SIDE LOAD COMPENSATING AIR SUSPENSION

Abstract: A vehicle suspension strut (310) incorporating an air­ spring (312) around a hydraulic shock absorber (318) is dis­ closed. The airspring design and orientation relative to the shock absorber axis (321) creates a side acting force which counteracts the bending torque acting on the strut during op­ eration in a vehicle and prevents bending of the shock absorber piston. The horizontal acting side load can be achieved by using an airspring piston (314) eccentrically mounted on the shock absorber (318). Alternatively the air­ spring (312) may be mounted offset and/or at an angle to the shock absorber axis (321). The flexible membrane (330) of the airspring (312) may also be cut in a plane oblique to the shock axis and mounted on the airspring piston (314) to form asym metric rolling lobes about the circumference of the piston (314).

Description: Background of the Invention This invention relates generally to strut type suspension members which utilize airsprings in conjunction with a damping member contained therein. In particular, conventional hydraulic shock absorbers provide the damping means and rolling lobe type airsprings provide the load support. The geometry used on helical spring strut suspensions for automobiles is such that the vehicle mass produces an angular displacement or torque which causes bending of the strut. This bending moment to the strut causes binding of the shock absorber piston which results in ride harshness. This harshness is pronounced at low amplitude undulation of the vehicle. Conventional helical coil spring MacPherson struts utilize a coil spring that is both offset and set at an angle to the strut axis. This geometry is an attempt to create compensating side loading to oppose the stress placed on the strut by the spring mass of the vehicle. The helical spring type struts, as represented by a MacPherson strut configuration cannot be adjusted to compensate for increased vehicle load. Thus, as load increases vehicle height decreases. Also, the coil spring is limited to a single or at best a very narrow range of spring rates which requires a design selection between a soft ride and a hard ride. U.S. Patent No. 4,332,397 illustrates a suspension strut having a damper means with an airspring therearound. The airspring piston is secured to the body of the damper means in a tilted position such that the axis of the airspring piston forms an angle with the axis of the damper means. Patent Abstract of Japan, Volume 6, No. 204 (M-164) [1082], 15th October, 1982 illustrates a suspension strut having a damper means with an airspring therearound. A lower tank is secured to the body of the damper means such that the axis of the tank is perpendicular to but non-coincident with the axis of the damper means. Neither reference teaches the use of an egg-shaped piston nor discloses an airspring sleeve or flexible member which has the end attached to the airspring piston cut non-perpendicularly to the axis of the flexible member. Both of these features create additional side-load compensating forces. An object of this invention is to provide a suspension strut utilizing an airspring which generates side load compensating force. This force counteracts the bending torque created by the mass of the vehicle in operation and minimizes stiction in the hydraulic damper of the strut. This yields a softer ride, variable spring rates, also, a constant vehicle height can be maintained regardless of load by adjusting the internal pressure in the airspring portion of the strut. The object is met by the invention as defined in the claims. Brief Description of the Drawings Figure 1 is a view partially in elevation, partially cross-sectional of an air strut suspension utilizing a non-symmetrical flexible member. Figure 2 shows in partial elevation and partial cross-sectional view an air strut suspension featuring an eccentric piston. Figure 3 is a free body or force diagram schematically showing the forces impinging on the airspring piston. Figure 4 is an enlargement of the mount which is the attachment means of Figure 2 where the piston rod extends through the upper retainer of the airspring. Detailed Description of the Invention Figure 1 shows a simple embodiment of a suspension strut 10 which is mounted between the sprung portions 12 of the suspension and the unsprung portions 14. The strut 10 is particularly useful in a steerable suspension for an automobile in which the unsprung portion 14 is attached to the road wheel 16 and the sprung portion 12 includes the remaining portions of the chassis which must be isolated from the road shocks. The strut 10 is composed generally of a shock absorber indicated generally as 18 and an airspring indicated generally as 20. The strut 10 includes an elongated tubular body 22 within which is located an oil-filled hydraulic cylinder 24 in which is mounted an axially moveable piston 26 which has extending there from a piston rod 28 which is rotatably and resiliently connected to the sprung portion 12 of the chassis. The strut 10 includes a bracket 30 which connects the elongated tubular body 22 to the unsprung portion 14. In the air suspension strut 10 shown, the airspring 20 is connected between the upper end 32 of the rod 28 and the elongated tubular body 22 of the shock absorber 18. The airspring piston 34 is fixedly and rigidly mounted on the tubular body 22. An upper retainer 36 is axially spaced away from the piston 34 and provided with a means for connecting the rod 28 to the retainer 36 such as a bore 35 and nut 38 for attaching the rod 28. A simple elastomeric mount 37 dampens the torque moment between the retainer 36 and rod 28 as well as absorbing compressive stress between the sprung portion 12 and the strut 10. A key feature of this embodiment which gives the air suspension strut 10 the capability to compensate for side load is the design and construction of the airspring flexible member 40 which yields a rolling lobe or meniscuses 42 and 44 which are unsymmetrical relative to the axis 41. The term "meniscus" is used interchangeably with the art recognized term of "rolling lobe" both of which refer to the form of the flexible member 40 when viewed in axial cross section that is naturally assumed as the flexible member 40 rolls down over the airspring piston 34 during the stroke of the rod 28. In conventional symmetric airsprings, the meniscus of the airspring as it rolls over the piston is symmetrical around the center line or rotational axis of the airspring. The unsymmetrical form of the meniscus 42 and 44 is achieved by cutting the tubular flexible member 40 at an angle relative to the axis 41. Another way of expressing this is that the flexible member is cut in a plane 43 which is non-perpendicular or oblique to the axis 41. The tapered end 46 of the flexible member 40 is sealably mounted to the upper end 46 of the piston 34. The means shown for mounting is a swage ring 48 which is compressed radially inward to sealably position the flexible member 40 against the piston 34. The opposite end 49 of the flexible member 40 is sealably affixed to the upper retainer 36 by swage ring 48'. It is understood that if the flexible member is of the beaded type which contains a sealing bead, the swage rings 48 and 48' would be unnecessary for sealably mounting the flexible member 40. The upper retainer 36, piston 34 and flexible member 40 form a working cavity 50 surrounding the rod 28. The characteristics of the flexible member 40, the piston 34 and the volume of the cavity 50 all contribute to determine the dynamic characteristics, in particular, the spring rate of the strut 10. It is desirable for smooth ride that the spring rate of the strut be as low as practical. Referring now to Figure 2 there is shown another embodiment of the invention in which the air suspension strut 60 achieves side load compensation. The configuration of the shock absorber portion of the strut 60 is similar in all respects to Figure 1. The main structural element is the elongated tubular body 62 which contains a hydraulic fluid reservoir and piston which are identical to 24 and 26 respectively of Figure 1. The rod 64 extends through the upper retainer 66 of the airspring 70 through a suitable means for absorbing torque between the rod 64 and the upper retainer 66 and a suitable means for providing cushioning between the strut 60 and the sprung portion 67 of the suspension represented by a specialized dual path mount 244 which is shown in greater detail in Figure 4. Mount 244 provides means for pivotal movement of the strut 60 as is necessary when the strut 60 is utilized on a steerable suspension assembly. It is understood, of course, that if this strut is used in a rear or nonsteerable suspension system that the attachment means for the rod end 65 need not have a rotational means. A fixed mounting is suitable for the nonsteerable positions. The flexible member 72 is a generally tubular reinforced rubber flexible membrane with bias-applied reinforcing fabrics 71. It may be sealably attached at both ends. The lower end 74 is, in this embodiment, of uniform axial length prior to mounting on the piston 76. It is unlike Figure 1 where the lower portion of the flexible member 40 was cut at an angle such that the axial dimension of the flexible member around the periphery of the piston was variable. In order to achieve the side load compensating characteristic desired in this embodiment, the piston 76 when viewed in a plane perpendicular to the center line 75 of the strut 60 will generally appear egg shaped, that is relative to the axis 75, there will be a larger radius side 78 and a smaller radius side 79. This egg configuration provides a shoulder 80 on the larger radius side 78 which shortens the axial length of the meniscus 83 relative to the smaller radius side of the piston 79 which has a meniscus 84 which is of greater axial dimension. This difference in axial distance from the upper retainer 66 of each meniscus, 83 and 84, on opposing sides of the nonsymmetrical piston 76 creates a side loading force. This force is illustrated in Figure 3 where a free body diagram showing the horizontal forces on the piston is represented. Figure 3 represents the horizontal component of pressure vectors causing side loading force on the piston 82 of all the airsprings of this invention. This free body force diagram is representative of the force vectors for Figures 1 and 2. These embodiments have in common a meniscus on one side of the piston which is greater in axial length than the meniscus on the radially opposite side of the piston. The pressure within the working cavity of the airspring exerts the disproportionate pressure vector P on the portion of the flexible member which has no balancing counterpart on the opposite side of the piston. The piston 82 of Figure 3 is a schematic representation in which the actual geometrical symmetry of the sides are irrelevant to the pressure vectors shown. Thus piston 82 is representative of both piston 34 and 76 of Figures 1 and 2 respectively. Only the horizontal force vector P is illustrated since the flexible member is cut such that the tension T exerted by the flexible member is vertical or perpendicular to P, and does not affect the magnitude of the force vector P in the horizontal direction. If larger magnitudes of side loading force are desired, the flexible membrane which is cut in a plane oblique or non-perpendicular to the axis of the flexible membrane shown in Figure 1 may be utilized with the eccentric piston shown in Figure 2.

Claims: A suspension strut (60) for connecting a sprung portion and an unsprung portion of a suspension (67) comprising: (a) a damper means (62) including a body containing an hydraulic fluid filled reservoir mounted in said body, a piston (26) mounted for coaxial reciprocal movement in said body having a rod (64) connected to said piston (26) extending upwardly from said tubular body (62), said body being concentric about a rotational axis (75) of said damper means and connected to said unsprung portion (67) of suspension, said rod being connected to said sprung portions of the suspension at an attachment point; and (b) a non-symmetrical airspring (70) operatively mounted surrounding said damper means (62) to form a sealed pneumatic working cavity therearound, said non-symmetrical airspring including an airspring piston ( 76 ) sealingly attached to said body of said damper means (62) such that the airspring piston ( 76 ) is mounted about the rotational axis (75) of said damper means, and an upper retainer (66) axially spaced apart from said airspring piston ( 76 ) by a tubular flexible member (72), said pneumatic working cavity being formed by a first end of said tubular flexible member being sealably secured to said upper retainer (66) and a second end of said tubular flexible member (72) being sealably secured to said airspring piston, said upper retainer being connected to said rod (64) proximate said sprung portion of said suspension, characterized in that said airspring piston (76) has a generally egg-shaped cross section in a plane perpendicular to the rotational axis (75) of the damper means, with a small radius portion (79) and a larger radius portion (78) relative to said axis (75) and in that a shoulder (80) is provided on said larger radius portion (78) of the airspring piston (76) whereby said tubular flexible member (72) forms rolling lobes (83,84) of unequal axial length as the flexible member rolls axially downward over said airspring piston. A suspension strut according to claim 2, characterized in that the tubular flexible member (40) has said first end cut (49) in a plane perpendicular to an axis of rotation of said flexible member and said second end cut in a non-perpendicular plane to said axis (41). A suspension strut according to claim 1, characterized in that the hydraulic fluid is oil.

Inventors: WARMUTH II, IVAN JOSEPH
Applicants: THE GOODYEAR TIRE & RUBBER COMPANY
Application year: 1986
Main classification: B60G15
IPC codes: B60G15, F16F9, B60G13