Abstract:
A low part count, light weight, low-rise air leaf suspension system is provided. One end of the leaf spring has a formed eye pivotally mounted by a pin to a lightweight bracket mounted to the vehicle frame. The leaf spring is tapered toward the ends to reduce weight. Light weight clamping blocks attach an axle to a central portion of the leaf spring. The other end of the leaf spring is curved down and laterally inward so that the end of the leaf spring is positioned directly underneath the vehicle frame and the air spring may be connected directly between the leaf spring and frame.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates generally to leaf spring suspension systems, and more particularly to leaf spring suspension systems having reduced weight and part count.  
       BACKGROUND OF THE INVENTION  
       [0002]     An automotive suspension system is designed to support a vehicle frame or body relative to a number of wheeled axles. The suspension system components work together to isolate the vehicle from the road so as to provide a soft, smooth ride for the vehicle occupants over an irregular road surface. The design of a suspension system seeks to balance the often conflicting goals of isolating the motion of the axle from the frame while providing desirable handling characteristics and minimizing manufacturing and operating costs.  
         [0003]     A suspension system design often used in long-haul trucks includes a leaf spring, air spring, and shock absorber. Typically, each end of an axle is mounted near the center of a leaf spring which has a forward end mounted to the vehicle frame so that leaf spring may pivot in a vertical plane perpendicular to the road surface. An air spring connects the rear end of the leaf spring to the vehicle frame. A shock absorber is also coupled between the leaf spring or axle and the vehicle frame. Flexing of the leaf spring combined with the operation of the air spring and shock absorber isolate and dampen vertical motion of the wheels as they negotiate the roadway, thereby providing a smoother ride.  
         [0004]     Although leaf spring, air spring, and shock absorber type suspension systems are successful, they tend to have a high number of component parts and are relatively heavy. The high number of parts contributes to high cost for manufacturing, assembly, inventory, and maintenance of the suspension system. A heavy suspension system reduces fuel economy and may also reduce useful load on roadways having axle weight limits. Thus, reducing suspension system weight is desirable.  
         [0005]     However, a suspension system must also be strong and durable. For example, a typical heavy duty truck may be driven an average of 100,000 miles per year, or more, and may be driven well over a million miles in its useful lifetime. Thus, suspension system components may have design lifetimes of up to 1.5 million miles.  
         [0006]     It would therefore be desirable to provide a leaf-air spring suspension system having fewer parts and a lower system weight without sacrificing system durability.  
         [0007]     It would also be desirable to provide a low-weight suspension system suitable for use in long-haul trucks and other vehicles.  
       SUMMARY OF THE INVENTION  
       [0008]     An object of the present invention is to provide a suspension system having fewer parts and lower weight than previously known suspension systems.  
         [0009]     These and other objects of the invention are achieved by a leaf spring-air spring suspension system. A forward end of the leaf spring has a formed eye pivotally mounted to a lightweight bracket connected to the vehicle frame. The leaf spring is shaped so that the rearward portion of the leaf spring is positioned underneath the vehicle frame so that an air spring may be connected between the leaf spring and frame without using a cross beam. 
     
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0010]     The above objects and advantages of the present invention will be readily apparent upon consideration of the accompanying detailed description taken in conjunction with the accompanying drawings in which like characters refer to like parts throughout and in which:  
         [0011]      FIG. 1  is an oblique view of a leaf-air suspension system in accordance with the principles of the present invention;  
         [0012]      FIGS. 2A and 2B  are an oblique top and bottom views of one embodiment of the leaf spring of  FIG. 1 ;  
         [0013]      FIG. 3  is an oblique view showing the pivot pin and frame bracket of  FIG. 1  in more detail;  
         [0014]      FIG. 4  is an oblique view of the upper axle clamp of  FIG. 1 ;  
         [0015]      FIG. 5  is an oblique view of a lower axle clamp;  
         [0016]      FIGS. 6A and 6B  are oblique views of alternative lower axle clamps; and  
         [0017]      FIGS. 7A and 7B  are oblique views of a shock absorber and air lift control valve. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]     The present invention relates to suspensions systems having a reduced part count and a reduced system weight. Although the suspension of  FIG. 1  is shown mounted to the left hand longitudinal beam of a heavy duty, large payload wheeled vehicle frame, such as for a long haul truck, the disclosed suspension system may be advantageously used in other devices or systems using leaf spring suspensions. More over, although only the left hand side of a single axle is shown in the figures, one skilled in the art will understand that a similar suspension system is provided to support the right hand side of an axle, and that a vehicle may be supported by multiple axles each having a similar suspension system.  
         [0019]     As shown in  FIG. 1 , suspension system  10  includes axle  12  disposed beneath and substantially perpendicular to frame  14 . The relative position of axle  12  with respect to frame  14  is maintained by operation of leaf spring  16  and air spring  18  as described herein below. As shown in  FIG. 2A , leaf spring  16  preferably tapers towards each end to reduce weight. Leaf spring  16  has eye  20  formed in the forward end thereof to accept bar pin assembly  22 . A relatively flat central portion of leaf spring  16  provides axle mounting area  24  for mounting axle  12  to leaf spring  16 . To provide a lower ride height, a portion of leaf spring  16  curves downward to accommodate the height of air spring  18 . The rearward portion of leaf spring  16  curves laterally inward toward frame  14  so that the end of the spring is positioned beneath frame  14 . This allows air spring  18  to be coupled between leaf spring  14  and frame  16  without requiring additional cross members thereby reducing suspension system weight. Note that leaf springs on opposite sides of the vehicle are mirror images of one another.  
         [0020]     Leaf spring  16  is subject to large static forces due to the weight of the vehicle and any load being carried. Leaf spring  16  is further subjected to large bending and tensile loads due to relative motions between vehicle frame  14  and axle  12  as the vehicle is driven. For instance, as a vehicle is driven over a roadway bumps and potholes in the road surface, the center of leaf spring  16  is deflected vertically relative to frame  14 . This deflection results in a bending force being applied to leaf spring  16  and causes leaf spring  16  to flex along its length. Vehicle acceleration and breaking cause forces generally parallel to the vehicle frame to be applied to leaf spring  16 , thereby subjecting leaf spring  16  to tensile and compressive loads. Accordingly, leaf spring  16  as well as the other component parts of suspension system  12  must be sufficiently strong and durable to withstand these forces over a significant length of time.  
         [0021]     The high forces applied to leaf spring  16  may result in failure of the spring during use. Such failure may result in uncontrolled motion of axle  12  relative to frame  14 . For example, a complete separation of leaf spring  16  between eye  20  and axle attachment area  24  may result in forward or rearward motion of one end of axle  12  relative to frame  14  so that axle  12  twists beneath the vehicle. Such a failure may result in a loss of control of a vehicle and has the potential to cause significant damage. To guard against such catastrophic failures, leaf spring  16  preferably comprises multiple layered components.  
         [0022]     In one embodiment of leaf spring  16 , leaf spring  16  comprises two spring leafs disposed one on the other as shown in  FIG. 2A . At the forward end the formed eye of one spring leaf is wrapped around the formed eye of the other spring leaf. A pin and recess, a through bolt, or some other mechanism is provided in the axle attachment area to maintain the alignment between the two spring leafs. Both spring leafs may have similar lengths so that the entire leaf spring from eye  20  to air spring mounting point  26  comprises two spring leafs. Alternatively, one spring leaf may be shorter that the other so that only the portion from eye  20  to axle attachment area  24  comprises two spring leafs. In either design, the leaf springs are designed so that in the event one spring leaf fails, the other spring leaf is sufficient to prevent catastrophic failure of the suspension system.  
         [0023]     In a second embodiment of the invention, leaf spring  16  comprises a single spring leaf with a safety strap disposed along a portion thereof. For example, as shown in  FIG. 2B , safety strap  27  is wrapped around eye  20  and disposed along a lower surface of leaf spring  16 . Clip  28  and pin  29  hold safety strap  27  in place around eye  20 , whereas a tail portion of safety strap  27  includes a hole or opening that fits over alignment pin  23  protruding from the bottom surface of spring leaf  16  as shown in  FIG. 2C .  
         [0024]     The forward end of leaf spring  16  is pivotally coupled to frame  14  by means of bar pin assembly  22  which is mounted to a frame bracket. This is shown in more detail in  FIG. 3 . Frame bracket  30  is formed from a lightweight metal or other material of sufficient strength and durability. Preferably, frame bracket  30  comprises an aluminum bracket designed using Finite Element Analysis techniques to provide reduced weight while maintaining the necessary strength and durability characteristics. For example, frame bracket  30  may include recesses and openings such as recess  32  and opening  33  to reduce the amount of material in bracket  30  and thereby minimize weight and material cost of the bracket. Frame bracket  30  includes holes  34  for securely mounting frame bracket  30  to vehicle frame  14  using bolts (not shown) or other suitable fastening methods.  
         [0025]     Frame bracket  30  has a transverse portion defining a surface substantially perpendicular to frame  14 . Bolt holes are provided in the transverse surface of bracket  18  for accepting bolts for attaching of bar pin assembly  22 . Bracket  30  is preferably configured so that when mounted to frame  14 , bar pin assembly  22  is substantially orthogonal to a face of frame  16  and parallel to the road surface. Preferably bracket  30  is symmetrical so that a single bracket design may be used for mounting a suspension on either the right or left side of the vehicle.  
         [0026]     Bar pin assembly  22  functions as a pivot point or axis about which leaf spring  16  rotates. Bus pin assembly  22  generally comprises bar  37  having a generally round central cross section designed to fit eye  20  in leaf spring  16 . Bushing  38  is disposed on bar  37  to reduce wear between eye  20  and bar  37 . Preferably, bushing  38  also includes a solid lubricant to reduce friction between eye  20  and bar  37 . For example, Delrin may be suitable for use as bushing  38 . The ends of bar  37  are flattened and have bolt holes formed therein corresponding to the bolt holes in frame bracket  30 . Bolts  38  securely attach bar pin assembly  22  to frame bracket  30 . Wear washers  38  are provided on bar pin assembly  22  to prevent wear between a eye  20  and frame bracket  30 .  
         [0027]     Advantageously, the arrangement of bracket  30  and bar pin  22  provides a convenient means for truing the alignment of axle  12  to frame  16  by the insertion or removal of shims  36  between bracket  30  and bar pin  22 . For example, removing shims  36  from between bracket  18  and bar pin  22  on the right side of a vehicle and and/or inserting shims  36  between bracket  18  and bar pin  22  on the left side of the vehicle twists the axle in a clockwise direction relative to frame  14  when viewed from above. Conversely, inserting shims  36  between bracket  18  and bar pin  22  on the right side of a vehicle and and/or removing shims  36  from between bracket  18  and bar pin  22  on the left side of the vehicle twists the axle in a counterclockwise direction relative to frame  14  when viewed from above.  
         [0028]     Axle  12  is mounted to central portion  24  of leaf spring  16  using, for example, u-bolts and suitably shaped brackets, saddles, and clamps. Referring now to  FIGS. 4-6 , axle  12  and leaf spring  16  are juxtaposed between upper saddle  41 , axle seat  42 , and lower saddle  51 , which are clamped together by u-bolts  43 . The position of axle  12  relative to leaf spring  14  is determined by locating pin  23  on the underside of leaf spring  16  as shown in  FIG. 2C . Pin  23  mates with a corresponding hole or recess in the top surface of axle seat  42 . Saddle  41  is positioned on top of leaf spring  16 . In a preferred embodiment of the present invention, axle seat  42  and saddle  41  are made of a ductile material, such as ductile iron, to provide light weight and suitable strength and durability. The lower surface of saddle  41  is relatively flat to provide a large contact area with leaf spring  16 . The upper surface of saddle  41  includes troughs  44  that that are configured to fit U-bolts  43 . Recessed portions  48  and  49  minimize the weight and material used to manufacture saddle  41  while maintaining sufficient cross section under u-bolts  43 .  
         [0029]     Preferably, saddle  41  also includes a integrate travel stop  46  that extends vertically above the uppermost extent of u-bolts  43 . When the suspension system is compressed to an extreme degree, due to driving over a large bump at high speed for instance, travel stop  46  may come into contact with travel limit  47  disposed from frame  14  as shown in  FIG. 1 . Contact between travel stop  46  and travel limit  47  prevents further compression of the suspension system and may prevent damage to suspension system and drive train components.  
         [0030]     Axle seat  42  fits between leaf spring  16  and axle  12  (see  FIG. 1 ) to prevent relative motion between the two. For example, axle seat  42  may include lips or ridges the project upwardly on either side of leaf spring  16  to prevent lateral motion of leaf spring  16 . Similarly, axle seat  42  may also include forward and aft projections to capture axle  12  and prevent for an aft motion of the axle relative to axle seat  42 .  
         [0031]     Lower axle clamp  51  is disposed beneath axle  12  and accepts the legs of U-bolts  43  as shown in  FIG. 5 . Two-piece nuts  52  on u-bolts  43  provide the tension needed to clamp axle  12  and leaf spring  14  between lower axle clamp  51  and upper saddle  41  and thereby rigidly couple axle  12  and leaf spring  14  together. Lower axle clamp includes an upper surface  53  adapted to mate with a lower surface of axle  12  as shown in  FIGS. 6A and 6B . For example, lower axle clamp  51  includes large, relatively flat areas  53  that abut the bottom surface of axle  12 , and raised side portions  54  that prevent lateral movement between axle  12  and lower axle clamp  51 . Lower axle claim  51  is preferably made of ductile iron, or similar material.  
         [0032]     In a preferred embodiment of the present invention, lower axle clamp  51  further includes a bracket for mounting a lower end of a shock absorber or other dampening device. Lower shock bracket  66  is disposed from a side or corner of lower axle clamp  51  and is adapted to accept an end of a shock absorber or similar device. In one embodiment of the invention, lower shock bracket  66  includes machined stud  67  which is press fit into a corresponding recess in lower shock bracket  66 . Bracket  66  is configured so that stud  67  is disposed at an angle suitable for mating to a corresponding lower eye in shock absorber  59 . Alternatively, lower shock bracket  58  may include a hole  68  or recess for accepting shock absorber  59  of the type having stud  57  in the end thereof as shown in  FIG. 6B .  
         [0033]     The rearmost end of leaf spring  16  is coupled to frame  14  by air spring  18 . When the vehicle is loaded, air spring  18  compresses and leaf spring  16  pivots on bar pin assembly  22  allowing axle  12  to move vertically relative to frame  14 . Leaf spring  16  may also flex somewhat. The air pressure in air spring  18  may be altered to adjust the position of leaf spring  16  relative to frame  14 , and thereby adjust the ride height of the vehicle and maintain adequate travel clearance for axle  12 . Preferably, the ride height adjustment is made automatically by a multi-way air valve suitably linked to the vehicle frame and axle. For example, as shown in  FIG. 7 , height control valve  71  is mounted to frame  14  near shock absorber  59 . Arm  73  on height control valve  71  is connected to stud  74  disposed from lower shock bracket  58  by linkage  75 . A source of high pressure air (not shown) is coupled to valve  71  and various air reservoirs (not shown) are connected air spring  18  as is known in the art.  
         [0034]     During normal driving, suspension system  10  compresses and extends within a normal operating range. When a vehicle is loaded, or encounters a large bump, suspension system  10  may be compressed beyond this normal operating range. When this happens, arm  74  and linkage  75  cause air valve  71  to operate to admit high pressure air to air-spring  18 . This increases the downward force on the end of leaf spring  16  provided by air-spring  18 , thereby opposing further compression of the suspension system. Conversely, when a vehicle is unloaded, suspension system  10  may become extended beyond its normal operating range. In this event, linkage  75  and arm  74  cause air valve  71  to vent high pressure air from air spring  18 , thereby reducing the force on the end of leaf spring  16 . Preferably, height control valve  71 , arm  73 , stud  75 , and linkage  75  are configured so that when suspension system  10  is fully extended an angle between arm  74  and linkage  75  is less than about 150 degrees, and during full compression of suspension system  10 , arm  74  and linkage  75  remain below the extended taper.  
         [0035]     The present invention is not limited to the specific examples described and typical variations within the ordinary skill in the are also considered to be within the scope of the present invention. Although the present invention has been fully described by way of examples with reference to the accompanying drawings, it is to be noted that various changes and modifications will be apparent to those skilled in the art. Therefore, such changes and modifications should be construed as being within the scope of the invention.