AIR SPRING ASSEMBLY

Abstract: A heavy duty rolling lobe air spring (12), especially for trucks and trailers, which has an open hollow piston (32) providing a reservoir (34) and an outer surface on which the lobe of a flexible sleeve (18) rolls. The surface includes a horizontal top (42), a gently curved outer surface (43) joining an inverted frustro-conical side (44) and terminating in an outwardly flared bottom portion (48). Previous rolling lobe air springs adapted for heavy design loads have a high spring rate which fails to provide a soft, smooth ride only achieved in air springs having a low spring rate. The rolling lobe air spring (12) achieves a low spring rate providing a soft, smooth ride for heavy design loads. The side surface (44) has an angle with respect to the axis of the piston (32) of about 23`. The volume of the piston (32) and sleeve (18) of 850 to 1500 cu. in. (13,900-24,600 cu. cm.) and the angle of the frustro-conical surface (44) are such that the effective area of the sleeve (18) decreases under jounce and the spring rate is in the range of 100 to 300 pounds per inch (17.5-52.5 KN/m) at a design load in the range of 1000-8000 pounds (454-3629 kg).

Description: AIR SPRING ASSEMBLY Technical Field This invention relates to air springs. In one of its aspects, the invention relates to an air spring of the rolling lobe type wherein flexible sleeves are expanded to the maximum diameter under load and deflections due to bumps and the like are taken up through rolling of an end of the sleeve on a piston or pedestal which telescopes within the sleeve. Background Art Air springs are well known in suspension systems for vehicles, especially heavy duty trucks and trailers. One particular type of air spring, known as the "rolling lobe" air spring, is disclosed in the Hirtreiter U.S. patent No. 3,043,582 issued July 10, 1962. This type of an air spring includes an expandible fabric sleeve which is expanded to a predetermined maximum diameter under load and a piston or pedestal, which is secured to one end (usually the bottom end) of the sleeve, tele- scopes within the sleeve. The sleeve is made of a plural¬ ity of ply of rubber and crossed sets of inextensible cords which run the length of the sleeve but are at an angle with respect to the axis of the sleeve. As the sleeve is expanded, the crossed sets of cords pantograph to an equilibrium angle of about 54°. Normally, under load, the sleeve is pressurized to a pressure of, for example, 30-50 psig (2.2 - 3.4 atm.) so that the load is supported through the sleeve assembly. A portion of the sleeve expands to the equilibrium angle of the cords and the piston or pedestal telescopes into an end of the sleeve, thereby forming a lobe which rolls on the pedestal when the spring is compressed. In this type of air spring, the spring rate, i.e. the change in the load per unit of deflection, is controlled by the shape of the pedestal. Hirtreiter discloses, for example, pedestals which have cylindrical sides, inverted frustr conical shapes and hourglass shapes. In the air spring assemblies incorporating those pedestals which have a decreasing diameter lobe rolling surface, the effective diameter of the air spring de¬ creases under compression, thereby providing a lower spring rate and a smooth ride. Generally, the lower the spring rate, the softer the ride. Thus, the softes ride would be achieved by a spring having a very low spring rate at design load. Spring rates at or near 0, or even negative spring rates, are theoretically possible but are not preferred because of the control systems which are used to pressurize the springs to maintain a design height. Certain rolling lobe air springs (for example GY 1100, assembly part No. 566-22-2-005) manufactured and sold by Goodyear Tire and Rubber Company of Akron, Ohio U.S.A. , have hourglass type of pedestals through which the effective area of the spring is decreased during compression. Further, the pedestal is open to the interior of the cylinder to provide an additional volume for the air spring. However, the spring rate is fairly high, for example, 1275 pounds per inch (22.30 KN/m) at 7200 pounds (3260 kg), and the load to spring rate ratio is about 5.6 in. (14.2 cm). Generally it is desirable to achieve a much lower spring rate, generally in the range of 100 to 300 pounds per in. (17.5 - 52.5 KN/m) and to achieve higher loads to achieve optimum operating conditions in heavy duty trailer and truck tractors. Heretofore, spring rates and ratios of load to spring rate in these ranges for heavier loads have not been obtained and wer thought to be unattainable, although theoretically poss ble for rolling lobe air springs. Another type of air spring purported to attain a minimum spring rate is a reversible diaphragm air sprin disclosed in the U.S. patent to Bank, 3,078,085, issued February 19, 1963. This type of air spring has a reser at the top and a flexible sleeve secured at an upper por¬ tion to the reservoir and at a lower portion to an hour¬ glass shaped pedestal. The lower portion of the sleeve is of a smaller diameter than the upper portion so that it telescopes therethrough during normal operation. The maximum inward convergence angle of the Bank pedestal is purported to be 19°. However, the effective area of the spring decreases during deflection at design loads so that a relatively low spring rate is achieved. However, the lobe of the Bank sleeve changes in size under compression because the sleeve is not fully expanded under load. The Bank spring is made for a relatively small load, for example, 1000 to 2000 pound range as would be provided in automobiles. in order to achieve the higher loading capabilities with the Bank type of spring, the size of the spring would have to be increased so that the volume is also increased. However, the volume of the spring has profound effects on the spring rate at higher loads and thus merely increasing proportions of the Bank spring will not necessarily result in the attainment of the same characteristics as in the smaller proportioned spring. Disclosure of Invention I have now discovered an air spring of the rolling lobe type which is adapted for heavy loads, for example, 5000 to 10,000 pounds (2268 - 4536 kg) but nevertheless achieves spring rates in the range of 100 to 300 pounds per inch (17.5 - 52.5 KN/m) with load-to-spring rate ratios in the range of 20 to 120 inches (50 - 300 cm) for these loads. The invention is applicable to those types of air springs wherein a hollow elastic sleeve is made from a plurality of ply of elastic material with sets of crossed inextensible cords which limit the expansion of the sleeve through pantographing movement to an equilibrium angle at a design load. The air springs have means for securing an upper end of the sleeve to a vehicle frame and a hollow piston adapted to be secured to a vehicle axle*and mount- ing a lower end of the sleeve. The piston provides an outer surface on which the lower end of the sleeve rolls in compression and rebound. Further, a reservoir in communication with the interior of the hollow sleeve is formed within the interior of the hollow piston. The invention is also applicable to air springs which have an expandable rubber sleeve which is otherwise restrained at a maximum diameter, as for example, by a metal sleeve. According to the invention, the exterior surface o the piston provides an outwardly extending top surface, adjoining a relatively large radius, downwardly curved surface on which the lobe of the hollow sleeve rests during normal loading condition. An inverted frustro- conical surface extends downwardly from the downwardly curved surface and provides an area of increasingly reduced diameter for the rolling lobe of the hollow sleeve during jounce. The angle of the frustro-conical surface and the volume of the air spring (including the hollow piston) are such that the ratio of load to spring rate of the air spring is the range of 20 to 120 inches. To achieve this range, the angle of an element of the frustro-conical surface with respect to the axis of the piston is greater than 20°, and preferably about 23°. In order to achieve the required volume for the ai spring, the interior of the piston is open to the interio of the flexible sleeve. Desirably, the volume of the piston is in excess of 100 cu. in. (1639 cu. cm) and the combined volume of the piston and sleeve is in the range of 850 to 1500 cu. in. (13,900 - 24,600 cu. cm) under design loads. Desirably, spring rates in the range of 100 to 300 pounds per inch (17.5 - 52.5 KN/m) at design loads in excess of 5,000 lbs (2268 kg) are achieved with the invention. The piston further comprises an outwardly tapered surface joining the bottom of the frustro-conical surface to provide an area of larger diameter, thereby increasing -5- the effective area of the air spring in the event that compression is significant .enough to drive the lobe past the minimum diameter of the piston. Further, a plate with an opening in the top thereof is provided at the top por- tion of the pedestal and a rubber bumper is secured at an upper portion of the sleeve to prevent compression of the sleeve past a predetermined point. Brief Description of the Drawings The invention will now be described with reference to the accompanying drawings in which: Figure 1 is a side elevational view in section of an air spring assembly according to the invention shown under normal loading conditions; Figure 2 is a view similar to Figure 1 showing the air spring under jounce condition; Figure 3 is a composite graph showing the relation¬ ship between deflection and the effective area and between deflection and load at various pressures. Best Mode for Carrying Out the Invention Referring now to the drawings, and to Figure 1 in particular, there is shown an air spring assembly 12 secured at an upper portion to a vehicle frame 14 and at a lower portion to a vehicle axle assembly or trailing arm 16. The air spring assembly comprises a rubber flexible sleeve 18 secured at an upper portion thereof to an upper retainer 20 and bumper 22 and at a lower portion to a piston member 32. Bolts 24 and 26 secure the air spring assembly through the upper retainer 20 to the vehicle frame 14. The rubber flexible sleeve is tubular shaped and is constructed from laminated rubberized fabric having inextensible cords crossed with respect to each other in the manner described in the U.S. patent to Hirtreiter, 3,043,582 (issued July 10, 1962). " The inextensible elements are positioned at an angle of about 30° with respect to the axis of the tubular flexible sleeve 18 -6- in unexpanded condition such that, upon expansion of the flexible sleeve 18, the angle between the cords and the axis of the flexible sleeve expands to about 54°. In • this condition, the flexible sleeve 18 achieves its maximu diameter. The sleeve 18, itself, is conventional and sleeves of this nature are commercially available from Goodyear Tire & Rubber Co. At an upper portion, the rubber flexible sleeve 18 has an annular wire ring 28 through which it is secured to the retainer 20. In like manner, a lower wire ring 30 at the lower portion of the flexible sleeve 18 is provided for securing the sleeve 18 to the piston 32 between a reservoir can 34 and the piston 32. As illustrated in Figure 1, the upper wire ring 28 has a greater diameter than the lower wire ring 30. The reservoir can 34 is secured to the axle 16 through a bolt 36 and provides a sealed interior chamber for the piston 32. A sealing compound or sealing washer (not shown) is provided for bolt 36 to maintain the reservoir can 34 air tight. A retainer plate 38 having an opening 40 is secured to the top of the reservoir can 34 through welding or other suit¬ able fasteners to provide an abutment surface for bumper 22 under very high jounce conditions. The piston 32 has a shape which is very important to the operating characteristics of the air spring assembly.. It has an outwardly extending top portion 42 having a relatively large radius, downwardly curved surface 43 which smoothly joins an inverted frustro- conical surface 44. An outwardly extending lower portion 48 joins the inwardly directed surface 44 at a minimum diametrical area 46. As seen in Figure 1, the diameter of area 46 is greater than that of the lower ring 30 but significantly less than that of the outer portion of surface 43. The outer surfaces of the piston 32 are smooth and circular in any horizontal section taken therethrough. The piston is conveniently cast from any suitable cast- able material and the outer surface can be machined s ooth, if desirable. The casting is desirably hollow, having an interior surface 50 shown in phantom lines in Figures 1 and 2, and has strengthening ribs 52 spaced at appropriate locations within the casting. The operation of the air spring under jounce, i.e. when the vehicle hits a bump, is illustrated in Figure 2. The lower portion of the flexible member 18 will roll along the surface 44, thereby decreasing slightly the effective area within the spring. In addition, the piston is dimensioned so that the spring rate is sub¬ stantially flat, i.e. in the range of 100 - 300 lbs/in. (17.5 - 52.5 KN/m) during the roll of the flexible member along the surface 44. However, when the flexible member 18 reaches the minimum diametrical, area 46, the effective area of the spring will increase rather quickly, thereby increasing the spring rate to stop the jounce before the spring "bottoms out" on the bumper 22. The angle of surface 44 with respect to the axis of the piston is quite important with respect to the opera- tion of the spring. This angle is measured by taking a section through the central axis of the piston 32 which is shown as phantom line 54 in Figure 1. The central axis 54 is perpendicular to the base of piston 32. The inter¬ section of the plane taken through the central axis 54 with the surface 44 forms an element of surface 44. An extension of an element is shown as phantom line 56 in Fig. 1. Thus, the angle between the surface 44 and the axis of the piston 32 is measured between phantom lines 54 and 56. Desirably, this angle is greater than 20°, preferably about 23°, but not more than 30°. The diameter of the piston with respect to the air spring is also of some considerable significance. The piston diameter must be small enough to permit rolling of the lobe on the relatively large return angle frustro- conical surface 44 without collapsing of the lobe. Typically, for a 13-in. (35.4 cm) diameter air spring, the diametrical difference between the air spring ID and the piston OD must be at least 3 in. (7.6 cm) and T RE __0MPI_ ' -8- preferably about 3.4 in. (8,6 cm). Diametrical differ¬ ences would be slightly greater for larger air springs and slightly smaller for smaller air springs. An air spring according to the invention was constructed with the following approximate dimensions: Sleeve - Goodyear sleeve part No. AS4-26-3-017 Max. diam. 336.6 mm (13.25 in.) Piston Height - 132.0 mm (5.20 in.) Maximum diameter at Curved surface 43 - 244.0 mm (9.61 in.) Radius of curved surface - 27.0 mm (1.06 in Height of area 46 - 33.0 mm (1.30 in.) Radius of surface - 24.0 mm (0.94 in.) Volume at area 46 - 1968 cm 3 (120 in. 3 ) Air spring assembly Design height - 304.8 mm (12 in.) Diam. of sleeve 18 - 336.6 mm (13.25 in.) Volume - 13880 cm 3 (970 in. 3 ) The effect of jounce in terms of effective area an deflection for the air spring of the example is illus¬ trated in Figure 3 to which reference is now made. At the upper portion of Figure 3 there is shown the rela- tionship between the effective area of the air spring sleeve and deflection in inches with 12 inches being the design height. Under jounce, the effective area actually decreases for about 2 inches and then increases significantly. At rebound, the effective area increases to dampen the oscillation of the air spring. In the lower portion of Figure 3 there are illus¬ trated curves showing the relationship between load on the air spring and deflection. At the design height, the spring rate is positive but only slightly so compared with the spring rate at higher jounce deflections. Note that the spring rate around the design height is rela¬ tively constant regardless of the degree to which the spring is loaded. 0Λ1P The following data was obtained from tests on an air spring according to the invention: Spring Spring rate Load/ Pressure at design height FN spring rate 30 psi (207K PA) 200 lb/in (35KN/M) 66 CPM 7.5 in (183 mm) 50 psi (245 KPA) 240 lb/iri (42 KN/M) 50 CPM 14.1 in (344 mm) 70 psi (43 KPA) 260 lb/in (45.5 KN/M) 43 CPM 19.2 in (468 mm) 90 psi (621 KPA) 130 lb/in (22.8 KN/M) 26 CPM 51 in (1243 mm) In an air spring constructed according to the invention, the reservoir 34 is significant in maintaining a relatively constant volume under jounce conditions. Desirably, the reservoir has a capacity in excess of 100 3 cu. in. (1639 cm ) and preferably about 120 cu. in. (1965 cu. cm) . The total volume of the air spring including the reservoir is preferably in the range of 850 cu. in. (1390 cu cm) .to 1500 cu. in. (2460 cu. cm), desirably at about 1000 cu. in. (16,390 cu. cm) . Thus, the reservoir adds significant volume to the air spring to assist in reaching the relatively small spring rate and the relatively large load to spring rate ratios. The air spring according to the invention provides a ride that is very smooth over rough roads so that very little shock is transmitted to the vehicle frame when the vehicle hits a bump. The .invention is particularly adapted to heavy loads such as carried by vehicles in the trucking industry. The smooth ride is the result of a low spring rate at design height. This spring rate has not been heretofore achievable in other designs at the higher loads. Reasonable variation and modification are possible within the scope of the foregoing disclosure and drawings without departing from the spirit of the invention which is defined in the accompanying claims. _0 j Wipo-

Claims: -10- ~ CLAIMS 1. In an air spring of the rolling lobe type wherein a hollow elastic sleeve is restrained from expanding past a predetermined diameter at a design load; wherein means are provided for securing an upper end of the sleeve to a vehicle frame; a hollow piston adapted to be secured to a vehicle axle mounts a lower end of the sleeve and provides an outer surface on which the lower end of the sleeve rolls in jounce and rebound; means are provided for securing the sleeve to an upper portion of the piston; and means provide an open communi cation between the interior of the hollow sleeve and the interior of the hollow piston whereby the interior of th piston provides a reservoir for the air spring; the improvement which comprises: the exterior surface of the piston providing an outwardly extending top surface joining a relative large radius downwardly curved surface on which the lobe of the hollow sleeve rests during normal loading and an inverted frustro-conical surface extending downwardly from the downwardly curved surface and providing an area of increasing reduced diameter for the rolling lobe of the hollow sleeve during jounce, the angle of the frustro-conical surface and the volume of the piston and sleeve being such that the spring rate is in the range of 100 - 300 lbs/in. (17.5 KN/m - 52.5 KN/m) at loads above 5,000 lbs (2268 kg.) . 2. An air spring according to claim 1 wherein th angle of an element of the frustro-conical surface with respect to the axis of the piston is greater than 20°. 3. An air spring according to claim 2 wherein th angle of the frustro-conical surface with respect to the axis of the piston is about 23°, 4. An air spring according to claim 2 and furthe -11- comprising a plate secured to an upper portion of the piston and an opening in the plate providing communication between the interior of the hollow sleeve and the interior of the piston; and a resilient bumper secured to the upper sleeve end securing means and adapted to strike the plate at extreme deflection positions of the air spring. 5. An air spring according to claim 4 wherein the piston further comprises an outwardly flared surface join- ing the bottom of the frustro-conical surface and provid¬ ing an area of larger diameter to increase the effective area of the air spring and retard further deflection thereof as the rolling lobe in deflection reaches the outwardly flared surface and prior to the striking of the plate by the resilient bumper. 6. An air spring according to claim 5 wherein the volume of the piston reservoir is in excess of 100 cu. in. (1639 cu. cm. ) . 7. An air spring according to claim 6 wherein the volume of the interior of the piston and hollow spring under load is in the range of 850 to 1500 cu. in. (13,900 - 24,600 cu. cm. ) . 8. An air spring according to claim 7 wherein the volume of the interior of the piston and hollow spring under load is about 1000 cu. in. (16,390 cu. cm.) . 9. An air spring according to claim 8 wherein the piston shape, the volume of the air spring and the piston are such that the ratio of load to spring rate for the air spring is about 20 in. (50.8 cm.) for loads in excess of 5,000 lbs (2268 kg.) . 10. An air spring according to claim 1 wherein the volume of the piston reservoir is in excess of 100 cu. in. (1639 cu. cm.) . 11. An air spring according to claim 10 wherein the volume of the interior of the piston and hollow sleev under load is in the range of 850 to 1500 cu. in. (13,900 - 24,600 cu. cm.) . 12. An air spring according to claim 1 wherein th piston further comprises an outwardly flared surface ad¬ joining the bottom of the frustro-conical surface and providing an area of larger diameter to thereby increase the effective area of the sleeve and retard further deflection of the air spring as the rolling lobe of the sleeve reaches the outwardly flared surface. 13. An air spring according to claim 1 wherein th volume of the interior of the piston and hollow sleeve under load is in the range of 850 to 1500 cu. in. (13,900 - 24 , 600 cu. cm. ) .

Inventors: PIERCE W
Applicants: LEAR SIEGLER INC
Application year: 1978
Main classification: F16F9
IPC codes: B60G11, F16F9