US3691268A

US3691268A - Method of making a flexible member having increased service life

Info

Publication number: US3691268A
Application number: US24931A
Authority: US
Inventors: Thomas E Burkley
Original assignee: Goodyear Tire and Rubber Co
Current assignee: Goodyear Tire and Rubber Co
Priority date: 1970-03-23
Filing date: 1970-03-23
Publication date: 1972-09-12
Anticipated expiration: 1989-09-12

Abstract

A method of making a flexible member having increased service life with the member being of the type designed for use in a fluid pressure system in which a predetermined flex wrinkle pattern or a modification thereof is imparted to a surface of the flexible member to improve the flexing properties while the member is operating in such system. This pattern may consist of a simulation of the actual flex wrinkle pattern of a previously operating flexible member or be a compromise which employs a plurality of grooves having substantially the same pitch as the wrinkles. This invention results in the increased flex life and improved low temperature performance of the flexible member.

Description

United States Patent Burkley [4 Sept. 12, 1972 [54] METHOD OF MAKING A FLEXIBLE 2,288,840 7/1942 Raiche ..l8/47 R X MEMBER HAVING INCREASED 2,958,148 11/1960 Sylvester et a1 ..264/220 X 3,313,873 4/1967 Dembiak ..264/219 X SERVICE LIFE 3,473,989 10/1969 Richmond ..264/227 X Inventor: Thomas E. Burkley, Akron, Ohio The Goodyear Tire 8: Rubber Company, Akron, Ohio Filed: March 23, 1970 Appl. No.: 24,931

Related U.S. Application Data Division of Ser. No. 679,731, Nov. 1, 1967, Pat. No. 3,598,155.

Assignee:

References Cited Primary Examiner-Robert F. White Assistant Examiner-Allen M. Sokal Attorney-F. W. Brunnerand Robert H. l-latton [5 7] ABSTRACT A method of making a flexible member having increased service life with the member being of the type designed for use in a fluid pressure system in which a predetermined flex wrinkle pattern or a modification thereof is imparted to a surface of the flexible member to improve the flexing properties while the member is operating in such system. This pattern may consist of a simulation of the actual flex wrinkle pattern of a previously operating flexible member or be a compromise which employs a plurality of grooves having substantially the same pitch as the wrinkles. This invention results in the increased flex life and improved low temperature performance of the flexible member.

12 Claims, 8 Drawing Figures "PATENTEDszmasn 3 691 68 smzu 1 er 2 FIG. 2

FIG. 3

4 INVENTOR.

THOMAS E BURKLEY ATTORNEY PATENTEBsEP 12 1812 3.651. 268

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2 or 2 INVENTOR. THOMAS E. BURKLEY ATTORNEY METHOD OF MAKING A FLEXIBLE MEMBER HAVINGINCREASED SERVICE LIFE This is a divisional application of my Co-pending application Ser. No. 679,731 filed Nov. 1, I967 now issued as U.S. Pat. No. 3,598,155.

BACKGROUND OF THE INVENTION This invention relates to a method of producing an improved flexible member of the type designed for use in a fluid pressure system. More specifically, this invention relates to a method of increasing the service life of a flexible member of the type used, for example, in a pneumatic suspension or brake control system referred to generally as the rolling lobe air spring and rolling sleeve diaphragm respectively.

Rolling lobe air springs are normally employed for shock absorbing, load supporting and vibration isolation in vehicle suspension systems and other industrial and military applications. The typical pneumatic pressure system of this type operates as follows. A tubular essentially cylindrical flexible member of fabric reinforced elastomeric material such as rubber or the like is positioned between retaining elements. This flexible member has clamping means at the peripheral edge portions thereof in order to attach the member to the retaining elements and form an airtight chamber capable of supporting a load of varying proportions. A piston, acting upon the flexible member, creates a rolling motion in the sidewall of the flexible member consequently causing the compression and expansion of the column of air confined in the chamber. An excellent detailed description of the construction, operation, and production of the rolling lobe type air spring is contained in Hirtreiter US. Pat. No. 3,043,582.

Similarly, rolling or sleeve diaphragms of the type used in pneumatic brake control systems employ a cup or hat-shaped flexible fabric reinforced member of elastomeric material with a cylindrical or frusto-conical sidewall which may have a closed base or may be open on both ends. The peripheral edge portion or lip of the diaphragm typically is attached to the central wall portion of a brake chamber. The closed end portion or the other peripheral edge portion of the open end attached to the piston thus forms an airtight compartment. In some instances, when air under pressure is admitted into this compartment, the diaphragm is deflected thereby creating a rolling motion in the sidewall of the diaphragm to move a plunger contained within the brake chamber.

Those skilled in the art are aware that one of the major problems encountered in such systems is the premature failure of the flexible member due to flex cracking in the area which is subjected to the maximum flexing during operation in such systems. This cracking may also occur prematurely when the flexible member is exposed to extremely low temperatures in frigid areas as the result of the consequently stiffened condition of the elastomeric material after such exposure.

The present invention discloses flexible diaphragms or members of an improved construction which prolongs substantially the flex lift even under severe low temperature conditions as well as a method of producing such a flexible member. It has been found that forming, prior to installation in a fluid pressure system, the flex wrinkle pattern on the surface of the flexible member at least in the area subjected to the maximum flexing, will control the flex characteristics and alleviate many of the normal deteriorating stresses when the flexible member is operating in the system. In other words, the actual flex wrinkle pattern is effectively simulated on the compression surface of the flexible member with the wrinkles therein acting as hinge points which facilitate the flexing in the area of the member most susceptible to failure or cracks due to flexing or low temperatures.

This is accomplished by reproducing on the compression surface of the flexible member, the actual flex wrinkle pattern, created on the compression surface of a flexible member by the operation of a similar diaphragm in a fluid pressure system for a period of time sufficient to create the flex wrinkle. This may be accomplished in a number of ways, some of which will be hereinafter described.

OBJECTS OF THE INVENTION The primary object of this invention is to provide a method which will control the flex characteristics and alleviate the stresses created in a flexible member to provide a substantial improvement in the general durability thereof without an appreciable increase in manufacturing costs.

Another important object of this invention is to significantly prolong the flex life of a flexible elastomeric member of the type used in a fluid pressure system such as an air spring suspension or pneumatic brake control system.

Still another object of this invention is to provide an improved flexible elastomeric member such as a rolling lobe air spring and rolling sleeve air brake diaphragm which will resist wall cracking when the product is operating during extreme cold weather exposures.

A further object of this invention is to facilitate the operation of a flexible member of the type designed for use in a fluid pressure system by providing an improved contour to reduce resistance to the rolling motion of such member particularly at low pressures.

Other objects and advantages of this invention will become apparent hereinafter as the description thereof proceeds, the novel features, arrangements and combinations being clearly pointed out in the specification as well as the claims thereunto appended.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of one type of flexible member illustrating this invention;

FIG. 2 is a section taken substantially through 2-2 of FIG. 1;

FIG. 3 is a modification of the invention shown in FIG. 2;

FIG. 4 is an elevation showing one method of producing the invention shown in FIG. 3;

FIG. 5 is a modification of the invention shown in FIG. 3;

FIG. 6 is another modification of the invention shown in FIG. 3;

FIG. 7 is a perspective view of another type of flexible member for which this invention is useful; and

FIG. 8 is a section taken substantially through 8-8 of FIG. 7 to more clearly illustrate the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Although specific examples will be illustrated showing certain common types of applications of flexible members, it is to be understood that the concept disclosed in this invention is equally applicable to flexible members of all sizes and shapes. These particular features will depend upon the apparatus in which the members are used. It should also be noted that although particular reference is made to pneumatic systems, the principle disclosed in this invention will apply equally to other fluid systems which use various liquids or gases such as oil or nitrogen.

For the purposes of illustration, FIG. 1 shows a flexible member 1 which, in this example, is of the type used in vehicle shock absorber systems referred to as a sleeve type rolling lobe air spring. As illustrated, this flexible member 1 is tubular with an essentially elongated cylindrical shape having an inside diameter of approximately 1 11/16 inches and a wall thickness of 0.110, plus or minus 0.010 inch and is generally about 1 foot in length. Preferably, it is formed of rubber or other elastomeric material with a fabric reinforcement contained therein.

FIG. 2, a section taken through 2-2 of FIG. I, illustrates the cord fabric reinforcement 2, usually nylon, and the normal flex wrinkle pattern 3 reproduced on the inner surface 4 of flexible member 1. The pattern 3 has been reproduced from the actual flex wrinkle pattern of a flexible member which has been subjected to normal operating conditions in a vehicle suspension system or facsimile thereof (such as a flex test unit) for a sufficient period of time to create the wrinkle pattern. Due to the particular operating characteristics of the rolling lobe air spring, the actual flex wrinkle pattern is formed on the inner or compression surface of the rolling torus of the flexible member. In this way, the actual flex wrinkle pattern is simulated on the inner surface 4 of the flexible member 1 with the wrinkles 5 acting as hinge points to locate and alleviate the stresses that will be created when flexible member 1 is operating in the system. The depth of the wrinkles 5 in the actual or simulated wrinkle pattern is generally in the range of 0.005 to 0.018 inch but, of course, will vary depending upon the length of time that the flexible member has been operating. Obviously, it is essential to reproduce the pattern 3 in at least the area of the flexible member 1 which is subjected to the maximum flexing. The location and extent of the area will depend upon the particular application and consequently must be determined for each application.

Various methods may be used to reproduce the actual flex wrinkle pattern thereby forming the predetermined flex wrinkle pattern on the surface of the flexible member. One method successfully employed is as follows:

1. Make a longitudinal cut in the flexible member of the rolling lobe air spring after it has operated for a sufficient period to create a flex wrinkle pattern.

2. Cut out the portion of the flexible member which has been subjected to the maximum flexing and therefore contains the actual flex wrinkle pattern.

3. Mount this portion on a substantially flat base by means of an adhesive.

4. Enclose the periphery of the mounted portion to form a mold.

5. Form a pattern of an opposite configuration or contour from that of the actual flex wrinkle pattern by pouring a substance such as polyurethane into this mold.

6. Attach the polyurethane pattern to a mandrel or molding core so as to be substantially flush with the surface. Preferably, the pattern is adhered to the mandrel by means of an adhesive vulcanized under heat and pressure.

7. Place a sleeve of unvulcanized elastomeric material over the mandrel then vulcanize under heat and pressure to produce the simulated flex wrinkle pattern on the inner surface of the flexible member.

The foregoing method, although effective, has the disadvantage of being time consuming and too costly when a large number of patterned mandrels must be produced to meet the production requirements of the flexible sleeves. Therefore, a compromise procedure has been developed in which the flex wrinkle pattern is approximated by determining the common or predominate distance or pitch of adjacent wrinkles of the actual flex wrinkle pattern then producing a plurality of grooves or corrugations at this spacing on the inner surface of the flexible member. The grooves are formed preferably in the surface of the flexible member during molding under heat and pressure but other methods may also be used, such as machining the grooves on the already vulcanized product. As a minimum, these grooves are placed in the portion of the flexible member which will be subjected to the maximum flexing during its operation in the fluid pressure system, but for convenience, they may be formed in other areas as well without affecting the operation of the flexible member. I Although any type of corrugated or convoluted contour will act to relieve the stresses in the flexible member, it is important that alternate flat or land portions of greater width than the grooves be provided between the grooves. This will prevent objectionable noise transfer and the possible interleaving of the corrugations during the rolling motion of the flexible member.

In the just described procedure, the grooves act as the hinge points to locate and alleviate the stresses created during the operating of the flexible member thus serving in much the same manner as the wrinkles of the flex wrinkle pattern. In addition, since the grooves are uniformly spaced, this structure has the advantage of uniformly located stress areas to provide for a uniform distribution of the stresses when the flex member in operating. It has been determined that the best general durability is obtained with a groove depth of 0.010 to 0.018 inch. In cold weather, in addition to the advantage of the hinge points provided by the corrugations, the reduced wall gauge at the grooves also imparts more flexibility to the flexible members. Furthermore, the grooves act to facilitate the operation of the flexible member by reducing the resistance to the rolling motion particularly at low pressures. These grooves may take various forms as will become apparent.

One form of the invention shown in FIG. 3 illustrates a flexible member produced by using the compromise procedure. The flexible member 1 is again of the type used in a rolling lobe air spring and has circumferential grooves 6 and alternate flat or land portions 7 uniformly positioned longitudinally along substantially the entire length of the flexible member 1. The pitch 8 of the grooves 6 is substantially equal to pitch 9 of the wrinkles 5 shown in FIG. 2. In theory, the wrinkle pitch 9 is generally determined by such characteristics as the size, shape wall thickness, inflation diameter, and roll radius of the flexible member as well as by the design of the particular piston assembly. For example, it has been determined that a flexible sleeve of a rolling lobe air spring with an inside diameter of 1 11/16 inches after operating for a period of one million cycles in a flex test unit has a wrinkle pitch of approximately 43 inch. Also it has been determined that this type flexible sleeve when removed from a vehicle shock absorbing system after 25,000 miles of normal usage developed essentially this same pitch. Accordingly, the pitch 8 of the grooves 6 should also be /8 inch. As previously mentioned, grooves 6 take the place of the wrinkles 5 of the predetermined flex wrinkle pattern 3 to control the flexing and alleviate the stresses in the flexible member I. As shown, a series of longitudinal ribs 10 are formed on the surface of the flexible member, from a series of corresponding longitudinal grooves in the mold, the purpose of which will be explained later.

One method of forming these circumferential grooves is shown in FIG. 4. As illustrated, a steel mandrel or molding core 11 has a plurality of circumferential ridges or peaks 12 on the outer surface and uniformly spaced along the length thereof with alternating flat or land portions 13 of greater width than the ridge l2 therebetween. Preferably, longitudinally extending grooves 14 on the surface of mandrel 11 serve as venting means to permit, during the molding operation, the escape of trapped air. The flexible member 1 is positioned over the mandrel l1 and vulcanized under heat and pressure thus forming grooves 6 and flat portions 7, as well as ribs 10 on the inner surface 4 of the flexible member 1. FIG. 5 is a modification of the invention shown in FIG. 3 in which the flexible member 1 contains a plurality of helical grooves 6A molded on its inner surface 4.

Another modification of the invention shown in FIG. 3 is illustrated in FIG. 6 in which flexible member 1A is tapered gradually in the longitudinal direction. The purpose of the tapered design is to further facilitate the functioning of the flexible sleeve rolling lobe air spring member which tends to take on a longitudinally tapered configuration after extended periods of operation. Of course, the grooves 6 may also be either circumferential or helical in this design. It is also important to recognize that in addition to the rolling lobe type air spring, the teaching of this invention may be applied to all piston type air springs with little or no modification required.

Another type of flexible member of the same general classification as that used in the rolling lobe air spring is the rolling sleeve diaphragm shown in FIG. 7 which is used in air brake control systems. Flexible member 1B is normally of a cup or hat-shaped configuration with closed base 15 and a cylindrical sidewall 16. It is generally composed of elastomeric material such as rubber or the like and reinforced by a textile cord or square woven fabric such as cotton or nylon. However, it may also contain no reinforcement and be formed of a material such as polyurethane. The maximum flexing in this member takes place on the inner or compression surface 17 of the rolling torus which is in proximity to the peripheral edge portion or lip 18 at the open end 19 of the flexible member 18. The predetermined flex wrinkle pattern may be imparted to this area of the flexible member 18 by means of a mold (not shown) having a molding surface of opposite configuration from that of the actual flex wrinkle pattern. Here again, however, it is much more practical and economical to use a molding surface, as previously described, containing a plurality of ridges or peaks positioned in the area of maximum flexing and having the required pitch between the ridges to form the product as shown in FIG. 8.

FIG. 8 is a section takenthrough 8-8 of FIG. 7 showing the fabric reinforcement 20 and a plurality of essentially circular grooves 21 substantially adjacent to the peripheral edge portion 18 on the inner surface 17 at the open end 19 of flexible member 13. These grooves 21, of course, function in the manner mentioned previously. Although particular reference has been made to the rolling sleeve diaphragm, it should be apparent to those skilled in the art that the invention is equally applicable to other forms of flexible diaphragms such as the long stroke, convoluted, or

dished type.

While certain representative embodiments and details have been shown for the purpose of illustrating the invention, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit or scope of the invention.

What is claimed is:

l. A method of increasing the service life of flexible resilient members of the type used in a fluid pressure system in which a first flexible resilient member undergoes a rolling motion which creates a flex wrinkle pattern on a surface of said first member after a period of flexing during the operation of such system, said method comprising the step of intentionally producing a simulation of said flex wrinkle pattern on a surface of a second flexible resilient member prior to its installation in a fluid pressure system by providing a plurality of grooves therein at least in the area of the surface of said second member which will be subjected to the maximum flexing during the movement of said second member, said grooves positioned to substantially sim ulate and correspond to said flex wrinkle pattern.

2. The method as claimed in claim 1 wherein the distance between the centerline of each adjacent groove is substantially equal to the distance between the centerline of each adjacent wrinkle of said flex wrinkle pattern with the grooves being uniformly spaced on the surface of the member.

3. The method as claimed in claim 2 wherein the member is a tubular fabric-reinforced of fabric elastomeric material containing a plurality of circumferential grooves uniformly positioned on the inner surface thereof.

4. The method as claimed in claim 2 wherein the member is an essentially hat-shaped member of fabricreinforced elastomeric material containing a plurality of circular grooves uniformly positioned on the inner surface and adjacent the peripheral edge of the open end thereof.

5. The method as claimed in claim 2 wherein the producing step comprises first vulcanizing said second flexible member and then machining said grooves into the surface of said second flexible member.

6. A method of producing flexible resilient pressureretaining members for use in fluid pressure systems of the kind in which at least one of the peripheral edge portions of such a flexible member is attached to the body structure of such system to create a fluid-tight chamber, said body structure containing elements movable in an axial direction relative to each other with the movement causing a rolling motion in the flexible member, said method comprising the steps of determining the actual flex wrinkle pattern created on the surface of a flexible member which has been subjected to a period of flexing in the operation of such system, and intentionally producing on the surface of subsequent flexible members, prior to their installation in such fluid pressure systems, in at least the area of said subsequent flexible members which will be subjected to maximum flexing in service in such system a pattern of grooves in at least substantially the same pattern as said actual flex wrinkle pattern to thereby control the flexing and distribution of stresses in said subsequent flexible members.

7. The method as claimed in claim 6 wherein the pat tern-producing step includes preparing from the actual flex wrinkles a mold to reproduce the flex wrinkle pattern on the surface of subsequent flexible members, and molding said subsequent flexible members in said mold whereby the flex wrinkle pattern is formed in at least the area of maximum flexing of the flexible members.

8. The method as claimed in claim 6 wherein the method includes approximating the flex wrinkle pattern by determining the predominate distance between the centerline of each adjacent wrinkle of the actual flex wrinkle pattern created on the surface of a flexible member after a period of flexing during the operation of such system, forming a plurality of ridges on a molding surface with the distance between the centerline of each adjacent ridge being substantially equal to the distance between the centerline of each said adjacent wrinkle of the flex wrinkle pattern, and molding a flexible member against said molding surface to conform the flexible member to the molding surface thereby forming a plurality of grooves on the surface thereof to provide hinge points to control the flexing of the flexible member.

9. The method as claimed in claim 6 wherein the member is a tubular sleeve of fabric-reinforced elastomeric material containing a plurality of circumferential grooves uniformly positioned on the inner surface thereof.

10. The method as claimed in claim 6 wherein the member is an essentially hat-shaped member of fabricreinforced elastomeric material containing a plurality of circular grooves uniformly positioned on the inner surface and adjacent the peripheral edge of the open end thereof.

11. The method as claimed in claim 6 wherein the distance between the centerline of each adjacent groove is substantially equal to the distance between the centerline of each adjacent wrinkle of the actual flex wrinkle pattern with the grooves being uniformly spaced on the surface of the member.

12. The method as claimed in claim 11 wherein the producing step comprises first vulcanizing said subsequent flexible members and then machining said grooves into the surface of said subsequent flexible members.

Claims

1. A method of increasing the service life of flexible resilient members of the type used in a fluid pressure system in which a first flexible resilient member undergoes a rolling motion which creates a flex wrinkle pattern on a surface of said first member after a period of flexing during the operation of such system, said method comprising the step of intentionally producing a simulation of said flex wrinkle pattern on a surface of a secOnd flexible resilient member prior to its installation in a fluid pressure system by providing a plurality of grooves therein at least in the area of the surface of said second member which will be subjected to the maximum flexing during the movement of said second member, said grooves positioned to substantially simulate and correspond to said flex wrinkle pattern.

4. The method as claimed in claim 2 wherein the member is an essentially hat-shaped member of fabric-reinforced elastomeric material containing a plurality of circular grooves uniformly positioned on the inner surface and adjacent the peripheral edge of the open end thereof.

6. A method of producing flexible resilient pressure-retaining members for use in fluid pressure systems of the kind in which at least one of the peripheral edge portions of such a flexible member is attached to the body structure of such system to create a fluid-tight chamber, said body structure containing elements movable in an axial direction relative to each other with the movement causing a rolling motion in the flexible member, said method comprising the steps of determining the actual flex wrinkle pattern created on the surface of a flexible member which has been subjected to a period of flexing in the operation of such system, and intentionally producing on the surface of subsequent flexible members, prior to their installation in such fluid pressure systems, in at least the area of said subsequent flexible members which will be subjected to maximum flexing in service in such system a pattern of grooves in at least substantially the same pattern as said actual flex wrinkle pattern to thereby control the flexing and distribution of stresses in said subsequent flexible members.

7. The method as claimed in claim 6 wherein the pattern-producing step includes preparing from the actual flex wrinkles a mold to reproduce the flex wrinkle pattern on the surface of subsequent flexible members, and molding said subsequent flexible members in said mold whereby the flex wrinkle pattern is formed in at least the area of maximum flexing of the flexible members.

10. The method as claimed in claim 6 wherein the member is an essentially hat-shaped member of fabric-reinforced elastomeric material containing a plurality of circular grooVes uniformly positioned on the inner surface and adjacent the peripheral edge of the open end thereof.