Gas spring with guide

In at least one embodiment, a gas spring includes a casing having an inner surface defining in part a gas chamber, a piston rod and a seal. The piston rod is received at least partially in the casing for reciprocation along an axis between extended and retracted positions. The piston rod has an internal cavity defining a hollow space, a stop and a rod guide disposed adjacent to the inner surface of the casing to guide the reciprocation of the piston rod at least in part. The seal generally is provided between the piston rod and the casing to prevent gas leakage from the gas chamber.

FIELD OF THE INVENTION

This invention relates generally to gas springs, and more particularly to a gas spring including a guide.

BACKGROUND OF THE INVENTION

Gas springs are well known and have been used in dies of presses for sheet metal stamping operations. Conventional gas springs have a gas chamber which receives a pressurized gas that provides a force on a piston and a solid piston rod which carries the piston to bias them to an extended position. The pressurized gas resists the movement of the piston and the piston rod from their extended position to a retracted position. Various housings and seals are provided in the gas spring to retain the piston and piston rod within a casing of the gas spring and to prevent leakage of the pressurized gas from the gas chamber.

The solid piston rod takes up significant volume in the gas spring and a conventional design has a relatively small diameter piston rod compared to the internal diameter of a casing in which the piston rod reciprocates. Because the ratio of piston rod diameter to casing diameter is small, the pressure increase during piston rod travel is less than 100% although the force curve is not very flat, as generally shown by line A inFIG. 10.

To gain more effective force, piston rods have been made larger in diameter. To avoid an undesired pressure increase during a stroke due to use of the larger diameter piston rod, the piston rod can be made to some degree hollow. However, as the depth of the blind bore increases, the cost to manufacture the piston rod increases dramatically. To achieve a longer stroke, a longer bearing surface is needed. But a longer bearing surface requires a longer piston rod, which in turn requires a deeper and much more costly bore. Further, the longer bearing assembly consumes gas chamber volume and thereby leads to a greater pressure increase during the stroke. The force increase during a piston rod stroke is higher in this type design, as shown by line B inFIG. 10.

SUMMARY OF THE INVENTION

In at least one embodiment, a gas spring includes a casing having an inner surface defining in part a gas chamber, a piston rod and a seal. The piston rod is received at least partially in the casing for reciprocation along an axis between extended and retracted positions. The piston rod has an internal cavity defining a hollow space, a stop and a rod guide disposed adjacent to the inner surface of the casing to guide the reciprocation of the piston rod at least in part. The seal generally is provided between the piston rod and the casing to prevent gas leakage from the gas chamber.

In one implementation, a gas spring includes a casing having an inner surface defining in part a gas chamber, and a piston rod received at least partially in the casing for reciprocation along an axis between extended and retracted positions. The piston rod may have a first portion extending out of the casing at least in the extended position of the piston rod and a second portion formed separately from the first portion and connected to the first portion for conjoint movement therewith along the axis. A rod guide carried by the second portion of the piston rod has at least a portion disposed adjacent to the inner surface of the casing and a seal is provided between the piston rod and the casing. In at least some applications, the two piece piston rod construction can facilitate providing a larger diameter and substantially hollow piston rod that can have a greater length at far less cost, and can have improved guided movement.

In one implementation, the second portion of the piston rod is a hollow tube connected to the first portion. The first portion may include a blind bore or cavity, although because the cavity is formed only in the first portion, it is not as deep compared to when the piston rod is formed in one piece and can be formed without great expense. Even though the cavity in the first portion is not deep, the addition of the tubular second portion provides an increased effective hollow length of the piston rod to reduce the volume of the gas chamber that is taken up by the piston rod. Further, in at least some applications, a stop that limits travel of the piston rod toward its extended position can be formed on the first portion of the piston rod and therefore, the second portion of the piston rod can be formed of a thinner and/or weaker material.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring in more detail to the drawings,FIGS. 1 and 2illustrate one presently preferred embodiment of a gas spring10, such as those used in mechanical presses (not shown). Generally, a plurality of gas springs10may be disposed in the mechanical press such that a piston rod12of each gas spring10is engaged and driven by a ram of the press as the ram advances to form a sheet metal blank in a die assembly of the press.

The gas spring has a casing14with a generally cylindrical wall16terminating at a generally closed end18, and at another end20that is substantially open for receiving the piston rod12therein. Generally, the closed end18is attached, for example through a weld joint, or formed as one piece with the cylindrical wall16. The wall16of the casing14has an inner surface22defining at least in part a gas chamber24, and an outer surface26. The inner surface22of the wall16has a circumferential retainer groove28constructed for receipt of a retainer, shown here by way of example as a snap ring30, to maintain the gas spring10in its assembled state. To facilitate mounting and locating the gas spring10within the press, a pair of longitudinally spaced circumferential grooves32,34are formed in the outer surface26of the casing14adjacent its ends18,20.

To admit gas into the gas spring10, the casing14has a passage or fill port42extending between the inner and outer surfaces22,26of the wall16, shown here as extending through the closed end18of the casing14. A fill valve (not shown) received in the fill port42acts as a one way valve and allows gas to be admitted into the gas spring10, while preventing the gas from unintentionally exiting the gas spring10. The fill valve preferably may be opened to release pressurized gas from within the gas spring10, when desired.

The piston rod12is acted on by gas in the gas chamber24and is received in the casing for reciprocation along an axis44between an extended position (FIG. 1) and a retracted position (FIG. 2). The piston rod12may include a first portion46and a second portion48that may be formed separately from each other, from separate pieces of material.

The first portion46has one end49preferably extending out of the casing14at least when the piston rod12is in its extended position and adapted for operable engagement with the ram of the press, and another end50received within the casing14. The first portion46may have a generally cylindrical outer surface52, and a cavity such as a blind bore54so that the end50is generally open. The depth of the blind bore54may be greater than the thickness of an end wall56defined between the blind bore54and the end49. The first portion46may carry a stop58, which in at least one implementation may include an outwardly extending annular flange59. In other implementations, the stop may include circumferentially spaced and radially extending tabs or other stop surface or surfaces. The stop58may be integrally formed in one-piece with the first portion46, or connected thereto or otherwise carried thereby.

The second portion48of the piston rod12may be hollow so that it does not take up significant volume in the gas chamber24. In one implementation, the second portion48is a generally thin-walled tube connected to the end50of the first portion46. The second portion48may be connected to the first portion46in any suitable manner such as by press-fit, adhesive, mating threads, weld, snap fit, retaining ring, etc. The second portion48may include a shoulder60or other surface that may limit insertion of the second portion48into the bore54of the first portion46, and/or provide an increased surface area of engagement between the first and second portions46,48to improve the rigidity and stability of their connection. A passage or opening62through the second portion48may be coaxially aligned with the blind bore54in the first portion46, and the second portion may be coaxially aligned with the first portion for conjoint movement therewith along the axis46. A groove66may be formed in the second portion48to facilitate connecting a rod guide68thereto as set forth in more detail below.

The rod guide68may be carried by one or both of the first portion46and the second portion48, and is shown in this embodiment as being carried by the second portion48. The rod guide68may be annular and disposed around a portion of the outer surface of the second portion48adjacent to the groove66. A retaining ring70may be disposed in the groove66and adjacent to the rod guide68to maintain the position of the rod guide on the second portion of the piston rod. As best shown inFIG. 3, the rod guide68may include an annular recess that is received over the retaining ring70. Then, as shown inFIG. 4, a depending skirt or annular flange71of the rod guide68may be crimped or partially rolled over the retaining ring70to firmly connect the rod guide68to the second portion48of the piston rod12.

The rod guide68may be generally annular with a peripheral surface72in which a groove74may be formed to receive an annular guide bearing76or wear strip. The guide bearing76may be constructed from any suitable low friction material and is sized to slidably engage the inner surface22of the casing14to guide the piston rod12for axial reciprocation within the casing14. One or more passages77may be formed through the rod guide68to prevent the rod guide from acting as a piston and/or unduly restricting gas flow in the gas chamber during a stroke of the piston rod12. This minimizes the temperature increase that could otherwise occur in use because of a restriction to gas flow across the rod guide68. As shown inFIG. 5, in another implementation, a rod guide68′ can be integrally formed in one-piece with a second portion48′ of a piston rod, and may carry a bearing76′ generally as previously described with regard to rod guide68and bearing76.

In one implementation, the rod guide68is retained on the second portion48of the piston rod12by a connection feature that is adapted to fail before the connection between the first portion46and second portion48fails. In this manner, the rod guide68may be adapted to be released from its rigid connection to the piston rod12before the second portion48of the piston rod is separated from the first portion46, due, for example, to unusual side loading on the second portion48or binding of the rod guide68. The connection feature can include any suitable manner or mechanism to connect the rod guide68to the piston rod12, such as the retaining ring70, adhesive, weld, threads, press-fit or the rod guide68could be a split ring received in a groove on the piston rod12, by way of examples without limitation. In the embodiment shown inFIGS. 1-4, the rod guide68can only be released from the piston rod12if the crimped or rolled flange71is deflected sufficiently to pass the retaining ring70such that the rod guide could then move along the second portion and toward the stop58. Engagement of the rod guide68with the retaining ring70prevents the rod guide from moving along the second portion in the opposite direction (i.e. in the direction tending to remove the rod guide68from the piston rod12). This may prevent damage to the other components of the gas spring by maintaining the rod guide trapped on the piston rod12.

As shown inFIGS. 1 and 2, the gas spring10has a bearing and seal assembly80that seals the open end of the casing14to prevent escape of gas from the gas chamber24and provide a bearing82that helps guide the piston rod12movement. Accordingly, the piston rod12is guided at two spaced apart locations by both the bearing76(carried by the rod guide68) and the bearing82. The bearing and seal assembly80includes a body84that carries the bearing82, a rod seal86(which may include a backup plate88or ring to prevent extrusion of the seal86between the rod12and body84), a casing seal90such as an o-ring and a wiper92to keep contaminants out of the bearing and seal assembly80. The body84may engage the retaining ring30received in the casing14to retain the body84and its components relative to the casing14. An end of the body84may define a stop surface98(FIG. 2) adapted to be engaged by the stop58of the piston rod12to limit movement of the piston rod12away from the closed end18of the casing14. In at least some embodiments, the engagement of the stop surfaces58,98may define the fully extended position of the piston rod12.

With the piston rod12received in the casing14, and the bearing and seal assembly80maintained within the casing14by the retaining ring30, the gas spring10may be charged with gas through the fill port42. The pressurized gas yieldably biases the piston rod12to its extended position wherein the piston rod stop58engages the stop98defined by the body. Typically, a plurality of charged gas springs10are received in a die assembly with a work piece clamp ring or binder ring resting on the ends48of the extended piston rods12.

As shown inFIG. 6, a rod guide68″ may be trapped between a shoulder99of a second portion48″ of a piston rod and a retaining ring70″ to maintain the rod guide68″ on the second portion48″. The failure mode of this connection may be a release of the rod guide68″ from the piston rod upon breaking of at least a portion of the retaining ring70″.

As shown inFIG. 7, in one embodiment an entire piston rod112and rod guide168can be formed in one piece and include an outwardly extending stop158and an outwardly extending rod guide168. A cavity154may extend substantially the entire length of the piston rod112, as desired.

In the embodiment shown inFIG. 8, a multiple piece piston rod212is shown. A first portion246is generally cylindrical and solid, that is, without any significant blind bore or cavity formed therein. A split ring retainer202is received in a groove204formed in an outer surface of the first portion246and extends radially outwardly of the first portion. In this manner, the retainer202defines the stop258adapted to engage a stop surface carried by the casing14(such as a stop98on the bearing and seal assembly80). A second portion248of the piston rod212is connected to the retainer202(which defines the stop), such as by threaded fasteners206or otherwise as desired. The second portion248may be generally axially aligned with the stop258and may include a rod guide portion268which may be adapted to receive a bearing276to help guide movement of the piston rod212. The second portion may also be at least partially hollow or tubular to define a cavity254of the piston rod212.

A different embodiment of a piston rod312is shown inFIG. 9. In this embodiment, the first portion346of the piston rod312may be formed similarly to the first portion46of the piston rod12shown inFIGS. 1 and 2except this first portion346does not include an integral flange like flange59on piston rod12. The first portion346therefore includes a cavity354such as blind bore. Instead, an annular retainer302is provided radially outwardly of an outer surface304of the first portion346to define a stop358. The retainer302is held in place against movement in one direction by a snap-ring306carried in a groove308in the first portion346and against movement in the other direction by its connection to a second portion348of the piston rod312. The second portion348may be tubular and may include a shoulder310that bears on an end312of the first portion346. The second portion348may be connected to the retainer302in any suitable manner, such as by threaded fasteners314. In this manner, the first portion346, second portion348and stop/retainer302are firmly held together, but they may be readily taken apart for service or repair, by removing the fasteners314. A rod guide368may be provided integrally with or as a separate component from the second portion348and may include a bearing376.

In at least some embodiments of the gas spring, the piston rod can be formed with a greater length without significantly increasing the volume of the gas chamber used up by the piston rod. As shown in line C ofFIG. 10, this permits the gas spring to have an increased effective force similar to that of prior gas springs of similar size and operating parameters that have piston rods with some hollow portion (e.g. of the type shown by line B) and higher than gas springs having a solid piston rod design (e.g. of the type shown by line A), while maintaining a relatively flat force v. travel curve compared to that shown by line B. Accordingly, the gas spring can provide an increased effective force with a maximized gas chamber volume for a given size and a relatively constant force over its stroke length.

In at least some embodiments, the hollow portion of the piston rod, defined by a cavity in the first portion (if any) and a tubular or at least partially hollow second portion, extends over half of the length of the piston rod, and may extend up to 95% of the piston rod length. Further, in at least some embodiments, the thickness of the end wall56of the piston rod12may be between about 40% and 100% of the diameter of the cavity or blind bore54in the first portion46.

Further, the piston rod12may have an increased effective guide length, which may be defined as the distance between the end of the bearing82closest to the end49of the piston rod12, and the opposite end of the bearing76carried by the rod guide. The minimum guide length occurs when the piston is in its extended position since in this position the rod guide is closest to the bearing82. In at least some implementations, the minimum effective guide length may be between about 100% to 200% of the diameter of the piston rod, and in some cases may be limited only by the length of the casing and piston rod. In other words, the effective guide length could be as long as the casing, or even somewhat longer if, for example, the bearing and seal assembly80extended out of the open end of the casing14. Further, the spaced guide bearings permits use of a smaller bearing and a smaller bearing and seal assembly to reduce the volume of the gas chamber consumed by these components while providing a long overall guide length.

It should be recognized that one ordinarily skilled in the art will recognize other embodiments encompassed within the scope of this invention. For example, when the piston rod is formed in more than one piece, the second portion of the piston rod may be attached to the first portion in any given manner or arrangement and the plurality of arrangements shown and described are merely exemplary and not a complete or exhaustive list or representation. Likewise, the rod guide can be carried by or formed integrally with the piston rod, or any portion of the piston rod, in any number of ways. Further, the bearing of the rod guide may be integral and in one-piece with the second portion rather than a separate part carried by the second portion. Of course, still other embodiments and implementations can be achieved in view of this disclosure. The embodiments described above are intended to be illustrative and not limiting. The scope of the invention is defined by the claims that follow.