Abstract:
A spring system that includes at least an inner spring and an outer spring disposed around the inner spring. The inner spring exhibits a stiffness k 1  and the outer spring exhibits a stiffness k 2  in an uncompressed state. The inner spring exhibits a stiffness k 3  and the outer spring exhibits the stiffness k 2  in an intermediate compressed state, and the inner spring exhibits the stiffness k 3  and the outer spring exhibits a stiffness k 4  in a fully compressed state. In this manner, the spring system of the present disclosure may provide a vehicle with variable rates of compression that assist in providing a smooth ride at lower loads or jounce levels.

Description:
FIELD 
       [0001]    The present invention relates to a coil spring system. 
       BACKGROUND 
       [0002]    Vehicles such as trucks or heavy-duty trucks generally utilize a leaf spring suspension system that enables the vehicle to carry heavy loads. Leaf spring systems, however, do not necessarily provide a very smooth driving experience when the vehicle is carrying a small load, or no load at all. In this regard, any jounce experienced by the system is more readily applied to the vehicle frame, which results in a more bumpy ride for the driver. Vehicles such as sedans or the like, therefore, may utilize a spring suspension system that provides a softer ride for the driver. As these vehicles are rarely used to transport heavy loads, however, these spring suspension systems are not readily adaptable to a vehicle such as a truck. In this regard, when carrying heavy loads, the spring suspension system will compress before experiencing jounce from the road. Due to the pre-compression of the spring suspension before experiencing jounce, the spring suspension system is more apt to translate the jounce directly to the frame of the vehicle rather than more fully absorb the jounce. It is desirable, therefore, for a vehicle such as a truck to include a spring suspension system that provides a softer ride when carrying a load, not carrying a load, or carrying a small load. 
       SUMMARY 
       [0003]    The present disclosure provides a spring system that includes at least an inner spring and an outer spring disposed around the inner spring. The inner spring exhibits a stiffness k 1  and the outer spring exhibits a stiffness k 2  in an uncompressed state. The inner spring exhibits a stiffness k 3  and the outer spring exhibits the stiffness k 2  in an intermediate compressed state, and the inner spring exhibits the stiffness k 3  and the outer spring exhibits a stiffness k 4  in a fully compressed state. In this manner, the spring system of the present disclosure may provide a vehicle with variable rates of compression that assist in providing a smooth ride at lower loads or jounce levels. 
         [0004]    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. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  is a schematic perspective view of a vehicle including a suspension system having a spring system according to a principle of the present disclosure; 
           [0006]      FIG. 2  is a perspective view of the spring system according to a principle of the present disclosure in an unloaded state; 
           [0007]      FIG. 3  is a plan view of the spring system illustrated in  FIG. 2 ; 
           [0008]      FIG. 4  is a perspective view of a first spring of the spring system according to a principle of the present disclosure; 
           [0009]      FIG. 5  is a perspective view of a second spring of the spring system according to a principle of the present disclosure; 
           [0010]      FIG. 6  is a perspective view of the spring system according to a principle of the present disclosure in an intermediately loaded state; 
           [0011]      FIG. 7  is a perspective view of the spring system according to a principle of the present disclosure in a fully loaded state; 
           [0012]      FIG. 8  is a graph illustrating a stiffness of the spring system according to the present disclosure as the spring system compresses; 
           [0013]      FIG. 9  is a perspective view of an alternative embodiment of the first or second spring according to a principle of the present disclosure; and 
           [0014]      FIG. 10  is a perspective view of another alternative embodiment of the first or second spring according to a principle of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    Disclosed herein is an exemplary spring system that utilizes at least a pair of springs that each have differing stiffnesses. As each spring of the spring system has differing stiffnesses, when the springs are compressed, the spring system provides multiple stages of differing stiffnesses based on a compression of each of the springs. 
         [0016]    To provide the exemplary spring system with differing stiffnesses, each spring includes a first zone having a first stiffness, and a second zone having a second different stiffness. As the springs are each compressed, the differing stiffnesses of each spring collaborate to provide the multiple stages of differing stiffnesses. To provide the distinct zones of each spring having different stiffnesses, the spacing of the coils in each zone may be adjusted as desired, a thickness of the coils in each zone may be adjusted, or an outer diameter of the spring coils may be adjusted in each zone. An alternative exemplary embodiment includes a configuration where the material of the spring in each zone is different. 
         [0017]      FIG. 1  illustrates an exemplary suspension system  10  that may include a spring system  12  according to a principle of the present disclosure. Suspension system  10  may include a pair of spring systems  12  coupled between a vehicle frame  14  and a vehicle rear axle  16 . Although suspension system  10  will be described relative to use on a heavy-duty vehicle such as a truck, it should be understood that the present disclosure should not be limited thereto. In particular, suspension system  10  and, more particularly, the exemplary spring system  12 , may be used in a variety of vehicles or applications where multi-stage damping is required due to variations in loads that may be applied to spring system  12 , without limitation. 
         [0018]    Each spring system  12  of suspension system  10  may be directly coupled to each of vehicle frame  14  and rear axle  16  by welding or some other attachment method. Alternatively, as illustrated in  FIG. 1 , each spring system  12  may be coupled to vehicle frame  14  and rear axle  16  through use of mounting brackets  18 . In this regard, brackets  18  may be coupled to vehicle frame  14  and rear axle  16  by welding or by fasteners (not shown). 
         [0019]      FIG. 2  illustrates an exemplary spring system  10  according to the present disclosure. Spring system  10  includes a first spring  20  and a second spring  22 . First spring  20  is preferably concentric with second spring  22 . That is, as best illustrated in  FIG. 3 , first spring  20  includes an outer diameter D 1  that is less than an outer diameter D 2  of second spring  22  such that first spring  20  may be entirely concentrically disposed within second spring  22 . Although first spring  20  is preferably concentric with second spring  22  to reduce the space that spring system  10  occupies, first spring  20  is not necessarily limited to being concentric with second spring  22 . In contrast, first spring  20  may be disposed in a non-concentric arrangement relative to second spring  22  without departing from the scope of the present disclosure. 
         [0020]    First spring  20 , in addition to having outer diameter D 1  that is less than outer diameter D 2  of second spring  22 , may generally be formed of a wire  24  having a diameter or thickness t 1  that is less than a wire  26  having a diameter or thickness t 2  of second spring  22 . Due to first spring  20  having an outer diameter D 1  and a wire diameter t 1  that are each less than both outer diameter D 2  and wire diameter t 2  of second spring  22 , first spring  20  exhibits a lower stiffness than second spring  22 . Accordingly, first spring  20  generally compresses to a greater extent than second spring  22  when experiencing jounce during operation of the vehicle, or when the vehicle is subjected to increased loads. 
         [0021]    First spring  20  includes at least a first zone  28  and a second zone  30 . As best illustrated in  FIG. 4 , in accordance with a first exemplary embodiment of the present disclosure, first spring  20  in first zone  28  includes coils  32  that are axially spaced a distance L 1 . By axially spacing coils  32  at distance L 1 , a stiffness of first spring  20  may be adjusted in first zone  28 . First spring  20  in second zone  30  includes coils  32  that are axially spaced a distance L 2 . 
         [0022]    As illustrated in  FIG. 4 , L 2  is greater than L 1 . By axially spacing coils  32  at distance L 2  that is greater than L 1 , a stiffness of first spring  20  may be adjusted in second zone  30  to be greater than the stiffness of first zone  28 . It should be understood that although first zone  28  is described as having a stiffness less than second zone  30 , the present disclosure should not be limited to such a configuration. That is, the present disclosure contemplates a configuration where second zone  30  may have a stiffness less than first zone  28 . Further, although first spring  20  is described as having first and second zones  28  and  30 , first spring  20  may also have a configuration that includes additional zones having differing stiffness relative to the first and second zones  28  and  30 . 
         [0023]      FIG. 5  illustrates second spring  22 . Similar to first spring  20 , second spring  22  also includes first zone  28 . First zone  28  of second spring  22  includes coils  34  that are axially spaced a distance L 3 . By axially spacing coils  34  at distance L 3 , a stiffness of second spring  22  may be adjusted in first zone  28 . Second spring  22  in second zone  30  includes coils  34  that are axially spaced a distance L 4 . 
         [0024]    As illustrated in  FIG. 5 , L 4  is greater than L 3 . By axially spacing coils  34  at distance L 4  that is greater than L 3 , a stiffness of second spring  22  may be adjusted in second zone  30  to be greater the stiffness of first zone  28 . It should be understood that although first zone  28  is described as having a stiffness less than second zone  30 , the present disclosure should not be limited to such a configuration. That is, the present disclosure contemplates a configuration where second zone  30  may have a stiffness less than first zone  28 . Further, although second spring  22  is described as having first and second zones  28  and  30 , second spring  22  may also have a configuration that includes additional zones having differing stiffness relative to the first and second zones  28  and  30 . 
         [0025]    First spring  20  and second spring  22  each having first and second zones  28  and  30  of varying stiffness collaborate to provide spring system  12  with multiple stiffness during use thereof. Again referring to  FIG. 2 , spring system  12  is illustrated in a state of non-compression. That is,  FIG. 2  illustrates spring system  12  when no load or jounce is applied thereto. In the state of non-compression, first spring  20  exhibits a stiffness k 1 , while second spring  22  exhibits a stiffness k 2 . Accordingly, the overall stiffness of spring system  12  in the state of non-compression may be expressed as k 1 +k 2 =k A . 
         [0026]    Now referring to  FIG. 6 , spring system  12  is subjected to a load or jounce that compresses spring system  12  a distance d 1 . As illustrated in  FIG. 6 , coils  32  in first zone  28  have begun to fully compress, while coils  32  in second zone  30  have not fully compressed. Because coils  32  have begun to fully compress in first zone  28 , first spring  20  will exhibit a stiffness k 3  rather than a stiffness k 1 . That is, the first spring  20  will begin to exhibit a stiffness of the second zone  30  rather than a stiffness of the first zone  28 . In contrast to first spring  20 , coils  34  of second spring  22  in first zone  28  have not begun to fully compress at distance d 1 . Second spring  22 , therefore, still exhibits a stiffness k 2  (i.e., second spring  22  still exhibits a stiffness of first zone  28 ). Accordingly, the overall stiffness of spring system  12  in the state of intermediate-compression may be expressed as k 2 +k 3 =k B . 
         [0027]    Now referring to  FIG. 7 , spring system  12  is subjected to a load or jounce that compresses spring system  12  a distance d 2 . Distance d 2  represents a fully loaded condition. As illustrated in  FIG. 7 , coils  32  in first zone  28  have fully compressed, while coils  32  in second zone  30  have begun to compress. Because coils  32  have fully compressed in first zone  28 , first spring  20  will exhibit a stiffness k 3  rather than a stiffness k 1 . Coils  34  of second spring  22  in first zone  28  have also fully compressed at distance d 2 . Second spring  22 , therefore, will exhibit a stiffness k 4 . That is, second spring  22  will exhibit a stiffness of second zone  30 . Accordingly, the overall stiffness of spring system  12  in the state of full-compression and beyond may be expressed as k 3 +k 4 =k C . 
         [0028]    According to the above, spring system  12  is capable of producing at least three states of stiffness k A , k B , and k C . In general, spring system  12  is designed such that k C &gt;k B &gt;k A .  FIG. 8  illustrates a spring system  10  stiffness curve that shows the transitions between k A , k B , and k C . By designing spring system  12  such that k C &gt;k B &gt;k A , a vehicle having a suspension system  10  that includes spring system  12  is subjected to a softer ride at lower loads or smaller jounces. Such a system, therefore, is particularly advantageous for a vehicle such as a heavy-duty truck that typically includes a stiffer ride when a conventional suspension system such as a leaf spring suspension system is used. 
         [0029]    First and second springs  20  and  22  may be formed to have additional zones of stiffness. For example, first and second springs  20  and  22  may each have three zones of stiffness, which would yield a spring system  12  capable of exhibiting at least six states of stiffness. Regardless, springs  20  and  22  may be formed to have as many zones of stiffness as desired. 
         [0030]    First and second springs  20  and  22  are preferably formed from a material such as steel or spring steel. Other materials such as titanium or the like may also be used. Although not illustrated in the figures, it should be understood that coils  32  and  34  of first and second springs  20  and  22  in at least first zones  28  may be provided with a sleeve or coating to reduce noise or damage to the springs  20  and  22  during compression of first and second springs  20  and  22  in first zone  28 . In this regard, the coating or sleeve may be formed of rubber or a polymeric material that prevents direct contact between adjacent coils  32  or  34 . 
         [0031]      FIG. 9  illustrates an alternative exemplary embodiment that may be applied to each of first spring  20  and second spring  22 . Similar to first and second springs  20  and  22  illustrated in  FIGS. 4 and 5 , spring  38  includes a first zone  28  and a second zone  30 . Instead of differing the spacing between coils  40  to adjust the stiffness of each zone  28  and  30 , however, the coils  40  of each zone  28  and  30  of spring  38  have different outer diameters. More particularly, an outer diameter D 3  of coils  40  in first zone  28  of spring  38  may be greater than an outer diameter D 4  of coils  40  in second zone  30 . 
         [0032]    In other words, spring  38  narrows radially inward from first zone  28  to second zone  30 . Such a configuration results in a greater stiffness in first zone  28  than in second zone  30 . As spring system  12  utilizes a pair of springs, one skilled in the art would appreciate that simply increasing a thickness t 3  of wire  42  that forms spring  38  would be sufficient to increase the stiffness of an outer spring that surrounds or is used in tandem with an inner spring having a wire thickness that is less than the outer spring to achieve the multi-state stiffness of spring system  12  described above. 
         [0033]      FIG. 10  illustrates yet another alternative exemplary embodiment that may also be applied to each of first spring  20  and second spring  22 . Similar to the above exemplary embodiments, the spring  41  illustrated in  FIG. 10  includes a first zone  28  and a second zone  30 . To provide differing stiffness in first zone  28  and second zone  30 , a thickness t 4  of wire  42  in first zone  28  is greater than a thickness t 5  of wire  42  in second zone  30 . Such a configuration results in a greater stiffness in first zone  28  than in second zone  30 . As spring system  12  utilizes a pair of springs, one skilled in the art would appreciate that simply increasing the thickness of the wire that forms an outer spring that surrounds or is used in tandem with an inner spring having a wire thickness that is less than the outer spring would be sufficient to achieve the multi-state stiffness of spring system  12  described above. 
         [0034]    First spring  20  and second spring  22  may each be formed of different materials in first zone  28  and second zone  30  to provide the varying stiffness in each zone. For example, first zone  28  of each spring  20  and  22  may be formed of steel, while second zone  30  of each spring  20  and  22  may be formed of a material such as titanium. Other materials combinations are contemplated, without limitation. Regardless, so long as a different stiffness is present in each zone  28  and  30 , first and second springs  20  and  22  may collaborate to provide spring system  12  with multiple stiffnesses as required. 
         [0035]    Lastly, although the above exemplary embodiments have been described relative to a two-spring system  12 , the present disclosure should not be limited thereto. More particularly, spring system  12  may be formed of more than two springs. For example, spring system  12  may include three or more springs each having zones of different stiffness, without limitation.