Gas strut

A gas strut includes a housing, a piston assembly, a dye, and a dye containment seal. The housing includes an inner surface defining a chamber extending along a centerline. The chamber includes a working portion and a dye storage portion disposed axially adjacent to the working portion. The piston assembly is constructed and arranged to reciprocate within the working portion, and the dye is located in the dye storage portion. The dye containment seal is disposed in the dye storage portion, and is constructed and arranged to transfigure from a normal state to a dye release state thereby releasing the dye upon the piston assembly.

INTRODUCTION

The subject disclosure relates to gas struts, and more particularly to gas strut wear indicators.

Gas struts are known to include a piston assembly that reciprocates within a pressure chamber defined by a housing. Typically, the pressure chamber contains an inert gas such as nitrogen. The piston assembly includes an enlarged head that slides within the housing, and a rod that extends from the head and out through one end of the housing. In operation, as the rod retracts within the housing, the total volume of the pressure chamber is reduced thus increasing the gas pressure within the chamber. The piston head may include valves or openings that communicate axially through the piston head to control and establish pressure equilibrium on both sides of the piston head regardless of the axial location of the head during a strut cycle. Because the surface area on a leading side of the piston head is larger than a surface area of the other side (i.e., the side that the rod attaches to), axial forces may not be equivalent. Therefore, as pressure increases within the pressure chamber as the strut retracts, a force that resists the retraction increases tending to bias the strut toward a fully extended position.

Regardless of gas strut position, the positive gas pressure within the gas strut is maintained or preserved via a seal that sealably slides against the reciprocating piston rod. As the seal wears, or through other components that may wear or require maintenance over time, the gas pressure in the pressure chamber may decrease with increasing wear on the seal. For example, a twenty percent decrease in gas pressure may be significant in some applications, and if the degraded pressure condition is known, may lead to strut maintenance or replacement. Unfortunately, known means to determine degraded gas pressure conditions is limited and/or impractical.

Accordingly, a robust wear indicator for gas struts is desirable.

SUMMARY

In one exemplary, non-limiting, embodiment of the present disclosure, a gas strut includes a housing, a piston assembly, a dye, and a dye containment seal. The housing includes an inner surface defining a chamber extending along a centerline. The chamber includes a working portion and a dye storage portion disposed axially adjacent to the working portion. The piston assembly is constructed and arranged to reciprocate within the working portion, and the dye is located in the dye storage portion. The dye containment seal is disposed in the dye storage portion, and is constructed and arranged to transfigure from a normal state to a dye release state thereby releasing the dye upon the piston assembly.

In addition to the foregoing embodiment, the inner surface defines a recess disposed radially outward from and in fluid communication with the working portion when the dye containment seal is in the normal state, the dye containment seal axially disposed adjacent to the working portion, the dye containment seal being in sealing contact with the inner surface, the transfigure of the dye containment seal being an axial translation from the normal state to the dye release state upon loss of internal pressure in the chamber, the recess being in fluid communication between the working portion and the dye storage portion when the seal is in the dye release state for the flow of the dye into the working portion.

In the alternative or additionally thereto, in the foregoing embodiment, the piston assembly includes a rod and a head engaged to the rod, and the dye deposits upon the rod when the dye containment seal is in the dye release state.

In the alternative or additionally thereto, in the foregoing embodiment, the housing includes a base end and an opposite working end through which the rod extends, and the dye storage portion is located at the base end.

In the alternative or additionally thereto, in the foregoing embodiment, the recess is a circumferentially continuous groove.

In the alternative or additionally thereto, in the foregoing embodiment, the recess is one of a plurality of recesses and each recess is spaced circumferentially from an adjacent recess.

In the alternative or additionally thereto, in the foregoing embodiment, the piston assembly is constructed and arranged to reciprocate in the chamber and between a retracted position with the rod being axially retracted within the housing and an extended position with the rod being axially extended out of the housing.

In the alternative or additionally thereto, in the foregoing embodiment, the base end is disposed above the working end when the gas strut is in at least one of the retracted and extended positions.

In the alternative or additionally thereto, in the foregoing embodiment, the dye is in liquid form.

In the alternative or additionally thereto, in the foregoing embodiment, the dye is fluorescent.

In the alternative or additionally thereto, in the foregoing embodiment, the gas strut includes a spring disposed in the dye storage area, and constructed and arranged to exert an axial force upon the seal.

In the alternative or additionally thereto, in the foregoing embodiment, the inner surface is cylindrical and the seal is disc-shaped.

In the alternative or additionally thereto, in the foregoing embodiment, at least one opening communicates axially through the head for the flow of a pressurized gas as the piston assembly reciprocates, and for the flow of the dye when the seal is in the dye release state.

In the alternative or additionally thereto, in the foregoing embodiment, the gas strut is one of a gas damper, a gas spring, and a shock absorber.

In the alternative or additionally thereto, in the foregoing embodiment, the piston assembly includes a rod and a head engaged to the rod, and the dye containment seal is in sealing contact with the rod.

In the alternative or additionally thereto, in the foregoing embodiment, the dye containment seal is a vessel for containing the dye when in the normal state, and is constructed and arranged to wear upon the rod and release the dye when in the dye release state.

A vehicle gas strut assembly according to another, non-limiting, embodiment includes a frame, a liftgate, and a gas strut. The gas strut includes a housing, a piston assembly, a dye, and a dye containment seal. The housing defines a chamber and is pivotally engaged to one of the frame and the liftgate. The piston assembly is constructed and arranged to reciprocate within the chamber and pivotally engages to the other of the frame and the liftgate. The dye is disposed in the chamber, and the dye containment seal is constructed and arranged to transfigure from a normal state to a dye release state indicative of strut wear.

Additionally to the foregoing embodiment, the chamber is a pressure chamber and includes a working portion through which the piston assembly reciprocates, a dye containment portion, and a recess, and wherein the recess is in fluid communication with the working portion when the dye containment seal is in a normal state and is in fluid communication with and between the working and dye containment portions when the dye containment seal is in a dye release state.

In the alternative or additionally thereto, in the foregoing embodiment, the dye containment seal is a vessel that contains the dye and includes a wall biased against a rod of the piston assembly, and wherein the wall is constructed and arranged to wear-through after a pre-determined number of piston cycles thereby releasing the dye.

DETAILED DESCRIPTION

In accordance with an exemplary embodiment,FIG. 1illustrates a gas strut assembly20that may be applied to a vehicle, and more specifically, to a vehicle liftgate22. In this example, a gas strut24of the gas strut assembly20may extend between and may be pivotally engaged to the liftgate22and a vehicle frame26. The gas strut24facilitates the lifting, and thus opening, of the liftgate22as the gas strut24pivotally moves from a retracted position28(i.e., illustrated in ghost) to an extended position30. In this and/or other applications, the gas strut24may be a gas spring, a gas damper, a shock absorber, and other similar embodiments.

Referring toFIG. 2, the gas strut24may include a housing32that may be a cylinder, a piston assembly34, a dye containment seal36, and a dye38. The piston assembly34reciprocates along a centerline C within the housing32. The housing32includes an inner surface40that faces radially inward and may be cylindrical. The inner surface40defines, in-part, a chamber42that includes a working portion44and a dye containment portion46axially located adjacent to the working portion44. The dye containment seal36may be generally located in the dye containment portion46and axially adjacent to the working portion44. In one embodiment, the chamber42may be a pressure chamber, and opposite sides of the dye containment seal36may axially, and respectively, define the working and dye containment portions44,46of the pressure chamber42.

The piston assembly34includes a rod48(also seeFIG. 1) and a head50that may be radially enlarged with respect to the rod48. The head50is adapted to reciprocate along an axial length of the working portion44of the chamber42. The head50may include a seal52that may be an o-ring, and at least one opening or valve54that axially communicates through the head50. In operation, the seal52sealably slides upon the inner surface40of the housing32, and a gas that may be pressurized, controllably flows through the openings54from one side of the piston head50to the other as the piston assembly34reciprocates. Sizing of the opening54(or configuration of a valve) affects the dampening ability of the gas strut24as is typically known by one skilled in the art.

Referring toFIGS. 1 and 2, the housing32may further include a base end56that may be pivotally engaged to the vehicle frame26, and an opposite working end58through which the rod48of the piston assembly34extends. The rod48may include a first end60attached to the piston head50and an opposite second end62pivotally engaged to the liftgate22. The gas strut24may further include a rod seal64capable of maintaining a positive gas pressure of the gas (e.g., nitrogen) in the chamber42, while sealably sliding against the rod48as the piston assembly34reciprocates between the retracted and extended positions28,30(seeFIG. 1). The rod seal64may be disposed in the chamber42proximate to the working end58of the housing32. An annular flange66of the housing32may project radially inward from the inner surface40. The rod seal64may be axially adjacent to the flange66. It is contemplated and understood that pivotal engagement of the end62of the piston rod48and the end56of the housing32may be reversed with the rod end62engaged to the vehicle frame26and the housing end56engaged to the liftgate22. Moreover, it is contemplated that the flange66may be, or may be part of, a dust boot typically known to one having skill in the art.

Referring toFIGS. 2 through 4, the inner surface40of the housing32may further define a recess68located radially outward from, and in fluid communication with, the working portion44of the chamber42during normal operation of the gas strut24. The dye containment seal36may be axially located between the recess68and the base end56of the housing32(seeFIG. 3). In one embodiment, the dye containment seal36may be disc-shaped, and may sealably slide against the inner surface40of the housing32in response to a differential pressure across the seal36. The gas strut24may further include a biasing member or spring69that may be a coiled spring. The spring69may be located in the dye containment portion46of the chamber42, and facilitates the exertion of an axial force that may bias the dye containment seal36toward the working portion44of the chamber42and toward the recess68. As illustrated, the recess68may be a circumferentially continuous groove. It is contemplated and understood; however, that the recess68may be circumferentially discontinuous, may be a plurality of circumferentially spaced recesses, and/or may be one or a series of relatively short channels that extend axially.

In operation and as the rod seal64wears over time, the gas pressure within the working portion44of the chamber42may become less than the pressure within the dye containment portion46. Once the force created by the differential pressure across the seal36becomes greater than an a opposing frictional force created by the sealing interface between the inner surface40of the housing32and the dye containment seal36, the seal may axially translate from a normal state70(seeFIG. 3), toward the recess68, and into a dye release state72(seeFIG. 4). When the dye containment seal36axially reaches the recess68and is in the dye release state72, the recess68is in fluid communication with both the working portion44and the dye containment portion46of the chamber42facilitating the release of the dye38from the dye containment portion46and into the working portion44(i.e. see arrow73indicating the direction of dye travel inFIG. 3).

With the dye38released into the working portion44, the dye may flow through the piston head openings54and upon the piston rod48. As the piston rod moves from the retracted position28and into the extended position30, the dye38is deposited upon the rod48and becomes visually exposed to a user of the gas strut24. The visual detection of the dye38upon the rod48is an indication that the gas strut24is worn and/or has lost gas pressure, and is in need of maintenance or replacement. It is contemplated and understood that the dye may discolor the rod48in any variety of ways. For example, the dye38may generally coat the rod48, may dry or harden upon the rod48, and/or may cause a chemical reaction with the rod48causing, for example, a chemical reaction with a plating of the rod that facilitates a discoloration of the plating that is visually obvious.

As illustrated inFIG. 1, when the liftgate22is generally closed, the gas strut24is in the retracted position28and the base end56of the housing32, along with the dye containment chamber44, is located vertically above the working portion44and the piston assembly34contained therein. This vertical relationship assists in the utilization of gravity to promote dye flow upon the piston assembly34when the gas strut24is worn and the dye containment seal36is in the dye release state72(seeFIG. 4).

In one embodiment, the dye38may be in liquid form and may be a vibrant color and/or fluorescent. The dye38may be any hydraulic, leak-detection, die including, but not limited to, Fluorescent Yellow 131SC, manufactured by the Dow Chemical Company, Midland, Mich.

Referring toFIG. 5, a second embodiment of a gas strut is illustrated wherein like elements to the first embodiment have like identifying numerals except with the addition of a prime symbol suffix. A gas strut24′ may include a housing32′, a piston assembly34′, a dye containment seal36′, and a dye38′. The piston assembly34′ reciprocates along a centerline C within the housing32′. The housing32′ includes an inner surface40′ that defines, in-part, a chamber42′, which includes a working portion44′ and a dye containment portion46′. The dye containment portion46′ is proximate to a working end58′ of the housing32′.

The dye containment portion46′ of the chamber42′ may have axial boundaries defined between, and by, a housing flange66′ and a rod seal64′. The rod seal64′ may be located between the dye containment portion46′ and the working portion44′ of the chamber42′. With this configuration, the dye containment portion46′ may not be pressurized. That is, the working portion44′ may contain a pressurized gas, and the dye containment portion46′ may generally be at atmospheric pressure.

The dye containment seal36′ may generally be a vessel adapted to hold or contain the dye38′ when the dye containment seal36′ is in a normal, unworn, state. The dye containment seal36′ is in sliding contact with a piston rod48′ of the piston assembly34′, and is constructed to wear upon the rod48′ as the rod reciprocates. When the dye containment seal or vessel36′ is sufficiently worn upon the rod48′, the dye38′ is released. That is, the seal36′ is worn to a point where an opening (not shown) is worn through a wall90of the seal36′ that is biased against the reciprocating rod48′. In one example, the gas strut24′ may be designed to cycle about 25,000 times before the wall90of the seal36′ is generally worn away. In this example, the 25,000 cycles is associated with the life expectancy of the gas strut24′. The strut life may be deemed expired upon, for example, a twenty percent (20%) decrease in gas pressure.

Advantages and benefits of the present disclosure may include a visual notification to the user that gas strut service may be needed.