Abstract:
A suspension strut includes a housing assembly including first and second opposed housing members. The first and second housing members are relatively movable along an axis. At least the first housing member includes an engagement surface. At least one compressible spring member is interposed between the first and second housing members. The spring member includes a peripheral portion. The strut is configured such that, when the first and second housing members are relatively displaced along the axis in a prescribed direction, the spring member is axially compressed to provide a spring force opposing further relative displacement between the first and second housing members in the prescribed direction, and the peripheral portion frictionally engages the engagement surface over an area of engagement to provide dynamic damping between the first and second housing members.

Description:
FIELD OF THE INVENTION 
     The present invention relates to suspension struts and, more particularly, to suspension struts having damping. 
     BACKGROUND OF THE INVENTION 
     Suspension struts may be employed to join a suspended mass with a suspending mass, for example, a vehicle body with vehicle wheels and/or other suspension components. For example, such suspension struts may be incorporated in mining vehicles and similar vehicles. The suspension struts of mining vehicles and the like may be subjected to large variations in load. More particularly, when a mining vehicle is empty, the suspension strut may bear only the relatively small load of the vehicle body. However, the full cargo load for which the vehicle is designed may exceed 80 tons. The suspension struts for such vehicles should be capable of sufficiently absorbing wheel travel or vibration for any load or displacement within the designed range of the vehicle in order to reduce or eliminate disruption of the vehicle or its cargo. It is particularly desirable to avoid bottoming out of the suspension strut in use. The suspension struts should also be durable, both in terms of fatigue resistance and resistance to damage from impacts, overloading and various environmental hazards. 
     It is also desirable to minimize rocking and oscillation of the mining vehicle or other suspended mass. To minimize these unsettling movements, damping of the suspension strut&#39;s compression and/or extension may be required. 
     SUMMARY OF THE INVENTION 
     According to embodiments of the present invention, a suspension strut includes a housing assembly including first and second opposed housing members. The first and second housing members are relatively movable along an axis. At least the first housing member includes an engagement surface. At least one compressible spring member is interposed between the first and second housing members. The spring member includes a peripheral portion. The strut is configured such that, when the first and second housing members are relatively displaced along the axis in a prescribed direction, the spring member is axially compressed to provide a spring force opposing further relative displacement between the first and second housing members in the prescribed direction, and the peripheral portion frictionally engages the engagement surface over an area of engagement to provide dynamic damping between the first and second housing members. 
     Preferably, the area of engagement between the peripheral portion and the engagement surface increases with relative displacement between the first and second housing members in the prescribed direction and thereby increases the amount of the dynamic damping. Preferably, the housing assembly and the spring member are relatively arranged and configured such that deflection of the spring member responsive to axial compression is limited by the housing assembly. 
     The spring member may be formed of an elastomeric material. The spring member may be toroidally shaped. A plurality of the spring members may be provided in stacked relation. A separator plate may be interposed between at least two of the spring members. 
     The spring member may include a projection extending from an outer periphery of the spring member, the peripheral portion forming a part of the projection. The first housing member may include a tubular sleeve having an inner surface with the engagement surface forming a part of the inner surface. 
     The suspension strut may include a second tube forming a part of the second housing member and slidably received in the first tube, the second tube having a second engagement surface, and a second spring element disposed in the second tube and frictionally engaging the second engagement surface. A spacer may be interposed between the first spring element and the second spring element. This spacer may be axially displaceable relative to each of the first and second tubes. A bearing member may surround the second tube and be interposed between said first and second tubes. 
     Objects of the present invention will be appreciated by those of ordinary skill in the art from a reading of the Figures and the detailed description of the preferred embodiments which follow, such description being merely illustrative of the present invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a suspension strut according to embodiments of the present invention; 
     FIG. 2 is a side elevational view of the suspension strut of FIG. 1; 
     FIG. 3 is a cross-sectional view of the suspension strut of FIG. 1 taken along the line  3 — 3  of FIG. 2, wherein the suspension strut is in a fully extended position; 
     FIG. 4 is a cross-sectional view of the suspension strut of FIG. 1 viewed along the same cross-section as shown in FIG. 3, but wherein the suspension strut is in a compressed condition; 
     FIG. 5 is a top plan view of a spring element forming a part of the suspension strut of FIG. 1; 
     FIG. 6 is a perspective view of the spring element of FIG. 5; 
     FIG. 7 is a cross-sectional view of the spring element of FIG. 5 taken along the line  7 - 7  of FIG. 5; 
     FIG. 8 is a side elevational view of a bearing member forming a part of the suspension strut of FIG. 1; 
     FIG. 9 is a perspective view of the bearing member of FIG. 8; 
     FIG. 10 is a top plan view of a separator plate forming a part of the suspension strut of FIG. 1; 
     FIG. 11 is a perspective view of a bearing forming a part of the suspension strut of FIG. 1; 
     FIG. 12 is a perspective view of a spacer forming a part of the suspension strut of FIG. 1; 
     FIG. 13 is a perspective view of the suspension strut of FIG. 1, but wherein a top tube and a bottom tube thereof are removed for clarity; 
     FIG. 14 is a schematic view of a spring element, adjacent separator plates and a tube wall forming a part of the suspension strut of FIG. 1; 
     FIG. 15 is a schematic view of the components shown in FIG. 14, but wherein an increased load is applied to the spring element; and 
     FIG. 16 is a load-deflection diagram including a first curve showing the compression response of the suspension strut of FIG. 1 and a second curve showing the release response of the suspension strut. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout. 
     With reference to FIGS. 1-4, a suspension strut according to embodiments of the present invention is shown therein and generally designated  100 . The suspension strut  100  includes a housing assembly  12  including a bottom housing  30  and a top housing  20  slidably and telescopingly received in the bottom housing  30 . With reference to FIG. 3, the bottom housing  30  includes a bottom tube  32  and a bottom end plate  36  connected (for example, by welding or other means) to the bottom tube  32 . A bottom bearing plate or boss  38  is connected to the bottom end plate  36 . A spherical bearing  38 A is press fit into the bearing plate  38  and is also held in place by retaining rings  38 B on either side. The top housing  20  includes a top tube  22  and a top end plate  26  connected thereto. A lower portion of the top tube  22  is disposed within the bottom tube  32  and an upper portion of the top tube  22  extends out through the opening  31  of the bottom tube  32 . A top bearing plate  28  (with a spherical bearing  28 A press fit therein and further held in place by retaining rings  28 B) is connected to the top end plate  26 . The tubes  22 ,  32 , the end plates  26 ,  36 , and the bearing plates  28 ,  38  are preferably formed of steel or other suitable material. 
     In order to prevent over-extension of the suspension strut  100  (i.e., to prevent the top housing  20  from overly telescoping out of the bottom housing  30 ), the upper peripheral edge of the bottom tube  32  may be crimped as shown in FIG. 3, to form an inwardly extending, circumferential stop flange  33 . The top tube  22  includes an upper circumferential stop flange  23  extending outwardly therefrom to cooperate with the stop flange  33 . The stop flange  23  is preferably integrally formed with the top tube  22 , but, alternatively, may be welded or otherwise secured to the top tube  22 . 
     With reference to FIGS. 3,  4 ,  8  and  9 , the top tube  22  also includes a lower circumferential stop flange  24 . A cylindrical bearing member  40  is seated between the flanges  23  and  24  and surrounds the portion of the top tube  22  therebetween. The bearing member  40  is preferably formed of a resilient polymeric material. The bearing member  40  includes a slit  42  which allows the bearing member  40  to be temporarily expanded to install the bearing member over the flange  24 . Preferably, the bearing member  40  is formed of a strong material having good wear and low friction characteristics such as oil-filled nylon. 
     As best seen in FIGS. 3,  5 - 7  and  13 , three spring elements  50 B are housed in the bottom housing  30  and two spring elements  50 A are housed in the top housing  20 . As shown in FIG. 3, the spring elements  50 B are larger than the spring elements  50 A. The spring elements  50 A are preferably substantially identical to each other and the spring elements  50 B are preferably substantially identical to each other. The spring elements  50 A and  50 B may be similarly shaped and may differ only in their relative dimensions. Turning to FIGS. 5-7, the spring element  50 B shown therein is exemplary of various embodiments of the present invention and has a generally toroidal or “doughnut” shape. The spring element  50 B has a main body  52  having an inner wall  54  defining an axial passage  53 , which in turn defines an axis B—B (see FIG.  7 ). A circumferential rib or projection  56  is integrally formed with and extends radially outwardly from the body  52 . The projection  56  includes upper and lower opposed, concave walls  57 . The projection  56  further includes a generally axially extending outer wall  58 B. 
     Preferably, the outer diameter OD (see FIG. 5) of the spring element  50 B defined by the outer wall  58 B is between about 95 and 120 percent of the corresponding inner diameter of the tube  32 . Preferably, the inner diameter ID (see FIG. 7) of the spring element  50 B defined by the inner wall  54  is between about 0 and 70 percent of the outer diameter OD. Preferably, the corresponding outer diameter of the spring element  50 A is between about 95 and 120 percent of the corresponding inner diameter of the tube  22 , and the corresponding inner diameter of the spring element  50 A is between about 0 and 70 percent of the outer diameter. Preferably, each of the concave walls  57  has a radius of between about 0.5 and 5 inches, and more preferably, of between about 0.5 and 1.5 inches. 
     Each of the spring elements  50 A,  50 B is preferably formed from a resilient, elastomeric material. More preferably, the spring elements  50 A,  50 B are formed of natural rubber or urethane. Neoprene or nitrile may also be used. Preferably, the spring elements are molded. Other elastomers having different inherent damping characteristics may be used to adjust the strut damping over different damping levels. 
     A plurality of separator plates  80 B and  80 A are positioned adjacent and between respective ones of the spring elements  50 A,  50 B to provide a rigid loading surface. An exemplary separator plate  80 B is shown in FIG.  10  and has a through hole  82  formed therein. Each of the separator plates  80 B preferably has an outer diameter P of between about 0.001 and 0.10 inch less than the inner diameter of the tube  32 . The separator plates  80 A may differ from the separator plates  80 B only in their outer diameters. Preferably, the outer diameter of each separator plate  80 A is between about 0.001 and 0.10 inch less than the inner diameter of the tube  22 . The separator plates  80 A,  80 B are preferably formed of a rigid material. Materials which may be used for the plates  80 A,  80 B include acetal, steel or any other suitable rigid material. The spring elements  50 A,  50 B may be bonded or adhered to the separator plates  80 A,  80 B. 
     As best seen in FIGS. 3 and 13, the lowermost spring element  50 B is captured within the tube  32  and between the inner surface  36 A of the end plate  36  and a separator plate  80 B. The middle and upper spring elements  50 B are captured by the tube  32  and between a pair of separator plates  80 B. Similarly, the uppermost spring element  50 A is captured within the top tube  22  and between the end plate surface  26 A and a separator plate  80 A. The lower spring element  50 A is captured within the tube  22  and between a pair of separator plates  80 A. As a result of the arcuate profiles of the projections  56 , voids  37  surround the spring elements  50 B and voids  27  surround the spring elements  50 A. 
     With continued reference to FIGS. 3 and 13, a spacer  70  and a spacer bearing  60  are interposed between the lowermost separator plate  80 A and the uppermost separator plate  80 B. The spacer  70  is received in a passage  66  (see FIG. 11) of the bearing  60 . An inner flange  64  of the bearing  60  is received in a complementary circumferential recess  74  in the spacer  70  (see FIG.  12 ). The bearing  60  also includes a circumferential flange  62 . The spacer  70  has a through passage  72  formed therein (see FIG.  12 ). Preferably, the spacer  70  is formed of a rigid material such as steel. Preferably, the spacer bearing  60  is formed of a rigid, relatively low friction material such as oil-filled nylon. 
     When the suspension strut  100  is in the fully extended position as shown in FIG. 3, an upper portion of the spacer bearing  60  and an upper portion of the spacer  70  extend through the lower opening  21  of the top tube  22 . The flange  24 , the flange  62 , the outer surface of the spacer bearing  60  and the interior surface  22 A of the tube  22  define a circumferential gap  68 . 
     As shown in FIG. 3, none of the spring elements  50 A,  50 B, the separator plates  80 A,  80 B, the spacer bearing  60  and the spacer  70  are secured to the top tube  22  or to the bottom tube  32 . Rather, these components are able to slide axially (i.e., up or down along the axis A—A of FIG. 4) relative to the tubes  22 ,  32 . The bearing  40  is captured between the flanges  23  and  24  and therefore will slide with the top tube  22 , but may slide axially relative to the bottom tube  32 . The flanges  23 ,  24  and the bearing  40  may assist in resisting cocking loads on the suspension strut  100 . 
     The suspension strut  100  may be installed by securing the top housing  20  directly or indirectly to a suspended mass, for example, a suspended vehicle body, by means of the mounting plate  28  and by securing the bottom housing  30  directly or indirectly to an unsuspended mass, for example, a wheel, by means of the mounting plate  38 . In use, the suspension strut  100  may be alternately loaded such that the mounting plate  28  is urged in a direction C (see FIG. 4) toward the mounting plate  38  and unloaded such that the mounting plate  28  is urged away from the bottom mounting plate  38 . Responsive to loading, the top housing  20  and the bottom housing  30  apply an axially compressive force to the spring elements  50 A,  50 B. The spring elements  50 A,  50 B assume a bulged, axially compressed condition as shown in FIG.  4 . In turn, the top tube  22  is permitted to slide farther into the bottom tube  32  and the spacer bearing  60  and the spacer  70  are permitted to slide farther into the top tube  22 . 
     As best seen in FIGS. 4,  14  and  15 , the area and force of contact between the surfaces  58 A,  58 B and the surfaces  22 A,  32 A will each increase with axial compression of the respective spring elements  50 A,  50 B. For example, when a spring element  50 B as shown in FIG. 14 which is subjected to a first load (which may be no load) is thereafter subjected to a greater load, the spring element  50 B may assume a condition as shown in FIG.  15 . That is, as the spring element  50 B is subjected to the greater load, the spring element will become further axially. compressed and will in turn bulge or deform radially and axially to further fill the voids  37  (and also the central void defined within the spring element  50 B) and increase the contact area between the outer surface  58 B of the spring element and the inner surface  32 A of the housing tube. Moreover, the radial load applied to the inner surface  32 A by the spring element outer surface  58 B is increased. 
     Notably, bulging (i e., deformation) of the spring elements  50 A,  50 B is limited or resisted by the adjacent inner tube surfaces  22 A,  32 A, the adjacent separator plates  80 A,  80 B and the end plate surfaces  26 A,  36 A. As a result, as the areas of contact between the surrounding separator plates  80 A,  80 B and tubes  22 ,  32  increase and the loads applied to these components by the spring elements increase, the load required to further axially compress each spring element  50 A,  50 B increases at a substantially greater rate both because of the increasing spring rate and friction between the spring elements  50 A,  50 B and the surfaces  22 A,  32 A. Thus, bulging of the spring elements is limited by the housings  20 ,  30  in such a way as to contribute to the compression spring rates of the spring elements. 
     For example, as shown in FIG. 16 which shows exemplary compression and release load-deflection response curves for a suspension strut according to the present invention, the strut  100  will have a relatively low spring rate for low loads (and low deflections) as demonstrated by the first, extended, substantially linear portion of each curve. However, as the strut  100  approaches its designed maximum deflection, the spring rate increases rapidly (with the curve approaching vertical) responsive to additional deflection. In this manner, the strut  100  may provide a more linear and softer spring rate through a relatively large deflection range, thereby enhancing isolation of the suspended mass (e.g., under normal operating conditions), while also providing a relatively high spring rate as the deflection approaches the maximum allowed deflection (e.g., to prevent bottoming out of suspension components as a result of large impulse loads or overloading). 
     The constraints on bulging of the spring elements  50 A,  50 B described above also provide a desired spring rate to the strut  100  while reducing the degree of deformation of the spring elements required. Such reduction in deformation may reduce the strain on the spring elements, thereby increasing the service life of the strut. 
     Additionally, as the suspension strut  100  is axially compressed or released from compression, the circumferential outer surface  58 B of each spring element  50 B engages and slides along a portion of the inner surface  32 A of the bottom tube  32 . Similarly, the circumferential outer surface  58 A of each spring element  50 A engages and slides along a portion of the inner surface  22 A of the top tube  22 . The surfaces  22 A,  32 A and the material of the spring elements  50 A,  50 B may be selected to provide a prescribed amount of frictional resistance therebetween. This frictional resistance in turn may provide dynamic damping for the suspension strut  100 . The frictional resistance provides both compression and rebound (i.e., release or extension) damping. In this manner, bouncing or oscillation of the suspended mass may be reduced or minimized. 
     As discussed above, responsive to increased axial compression, the contact areas and loads between the spring element surfaces  58 A,  58 B and the tube inner surfaces  22 A,  32 A increase. As a result, the frictional resistance between the spring element  50 A,  50 B and the inner surface  32 A is increased, thereby providing increased damping. Hence, the suspension strut  100  may provide greater damping for greater deflections and, hence, for higher loads. 
     The foregoing discussion with reference to FIGS. 14 and 15 is exemplary of the behavior of each of the spring elements  50 A,  50 B and the respective tube surfaces  22 A,  32 A. However, the amount of frictional resistance provided by a given spring element  50 A,  50 B may vary. In particular, for a given compression of the suspension strut  100 , those spring elements  50 A,  50 B near the spacer  70  will typically travel farther relative to the engaging surface  22 A,  32 A, and thereby may provide greater damping forces than those spring elements  50 A,  50 B nearer the end plates  26 ,  36 , respectively. 
     The above-described frictional damping may provide a number of advantages. The frictional damping may supplement the material damping of the spring elements  50 A,  50 B (i.e., resulting from the material&#39;s loss factor). Accordingly, the maximum amount of damping which may be provided for a given selection of spring element material, spring element geometry and strut size may be increased. A wider range of damping rates may be provided across the range of deflection. Also, the rate of increase in damping as a function of deflection may be increased for greater deflections as compared to the rate of increase in damping as a function of deflection for lesser deflections (see FIG.  16 ). The materials of the spring elements  50 A,  50 B and the engaging surfaces  22 A,  32 A of the housing  12  may be selected to provide combinations of frictional and deformation properties as desired for each intended application. The damping rate of the strut may be more easily and effectively tuned by adjusting one or more of several parameters. For example, the damping behavior may be adjusted by: 
     1) changing the elastomeric material of the spring elements  50 A,  50 B; 
     2) changing the geometry of or eliminating the holes in the spring elements  50 A,  50 B; 
     3) changing the heights of the spring elements  50 A,  50 B; 
     4) changing the shapes of the spring elements  50 A,  50 B; 
     5) changing the frictional properties of the inner housing engagement surfaces  22 A,  32 A. This may be accomplished, for example, by selection of the materials of the tubes  22 ,  32  or by applying a coating such as a resin-bonded lubricant coating such as Emralon™  333  coating available from Acheson Colloids Company of Port Huron, Mich., a teflon-based coating, or other suitable coatings; 
     6) providing a lubricant between the spring element surfaces  58 A,  58 B and the inner housing engagement surfaces  22 A,  32 A; 
     7) changing the outer diameters of the spring elements  50 A,  50 B relative to the corresponding inner diameters of the tubes  22 ,  32 . For example, the outer diameters of the spring elements  50 A,  50 B may be substantially the same as or less than the corresponding inner diameters of the tubes  22 ,  32  so that the spring elements  50 A,  50 B are slip fit into the tubes  22 ,  32 . Alternatively, the outer diameters of the spring elements  50 A,  50 B may be greater than the corresponding inner diameters of the tubes  22 ,  32  so that the spring elements  50 A,  50 B are interference fit into the tubes  22 ,  32 , thereby providing one or more of the spring elements  50 A,  50 B with radial pre-compression. Accordingly, the strut  100  may allow substantial flexibility in tuning the damping of the strut, whether the desired state of tune is critical damped, under-damped or over-damped. 
     Holes  53 ,  72  and  82  facilitate air flow through the suspension strut  100 , both for cooling and to minimize or eliminate the effects of compressing trapped air which may affect the spring rate or other performance of the suspension strut. Additionally, the holes  53 ,  72  and  82  may be used to assist in assembling and disassembling the strut. For example, a hooked wire or similar tool may be inserted through the holes to pull the stack of components out of the housing  12 . 
     While the foregoing components have been described with regard to “top” and “bottom” orientations, it will be appreciated that the orientations may be reversed. Moreover, the suspension strut  100  may be horizontally oriented or oriented at an angle between vertical and horizontal. 
     In addition to the foregoing benefits, the housings  20 ,  30  may protect the spring elements  50 A,  50 B from impacts, dust, corrosives and other environmental hazards. 
     While in the illustrated embodiment spring elements are shown in both of the housings  20 ,  30 , such provision is not necessary in keeping with other embodiments of the invention. Moreover, according to further embodiments, the spacer  70  and the bearing  60  may be omitted. 
     The foregoing is illustrative of the present invention and is not to be construed as limiting thereof. Although several embodiments of this invention have been described, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the claims. Therefore, it is to be understood that the foregoing is illustrative of the present invention and is not to be construed as limited to the specific embodiments disclosed, and that modifications to the disclosed embodiments, as well as other embodiments, are intended to be included within the scope of the appended claims. The invention is defined by the following claims, with equivalents of the claims to be included therein.