Patent Publication Number: US-11660926-B2

Title: Progressive rate leaf spring for vehicle suspension system

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to U.S. patent application Ser. No. 16/793,477, filed Feb. 18, 2020, which claims priority to U.S. Provisional Patent Application No. 62/807,519, filed on Feb. 19, 2019, the disclosures of which are each incorporated by reference herein in their entireties. 
    
    
     FIELD OF THE INVENTION 
     This invention relates generally to leaf spring suspension systems for vehicles. 
     BACKGROUND 
     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 substantially 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. Unfortunately, typical steel leaf spring arrangements are heavy. 
     Some spring arrangements include features that provide a multi-plate arrangement with a multi-stage spring rate that dictates, in part, the response to certain driving maneuvers that is felt by an occupant of the vehicle. The multi-plate, multi-stage spring rate designs often suffer from abrupt changes that are felt by the user in an undesirable manner. 
     SUMMARY OF THE INVENTION 
     According to an aspect of the disclosure, a variable rate leaf spring vehicle suspension system includes a vehicle frame. The suspension system also includes a single leaf spring extending from a first end to a second end. The suspension system further includes a tension shackle pivotably coupled to the vehicle frame about an axis, the tension shackle defining a channel, the second end of the leaf spring disposed within the channel of the tension shackle, wherein the axis about which the tension shackle is pivotable is below the second end of the leaf spring. 
     According to another aspect of the disclosure, a variable rate leaf spring vehicle suspension system includes a vehicle frame. The suspension system also includes a single leaf spring extending from a first end to a second end. The suspension system further includes a tension shackle pivotably coupled to the vehicle frame about an axis, the tension shackle defining a channel, the second end of the leaf spring disposed within the channel of the tension shackle, wherein pivoting of the tension shackle in response to an increasing, upward load reduces the effective length of the leaf spring. 
     According to yet another aspect of the disclosure, a variable rate leaf spring vehicle suspension system includes a vehicle frame. The suspension system also includes a first leaf spring extending from a first end to a second end. The suspension system further includes a second leaf spring extending from a third end to a fourth end. The suspension system yet further includes a tension shackle pivotably coupled to the vehicle frame about an axis, the tension shackle defining a channel, the second end of the first leaf spring disposed within the channel of the tension shackle, wherein the axis about which the tension shackle is pivotable is below the second end of the first leaf spring. The suspension system also includes a first bumper disposed between a top surface of the first leaf spring and the vehicle frame. The suspension system further includes a second bumper disposed between a top surface of the second leaf spring and a bottom surface of the first leaf spring, the second bumper spaced from the first leaf spring in a first load condition of the second leaf spring and configured to provide a first overall spring rate, and in contact with the first leaf spring in a load second condition of the second leaf spring, contact between the second bumper and the first leaf spring configured to provide a second overall spring rate, the first bumper spaced from the vehicle frame in a third load condition of the second leaf spring and configured to provide a third overall spring rate, and in contact with the vehicle frame in a fourth load condition of the second leaf spring, contact between the first bumper and the vehicle frame configured to provide a fourth overall spring rate. 
     These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG.  1    is a perspective view of a vehicle suspension system; 
         FIG.  2    is a side, elevational view of a leaf spring of the vehicle suspension system according to an embodiment; 
         FIG.  3    is a side, elevational view of a first end of the leaf spring of  FIG.  2    having a bumper thereon; 
         FIG.  4    is a side, elevational view of a second end of the leaf spring of  FIG.  2    disposed in a tension shackle; 
         FIG.  5    is a side, elevational view of the leaf spring of  FIG.  2    deflecting during operation; 
         FIG.  6    is a perspective view of the second end of the leaf spring of  FIG.  2    deflecting during operation; 
         FIG.  7    is a side, elevational view of a leaf spring of the vehicle suspension system according to another embodiment; 
         FIG.  8    is a perspective view of a second end of the leaf spring of  FIG.  7    disposed in a compression shackle; 
         FIG.  9    is a side, elevational view of the leaf spring of  FIG.  7   ; 
         FIG.  10    is side, elevational view of the leaf spring of  FIG.  7    deflecting during operation; and 
         FIG.  11    is a plot of rate of the leaf spring against deflection comparing the leaf spring disclosed herein vs. a typical steel spring arrangement. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG.  1   , illustrated is a vehicle suspension system  10  having a chassis generally designated with numeral  12 . The chassis  12  includes a first chassis rail  14  and a second chassis rail  16  that are arranged substantially parallel to each other. The first and second chassis rails  14 ,  16  are coupled to each another by at least one cross brace, such as a first cross brace  18  and a second cross brace  20 , as shown. A differential drive arrangement  22  is fixedly coupled to the chassis  12  and converts the rotary motion of a drive shaft (not shown) to substantially orthogonal rotary motion at axle  24 . The axle  24  includes an associated pair of universal joints (not specifically designated) that are arranged to be proximal and distal with respect to the differential drive arrangement  22 . Thus, the axle  24  has an associated longitudinal axis to accommodate transaxial motion. It is to be appreciated that the axle  24  refers to a pair of half shafts in some embodiments. The half shafts may be disposed within a single sleeve or uncovered. 
     A leaf spring  32  is operatively coupled at a first end  33  and a second end  35  to the chassis rail  14 . In some embodiments, the leaf spring  32  is operatively coupled, at least in part, to the chassis rail  14  with an eye spring bushing arrangement  41  at the first end  33 . For purposes of discussion, only leaf spring  32  has been described in detail, but it is to be appreciated that a corresponding leaf spring is located on an opposing side of the chassis  12  proximate chassis rail  14 . 
     The above-described spring  32  may be referred to as a “semi-elliptical” spring configured as an arc-shaped length segment. The spring is formed of a composite material to reduce the weight of the leaf spring  32  in some embodiments. However, it is to be appreciated that spring  32  may be formed of steel in other embodiments. 
     Referring now to  FIG.  2   , a first embodiment of the leaf spring  32  is illustrated in greater detail. Disposed between the first end  33  and the second end  35  of the leaf spring  32  is a retention assembly  34  to operatively couple (directly or indirectly) the leaf spring  32  to the axle  24 . The retention assembly  34  may be a cage U-bolt plate, or any other suitable structure for operatively coupling the leaf spring  32  to the axle  24 . A bumper  36  is located proximate the first end  33  of the leaf spring  32 . The bumper  36  may be operatively coupled to, or integrally formed with, the eye spring bushing arrangement  41  (as illustrated) or the leaf spring  32  itself. Location of the bumper  36  being proximate to the first end  33  of the leaf spring  32  is defined by the bumper  36  being located closer to the first end  33  relative to a distance between the bumper  36  and a mid-point of the leaf spring  32 . The bumper  36  may be formed of any suitable resilient material, including a polymeric material or rubber, for example. 
       FIG.  3    illustrates the first end  33  of the leaf spring  32  in greater detail. The bumper  36  is positioned on a top side of the eye spring bushing arrangement  41  to contact the frame (e.g., chassis rail  14 ) during vertical deflections of the leaf spring  32  in response to various movements of the vehicle, such as acceleration, braking, lateral movement due to turning maneuvers, movement due to changing road surfaces, etc. It is contemplated that the bumper  36  is disposed on another structure that the leaf spring  32  is engaged with, or even the leaf spring  32  itself. The bumper  36  is shown in close proximity to, or engagement with, the chassis rail  14  in  FIG.  3   . The resilient material of the bumper  36  softens the engagement of the bumper (and therefore the eye spring  41  and leaf spring  32 ) with the vehicle frame. 
     Referring again to  FIG.  2   , as well as  FIG.  4   , the second end  35  of the leaf spring  32  is disposed within a channel  37  defined by a tension shackle  38  that is coupled to a portion of the vehicle frame, such as chassis rail  14 . The tension shackle  38  is pivotably coupled to the vehicle frame about axis A in any suitable manner. In the illustrated embodiment, the tension shackle  38  includes a first leg  40  and a second leg  42  that are spaced from each other to define channel  37 . The channel  37  is dimensioned to effectively clamp the second end  35  of the leaf spring  32  therein. 
     Engagement of the bumper  36  with the chassis rail  14  in response to spring deflection relative to chassis rail  14  initiates a second spring rate of the leaf spring  32  to provide desirable spring characteristics that facilitate specified suspension dynamics. The precise location of the bumper  36  along the length of the leaf spring  32  may be adjusted to determine how much spring deflection is required before contact between the bumper  36  and the chassis rail  14  occurs. Additionally, the tension shackle  38  that clamps the second end  35  of the leaf spring  32  allows the “effective length” of the leaf spring  32  to be further shortened, thereby increasing the spring rate of leaf spring  32  during deflection. Reducing the effective length of the leaf spring  32  refers to changing the fulcrum location of the leaf spring  32  from outermost ends to a different (i.e., inward) location. 
     The tension shackle  38  pivots about axis A during deflection of the leaf spring, as shown in  FIG.  4   , to gradually decrease the effective length of the leaf spring  32 , thereby increasing the rate of the leaf spring  32 . With the bumper  36  and the tension shackle  38 , each side  33 ,  35  of the leaf spring  32  provides parameters to adjust the rate progression without having to change the curvature or thickness profile of the leaf spring  32 . By controlling the engagement of the bumper  36  and parameters of the tension shackle  38 , the seat angle of the leaf spring  32  can be adjusted to a desired direction. The height of the bumper  36  and resiliency of the bumper material are factors that facilitate customization of the rate progression. Regarding the tension shackle  38 , the radius R defined by the distance between axis A and arc length C ( FIG.  4   ), as well as the clamp length L, similarly facilitates customization. An additional customization parameter is defined by the angle between axis A and the portion of arc length C that is along the leaf spring  32 .  FIGS.  5  and  6    illustrate the leaf spring  32  during deflection. 
     Referring now to  FIG.  7   , as with the embodiments of  FIGS.  2 - 6   , the first end  33  of the leaf spring  32  includes a bumper  36  is positioned on a top side of the eye spring bushing arrangement  41  to contact the frame (e.g., chassis rail  14 ) during vertical deflections of the leaf spring  32  in response to various movements of the vehicle, such as acceleration, braking, lateral movement due to turning maneuvers, movement due to changing road surfaces, etc. It is contemplated that the bumper  36  is disposed on another structure that the leaf spring  32  is engaged with, or even the leaf spring  32  itself. The bumper  36  is shown spaced from the vehicle frame in  FIG.  7    and in close proximity to, or engagement with, the chassis rail  14  in  FIG.  10   . The resilient material of the bumper  36  softens the engagement of the bumper (and therefore the eye spring  41  and leaf spring  32 ) with the vehicle frame. 
     Referring now to  FIGS.  8 - 10   , with continued reference to  FIG.  7   , the second end  35  of the leaf spring  32  is disposed within a channel  137  defined by a compression shackle  138  that is coupled to a portion of the vehicle frame, such as chassis rail  14 . The compression shackle  138  is coupled to the vehicle frame in any suitable manner. In the illustrated embodiment, the compression shackle  138  includes a first portion  140  that defines channel  137 . The channel  137  is dimensioned to effectively clamp the second end  35  of the leaf spring  32  therein. 
     Engagement of the bumper  36  with the chassis rail  14  in response to spring deflection relative to chassis rail  14  initiates a second spring rate of the leaf spring  32  to provide desirable spring characteristics that facilitate specified suspension dynamics. The precise location of the bumper  36  along the length of the leaf spring  32  may be adjusted to determine how much spring deflection is required before contact between the bumper  36  and the chassis rail  14  occurs. Additionally, the compression shackle  138  that clamps the second end  35  of the leaf spring  32  allows the “effective length” of the leaf spring  32  to be further shortened, thereby increasing the spring rate of leaf spring  32  during deflection. Reducing the effective length of the leaf spring  32  refers to changing the fulcrum location of the leaf spring  32  from outermost ends to a different (i.e., inward) location. 
     The compression shackle  138  includes the above-noted first portion  140  which defines the channel  137 . A shackle bumper  141  is operatively coupled to a top side of the first portion  140  of the compression shackle  138 . As with bumper  36 , the shackle bumper  141  may be formed of any suitable resilient material, including a polymeric material or rubber, for example. A second portion  142  of the compression shackle  138  is coupled to the first portion  140  in a manner that allows relative rotation of the first and second portions  140 ,  142 . The second portion  142  includes a contact member  144  that is positioned to contact the shackle bumper  141  after sufficient deflection of the leaf spring  32  during operation. 
     Contact of the bumper  36  and/or the shackle bumper  141  during deflection of the leaf spring, as shown in  FIG.  10   , gradually decreases the effective length of the leaf spring  32 , thereby increasing the rate of the leaf spring  32 . With the bumper  36  and the compression shackle  138 , each side  33 ,  35  of the leaf spring  32  provides parameters to adjust the rate progression without having to change the curvature or thickness profile of the leaf spring  32 . By controlling the engagement of the bumper  36  and parameters of the compression shackle  138 , the seat angle of the leaf spring  32  can be adjusted to a desired direction. The height of bumper  36  and/or shackle bumper  141 , and resiliency of the material of the bumpers are factors that facilitate customization of the rate progression. Regarding the compression shackle  138 , the radius of curvature, as well as the clamp length L, and position of contact between the shackle bumper  141  and the contact member  144  similarly facilitates customization. 
     It is further contemplated in another aspect of the invention that a second leaf spring is provided, with the additional leaf spring clamped to the leaf spring  32  with the retention assembly  34  in a stacked arrangement. Any of the previously described embodiments may be utilized with the stacked arrangement described herein. The additional leaf spring does not extend a distance that spans an entirety of the leaf spring  32  in some embodiments. Bumpers may be fixed to the additional leaf spring proximate ends thereof on a side of the additional leaf spring that is adjacent the leaf spring  32 . In a relaxed condition of the leaf spring arrangement, the bumpers are spaced from the leaf spring  32 . 
     Engagement of one or both of the bumpers with the leaf spring  32  in response to spring deflection initiates a third spring rate of the leaf spring arrangement to provide desirable spring characteristics that facilitate specified suspension dynamics. The precise location of the bumpers along the length of the additional leaf spring may be adjusted to determine how much spring deflection is required before contact between the bumpers and the leaf spring  32  occurs. Initiation of the third spring rate of the additional leaf spring may be adjusted based on the location of the bumpers. As with the bumpers of the leaf spring  32 , such an arrangement provides flexibility of the spring response characteristics, while avoiding the need for a second leaf spring arrangement, thereby reducing the weight of the suspension system  10  and the overall vehicle. 
     The order of engagement of the bumpers  36 ,  141  of the leaf spring  32  with the chassis rail  14  relative to engagement of the additional leaf spring bumpers with the leaf spring  32  may be adjusted to control the spring response characteristics. In other words, bumpers of leaf spring  32  engage the chassis rail  14  prior to engagement of the bumpers of the additional leaf spring with the leaf spring  32  in some embodiments. In other embodiments, additional leaf spring bumpers engage the leaf spring  32  prior to engagement of the bumpers of leaf spring  32  with the chassis rail  14  in some embodiments. The use of the bumpers at the eye spring arrangement location avoids undesirable contact and rubbing of components with the composite material. Such contact and rubbing is detrimental to a composite spring and is a consideration that is not of concern to steel spring arrangements. It is to be appreciated that the multi-spring arrangement embodiments described herein may include springs that are each formed of steel, each formed of a composite, or a combination thereof. For example, in a two-spring arrangement, a main spring plate may be formed of steel, while a secondary spring plate may be formed of a composite material, or vice versa. Alternatively, the main spring plate and the secondary spring plate may be both formed of steel. Another alternative includes a main spring plate and a secondary spring plate that are both formed of a composite material. It is easily understood that the above-described example may be carried on to three or more spring arrangements. 
       FIG.  11    illustrations a plot of rate of the leaf spring against deflection comparing the leaf spring disclosed herein vs. a typical steel spring arrangement. In particular, curve  200  depicts the rate change of the leaf spring  32  disclosed herein, when used in conjunction with the tension shackle or the compression shackle. The curve  200  is smooth when compared to the steep jump in rate change associated with prior multi-plate, multi-stage spring designs (represented with line  202 ). 
     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 described herein. 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