Patent Application
20090115157
The subject invention relates to a composite leaf spring for a vehicle suspension having an improved end mount interface for connection to a vehicle structure.
Vehicle suspensions include springs that cooperate with other suspension components to improve ride and handling characteristics for a vehicle. One type of suspension is a front axle suspension that uses one or more leaf springs formed from steel. In this suspension configuration, the leaf spring has a free end coupled to a shackle assembly, which is mounted to a vehicle structure. This conventional shackle mount interface accommodates longitudinal displacement due to flexing under load as the leaf spring moves from a curved condition towards a flat condition. A typical shackle assembly is comprised of several plates, two bushings, and a bracket.
Trailer suspensions utilize a sliding end bracket configuration to accommodate longitudinal displacement. This is effective for trailer applications but has a disadvantage of having lateral gaps at sides of the leaf spring, resulting in lateral slack. In steering applications, lateral gaps cause objectionable steering center feel due to low central lateral stiffness, and have objectionable noise and clattering due to lateral and vertical free play. Lateral play may initially be set to zero by using a bolt to clamp sides of a slider bracket; however, lateral play develops as components wear.
Another sliding end configuration uses a cam that is attached to a bracket in a vehicle frame or chassis. The cam supports a vertical force experienced by the leaf spring. In conventional configurations, the leaf spring and the cam are both formed from steel, and due to the stiffness of the cam, a very high contact pressure is created, which can result in premature wear of the cam or leaf spring.
Some suspensions utilize composite leaf springs instead of using traditional steel leaf springs in order to reduce weight. The existing solutions discussed above for free end mounting of steel leaf springs do not perform well for front axle applications. Further, these existing solutions would be very expensive to incorporate into composite springs.
Thus, there is a need for an improved mounting interface for composite leaf springs that overcomes the deficiencies in the prior art discussed above.
A leaf spring for a vehicle suspension is formed from a composite material and includes a central portion to be supported by an axle and at least one free end that extends from the central portion in a longitudinal direction. The free end is coupled to a vehicle frame or chassis with a slider bracket. A contact element is fixed to the slider bracket to contact an upper surface of the free end to accommodate vertical forces. The free end is slidably movable relative to the contact element along a longitudinal axis and is pivotable relative to the contact element about a lateral axis.
In one disclosed embodiment, the contact element comprises a cam that is formed as part of the slider bracket. In one example, the cam is comprised of an elastomeric material that is covered with a layer of wear resistant material. The cam can include a curved surface that contacts the free end of the leaf spring or can comprise a pivoting cam coupled to a pivot pin, for example. In another example, the cam comprises an upper roller and a lower roller that are formed from materials that have different stiffness properties.
In one disclosed embodiment, the cam extends over the upper surface of the free end and laterally spaced pads are attached to legs of the slider bracket. The laterally spaced pads are positioned at opposing lateral edges of the free end of the leaf spring. In one example, the pads are formed from an elastomeric material and are covered with a layer of wear resistant material. The pads provide increased lateral stiffness.
In one disclosed embodiment, the contact element comprises a resilient block that extends over the upper surface of the leaf spring. The resilient block is formed from an elastomeric material and includes a plurality of laterally extending holes that are formed within a body of the resilient block in a pattern that is distributed away from a center of the resilient block. This provides a desired level of vertical stiffness.
These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.
A suspension assembly 10 is shown schematically in
The leaf spring 12 extends in a longitudinal direction along a vehicle length and includes a central portion 12a that is supported on an axle 14 and a free end 12b that extends away from the central portion 12a in the longitudinal direction. The central portion 12a is not defined as a center of the leaf spring but may incorporate such an area. Further, the central portion 12a is descriptive of a spring portion that is located anywhere between ends of the leaf spring, and which is associated with the axle 14.
The free end 12b is coupled to a vehicle structure 16, such as a frame member or chassis for example, with a slider bracket 18. The axle 14 supports wheels (not shown) and extends in a lateral direction across a vehicle width. The axle 14 can be a front, rear, or trailer axle and further can be a steer, drive, or non-drive axle that includes a beam, housing, or axle tube, for example.
The slider bracket 18 is shown in greater detail in
The free end 12b of the leaf spring 12 can slide relative to the contact element 30 along a longitudinal axis as indicated at arrow 32 and/or can pivot relative to the contact element 30 about a lateral axis as indicated at arrow 34. In the example shown in
The cam 36 is comprised of a resilient material such as a polymeric or elastomeric material, and is covered with a layer of wear resistant material to improve wear life. The wear resistant material should have a certain level of compliance to create a large load foot print with the mating leaf spring 12. The stiffness of the cam 36 can be tailored to mimic traditional steel cams, which provide for a variable spring rate by modifying an effective spring length. The cam 36 can be ribbed (see dashed lines 42) and/or hollowed (see dashed lines 44) to provide variable stiffness to accommodate spring angular displacement at the free end 12b, while still maintaining a large load foot print.
A rebound bolt 46 is also fixed to the slider bracket 18. The contact element 30 is positioned vertically above the free end 12b while the rebound bolt 46 is positioned vertically below the free end 12b by a gap, which is shown exaggerated for clarity purposes. The rebound bolt 46 defines a vertical stop for the free end 12b during a rebound event. The rebound bolt 46 can be moved vertically closer to the free end 12b and/or a rubber tube 48 can be used to surround the rebound bolt 46 to maintain the free end 12b in contact with the contact element 30 depending upon the vehicle application and desired performance characteristics.
Another example of a contact element 30 is shown in
Like the cam 36 discussed above, the pivoting cam 50 is formed from a resilient material such as a polymeric or elastomeric material, for example. A pad or layer of wear resistant material 60 is bonded to the base surface 54 for direct contact with the upper surface 40. Again, the wear resistant material should have a certain level of compliance to create a large load foot print with the mating leaf spring 12. Further, the free end 12b of the leaf spring 12 can slide relative to the pivoting cam 50 along the longitudinal axis as indicated at arrow 32 and/or can pivot relative to the pivoting cam 50 about the lateral axis as indicated at arrow 34.
The cams shown in the examples above can be molded directly onto the slider bracket 18 to simplify assembly. The cams are configured to support the vertical forces on the leaf spring 12 and to distribute these vertical forces over a large area to reduce pressure and wear accordingly.
Another example of a contact element 30 is shown in
Another example of a contact element 30 is shown in
The resilient block 70 includes a plurality of holes 72 that extend in a lateral direction. The holes 72 can be formed to have different diameters and spacing patterns to tune/control vertical stiffness depending upon desired characteristics. In the example shown, the holes 72 are formed in a pattern that is distributed away from a center 74 of the resilient block 70 such that vertical stiffness is greater at the center 74.
Additionally, side pads 76 can be mounted to the first 22 and second 24 legs of the slider bracket 18 to increase lateral stiffness. The side pads 76 can be formed from a polymeric or elastomeric material and coated with a wear resistant material. The side pads 76 are positioned very close to the lateral side edges of the free end 12b such that there is minimal lateral play. In one example, the free end 12b is press fit between the two side pads 76. The side pads 76 can be molded as one piece with the slider bracket 18 to simplify assembly.
Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.
