 , suspension system  10  can be adapted for use in a variety of vehicles including heavy duty trucks, light trucks, buses, tractors, locomotives, and passenger vehicles, without limitation. 
     Lastly, it should be appreciated that use of a fulcrum bracket  42  to engage leaf spring assemblies  28  enables the use of bushings and eyelets to connect leaf spring assemblies  28  to frame  14  and axle  12 . By connecting leaf spring assemblies  28  to frame  14  and axle  12  in this manner, both the axle  12  and frame  14  can be isolated from leaf spring assemblies  28  when leaf spring assemblies are not engaged. Conventional leaf spring assemblies (e.g., Hotchkiss and cantilever) do not simultaneously isolate both axle  12  and frame  14 . The ability for full isolation of both axle  12  and frame  14  assists in eliminating unwanted noises and vibration from suspension system  10  when leaf spring assemblies  28  are not in use.