WO2003014590A2

WO2003014590A2 - Improved gas spring

Info

Publication number: WO2003014590A2
Application number: PCT/US2002/024768
Authority: WO
Inventors: James T. Bertram
Original assignee: ArvinMeritor Inc
Current assignee: Meritor Inc
Priority date: 2001-08-08
Filing date: 2002-08-06
Publication date: 2003-02-20
Anticipated expiration: 2004-02-08
Also published as: AU2002323007A1; WO2003014590A3

Abstract

A gas spring (20) is connectable between a movable object (22) and a relatively fixed object (24) for assisting in moving the movable object between a first position and a second position. The gas spring includes a cylinder (28) having a closed end (32) and an open end (34). A piston rod extends (42) into the cylinder through the open end in a sealing relationship thereto for axial movement relative to the cylinder. A piston assembly (64) is carried by the rod for axial movement within the cylinder. The piston and the rod move in a compression direction when the movable object moves towards its first position and an extension direction when the movable object moves towards its second position. A resilient annular seal (72) carried by the piston assembly has a flexible outer portion configured to provide a gas seal between the piston assembly and the cylinder sufficient to maintain the movable object at a stopped position at any point between its first and second positions

Description

TITLE IMPROVED GAS SPRING

RELATED APPLICATIONS This application claims priority of U.S. provisional application Serial No.

60/311,041, which was filed August 8, 2001 and is entitled "Improved Double Stop Dynamic Gas Spring." This application is a continuation-in-part of U.S. utility patent application Serial No. 09/787,615, which was filed July 3, 2001 and is entitled "Improved Gas Spring," and which claims priority of U.S. provisional application Serial No. 60/149,754, filed August 19, 1999 and entitled "Improved Double Stop

Gas Spring." The disclosures of the 041 and the 754 provisional applications and the 615 utility patent application are incorporated herein, in their entirety, by reference.

BACKGROUND OF THE INVENTION

The present invention relates to an improved gas spring, and more particularly, to an improved multiple stop gas spring where the movement of the gas spring shaft may be selectively stopped at an infinite number of intermediate positions between its fully extended and fully compressed positions, while still providing assistance in moving an object.

Gas springs have been used in many fields to facilitate and control the movement of movable objects with respect to relatively fixed objects. One field in which gas springs have found widespread utility is the automotive field where they have been employed to facilitate and control the movement of hoods, trunks, hatches, lids and lift gates. Generally speaking, gas springs include, among other components: a tube or cylinder that defines an internal tubular cavity extending between the ends of the tube; a metering piston assembly, which is reciprocally moveable within and which divides the tubular cavity into compression and extension working chambers; a shaft connected moveable with the piston assembly, with one end of the shaft projecting out of an end of the tubular cavity; and end closures or caps for closing the ends of the tubular cavity, with one of the end closures also including a bushing seal for the reciprocally moveable shaft as it moves with respect to the tube. Conventional gas springs are designed to move between two positions, namely a fully compressed position and a fully extended position. In use, an external latching mechanism, such as a trunk latch on an automobile, is used to normally maintain the movable object, e.g. the trunk lid, at its closed position. When the trunk lid is closed, the gas spring is at its fully compressed position. The trunk lid can be opened by releasing the latch. When the latch is released, the gas spring acts on the lid to bias it towards its open position. In some applications, the gas spring is designed to lift the lid when the latch is released. In other applications, the gas spring is designed to assist the operator in lifting the lid. In many applications, such as tanning beds, toolbox lids, and automobile hoods and trunk lids, it is desirable to provide multiple open positions. For example, in a tanning bed it is desirable for the user to be able to position the top portion, i.e., the lid, of the bed at various heights. However, conventional gas springs do not provide multiple open positions. Moreover, known gas springs that are capable of providing multiple open positions typically rely on additional component, and/or extensive internal modifications that increase the price of the gas spring system dramatically.

BRIEF SUMMARY OF THE INVENTION According to certain aspects of an embodiment of the present invention, a gas spring is connectable between a movable object and a relatively fixed object for assisting in moving the movable object between a first position and a second position. The gas spring includes a cylinder having a closed end and an open end. The closed end of the cylinder is configured for connection with either of the movable object or the relatively fixed object. A piston rod extends into the cylinder through the open end in a sealing relationship thereto for axial movement relative to the cylinder. The piston rod has an external end configured for connection with the other of the movable object or the relatively fixed object. The cylinder contains a gas under pressure. A piston assembly is carried by the rod for axial movement within the cylinder. The piston and the rod move axially in a compression direction when the movable object is moved towards its first position and an extension direction when the movable object is moved towards its second position. The gas spring includes a means carried by the piston assembly for maintaining the movable object at any point between its first and second positions. The means may comprise a resilient seal having a flexible, annular outer portion configured to provide a gas seal between the piston assembly and the cylinder sufficient to maintain the movable object at a stopped position at any point between its first and second positions. The resilient seal may include a central body portion and an annular lip portion which extends radially outwardly from the body portion and sealing engages with the inner diameter of the cylinder. The output force of the gas spring may be matched to the application by adjusting, e.g., during manufacture, the charge pressure such that the output force does not auto lift the movable object from the compressed position, but does provide sufficient force to maintain the movable object at infinite positions intermediate the fully extended and fully compressed positions.

A backing member may be disposed adjacent to the body portion of the resilient seal to support the body portion. The backing portion has an outer diameter which is less than the outer diameter of the resilient seal so that the lip portion can flex inwardly relative to the inner diameter of the cylinder to allow gas to bypass between the piston assembly and the cylinder when an external force of a predetermined magnitude is exerted on the piston rod in one of the compression and extension directions.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

Figures 1-3 illustrate the use of an embodiment of an improved gas spring according to certain aspects of the present invention, where the gas spring is connected to operate the lift gate of a hatchback style automobile. Figure 1 shows the lift gate at its fully closed position. Figure 2 shows the lift gate stopped at an intermediate position. Figure 3 shows the lift gate at its fully open position.

Figure 4 is an axial, cross-sectional view of one embodiment of an improved gas spring according to certain aspects of the present invention.

Figure 5 is an enlarged, cross-sectional view of the piston assembly of the gas spring of Figure 4, showing the flow path of the gas passing across the piston assembly during an extension stroke of the gas spring.

Figure 6 is a cross-sectional view, similar to Figure 5, showing the flow path of gas passing across the piston assembly during a compression stroke of the gas spring. The foregoing summary, as well as the following detailed description of the preferred embodiments of the present invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the preferred embodiments of the present invention, there is shown in the drawings, embodiments which are presently preferred. It should be understood, however, that the present invention is not limited to the arrangements and instrumentality shown in the attached drawings.

DETAILED DESCRIPTION OF THE INVENTION Figure 1 through 3 illustrate an embodiment of a gas spring 20 according to certain aspects of the present invention, where the gas spring 20 is connected to assist in opening the lift gate 22 of a hatchback style automobile 24. The gas spring 20 has one end connected to the automobile's body and the other end connected to its lift gate 22. When the lift gate 22 at its fully closed position (see Figure 1), the gas spring (not shown in Figure 1) is at or near its fully compressed position. When the lift gate 22 is stopped at an intermediate position (see, e.g., Figure 2), the gas spring 20 is at a position that is less than its fully extended stroke position. When the lift gate 22, at its fully open position (see Figure 3), the gas spring 20 is at or near its fully extended stroke position.

The lift gate 22 is normally maintained in a fully closed position (Figure 1) by a latch (not shown). The lift gate 22 can be opened by releasing the latch and lifting on the bottom of the lift gate 22. When the latch is released, the gas spring 20 extends towards its fully extended position to assist in moving the lift gate 22 towards its fully open position. The gas spring 20 operates to assist in moving the lift gate from its closed position towards its open position, and also to maintain the lift gate at its fully opened position (Figure 1) and at an infinite number of intermediate or partially opened positions (one shown in Figure 2). The ability to maintain the lift gate 22 at intermediate positions, such as shown in Figure 2, is a desirable feature because, for example, it permits persons of shorter stature to be able to easily lift the lift gate 22 to a position where ready access can be obtained to the rear compartment of the automobile 24 while not having to strain to reach the lift gate when trying to close the gate. This intermediate stop position feature is also beneficial in numerous other applications, such as tool box lids and tanning beds, where it is desirable to provide multiple stop positions between the fully extended and fully compressed positions while still providing lift assistance.

Figures 4-6 illustrate the gas spring 20 in greater detail. The gas spring 20 a cylindrical tube 28 that has a first end 32 and a second end 34. The tube 28 includes a tubular cavity 36, which is filled with gas under pressure as is conventional in the gas spring art. A conventional end cap 38 closes and seals the first end 32 of the tube 28.

The gas spring 20 also includes a reciprocally moveable shaft 42. As is conventional, the shaft 42 is disposed, in part, in the tubular cavity 36 so that the longitudinal axes of the shaft and the tubular cavity are coaxial. The shaft 42 has a first end 44, which is positioned within the tubular cavity 36, and a second end 46, which projects out of the tube 28.

A conventional bushing assembly 48 is disposed adjacent the second end 34 of the tube 28. The bushing assembly 48 surrounds the shaft 42 so as to provide a gas and oil seal for the shaft as the shaft reciprocally moves within the tube 28 in a conventional manner. In the illustrated embodiment, the bushing assembly 48 includes a front bushing 52, a washer 56, an annular front seal 58, all of which are disposed about the shaft 42. The bushing 52 is generally cylindrical-shaped, with one side of the bushing facing outside of the gas filled cavity 36 to the left in Figure 4, and the opposite side facing into the gas filled cavity to the right in Figure 4. The washer

56 is positioned on the shaft 42 between the bushing 52 and the front seal 58. The washer 56 may, for example be formed from Teflon®. It will be appreciated that the bushing assembly 48 may take numerous other forms. For example, as is illustrated in the aforementioned 615 utility application, the bushing assembly may include an "O" ring positioned between the bushing 52 and the ID of the tubular cavity 36.

A piston assembly 64 is connected with and moveable with the first (or inner) end 44 of the shaft 42. In the illustrated embodiment, the piston assembly 64 is mounted on a reduced diameter portion 60 formed in the first end 44 of the shaft 42. The piston assembly 64 divides the tubular cavity 36 into an extension chamber 65, which is located between the piston assembly 64 and the second end 34, and a compression chamber 67, which is located between the piston assembly 64 and the first end 32. The sizes of the chambers 65, 67 vary depending on the location of the piston assembly 64 within the tubular cavity 36. The piston assembly 64 functions to meter the flow of gas past the piston assembly 64 as the assembly 64 moves within in the tubular cavity 36. The piston assembly 64 includes an orifice plate 68, a valve body 70, an annular, resilient lip seal 72 and a washer 74. The orifice plate 68 is secured, e.g., by formed rivet 50, on the distal end of the reduced diameter shaft portion 60. The valve body 70 is mounted on the reduced diameter shaft portion 60, between the orifice plate 68 and an annular flange (or shoulder) 76, which is formed at the proximal end of the portion 60.

The valve body 70 includes an enlarged diameter portion 77, which is positioned adjacent to the shoulder 76, and a reduced diameter portion 78, which faces toward the orifice plate 68 (and the end 32 of the tube 28). The outer diameter

(OD) of the portion 77 is slightly less than the inner diameter (ID) of the tube so as to permit fluid flow therebetween.

A backing portion 80 is formed on the valve body 70 at the proximal end of the reduced diameter portion 78, that is, on the end of the portion 78 closest to the second end 34 of the tube 28. In the illustrated embodiment, the backing portion 80 is integrally formed with the valve body 70. It will be appreciated, however, that the backing portion 80 could be separately formed from the valve body 70, in which case the backing portion 80 would be mounted on the reduced diameter portion 78.

The lip seal 72 is mounted about the reduced diameter portion 78, adjacent to the backing portion 80. The washer 74 is mounted on the reduced diameter portion

78, between the lip seal 72 and the orifice plate 68. The lip seal 72 and the washer 74 are sized so that they can move relatively freely (or shuttle axially) along the reduced diameter portion 78, between the backing member 80 and the orifice plate 68. The OD of the backing portion 80 is less than the OD of the lip seal 72 so that when the seal 72 and backing portion 80 are in contact with each other, the backing portion 80 supports and reinforces a central portion 82 of the seal 72. The annular outer portion 84 of the seal 72 is flexible and includes an axially extending, radially outwardly extending lip 86. The lip portion 86 is angled towards the second end 34 of the tube. The outer surface of the lip portion 86 engages in sealing contact with the ID of the cylindrical tube 28. The backing portion 80 presents an angled surface 90 which engages against a mating angled surface 92 formed on the lip seal 72.

Figures 5 and 6 illustrate how the gas in the tubular cavity 36 may pass across both the piston assembly 64 when the shaft is moved in the extension direction

(Figure 5) and in the compression direction (Figure 6). Referring to Figure 5, when the shaft 42 is moved in the extension direction, i.e., to the left in Figure 5, the lip seal 72 shuttles axially away from contact with the backing portion 80 and into contact with the washer 74 so that gas can pass in the annular space between the ID of the seal 72 and OD of the reduced diameter portion 78 of the valve body 70. The relative dimensions of the orifice in the plate 68, the valve body 70, the lip seal 72 and the washer 74 determine the rate at which gas can be metered or passed across the assembly 64 when the piston is moved in the extension direction (i.e., to the left in Figure 5). When the piston is stopped at an intermediate position in the chamber, the shaft 42 and the valve body 70 will move a short distance in the compression direction until the lip seal 72 engages against the backing portion 80 of the valve body 70, thereby blocking the flow of gas between the lip seal and the valve body. The interface between the lip seal 72, the backing portion 80 and the ID of the tube 28 serve to prevent further movement in the compression direction (i.e., to maintain the piston in the intermediate position) until sufficient external force is exerted on the shaft 42 in the compression direction to overcome the pressure differential caused by the contact between the lip portion 86 of the seal 72 and the ID of the tube 28. The output force of the spring 20 is preferably matched to the specific application, e.g., the lift gate 22 in the illustrated embodiment, such that the spring 20 does not auto lift the lid 22 absent an external lifting force, e.g., from a person when a person applies a small external lifting force to the lid 22, the gas spring extends to assist in lifting the lid. When the person stops lifting the lid 22, the gas pressure, in combination with the lip seal, maintains the lid at that location.

As is shown in Figure 6, the piston assembly 64 can be moved in the compression direction (i.e., to the right in Figure 6) by exerting an external compression force on the shaft 42, e.g., by pushing down on the lift gate 22 in Figure

1, which is sufficient to create a large enough pressure differential across piston assembly 64 to bias (deform) the flexible lip 86 away from the ID of the tube 28 so that gas can flow between the lip seal 72 and the ID of the tube 28. The pressure differential created across the piston assembly 64 is determined by the geometry of the lip seal 72, the material properties of the lip seal 72, and the diameter and shape of the supporting backing portion 80. By increasing the OD of the backing portion 80, the lip portion 86 will stand higher pressures before deforming and bypassing due to a pressure differential. By reducing the OD of the backing portion 80, the lip portion 86 will deflect and bypass at a lower pressure differential. The use of the backing portion 80 with the lip seal 72 allows those working in this art to "tailor" the piston assembly 64 for individual gas spring applications.

The lip seal 72 may be made from a material that has a predictable force/pressure balance to counter a differential pressure applied across it. Such materials may include Nitrile, EPDM, elastomeric material, rubber, TPR, etc. Any material used for the seal 72 should provide a near absolute seal when the piston is stopped at an intermediate position within the tubular cavity 36.

While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the invention. For example, in the illustrated embodiment the piston assembly 64 may be reversed on the shaft 42 such that the intermediate stopping function may occur in the extension direction (to the left in Figure 6). In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from its scope. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.

Claims

1. In a gas spring adapted to be connected between a movable object and relatively fixed object and to be used to facilitate and control the movement of the movable object with respect to the relatively fixed object, where the gas spring includes: a tube that has a first closed end which is adapted to be connected with one of the movable objects or the relatively fixed object, a second end, and a tubular cavity which extends between the first and second ends of the tube and which is filled with gas under pressure and that has a longitudinal axis extending between the first and second ends, a shaft that has a first end and a second end which is adapted to be connected with the other of the movable object or the relatively fixed object, that has a longitudinal axis extending between the first and second ends of the shaft, and that is disposed, in part, in the tubular cavity so that the longitudinal axis of the tube and shaft are coaxial, so that the first end of the shaft is within the tubular cavity, so that the second end of the shaft is disposed outside of the tube, and so that the shaft may reciprocally move, selectively in one of a first axial direction or a second axial direction, through a preselected stroke, and with respect to the tube; a bushing assembly that is disposed adjacent to the second end of the tube and that provides a gas seal about the shaft as the shaft moves with respect to the tube; the improvement comprising: a piston assembly connected to first end of the shaft for movement within the tubular cavity between a first position proximal to the first end of the tube and a second position proximal the second end of the tube, the piston assembly comprising: a resilient lip seal having a central body portion and an annular lip portion which extends radially outwardly from the body portion and sealing engages with the inner diameter of the tubular cavity; a backing portion disposed adjacent to the body portion of the lip seal to support the body portion of the lip seal, the backing portion having an outer diameter which is less than the outer diameter of the lip seal; and wherein the outer diameter of the lip portion of the lip seal is selected so that when the shaft is moved in the first direction, the lip seal is capable of providing a gas seal between the outer diameter of the piston assembly and the inner diameter of a the tubular cavity at any point between the piston assembly first and second positions.

2. The gas spring of claim 1, wherein the lip seal is movable longitudinally, with respect to the piston assembly between a first position at which the lip seal is capable of providing a gas seal between the outer diameter of the piston assembly and the inner diameter of the tubular cavity, and a second position in which gas may pass longitudinally across the piston assembly without restriction from the lip seal.

3. The gas spring of claim 2, wherein the lip seal is moved to the first position when the shaft moves in the first direction; and wherein the lip seal is moved to the second position when the shaft moves in the second direction.

4. A gas spring connectable between a movable object and a relatively fixed object for assisting in moving the movable object between a first position and a second position, comprising: a cylinder having a closed end and an open end, the closed end connectable with either of the movable object or the relatively fixed object; a piston rod extending into the cylinder through the open end in a sealing relationship thereto for axial movement relative to the cylinder, the piston rod having an external end connectable with the other of the movable object or the relatively fixed object; a gas under pressure in the cylinder; a piston assembly carried by the piston rod for longitudinal movement within the cylinder, the piston rod and piston assembly being movable in a compression direction when the movable object is moved towards its first position and an extension direction when the movable object is moved towards its second position; and a resilient annular seal carried by the piston assembly, the seal having a flexible outer portion which is configured to provide a gas seal between the piston assembly and the cylinder sufficient to maintain the movable object at any point between its first and second positions.

5. The gas spring of claim 4, wherein the flexible outer portion of the seal is configured to be biased out of sealing engagement with the cylinder to allow gas to bypass between the piston assembly and the cylinder when an external force of a predetermined magnitude is exerted on the piston rod in one of the compression and extension directions.

6. The gas spring of claim 4, wherein the seal is movable longitudinally with respect to the piston assembly between a first position at which the seal is capable of providing a gas seal between the piston assembly and the cylinder, and a second position at which gas may pass across the piston assembly without restriction from the seal.

7. The gas spring of claim 6, wherein the seal is moved to the first position when the piston assembly moves in the extension direction; and wherein the seal is moved to the second position when the piston assembly moves in the compression direction.

8. The gas spring of claim 4, wherein the seal has a central body portion and wherein the flexible outer portion comprises an annular lip portion which extends radially outwardly from the body portion and sealing engages with the inner diameter of the cylinder.

9. The gas spring of claim 8, wherein the piston assembly further comprises a backing portion disposed adjacent to the body portion of the seal to support the body portion of the seal, the backing portion having an outer diameter which is less than the outer diameter of the lip portion so that the lip portion can flex inwardly relative to the inner diameter of the cylinder to allow gas to bypass between the piston assembly and the cylinder when an external force of a predetermined magnitude is exerted on the piston rod in one of the compression and extension directions.

10. A gas spring connectable between a movable object and a relatively fixed object for assisting in moving the movable object between a first position and a second position, comprising: a cylinder having a closed end and an open end, the closed end being configured for connection with either of the movable object or the relatively fixed object; a piston rod extending into the cylinder through the open end in a sealing relationship thereto for longitudinal movement relative to the cylinder, the piston rod having an external end connectable with either the other of the movable object or the relatively fixed object; a gas under pressure disposed in the cylinder; and a piston assembly carried by the piston rod for longitudinal movement within the cylinder in a compression direction when the movable object is moved towards its first position and an extension direction when the movable object is moved towards its second position; and means carried by the piston assembly for maintaining the movable object at a stopped position at any point between its first and second positions.

11. A gas spring as set forth in claim 10, wherein the means comprises a resilient seal having a central body portion and an annular lip portion which extends radially outwardly from the body portion and sealing engages with the inner diameter of the cylinder.

12. A gas spring as set forth in claim 11, wherein the means further comprises a backing member disposed adjacent to the body portion of the resilient seal to support the body portion of the resilient seal, the backing portion having an outer diameter which is less than the outer diameter of the resilient seal.