Abstract:
A jounce bumper plate for a damping module of a type commonly employed automotive suspension system having a hydraulic cylinder with an upper end cover, a piston rod slidably extending from the upper end of the cylinder and ajounce bumper mounted upon the piston rod. The jounce bumper plate mounted on an upper end of the cylinder and includes a central bore therethrough to allow slidable passage of the piston rod, and includes a series of arches extending about the outer periphery of the plate. The arches increase in curvature from the central bore to the outer periphery, thereby forming gaps between the jounce bumper plate and the associated hydraulic cylinder to facilitate the expulsion of moisture and contaminants from the upper end of the hydraulic cylinder during compression and extension cycles of the associated cylinder.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to suspension systems and, more particularly, to jounce bumper plates for use with hydraulic dampers in vehicular suspension systems. 
     In automotive applications, hydraulic dampers are used in combination with coil springs to absorb relative displacements between a sprung component, such as an automotive vehicle body, and an unsprung component, such as a wheel assembly or vehicle chassis, to absorb the shock of impact sustained by the unsprung component. Vehicular suspension systems utilize various types of well-known hydraulic dampers including shock absorbers and struts. 
     In a typical strut suspension system, the strut is mounted between the vehicle chassis and the vehicle body. The strut typically includes a hydraulic cylinder with an attached piston and piston rod. The piston rod slidably extends from the upper end of the hydraulic cylinder and is connected to the vehicle body through a flexible connection. The hydraulic cylinder is attached to the vehicle chassis at the lower end of the cylinder. The impact of shocks from the road surface causes movement of the piston through fluid contained in the hydraulic cylinder. The resistance of movement of the piston through the cylinder is proportional to the rate of displacement, thereby damping the movement of the associated spring and preventing excessive bouncing of the vehicle body. 
     Since displacement of the vehicle chassis causes displacements of the strut, the strut undergoes cycles of compression and extension in response to the displacement of the vehicle chassis. Provision must be made for protecting the strut assembly and the vehicle body from the extreme jounce forces associated with severe irregularities in the road surface. A strut is typically provided with a jounce bumper mounted axially on the piston rod and ajounce bumper plate mounted on the upper end of the hydraulic cylinder. The jounce bumper is an elongated, generally cylindrical member of a compressible, elastomeric material that extends around the piston rod. During jounce motions of the strut, the damper bottoms out and the jounce bumper moves into contact with the jounce bumper plate and compresses to dissipate energy. 
     The jounce bumper and jounce bumper plate assembly are configured to protect the upper end of the hydraulic cylinder and the rod seal assembly. Jounce bumper plates are typically made of steel and are welded to the seal cover on the upper end of the hydraulic cylinder. An annular piston rod seal provides a fluid-tight seal between the seal cover and the piston rod to maintain the working fluid within the hydraulic cylinder. Jounce bumper plates typically have a central bore for receiving the piston rod and are configured to prevent damage to the rod seal from water and other contaminants. Dirt or moisture accumulating on the piston rod can be forced through the rod seal when the jounce bumper moves into contact with the jounce bumper plate and compresses the air between the jounce bumper plate and the seal cover. Therefore, jounce bumper plates typically provide a gap or channel between the jounce bumper plate and the seal cover that facilitates expulsion of contaminants and water that become trapped within the central bore of the jounce bumper plate. 
     Conventional jounce bumper plates are prone to deformation under the greater loads associated with recently developed active suspension systems and larger, heavier vehicles. Deformation of the jounce bumper plate around the seal cover inhibits the expulsion of water and other contaminants from the seal area and also results in a rough contact surface during the initial deflection of the jounce bumper. Therefore, there is a need for a jounce bumper plate which provides a smooth structural impact area for the jounce bumper with reduced plate deformation and improved wear characteristics at the jounce bumper/plate interface, allows proper venting to remove debris and other contaminants from the damper seal location, prolongs damper life by protecting the seal area of the damper and improves jounce bumper “entry feel” by providing a smooth interface where the jounce bumper contacts the jounce bumper plate. 
     SUMMARY OF THE INVENTION 
     The present invention is an improved jounce bumper plate for use with a damping module, which fulfills the needs of the prior art. The damping module is of a type having hydraulic cylinder having a cover at its upper end, a piston rod slidably extending from the upper end of the hydraulic cylinder and a jounce bumper attached to the piston rod. The jounce bumper plate is mounted on the upper end of the hydraulic cylinder. The jounce bumper plate has a central bore therethrough shaped to receive the piston rod of the cylinder and is shaped to form a series of peripheral arches extending about the outer edge of the jounce bumper plate. The upper surfaces of the arches provide a smooth structural impact area for the jounce bumper and are capable of withstanding significant jounce motions of the cylinder without permanent deformation. The arches provide gaps between the jounce bumper plate and the associated seal cover, thereby facilitating expulsion of water and other contaminants from the area adjacent to the damper seal. 
     Accordingly, it is an object of the present invention to provide a jounce bumper plate for a damping system which is capable of withstanding high loads without deformation; a jounce bumper plate which provides a smooth structural impact area for the jounce bumper; a jounce bumper plate which improves wear characteristics at the jounce bumper/jounce bumper plate interface; a jounce bumper plate which provides venting to remove contamination from the damper seal location; and a jounce bumper plate which prolongs damper life by protecting the seal area of the damper; and improves jounce bumper “entry feel” by providing a smooth jounce bumper and jounce bumper plate interface. 
     Other objects and advantages of the present invention will be apparent from the following description, the accompanying drawings and the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a partial side elevation in section of the upper portion of a damping module showing a preferred embodiment of the jounce bumper plate of the present invention; 
     FIG. 2 is a perspective view of the jounce bumper plate shown in FIG. 1; 
     FIG. 3 is a top plan view of the jounce bumper plate of FIG. 2; 
     FIG. 4 is a side elevational view in section of the jounce bumper plate taken at line  4 — 4  of FIG. 3; 
     FIG. 5 is perspective view of a prior art jounce bumper plate; 
     FIG. 6 is a top plan view of the jounce bumper plate of FIG. 5; and 
     FIG. 7 is a side elevational view in section of the jounce bumper plate taken at line  7 — 7  of FIG.  6 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     As shown in FIG. 1, a strut module assembly for an automotive suspension system, generally designated  10 , is operatively connected between the unsprung portion of a vehicle (not shown) and the sprung portion of a vehicle (not shown) in a well-known manner. 
     The suspension system  10  includes a hydraulic cylinder  12  having a reservoir tube  13  which provides a reservoir for hydraulic damping fluid. A cylindrical piston rod  14  extends along the central axis of the cylinder  12  and is attached at one end to a conventional valved piston (not shown) slidably mounted in a cylindrical inner tube (not shown) concentric with and spaced inwardly from the reservoir tube  13 . Seal cover  16 , welded or otherwise secured to the reservoir tube  13 , closes the upper end of the hydraulic cylinder  12 . The piston rod  14 , which extends upwardly through an opening  17  in the seal cover  16 , has a reduced diameter threaded portion  18 . An upper support housing  19  is used to attach the strut assembly  10  to an automobile frame (not shown), usually by insertion of frame bolts  20  through corresponding openings in the automobile frame. The piston rod  14  is attached to the upper support housing by threadable connection of nut  21  secured to the piston rod upper threaded portion  18  extending through the upper support housing  19 . 
     The strut module assembly  10  also includes a coil spring  22  mounted between the upper support housing  19  and a lower support housing  23  (partially  25  shown). An elastomeric boot  24  encloses the upper portion of the hydraulic cylinder  12 . The boot  24  is mounted within the spring  22  and is secured to the upper support housing  19  and the lower support housing  23 . 
     A generally cylindrical, elastomeric jounce bumper  26  is mounted on piston rod  14  and secured to the upper mount assembly  19 . The jounce bumper  26  preferably is formed from a compressible foam or elastomeric material having a density of between 0.40-0.63 gm/cm 3 . Under full jounce, the jounce bumper compresses to about 20% of its initial length. 
     A jounce bumper plate  28  is welded or otherwise secured to the seal cover  16  on the hydraulic cylinder  12 . The jounce bumper plate  28  is generally configured as an annular disc having a central bore  29  shaped to receive the piston rod  14 . Jounce bumper plate  28  is constructed such that a gap  30  is formed when the jounce bumper plate is secured to the seal cover. Moisture or other contaminants accumulating on top of the piston rod  14  are expelled through the gap  30  rather than being forced through the seal cover  16  and into the hydraulic cylinder  12 . A fluid-tight elastomeric seal  32  is positioned between the piston rod  14  and the seal cover  16  on top of the reservoir tube  13  at the exit of the piston rod from the tube. The elastomeric seal  32  prevents dirt, water, and other contaminants from moving along the rod and subsequently passing through the seal cover and into the hydraulic cylinder  12 . However, without the gap  30  between the seal cover  16  and the jounce bumper plate  28  dirt, moisture, or other contaminants could be forced past the seal  32  under the pressure generated during jounce contact between the jounce bumper  26  and the jounce bumper plate  28 . 
     FIGS. 2,  3  and  4  show a preferred embodiment of the jounce bumper plate  28  of the present invention. The jounce bumper plate  28  of the invention is generally disc-shaped having a central bore  29  shaped to slidably receive the piston rod  14  of the damper (see FIG. 1) and a scallop-shaped outer periphery  34 . A series of arches  36  extend from the central bore  29  to the outer periphery  34  and are defined by a plurality of linear creases  38  extending radially from the bore to the outer periphery  34 . Adjacent arches  36  intersect at creases  38  formed in the top of the jounce bumper plate  28  and form corresponding radially-extending linear support surfaces  40  on the bottom of the plate. 
     In the preferred embodiment of the present invention, the jounce bumper plate  28  is constructed of steel having a gage of between about 2.5 to 3.5 mm, preferably 3.1 mm. Each support surface  40  forms an arc  A  at the outer circumferential edge  34  having an arc radius of between about 2 to 8 mm, preferably 4 mm. Each corresponding linear crease  38  on the top of the jounce bumper plate  28  forms an arc  B  at the outer circumferential edge  34  having an arc radius of between 0.5 to 2 mm, preferably 1 mm. Each arch  36  is an arc having an arc radius of between about 15 to 30 mm, and preferably between about 20 to 25 mm. A plane defined by the apex of each arch  36  on the top surface of the plate is essentially coplanar with the plane which includes the top of the plate adjacent to the central bore  29 . The lower surfaces at the apex of each arch define a plane parallel to a plane defined by points located at the end of the linear support surfaces  40  at the outer circumferential edge  34  wherein the distance between the two planes is from about 2 to 6 mm, preferably from about 4.5 to 5.5 mm. 
     The continuously curved arches  36  provide a smooth, continuously-arching top surface of the jounce bumper plate  28  for the jounce bumper  26  (see FIG. 1) to contact during a jounce cycle. The smooth structural impact area for the jounce bumper  26  improves the wear characteristics at the jounce bumper/jounce plate interface and also improves the entry feel during the initial contact of the jounce bumper  26  with the jounce bumper plate  28 . 
     The support surfaces  40  preferably are spot welded or otherwise mounted on the seal cover  16  (see FIG. 1) at a point on each support surface approximately midway between the central bore  29  and the outer circumferential edge  34 . Arches  36  extending between adjacent contact points produce gaps  30  between the seal cover and the jounce bumper plate that facilitate expulsion of air and contaminants from around the seal cover area. The gap  30  formed by each arch  36  over the seal cover  16  has a height of at least 1 mm and preferably 2 mm as measured at the outer circumferential edge  34  of the jounce bumper plate  28  with respect to a plane formed by the top surface of the seal cover  16 . The continuously curved arch configuration of the present jounce bumper  26  is better able to withstand high loads associated with active suspension systems without deformation. Accordingly, the gap  30  between the seal cover  16  and the jounce bumper plate  28  is maintained at its proper height and facilitates proper venting of the seal cover area to protect the seal from contaminants. 
     The jounce bumper plate  28  preferably is able to withstand 50,000 compression cycles at 40 kN load. In the preferred embodiment, the jounce bumper plate  28  is composed of steel although other materials such as plastic and composites may also be used. The number of arches preferably is six although any number of arches can be used provided that water and other contaminants around the seal cover area are properly expelled. 
     As an associated vehicle chassis and suspension is subjected to irregularities in the road surface, the piston rod  14  moves within hydraulic cylinder  12  to reduce the transmission of vibrations and noise to the associated vehicle body. During full jounce, the piston rod  14  nears the end of its compression stroke within the hydraulic cylinder  12  and the jounce bumper  26  engages the jounce bumper plate  28  to prevent metal to metal contact and damage to the hydraulic cylinder. Full compression of the strut and the corresponding full compression of the jounce bumper  26  as it impacts the jounce bumper plate  28  create significant air pressure which forces contaminants through the gap  30  between the seal cover  16  and the jounce bumper plate  28 . 
     Details of a prior art jounce bumper plate are shown in FIGS. 5,  6  and  7 . The prior art jounce bumper plate  42  is generally disc shaped having a central bore  44  shaped to slidably receive the piston rod  14  (see FIG.  1 ). The jounce bumper plate is generally flat, but also includes a plurality of indentations  46  extending from the top  48  to the bottom  50  of the jounce bumper plate. The indentations  46  produce corresponding mesas  53  on the top surface of the jounce bumper plate  42  which provide a contact surface for the jounce bumper  26  (see FIG. 1) under a jounce stroke. The bottom of the indentations  46  are spot welded to the top of the seal cover  16  thereby producing a plurality of gaps  54  (see FIG. 5) between the seal cover  16  and the jounce bumper plate  42 . Under the greater loads associated with active suspension systems in current vehicles, prior art jounce bumper plate  42  can become permanently deformed. Such permanent deformation of bumper plate  42  typically takes the form of a collapsed outer periphery, which wraps downwardly and around the seal cover  16 . A jounce bumper plate  42  thus deformed inhibits proper venting of the seal area and provides a rough surface during jounce bumper initial deflections (entry feel). A deformed prior art jounce bumper plate  42  also inhibits proper venting by restricting or completely sealing off the gaps  54  normally present between the seal cover  16  and the jounce bumper plate  42 . Without proper venting, contaminants, such as dirt and moisture, tend to be forced past the seal  32  and into the hydraulic cylinder  12  under the air pressure generated during severe jounce. Contaminants forced through the seal  32  can damage the hydraulic cylinder  12  and the piston rod  14  resulting in fluid leakage from the hydraulic cylinder  12 . Furthermore, the deformed jounce bumper plate presents a rough surface which causes corresponding disruptions in the initial deflections of the jounce bumper as it comes in contact with the jounce bumper plate (known as “entry feel”). The poor entry feel associated with the rough surface of the deformed jounce bumper plate results in undesirable vibrations being transmitted to the vehicle body. 
     Although the present invention has been described with reference to a preferred embodiment, those skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. The relative terms used in this description such as “top” and “bottom” are used for ease-of-reference and are not intended to limit the scope of the invention.