Snap ring closure system

A snap ring closure system is particularly useful in securing a rod guide in an end of a tube of a hydraulic damper. The snap ring closure system utilizes an end cap or rod guide having a double-lobed groove and a peripheral flange about its outer end. The double-lobed groove includes an outer lobe and an inner lobe of a lesser depth than the outer lobe. A groove is formed on the tube and is positioned to design with the doubled-lobed groove when the end cap is inserted in the tube. The end cap includes a first snap ring in the outer lobe which expands outwardly into the tube groove when the cap is first inserted. The cap is secured by engagement of the first snap ring with the inner more shallow lobe. A second snap ring is placed between the flange and the end of the tube to remove any play between the end cap and tube.

TECHNICAL FIELD
 The present invention is directed to closures, and more particularly to
 blind closures for retaining end caps or rod guides in hydraulic dampers.
 BACKGROUND
 Shocks, struts and other dampers, generally known as hydraulic dampers or
 monotube dampers, typically are used in vehicle shock absorbing systems to
 dissipate vibrational, shock and other forces applied to the wheel
 assemblies of motorized vehicles. Such dampers typically operate by
 transmitting the forces that are sustained by the wheel assemblies to a
 rod/piston combination. The rod/piston is slidably mounted in a
 fluid-filled chamber in the damper. As the piston is urged through the
 chamber, the hydraulic fluid in the chamber is forced through and around
 the piston. The movement of fluid through and around the piston resists
 movement of the piston with a force directly proportioned to the force
 sustained by the wheel assembly. In this manner vibrational and shock
 forces applied to an associated wheel assembly are dampened.
 Hydraulic dampers of this type typically include a cylinder that is sealed
 by an end cap at one end and include a rod guide assembly at the other
 end. The rod guide assembly guides and centers the rod and piston as they
 reciprocate within the cylinder. While the end cap generally can be welded
 to the cylinder, the rod guide must be secured in the cylinder after the
 hydraulic fluid and piston assembly are installed in the cylinder.
 Accordingly, in order to insure that hydraulic fluid does not leak from a
 hydraulic damper, it is desirable for a rod guide to be secured in a
 fluid-tight relationship with the cylinder. Additionally, due to the
 above-mentioned design constraints with the damper, it is desirable for
 the rod guide to be secured in a "blind" configuration, meaning that
 access to the underside of the rod guide is not required in order to
 secure the rod guide into the end of the cylinder. While blind fastening
 devices are useful in many applications, they are particularly useful in
 sealed hydraulic fluid applications, such as the above described hydraulic
 dampers, for a variety of reasons. In particular, access to the underside
 of the rod guide can be difficult due to the relatively long length and
 narrow diameter of the cylinder. Furthermore, after the hydraulic fluid
 has been dispensed into the cylinder, access to the underside of the rod
 guide becomes extremely difficult.
 Prior art closure methods and devices have used blind snap ring closures in
 hydraulic damper applications with some success. For example, U.S. Pat.
 No. 3,650,182 to Phillips discloses the use of a snap ring closure
 apparatus for securing a piston rod bearing into a cylindrical barrel.
 However, that snap ring closure apparatus uses only a single snap ring to
 secure the bearing into the barrel. Thus, all of the movement of the
 bearing inward and outward of the barrel is prevented by a single snap
 ring, thereby placing a large amount of stress on this single element.
 Furthermore, the design of that snap ring is such that the snap ring needs
 to be compressed and fitted into a groove in the barrel after insertion of
 the bearing, but before the bearing is moved into final position. This can
 be a difficult procedure to accomplish effectively since the assembly
 requires holding the bearing in place with one hand while compressing and
 installing the snap ring with the other hand. Additionally, a great deal
 of pressure (either hydraulic or mechanical) is necessary to "force" the
 bearing onto the snap ring. Thus, the assembly of a hydraulic damper using
 such snap ring devices can be difficult and time consuming.
 Another type of snap ring closure is disclosed in U.S. Pat. No. 3,494,652
 to Langland. That snap ring closure uses two snap rings and a retainer
 ring to secure the hydraulic damper head in the cylindrical sleeve. While
 the configuration of that snap ring closure does distribute the stress
 created by the movement of the head over more than one snap ring, it also
 requires a relatively complex assembly. In particular, the first snap ring
 must be forced into a groove in the sleeve after insertion of the head but
 prior to completion of the assembly. Then, once the head is moved into
 contact with the snap ring, a retainer ring must be placed adjacent to a
 beveled edge of the sleeve and a second snap ring must be secured in a
 groove in the head into an interference fit with the retainer ring.
 Accordingly, three separate assembly operations are required to secure the
 head in the sleeve using such closure systems. Furthermore, while the
 second snap ring used in that retainer ring against the beveled edge of
 the cylindrical sleeve absorbs some of the stress from the movement of the
 head outward of the cylinder, it does not create a seal that is as strong
 as might be desired or could be achieved if the force were received by a
 flange that was integral with the head.
 Thus, given the disadvantages of prior art blind closures, there is a need
 for a blind closure useful in hydraulic damper applications that is
 relatively easy and simple to secure, and relatively easy to fabricate.
 SUMMARY OF THE INVENTION
 The present invention is a snap ring closure system suitable for use in a
 vehicle damping system, particularly for securing a rod guide, or in some
 instances an end cap, in a hydraulic damper or shock absorber. The snap
 ring closure system consists of a cylindrical rod guide or end cap having
 an annular, double-lobed groove formed about its outer circumference and a
 flange located at an outer end thereof, and a cylinder for receiving the
 rod guide, having an annular groove formed in the inner circumference
 thereof, which is aligned with the double-lobed groove. The closure system
 includes two snap rings. The first snap ring is slightly oversized and is
 seated in the double-lobed groove in the cylindrical rod guide. The second
 snap ring is positioned between the flange and the top of the cylinder.
 The lobes of the double-lobed groove are of varying depths, with the outer
 lobe (closer to the flange) having a greater depth than the inner lobe.
 The first snap ring initially is positioned in the outer (deeper) lobe of
 the double-lobed groove, so that when the rod guide is initially inserted
 and pressed into the cylinder, the first snap ring is moved fully into the
 outer lobe, thereby providing sufficient clearance with the cylinder and
 is prevented from outward expansion by the walls of the cylinder. Then,
 when the first snap ring reaches the annular groove in the cylinder wall,
 the first snap ring expands outwardly into the annular groove.
 The rod guide is then pulled slightly outwardly until the first snap ring
 contacts the bottom face of the second (shallower) lobe of the
 double-lobed groove, thereby preventing further outward movement of the
 rod guide from the cylinder. Finally, the second snap ring is positioned
 between the top edge of the cylinder and the rod guide flange. The second
 snap ring is positioned on the underside of the rod guide flange and
 prevents inward movement of the rod guide, thereby maintaining the locking
 engagement between the first snap ring and the cylinder groove. In this
 manner, the rod guide is secured to the end of the cylinder.
 Accordingly, it is an object of the present invention to provide a snap
 ring closure system, particularly useful in securing the rod guide or end
 cap to a cylinder in hydraulic damper applications; a closure system that
 is relatively easy and simple to secure; that is relatively easy to
 fabricate and is durable; a closure system that provides a strong seal and
 prevents fluid leakage; and a closure system that is inexpensive to
 assemble.

DESCRIPTION OF THE PREFERRED EMBODIMENT
 As shown best in FIGS. 1 and 2, a preferred embodiment of the snap ring
 closure system 10 of the present invention is incorporated in a hydraulic
 damper 20. However, the snap ring closure system 10 of the present
 invention may be used in a variety of applications beyond hydraulic
 dampers, shock absorbers, or struts, and the embodiment shown in FIGS. 1
 and 2 is illustrative of a single application only. The hydraulic damper
 20 includes a cylinder 22 and a rod guide assembly 24. The rod guide
 assembly 24 is shaped to be inserted into and received by the cylinder 22
 and includes a rod guide or end cap 25 having a central bore 26 for
 receiving a piston rod 28 axially therethrough. A rod seal 29 is seated in
 a counterbore 31 and seals the rod 28 relative to the hydraulic
 fluid-filled interior of the cylinder 22. The inner end of the rod 28 is
 attached to a piston (not shown). The rod guide 25 is generally
 cylindrical in shape and includes a radially-extending flange 32 located
 on its outer end. The rod guide assembly 24 also includes an outer seal
 34, such as an O-ring, seated in an outer annular recess 36 formed in the
 rod guide 25. The seal 34 prevents the leakage of fluid from the interior
 of the cylinder 22.
 The rod guide assembly 24 guides the relative movement of the piston rod 28
 through the rod seal 30 and into the cylinder 22. The piston rod 28 is
 operatively connected to, for example, a vehicle wheel assembly. The
 piston rod 28 and piston are displaced in response to shock loads
 sustained by the vehicle wheel assembly, translated through the cylinder
 22 to the hydraulic fluid located therein. The impingement of the
 hydraulic fluid on the piston that the piston is forced through in the
 cylinder 22 resists movement of the piston and acts to dampen movement of
 an associated vehicle spring.
 The rod guide assembly 24 is secured in place using the snap ring closure
 system 10. The snap ring closure system 10 of the present invention
 includes a double-lobed groove 40 formed around the outer circumference of
 the rod guide 24, preferably relatively near an inner end 42 thereof. The
 double-lobed groove 40 includes an outer lobe 44 and an inner lobe 46. The
 outer lobe 44 is deeper than the inner lobe 46 and is shaped to receive a
 first snap ring 48 such that it is recessed below the outer surface 49 of
 the rod guide 25 when compressed. The first snap ring 48 is made of spring
 steel and has a circular cross-section. However, many kinds of durable,
 compressible, resilient materials, such as carbon steel, stainless steel,
 etc. would be operative and are considered within the scope of the
 invention. Furthermore, while a first snap ring 48 having a circular
 cross-section is preferred, snap rings having cross sections which are
 oval, triangular, trapezoidal, hexagonal or polygonal would be operative
 and are considered within the scope of the invention as well. The closure
 system 10 additionally includes an annular groove 50 formed in the
 interior wall of the cylinder 22. The annular groove 50 is positioned at a
 depth within the cylinder 22 such that when the rod guide 25 is inserted
 into the cylinder 22, the outer lobe 44 of the double-lobed groove 40
 aligns with the annular groove.
 The snap ring closure system 10 further includes a second snap ring 54.
 After the rod guide 24 is pulled outward of the cylinder 22 engaging the
 first snap ring 48 against the bottom lobe 46 of the double-lobed groove
 40, the second snap ring 54 is expanded over the top 56 of the rod guide
 24 and is received between the underside of the flange 32 and the top edge
 52 of the cylinder 22. As with the first snap ring 48, the second snap
 ring is also preferably made of spring steel and is circular in
 cross-section. However, many other materials, such as carbon steel,
 stainless steel and other cross-sections, such as triangular, trapezoidal,
 rectangular, elliptical, polygonal, etc. are within the scope of the
 present invention.
 As best shown in FIGS. 3-5, the snap ring closure system 10 is utilized in
 the assembly of a hydraulic damper in the following manner. Initially, an
 end cap (not shown) is secured to the bottom of the cylinder 22 and the
 cylinder 22 is filled with hydraulic fluid (not shown). Next, as shown
 best in FIG. 3, a rod guide 24, having a piston rod 28 inserted
 therethrough, is inserted in the top of the cylinder 22. A first snap ring
 48 is positioned within the outer lobe 44 of the double-lobed groove 40.
 The ring 48 is compressed into the lobe 44 and rod guide 24 is then pushed
 into the cylinder 22 until the first lobe 44 of the double-lobed groove 44
 is aligned with the annular groove 50. At this point, as shown in FIG. 4,
 the snap ring 48 expand into the annular groove 50. Then, as shown in FIG.
 5, the rod guide 24 is pulled slightly outwardly of the cylinder 22 until
 the engagement of the first snap ring 48 against the bottom lobe 46 of the
 double-lobed groove 44 prevents further outward movement of the rod guide
 24. Finally, the second snap ring 54 is expanded over the top of the rod
 guide 24, and seated between the underside of the flange 32 and the top
 edge 52 of the cylinder 22. The placement of the second snap ring 54
 thereby prevents inward movement of the rod guide 24 in the cylinder 22.
 The location of the annular groove 50 is critical because the first snap
 ring 48 must be able to decompress and engage the annular groove 50 when
 the top lobe 44 of the double-lobed groove 40 is aligned with the annular
 groove 50. Additionally, the positioning of both the double-lobed groove
 40 and the annular groove 50 must be chosen so that the proper space is
 maintained between the underside of the flange 32 and the top edge of the
 cylinder 52 to receive the second snap ring 54. This is because the
 location of the second snap ring 54 on the underside of the flange 32 and
 the top edge of the cylinder prevents movement of the rod guide 24 inward
 of the cylinder 22.