END RETAINER FOR AIR SPRING IN STRUT SUSPENSION

Abstract: A top end retainer (78) for an air spring sleeve (54) in an automotive strut suspension system includes a elliptical clamping flange (80) having a perimeter equal to the circumference of the top end of the air spring sleeve (54) so that the sleeve (54) fits over the clamping flange (80) without stretching. A bushing aperture (84) in a centre web (82) attached to the clamping flange (80) is offset to an end of the flange (80). A piston rod (34) of the strut (10) is received in the bushing aperture (84) through an elastomeric bushing (94) and the centre web (82) is connected to the sprung mass (12) for rotation so that the strut (10) and the air spring (46) are rotatable about a steering axis. The geometric centre of the elliptical flange (80) is further offset from the longitudinal axis (28) of the strut (10) than would be the case with a circular flange having a diameter equal to the diameter of the top end of the air spring sleeve (54) so that the top end retainer (78) according to this invention contributes to optimization of the inclination of the line (102) along which the air spring resultant force (F2) is directed.

Description: Field of the Invention This invention relates to automotive air spring strut suspension systems having side-load compensation as specified in the preamble of claim 1, for example as disclosed in US-A-4,778,198. Background of the Invention Typical automotive strut suspension systems include a damper tube connected to the unsprung mass of the vehicle, a piston rod slidable on the damper tube and connected to the sprung mass of the vehicle, and a spring around the strut reacting against a seat on the damper tube and against a seat on the sprung mass. The spring may be a coil spring or an air spring of the type having a reinforced flexible sleeve sealed at the bottom on an air spring piston on the damper tube and at the top on an end retainer on the sprung mass. To minimize side loads on the rod and on the piston, the springs in some strut suspension systems are tilted relative to the struts so that the spring resultant forces more closely approach a theoretical optimum inclination. An air spring top end retainer according to the present invention is characterised by the features specified in the characterising portion of claim 1. An air spring end retainer according to this invention contributes to optimization of the angle of inclination of an air spring in a strut suspension system. Summary of the Invention This invention is a new and improved end retainer for an air spring in an automotive strut suspension system, the air spring being of the type having a reinforced flexible sleeve with a circular top end adjacent the end retainer. The end retainer according to this invention includes an elliptical clamping flange having a perimeter length equal to the perimeter length, i.e., the circumference of the top end of the air spring sleeve so that the sleeve fits over the flange without stretching. The end retainer further includes a centre web rigidly connected to the elliptical flange and a bushing aperture in the centre web tangent to the elliptical clamping flange at a major dimension end of the flange. The end retainer according to this invention is supported on the sprung mass of the vehicle at a angle relative to the longitudinal axis of the strut and with the piston rod of the strut in the bushing aperture. An elastomeric bushing is secured in the bushing aperture of the web of the end retainer and is connected to the piston rod of the strut whereby the piston rod is connected to the sprung mass of the vehicle. The geometric centre of the elliptical clamping flange co-operates with the geometric centre of the rolling lobe at the other end of the air spring sleeve in defining the line of action of the air spring resultant force. Brief Description of the Drawings Figure 1 is a partially broken-away, elevational view of an automotive air spring strut suspension system having an air spring end retainer according to this invention; Figure 2 is an enlarged view of a portion of Figure 1 showing the air spring end retainer according to this invention; and Figure 3 is a view taken generally along the plane indicated by lines 3-3 in Figure 2. Description of Preferred Embodiment Referring to Figure 1, a strut suspension system 10 is disposed between a fragmentarily illustrated sprung mass 12 of an automobile and an unsprung mass represented by a wheel support 14 and a wheel 16 mounted thereon for rotation about an axis 18 of the support. A ball stud 20 on the wheel support defines part of an articulated joint between the support and a lateral control arm, not shown, of the vehicle aligned on a transverse axis 22 thereof. The centre of the articulated joint is represented by a point 24, Figure 1, located at the intersection of the axis 22 and the centre of the spherical bearing end of the ball stud 20. The wheel support 14 is also connected to the sprung mass 12 of the vehicle by a strut 26 having a longitudinal axis 28. The strut includes a cylindrical damper tube 30 bolted to the wheel support through a lug 32, a rod 34 slidable along the strut axis 28 in a rod guide 36 on the damper tube, and a piston 38 on the rod slidable along the strut axis 28 on an inside wall 40 of the damper tube 30. The piston divides the inside of the damper tube into an upper working chamber 42 and a lower working chamber 44 which are preferably gas-filled but which may be liquid-filled. The piston 38 carries valving, not shown, for controlling fluid flow across the piston. An air spring 46 is disposed around the strut 26 between the damper tube 30 and the sprung mass 12. The air spring 46 includes an air spring piston 48 rigidly attached to the damper tube 30 around the rod guide 36. The air spring piston has a clamping perimeter 50 above an irregularly-shaped outside surface 52. A cord-reinforced, flexible sleeve 54 of the air spring has a circular lower end 56 sealingly clamped against the clamping perimeter 50 of the piston. The sleeve 54 folds outwards from the clamping perimeter to define an inside wall 58 of the air spring which lays against the outside surface 52 of the piston. The sleeve 54 folds outward at a rolling lobe meniscus 60 and defines an outer cylindrical wall 62 around the rod 34 which outer wall includes a small-diameter part at the bottom adjacent the rolling lobe meniscus 60 and a big-diameter part at the top of the outer wall 62. Referring to Figures 1-3, an upper bearing assembly 64 between the sprung mass 12 and the strut 26 and the air spring 46 includes an annular upper support 66 bolted to the sprung mass 12 around an aperture 68 therein and an annular lower support 70 below the upper support. The lower support has a tubular extension 72 projecting into the aperture 68 in the sprung mass. A bearing 74 is disposed between the upper and lower supports 66 and 70 so that the two are relatively rotatable. The lower support 70 is retained on the sprung mass 12 by a ring 76 around the tubular extension of the lower support. The lower support 70 is connected to the air spring 46 and to the rod 34 of the strut by an end retainer 78 according to this invention. The end retainer 78 resembles an inverted cup and includes a clamping flange 80 and an integral centre web 82. When viewed perpendicular to the plane of the flange 80, Figure 3, the clamping flange is elliptical in shape and has a major dimension D1 and a minor dimension D2. The centre web 82 is slightly conical, Figure 2, and has a circular bushing aperture 84 therein at a major dimension end of the elliptical flange 80. The edge of the aperture 84 is substantially tangent to or just touches the elliptical clamping flange 80, Figure 3. The end retainer 78 is attached to the lower support 70 through a filler plate 86, Figures 1 and 2. The filler plate 86 has a hole 88 therein through which a flange 90 around the bushing hole 84 in the end retainer 78 protrudes. The protruding flange 90 is spun-over and welded to the filler plate so that the end retainer is rigidly attached to the filler plate. The filler plate is attached to the lower support 70 by a plurality of screws, only a single screw 92 being shown in Figure 1, so that the end retainer 78 is rotatable relative to the sprung mass 12 of the vehicle. An elastomeric bushing 94 is fixed in the bushing aperture 84 by conventional means and has a centre bore therethrough which receives the top end of the rod 34. A pair of retainers 96 on the rod above and below the bushing 94 prevent vertical sliding movement of the rod relative to the bushing and, hence, relative to the sprung mass 12. The strut 26 and wheel 16 are steerable relative to the sprung mass 12 about a steering axis, not shown, which extends through the point 24 at the spherical centre of the ball stud 20 and through the centre of the bearing 74. Because of the non-stretchable nature of the cord-reinforced flexible sleeve 54 of the air spring in its fully-inflated condition, the perimeter of the clamping flange 80 is calculated to equal the perimeter, i.e., the circumference of the circular top end of the outer wall 62 of the inflated air spring sleeve 54 so that the latter fits snugly over the clamping flange 80 without being stretched beyond its limit. Once fitted over the clamping flange, the outer wall 62 is sealingly held thereagainst by a clamp 98 so that a sealed gas chamber 100 is defined within the air spring 46. As seen best in Figure 1, a resultant road force on the wheel 16 is represented by a force arrow F1 acting vertically on the wheel. That force is partially balanced by an air spring resultant force represented by a force arrow F2 which acts along a theoretical resultant force line 102 of the spring. For static equilibrium, the road force is also partially balanced by a third force represented by a force arrow F3 acting on the wheel support 14 through the point 24 at the spherical centre of the ball stud and directed along the transverse axis 22. With respect to side loading on the rod 34 and on the piston 38, an optimum condition obtains when the resultant force line 102 intersects the transverse axis 22 in the plane of the wheel 16 containing the force arrow F1, as at a theoretical point 104. In that condition, there is no side loading on the rod 34 or the piston 38 because the forces represented by force arrows F1, F2 and F3 all act through the theoretical point 104. If the resultant force line 102 passes laterally inboard of the theoretical point 104, side loads develop at the rod guide 36 and at the piston 38 on the inside wall 40 of the damper tube, the magnitudes of which increase as the distance inboard from the theoretical point 104 increases. Accordingly, optimum inclination of the air spring 46 is characterized by intersection of the resultant force line 102 and the theoretical point 104. The inclination of the resultant force line 102 of the air spring 46, which in the illustrated embodiment is not the optimum inclination as defined above, is determined by the locations of the geometric centres of the end retainer 78 and the rolling lobe meniscus 60. As a practical matter, the geometric centre of the rolling lobe meniscus 60 cannot be moved very far outboard of the longitudinal axis 28 of the strut. For example, a point 106, Figure 1, within the confines of the rod 34 represents the geometric centre of the rolling lobe meniscus 60 under static, design load conditions. Instead, the more practical approach has been to move the location of the geometric centre of the upper retainer 78 laterally inboard, or to the right, Figure 1, to achieve incremental increases in the inclination of the resultant force line towards the optimum inclination as defined above. The end retainer 78 according to this invention represents an implementation of the aforesaid more practical approach. Referring to Figure 3, the improvement afforded by the end retainer 78 is described by the following example. The perimeter of the elliptical flange 80 on the end retainer 78 is relatively closely approximated by the following equation: P=3.1416 2(a²+b²) where P is the perimeter, a is one half the long dimension D1 of the flange and b is one half the short dimension D2 of the flange. If the elliptical flange 80 has a long dimension D1=127mm and a short dimension D2=95mm, the perimeter P of the flange equals about 352mm. An air sleeve having a circular top end inflated diameter of 112mm has an equal circumference to this perimeter. Thus, the top end of an air sleeve of that diameter fits snugly over the elliptical flange 80 without being stretched beyond its limit. If the end retainer 78 has a circular clamping flange in accordance with prior teaching instead of the elliptical flange 80, the diameter of the circular flange and of the top end of the air spring sleeve must be about 127mm in order to maintain the same eccentricity or offset between the geometric centre of the flange and the axis 28 of the strut. At that eccentricity, the inclination of the resultant force line 102 is the same as achieved by the end retainer 78 with elliptical flange 80 but at the additional expense of an air spring sleeve having an inflated top end diameter of the order of 15mm larger than required with the above example. Stated somewhat differently, for an air spring sleeve having a given inflated top end diameter, the resultant force line 102 of the air spring is inclined more toward the theoretical point 104 with the end retainer 78 according to this invention than with a similar end retainer having a circular end flange of the same diameter as the inflated diameter of the top end of the air spring sleeve.

Claims: An air spring top end retainer (78) in an automotive strut suspension system including a strut (10) having a damper tube (30) connected to an unsprung mass (14,16) and constrained for generally vertical movement relative to a sprung mass (12), a rod (34) slidable relative to said damper tube (30) along a longitudinal axis (28) of said strut (10), and a piston (38) on said rod (34) slidable along said longitudinal axis (28) within said damper tube (30); a cord-reinforced, cylindrical, flexible air spring sleeve (54) having a circular first end (56) and a circular second end; an air spring piston (48) on said damper tube (30) sealingly connected to said air spring sleeve (54) at said first end (56) so that a rolling lobe meniscus (60) is defined around said air spring piston (48) and the geometric centre (106) of said rolling lobe meniscus (60) defines a first point through which the resultant force of said air spring on said damper tube (30) is directed; said air spring top end retainer (78) includes a centre web (82) including a bushing aperture (84); said centre web (82) is connected to said sprung mass (12) with said rod (34) of said strut (10) projecting into said bushing aperture (84); and there is a resilient bushing (94) between said rod (34) of said strut (10) and said centre web (82), characterised in that said air spring top end retainer (78) includes an elliptical clamping flange (80) having a perimeter length substantially equal to the circumference of said circular second end of said air spring sleeve (54) so that said circular second end fits closely over said elliptical flange (80) without stretching; said centre web (82) is connected to an edge of said elliptical clamping flange (80); said bushing aperture (84) is tangential to said elliptical flange (80) at a major dimension end thereof; and said circular second end of said air spring sleeve (54) is sealingly clamped to said elliptical flange (80) so that the geometric centre of said elliptical flange (80) defines a second point through which the resultant force of said air spring is directed. An air spring top end retainer (78) according to claim 1, in which said centre web (82) is connected to said sprung mass (12) by means of a bearing (74) between said centre web (82) and said sprung mass (12) so that said top end retainer (78), said air spring (46) and said strut (10) are rotatable relative to said sprung mass (12).

Inventors: PEES, JAMES MITCHELL
Applicants: GENERAL MOTORS CORPORATION
Application year: 1990
Main classification: B60G15
IPC codes: F16F9, B60G15