Rapid release mechanism with damping control

Abstract: A mechanism (10) for releasing pressurized fluid from a pressure vessel has rupture disk (22) sealing an opening in a pressure vessel, supporting means (125) for supporting the rupture disk, opening means (42) for selectively opening the rupture disk by removing the supporting means and, damping control means for damping the supporting means and also regulating the release of the high pressure fluid. To release pressurized fluid from the pressure vessel, the supporting means is removed out of supporting relationship with the rupture disk. Next the supporting means is moved along its axis without damping, then with damping and, finally, with relatively light damping.

Description: This invention pertains to the art of methods and apparatuses for use with high pressure fluid systems, and more specifically to a mechanism for use in releasing high pressure fluid from a pressure vessel. It is well known to require the rapid release of pressurized fluid from a pressure vessel in a controlled manner. A prime example is airbags and similar inflatable vehicle occupant restraints which need to release the pressurized fluid quickly and yet also have a requirement that at the very beginning of the discharge the release should be somewhat gentle. Other technologies may also have similar needs. For example safety relief valves for over pressure protection of the pressure vessel may have downstream piping which could be subject to damage from fluid hammer phenomena if the initial opening were instantaneous. EP-A-0134447 describes a valve for a high pressure fluid container. The valve includes a rupture disc for sealing the container. The disc is supported by a support which is held in place by a latch. The support is removed by pulling a trigger pin connected to the latch. Removal of the support results in the disk rupturing under pressure, allowing fluid from the container to flow out through the valve. According to the invention there is provided a mechanism for releasing pressurised fluid from a pressure vessel having an opening as set out in claim 1. Preferred embodiments of the invention are defined in the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a cutaway side view of the spin-and-drop release mechanism of this invention. Figure 2 is a cutaway side view showing the release mechanism after the rupture disk has been ruptured. Figure 3 is a cutaway side view showing the release mechanism in the midst of the highly damped descent stage. Figure 4 is a cutaway side view showing the release mechanism at the beginning of the lightly damped descent stage. Figure 5 is a cutaway side view showing the release mechanism in the midst of the lightly damped descent stage. Figure 6 is a perspective front view of the rotor used in this invention. Figure 7 is a top view of the rotor. Figure 8 is a front view of the rotor taken along the line 8-8 of Figure 7. Figure 9 is a side view of the rotor taken along the line 9-9 of Figure 7. Figure 10 is a perspective top-side view of the rotor and rotor holder of this invention. Figure 11 is a perspective bottom-side view of the rotor and rotor holder of this invention. Figure 12 is a perspective top-side view of the rotor and rotor holder of this invention. Figure 13 is a perspective bottom-side view of the rotor and rotor holder of this invention. Figure 14 is a cutaway side view of an alternate release mechanism embodiment. Figure 15 is an enlarged cutaway side view showing the release mechanism in the midst of the lightly damped descent stage. Figure 16 is a simplified top view Figure 17 is a cutaway side view of an alternate release mechanism embodiment. Figure 18 is a close-up side view of the rotor shown supporting the rupture disk. Figure 19 is a simplified side view that illustrates the surface area of an imaginary cylinder that the pressurized fluid at a second flow rate passes through. Figure 20 is a Pressure/Time graph showing how the pressure of the pressurized fluid inside the pressure vessel changes over time. Figure 21 is a close-up side view of the rotor shown supporting the rupture disk. Figure 22 is a close-up side view of the rotor shown supporting the rupture disk. Figure 23 is a side view of an alternate release mechanism embodiment taken along the line 23-23 of Figure 25. Figure 24 is a cutaway side view taken along the line 24-24 of Figure 23. Figure 25 is a cutaway bottom view taken along the line 25-25 of Figure 24. Figure 26 is a cutaway bottom view showing the protractor after its piston has been extended. Figure 27 is a close-up perspective view of the support member and pin used in the release mechanism of Figure 23. Figure 28 is a close-up cutaway side view of the release mechanism of Figure 23. Figure 29 is a cutaway side view of another spin-and-drop embodiment of this invention. Figure 30 is a close-up side view of the rotor . Figure 31 is a simplified top view that illustrates the exit flow area at the top of the variable bore. Figure 32 is a simplified top view. Figure 33 is a simplified top view. Figure 34 is a simplified top view. Figure 35 is a Pressure/Time graph showing how the pressure of the pressurized fluid inside the pressure vessel changes over time when a variable bore is used. DETAILED DESCRIPTION OF THE INVENTION Referring now to the drawings wherein the showings are for purposes of illustrating the invention only and not for purposes of limiting the same, Figures 1-5 show the release mechanism 10, herein after known as the spin-and-drop embodiment, of the present invention. This invention works with both compressible and non-compressible fluids over a very wide pressure and temperature range. Although the embodiments herein disclosed are directed to inflatable vehicle occupant restraints, this invention is applicable to fire suppression systems and other uses as well. To assist in explanation, the following discussion will be divided into the five primary stages used in the deployment of the release mechanism 10. The first stage, shown in Figure 1, is the support stage which is the position occurring during normal driving prior to the release of pressurized fluid 14. The second stage, which occurs between Figure 1 and Figure 2, is the removal of support stage. In this stage, rotor 20 is moved out of its supporting relation with rupture disk 22. Stage three, which also occurs between Figure 1 and Figure 2, is the free descent stage. This stage features the descent of rotor 20 wherein it free falls, i.e., nothing restricts or damps its descent. Figure 2 shows stage three at its completion. The fourth stage, which occurs between Figure 2 and Figure 4, is the highly damped descent stage. In this stage, the descent of rotor 20 is controlled or damped by damping substance 53. The damped motion of rotor 20 is used to regulate the release of pressurized fluid 14. The fifth and final stage, which occurs beginning with Figure 4, is the lightly damped descent stage. For this stage, the damping of the rotor's descent is reduced allowing the remaining pressurized fluid 14 to exit the release mechanism 10 more rapidly. Stage 1 - The Support Stage With reference to Figures 1 and 18, the release mechanism 10 is for use with a pressure vessel 12 which contains pressurized fluid 14. Pressure vessel 12 is generally cylindrical and necks down to a skirt 16 which has holes 17 for diffusing the pressurized fluid 14 into an airbag (not shown). The release mechanism 10 includes rotor holder 18 which holds rotor 20. Mounted across upper surface 19 of rotor holder 18 is rupture disk 22. Rupture disk 22, which is best seen in Figure 18, is a flat piece of foil or shim stock, since this is well suited to the present application and is the simplest and most inexpensive way to make a rupture disk. It should be noted that other known rupturable disk means chosen with sound engineering judgement can also be used in this invention. Since rupture disk 22 forms part of the pressure boundary against leakage of the pressurized fluid 14 while it is stored within pressure vessel 12, it is welded to rotor holder 18 by weld 23. Similarly, rotor holder 18 is fixedly attached to skirt 16 by a weld 25 which is a structural connection between rotor holder 18 and pressure vessel 12 and also forms part of the pressure boundary. With continuing reference to Figures 1 and 18, rupture disk 22 is relatively weak compared to the pressure of the pressurized fluid 14 which is sealed within pressure vessel 12. In other words, if it did not have some kind of support underneath it, rupture disk 22 by itself would be far too weak to withstand the pressure and would rupture spontaneously. This feature makes it possible to insure that the present invention will successfully open selectively even at pressures much lower than the maximum design pressure. When it is supported, on the other hand, rupture disk 22 maintains the integrity of the pressure boundary. In this embodiment, the rupture disk 22 is supported by rotor 20. With reference to Figure 1, release mechanism 10 also includes damper body 50 which is fixedly attached to skirt 16 by weld 24. Damper body 50 has first and second cylindrical bores 52, 69 which enable damper body 50 to operate as a cylinder as will be discussed further below. Within damper body 50, below lower end 32 of rotor 20, is a holding region 54 which is filled with a damping substance 53. For some applications such as airbags, the damping substance 53 is preferably a hydraulic fluid. In such cases various liquids that are incompressible or nearly incompressible chosen with sound engineering judgment can be used for the damping substance 53. An example is the petroleum-based hydraulic fluid typically used in automotive brake cylinders, whose properties have been found to be reasonably insensitive to changes in ambient temperature. For other applications, however, it may be desirable to place a compressible fluid within holding region 54. If, for example, the pressurized fluid 14 was carbon dioxide, it may be advantageous to use air as the damping substance 53. In general any fluid chosen with sound engineering judgment could be used for the damping substance 53. The bottom of damper body 50 is closed off by closure plate 59 which is shown as a separate part attached to either damper body 50 or skirt 16, although it could be made integral with damper body 50. With reference now to Figures 1, 10-13 and 18, rotor holder 18 has, as best seen in Figure 18, a first cylindrical bore 26 having a diameter D1 which is preferably concentric with outer surface 21 of rotor holder 18. Disposed farther from rupture disk 22, rotor holder 18 has a second cylindrical bore 28 which is concentric with first cylindrical bore 26 and has a diameter D2 which is preferably larger than diameter D1. The axial positions of first and second cylindrical bores 26, 28 are parameters which are important in determining damping characteristics as will be discussed further below. With reference to Figures 1 and 6-13, rotor 20 has upper surface 30 which in this embodiment is generally round and contacts the bottom portion of ruptures disk 22, supporting it against the pressure of the pressurized fluid 14. The rotor 20 has first and second arms 29, 31 that extend out from its axis. Preferably first and second arms 29, 31 are substantially perpendicular to the axis of the rotor. It may also be desirable, however, to position first and second arms 29, 31 at angles that are not perpendicular to the axis of rotor 20. In this preferred embodiment, first and second arms 29, 31 are spaced in the range of 90° to 180° apart from each other. They are shown 180° apart from each other in the Figures. First and second arms 29, 31 are received by first and second ears 33, 35. The pressurized fluid 14 exerts a pressure force 13 on the relatively flimsy rupture disk 22 and in turn the pressure force 13 is placed on the upper surface 30 of rotor 20. This pressure force 13 is then carried by first and second arms 29, 31 to first and second ears 33, 35 of rotor holder 18 which are best seen in Figure 12. It may be desirable to measure or monitor this pressure force 13 because it is generally necessary in the airbag industry to have a means for measuring the pressure of the pressurized fluid 14 in the pressure vessel 12 so as to detect possible leakage over the life of a vehicle (not shown) and the pressure force 13 can be used, as is commonly known in the art, to determine this pressure. There are many places and means, chosen with sound engineering judgment, for measuring the pressure force 13. The two principal measuring means for use in this preferred embodiment are (1) measuring the deformation of the solid metal such as by bending, which could be measured with a strain gage; and (2) measuring the force transferred from the rotor to the ears by means of a force-sensing pad 80 placed between them. It should be noted that measuring the pressure of the pressurized fluid 14 may also involve measuring its temperature, since the pressure is temperature-dependent. The numbers of arms and ears could be greater than two but for practical purposes two is the minimum and probably most convenient so that is what is used in this preferred embodiment. Preferably, whenever a plurality of arms and ears are used their geometry will assure that upon actuation all of the arms fall off all of the ears at substantially the same angular position. Of course it may be desirable to arrange the arms and ears such that the arms fall off the ears one at a time i.e., at different angular positions. As explained above, rotor holder 18 is structurally connected to pressure vessel 12 and thus the force caused by the pressurized fluid 14 is fully supported. Rotor 20 also has a lower end 32 which operates like a piston and will be discussed further below. For this reason rotor 20 can be considered to be a piston. With reference to Figures 6 and 10-11, an important characteristic of first and second arms 29, 31 and first and second ears 33, 35 is that their surfaces, which are in contact with each other, preferably lie on a plane 38 which is perpendicular to the axis 40 of rotation of rotor 20 which also coincides with the principal axis of rotor support 18. It should be noted however, as discussed above, first and second arms 29, 31 may be positioned at angles not perpendicular to the axis of rotor 20. In that case, the surfaces of first and second arms 29, 31 may not lie on a plane perpendicular to the axis of rotor 20 and, in fact, may not lie on a plane at all. When they do lie on plane 38 the only force against which the protractor 42 must work is the friction due to the load on the rupture disk 22. Prior to the actuation of protractor 42, first and second arms 29, 31 will simply remain seated against first and second ears 33, 35. It can also be appreciated that rotor holder 18 can be machined fairly simply from cylindrical stock (not shown) by passing a milling cutter (not shown) having a T shape all the way across the piece. That would leave a continuous ear (not shown) across the piece from one side to the other on both sides of the cutter. As shown here the only portions of the continuous ear that remain are first and second ears 33, 35. The removal of the missing material could be accomplished by a standard milling cutter. It is not absolutely necessary to remove this material to shape the ears as shown, but if the missing material were to remain there might be a chance of that material interfering with the descent of rotor 20 which will be explained below. With reference now to Figures 1 and 12-13, selective actuation of release mechanism 10 is achieved by actuation means which is preferably a piston actuator such as protractor 42. Other actuation means such as electromagnetic or pneumatic devices are also possible. These other actuation means may be especially suited to applications other than for airbags. A piston actuator, also called a pressurized fluid motor or protractor, contains a small quantity of explosive material which is ignited by an electrical signal through a bridge wire (miniature resistive heater wire) in contact with the explosive material. The explosive material is enclosed within the body 44 of the protractor 42. The protractor 42 has electrical contact means 48 for receiving an electrical control signal which selectively ignites the explosive material. When the explosive material ignites, it generates a large pressure inside the body 44 of the protractor 42 which pushes piston 46 outward until it reaches a stop. This motion of piston 46 can be used for mechanical work such as pushing or puncturing objects. The products of combustion are contained inside the body 44 of the protractor 42 and have no escape path. This means that the protractor 42 releases nothing to the environment and is totally clean and self-contained. In order to maintain the contents of the protractor 42 after deployment to a range that can reasonably be contained inside the body 44, the amount of explosive in the protractor 42 and thus the mechanical work produced by the protractor 42 must be limited to fairly modest magnitudes. However, an advantage of such a device is that because of the retention of the combustion products inside the body 44 and because the amount of explosive that is present is small, frequently such a device can be classified for shipping and handling purposes as a non-explosive or non-pyrotechnic mechanism. This reduces the expense and the necessary precautions for shipping and handling. In addition, of course, there is no combustion product added to the pressurized fluid 14 exiting the release mechanism 10, making the release mechanism 10 totally clean and free of combustion products. Piston actuators are commercially available. The proper size and type of piston actuator is selected by sound engineering judgement depending on the use for the release mechanism 10. The preferred protractor 42 for this embodiment is available from ICI Nobel's Explosives of Ayrshire, Scotland. Though preferred, it is not essential that a self-contained protractor 42 be used in this invention. A piston actuator, such as protractor 42, does have expense, complexity and extra parts associated with keeping the combustion products contained inside its body 44. Similar explosive devices are also commercially available in which the explosion is not contained or confined. Such non-contained devices are often referred to as squibs. If a mechanical object is positioned close to the point of explosion of a squib, significant force will still be exerted on the object during the brief period in which the explosion takes place, even though the explosion is non-contained. The combustion products from the explosion would then mix with the pressurized fluid 14 stored inside pressure vessel 12 as it exits. Accordingly, it would be possible to have a similar design in which an non-contained explosive device is pointed at an arm, such as second arm 31, causing it to move upon explosion. This type of design would save some amount of cost and complexity represented by certain internal parts of the piston actuator such as piston, cylinder, and O-ring. Dimensionally, it would be shorter than protractor 42 which would also provide more design freedom in positioning the device along the axial direction of the release mechanism 10, thereby resulting in a slight shortening of the overall length. With reference to Figures 1 and 20, each of the five stages will be discussed with reference to Pressure/Time graph 100 which has a time axis 102 where the time value begins at zero at point 101 and increases in direction 103 and a pressure axis 104 where the pressure value begins at zero at point 101 and increases in direction 105. Curve 107 shows directionally how the pressure of pressurized fluid 14 inside pressure vessel 12 changes over time and curve 109 shows directionally how the pressure inside a closed receiving tank (not shown but used to receive pressurized fluid 14 in testing the release mechanism 10) changes over time. It should be noted that the scales of pressure for the curves 107, 109 are different. Typically, the receiving tank (not shown) is much bigger than the pressure vessel 12. Thus, the scale of pressure in the receiving tank (not shown) is much smaller. In one experimental case, for example, the final pressure value in the receiving tank was 3.1 Bars and the initial pressure value in the pressure vessel 12 was 413 Bars. In that case, the scales of pressure differed by a factor of slightly more than 100. Therefore, Pressure/Time graph 100 is directionally accurate and illustrates well the operation of release mechanism 10 but it does not reflect a common pressure scale. Curves 107, 109 illustrate the damping occurring with release mechanism 10. The first stage, the support stage, occurs between points 101, 111 along the time axis 102. Note that the pressure inside pressure vessel 12 remains at its maximum value, shown at point 108, while the pressure in the receiving tank (not shown) remains at its minimum value, zero, during this first stage. The time interval between points 101, 111 is essentially only the time required for the protractor 42 to actuate, which for airbag applications must be at most several milliseconds. Stage 2 - The Removal of Support Stage With reference now to Figures 1-2, 6-13 and 18, when it is desired to release the pressurized fluid 14 from the pressure vessel 12, rotor 20 must be removed from its supporting relation with rupture disk 22. To initiate this action, an electric signal is selectively sent through electrical contact means 48 which causes the explosive material within body 44 of protractor 42 to ignite. This ignition extends piston 46 which pushes on first arm 31 of the rotor 20 in direction 47 which is approximately perpendicular to the principal direction of first arm 31 so as to cause rotation of rotor 20 around axis 40 in direction 36. The dimensions of first and second arms 29, 31 and first and second ears 33, 35 are such that rotation of rotor 20 through a predetermined angular rotation, that is preferably in the range of 10° to 30°, is sufficient to move first and second arms 29, 31 out of first and second ears 33, 35 thus causing first and second arms 29, 31 to become completely unsupported. Other dimensions and angular rotations chosen with sound engineering judgement are also possible. The rotor 20 has an upper end 34 having an exterior cylindrical surface 37 which is located, at this stage, inside first cylindrical bore 26. Similarly the exterior cylindrical surface 39 of the lower end 32 of rotor 20 is located inside first cylindrical bore 52 of damper body 50. Both of these cylinder-to-bore interfaces provide a guidance and restraining action which approximate a journal bearing as rotor 20 is rotated. As soon as rotor 20 has rotated through a sufficient angle, first and second arms 29, 31 no longer rest on first and second ears 33, 35 of rotor holder 18. This leaves rotor 20 no longer supported and the pressure of pressurized fluid 14, acting through the relatively weak rupture disk 22, will cause the rupture disk 22 to rupture and will subsequently cause rotor 20 to move in a downward direction 41. With reference to Figures 1-2 and 20, the second stage, the removal of support stage, occurs instantaneously at point 111 on the time axis 102. Thus, at the moment the rotor 20 is removed from supporting rupture disk 22, the pressure inside pressure vessel 12 remains at its maximum value, shown at point 108, while the pressure in the receiving tank (not shown) remains at its minimum value, zero. Stage 3 - The Free Descent Stage With reference now to Figures 1-2, 6-13 and 18, when first and second arms 29, 31 fall off of first and second ears 33, 35, it is helpful to have a relatively small distance (typically about 0.75 mm) of free drop or free descent for the rotor 20 in which little or no damping is exerted on it. This ensures that rupture disk 22 ruptures cleanly and as soon as support has been lost. As lower end 32 of rotor 20 descends, it combines with first cylindrical bore 52 of damper body 50 to form a piston-cylinder combination. The free descent can be accomplished by providing a compressible material of known volume in the damping substance 53 within holding region 54, provided that the damping substance 53 is a liquid, i.e. nearly incompressible. The compressible material is preferably a bubble of air 56 sized according to the desired time interval for the free descent stage. Other compressible materials, chosen with sound engineering judgment could also be used. The bubble of air 56 is extremely compressible compared to the damping substance 53, and given the large storage pressures anticipated within pressure vessel 12, whenever rotor 20 is forced in downward direction 41 the bubble of air 56 will compress to essentially zero volume and provide essentially a free descent for rotor 20 until then. With reference to Figures 1-2 and 6-14, an alternate way of providing the free descent is to replace the current rotor 20 with two parts having a gap between them. This is shown in Figure 14 which shows release mechanism 60 which is also a spin-and-drop embodiment and includes rotor 61 and piston 62 which are separated by a distance X1. In this embodiment the rotor 61 would have to fall, in a literal free fall, a distance X1 before contacting piston 62 and initiating damping. In the preferred embodiment shown in Figures 1-2, however, to simplify and minimize the number of parts, rotor 20, a single part, has a lower end 32 which operates like a piston. This piston action will be discussed below. With reference now to Figures 1-2, 6, 8, 15-16 and 18, during the time of free descent, an annular first gap G1, seen in Figure 18, exists between the exterior cylindrical surface 37 of upper end 34 of rotor 20 (which has a diameter D3) and the first cylindrical bore 26 of rotor holder 18 (which has a diameter D1). To help visualize first annular gap G1, Figure 16 shows a simplified top view that illustrates upper surface 30 of rotor 20 which has first circle C1 as an outer edge, first cylindrical bore 26 which has second circle C2 as an outer edge, and second cylindrical bore 28 which has third circle C3 as an outer edge. Annular first gap G1 is the smallest gap between exterior cylindrical surface 37 and any bore of rotor holder 18. This closeness of rotor 20 to rotor holder 18 helps to minimize the unsupported area of rupture disk 22 during conditions of pressurized fluid 14 storage. During the time of free descent, pressurized fluid 14 would be exposed to the area within second circle C2 including the area of first circle C1. Since rotor 20 is now unsupported, it would complete its free descent very quickly. With reference to Figures 1-2 and 20, the third stage, the free descent stage, occurs almost instantaneously when the rotor is removed from supporting rupture disk 22. Thus the third stage, like the second stage, is shown as occurring at point 111 on the time axis 102. For practical purposes, it is after the free descent stage that the pressure inside pressure vessel 12 and the pressure in the receiving tank (not shown) change from their initial values, maximum and zero respectively. Stage 4 - The Highly Damped Descent Stage With reference now to Figures 2-4, for applications such as automotive airbag inflators, the storage pressures of the pressurized fluid 14 (typically several hundred Bars), are such that the unsupported rotor 20 would move in downward direction 41 the full extent of its travel in well under one millisecond if there were no damping control mechanism. While it is desirable to have pressurized fluid 14 begin to flow as quickly as possible after the deployment signal, it is not desirable to have the exit flow area open fully in a fraction of a millisecond. Instead, the output flow rate of the pressurized fluid 14 must be pulse-shaped in order to provide a controlled unfolding of the associated airbag (not shown) and to lessen the impact of the airbag on a passenger who might possibly be seated too close to the inflator. It is desired to have a more gentle flow rate, which occurs during the highly damped stage, for the first ten milliseconds or so and then a more rapid flow rate, which occurs during the lightly damped stage, for the rest of the time of airbag inflation. The value 10 milliseconds is typical of passenger side airbag inflators. This can be done by damping control means which in this preferred embodiment is achieved by mechanically controlling the rate of descent of rotor 20 and thereby also controlling the exit flow area for the pressurized fluid 14. This will now be described. With reference to Figures 2-4, 15-16 and 18, when rotor 20 completes its free descent in the downward direction 41, the highly damped stage begins, as shown in Figure 2, when lower end 32 begins to push damping substance 53 out of holding region 54 through first bleed hole 58. Meanwhile, as seen in Figure 3, pressurized fluid 14 begins to flow out of pressure vessel 12 at a first flow rate R1. First flow rate R1 is relatively gentle because pressurized fluid 14 can only flow through first area A1 which is the exit flow area available for pressurized fluid 14 during the highly damped descent of rotor 20. As best seen in Figures 16, 18, second annular gap G2 helps to define first area A1 (the shaded annular portion in Figure 16) and is larger than first annular gap G1. As mentioned above, third circle C3 represents the outer edge of second cylindrical bore 28. Second annular gap G2 also helps to insure that the edges of the now ruptured rupture disk 22 (shown in Figure 1) do not form a wiper seal against first cylindrical bore 26. With reference now to Figures 3-4 and 15, when the damping substance 53 is pushed out through first bleed hole 58, it enters first collecting region 55. The purpose of first collecting region 55 is simply to retain damping substance 53 and prevent it from escaping, thereby for example, avoiding contamination of the exiting pressurized fluid 14 by entrainment of damping substance 53. First collecting region 55 is bordered by a groove 51 in the outer surface 67 of damper body 50 together with the interior surface 15 of skirt 16. During the highly damped descent stage then, first damping substance flow path 66 is the flow path of the damping substance 53 from holding region 54 through first bleed hole 58 and into first collecting region 55. With reference to Figures 2-4, 6 and 10-11, the area of surface 64 which is the bottom surface of lower end 32 is substantially the same as the area of upper surface 30 which is the surface of rotor 20 used to support rupture disk 22. For this reason the peak pressure in the damping substance 53 within holding region 54 will be approximately the same as the peak pressure of pressurized fluid 14. These two areas, of surface 64 and upper surface 30, may be varied with sound engineering judgement realizing that the pressure exerted on the damping substance 53 varies approximately by the ratio of the two areas as is commonly known in the art. With reference now to Figures 3-5, 8-9 and 15, during all the five primary stages used in the deployment of release mechanism 10, it is necessary to prevent leakage of the damping substance 53 into the exiting pressurized fluid 14. For this reason sealing means such as slidable sealing O-ring 63 is provided to seal off holding region 54 from the holes 17 in the skirt 16 of the pressure vessel 12 during the first 4 primary stages. The sealing means for the fifth primary stage will be discussed below. Slidable sealing O-ring 63 is positioned in groove 68 which is located in the lower end 32 of rotor 20. Other methods for sealing means chosen with sound engineering judgement, such as a wiper seal are also possible. Fluid retention O-ring 65 is positioned in groove 51 on the outer surface 67 of damper body 50. Fluid retention O-ring 65 serves as a sealing means to cover first bleed hole 58 prior to the release of pressurized fluid 14 so that the damping substance 53 stays inside holding region 54. During the release of pressurized fluid 14, however, rotor 20 will transmit relatively high pressure to damping substance 53. Such relatively high pressure will cause fluid retention O-ring 65 to be easily moved out of the way, allowing damping substance 53 to exit through first bleed hole 58. There are also other sealing means chosen with sound engineering judgement that could take the place of fluid retention O-ring 65. With reference to Figures 3-4 and 17, a recent trend within the airbag industry is toward the use of intelligent occupant restraint systems which will continuously sense variables such as the weight of the occupant, the position of the occupant, the speed of a crash, and the presence and position of an infant car seat, and will adjust the airbag characteristics accordingly. Thus, it should be appreciated that the damping characteristics of rotor 20, and therefore the regulating characteristics of the release of pressurized fluid 14, are significantly affected by the flow area and orientation of first bleed hole 58. In this embodiment bleed hole 58 is radially oriented but it should be noted that the orientation can be varied using sound engineering judgement. Since first bleed hole 58 is outside the pressure boundary of the stored pressurized fluid 14, it is very accessible for adjustment. If the flow area of first bleed hole 58 is relatively large (typically a bleed hole will have a diameter of about 0.5 mm), the duration of the gentle flow rate of pressurized fluid 14, which in this embodiment is first flow rate R1, will be relatively brief. If, on the other hand, the flow area of first bleed hole 58 is smaller, the duration of first flow rate R1 will be relatively longer. Accordingly, by using adjusting means to adjust the flow area of first bleed hole 58, the damping characteristics of release mechanism 10 can be varied. Alternatively, as shown in Figure 17, a release mechanism 90 can have first and second bleed holes 91, 92 to adjust the damping characteristics. In this embodiment when the most rapid descent of rotor 94 is desired, first and second bleed holes 91, 92 are selectively opened in combination. If less rapid descent is desired, only one bleed hole, for example first bleed hole 91, is selectively opened. Thus release mechanism 90 provides a step-wise adjustability of the damping. Of course any number of bleed holes chosen with sound engineering judgement could be used for damping control. The devices used for adjusting means could be of any type currently known in the art such as stepper motors, solenoids, metering pins or needle valves. All such devices can be used to provide a means of intelligently adjusting the damping characteristics. With reference to Figures 2-4, 20, the fourth stage, the highly damped descent stage, occurs between points 111, 113 along the time axis 102. Note that the pressure inside pressure vessel 12 gradually decreases while the pressure in the receiving tank (not shown) gradually increases during this stage. These relatively gradual changes in pressure demonstrate that the pressurized fluid 14 is being released at a relatively slower flow rate thereby achieving the gentle early portion of a pulse-shaped discharge. In another embodiment, with reference to Figures 29-35, release mechanism 134 which includes rotor 95 and rotor holder 98 provides more variation during the highly damped descent stage by replacing the second cylindrical bore 28 (shown in Figures 1, 18 and 21-22) of previous embodiments with variable bore 135. With this arrangement second annular gap G2 (shown in Figures 18 and 21-22) is replaced with variable gap G3 which is the radial distance between variable bore 135 and the top 118 of rotor 95. Rotor 95 has a diameter D10. Preferably variable bore 135 has a slightly tapered cone-shape and increases in diameter in downward direction 99. Thus, at the top 136 of variable bore 135 diameter M1 provides an exit flow area E1 (the shaded area shown in Figure 31) between the top 118 of rotor 95 and rotor holder 98 for the pressurized fluid 97 to escape pressure vessel 119. As the rotor 95 descends in downward direction 99, variable gap G3 continues to increase as does the varying exit flow area. At mid-section 137 diameter M2 provides an exit flow area E2 (the shaded area shown in Figure 32) which is larger than E1. As the rotor 95 descends to the bottom 138 of variable bore 135, variable gap G3 increases still further as does the varying exit flow area. Diameter M3 provides an exit flow area E3 (the shaded area shown in Figure 33) which is larger than both E1 and E2. To help visualize the variation in diameter, Figure 34 is a simplified top view that illustrates the following: upper surface 96 of rotor 95 which has first circle L1 as an outer edge and a diameter D10, first cylindrical bore 117 which has second circle L2 as an outer edge and a diameter D11, the top 136 of variable bore 135 which has a third circle L3 as an outer edge and diameter M1, the mid-section 137 of variable bore 135 which has a fourth circle L4 as an outer edge and diameter M2 and, the bottom 138 of variable bore 135 which has a fifth circle L5 as an outer edge and diameter M3. The use of variable bore 135 means that the pressurized fluid 97 flows out of pressure vessel 119 through an opened varying exit flow area at a variable flow rate R3 during this stage. The associated pressure verses time relationship is shown in Pressure/Time graph 139 which is similar in scale values to Pressure/Time graph 100. The highly damped descent stage occurs between points 154 and 156. Note that now the pressure inside pressure vessel 119, shown by curve 158 decreases in a non-linear fashion for this stage. Of course other variable bore designs chosen with sound engineering judgment could also be used for this invention. Stage 5 - The Lightly Damped Descent Stage With reference now to Figures 4-6, 12, 15, 19, after a certain time of highly damped descent when the pressurized fluid 14 exits at a first flow rate R1 (shown in Figure 3), it is desirable that the exit flow area open to a second area A2 which is larger than first area A1 to let the rest of the pressurized fluid 14 exit at second flow rate R2 which is much more rapid. To accomplish this it is necessary to significantly reduce the damping on rotor 20. Otherwise, rotor 20 might never get pushed down as far as necessary or this would only happen very late in the transient. The reduction in damping is achieved in this embodiment by the opening of damping substance passageway 70. This is accomplished when slidable sealing O-ring 63 descends to the position where it loses contact with the first cylindrical bore 52 and enters second cylindrical bore 69 of damper body 50. Second cylindrical bore 69 has a larger diameter, in this preferred embodiment, than first cylindrical bore 52, which permits damping substance 53 to flow around the lower end 32 of rotor 20 and enter second collecting region 57. Figure 4 shows slidable sealing O-ring 63 just prior to its losing contact with first cylindrical bore 52 while Figure 5 shows it after it has lost contact. During this lightly damped descent stage slidable sealing O-ring 63 does not function as a seal. Instead, the sealing of the damping substance 53 is accomplished by the close clearance between ridge 73 and the first cylindrical bore 52 of damper body 50. The time required for rotor 20 to descend from its position at the beginning of this stage, shown in Figure 4, to its final position where it remains for the rest of this stage, shown in Figure 5, is so short that this descent can be thought of as happening instantaneously. Simultaneous with the descent of sealing O-ring 63 out of contact with first cylindrical bore 52, the upper surface 30 of rotor 20 descends into region 72 of rotor holder 18 in which first and second ears 33, 35 have been machined. This allows the pressurized fluid 14 to exit pressure vessel 12 at a second flow rate R2. Second flow rate R2 is substantially greater than first flow rate R1 because the corresponding exit flow area, second area A2, is substantially increased. As best seen in Figure 5, the pressurized fluid 14 flowing at second flow rate R2 passes through first and second cylindrical bores 26, 28, contacts the upper surface 30 of rotor 20, makes 90° turns to go radially outward in all directions, then turns downward and exits through holes 17. The minimum or controlling exit flow area in this case is the surface area of an imaginary cylinder 78 that pressurized fluid 14 passes through as it makes its 90° turn. The imaginary cylinder 78, as best seen in Figure 19, has dimensions based on the diameter D2 of second cylindrical bore 28 and the distance H1, shown in Figure 15, between the upper end 34 of rotor 20 and the bottom 27 of second cylindrical bore 28. Thus, imaginary cylinder 78 provides second area A2 as the exit flow area for pressurized fluid 14 and second flow rate R2 as the corresponding flow rate. With reference to Figures 5, 8-9, 15, after damping substance passageway 70 opens up, the damping substance can still flow through first damping substance flow path 66 but now there is also a second fluid path (damping substance passageway 70) of much larger area for the damping substance to flow through. Second collecting region 57 is bordered by the recess 71 in the rotor 20 just above slidable sealing O-ring 63 and first cylindrical bore 52 of the damper body 50. It should be noted that recess 71 has an upper edge formed from ridge 73 on rotor 20 that enters first cylindrical bore 52 just as slidable sealing O-ring 63 descends to the position where it loses contact with first cylindrical bore 52. Ridge 73 extends circumferentially around rotor 20. Opening up damping substance passageway 70, which had previously been unavailable, is a way of providing a drastic decrease in the damping, which is desired. With reference to Figures 4-5, 20, the fifth stage, the lightly damped descent stage, occurs between points 113, 115 along the time axis 102. Point 115 represents the end of the release of pressurized fluid 14 as at this point the pressure inside pressure vessel 12 is substantially zero. Note that the pressure inside pressure vessel 12 in this stage decreases rapidly while the pressure in the receiving tank (not shown) likewise increases rapidly. These relatively rapid changes in pressure demonstrate that the pressurized fluid 114 is only slightly controlled or regulated as it is released. It should be noted that the results of release mechanism 10 shown in Pressure/Time graph 100 have been experimentally shown to be very repeatable. Self-Relieving Means With reference now to Figures 1, 16, 21, another feature generally necessary in the airbag industry is an automatic means of self-relieving the pressurized fluid 14 in pressure vessel 12 should the pressure become too large. An underlying principle of release mechanism 10, as mentioned above, is that rupture disk 22 is weak compared to the pressure of pressurized fluid 14 such that if rupture disk 22 was entirely unsupported it would burst at a pressure far below the operating pressure. As discussed above and shown from a top view in Figure 16, annular first gap G1 is located outside of rotor 20 between the exterior cylindrical surface 37 of upper end 34 (which has a diameter D3) and the first cylindrical bore 26 of rotor holder 18 (which has a diameter D1). Thus, there is an unsupported region 81 of rupture disk 22 which is relatively small and of annular shape. In extreme close-up, shown in Figure 21, it can be expected that under normal conditions there will be a slight bulging out of unsupported region 81, providing an annular-shaped rupture disk. This small unsupported region 81 of rupture disk 22 will have a spontaneous rupture pressure. Thus, by designing with sound engineering judgment specific combinations of important variables including, the dimension of unsupported region 81 (typically on the order of a few millimeters on the diameter), the thickness of rupture disk 22 (also typically on the order of a few millimeters), the material used to make rupture disk 22, and the internal pressure of pressurized fluid 14 inside pressure vessel 12, the spontaneous rupture pressure of unsupported region 81 can be made to be a desired value. In this way, unsupported region 81 can be used for overpressure self-relief. With reference now to Figures 1, 22, another way to provide automatic means for self-relieving the pressurized fluid 14 in pressure vessel 12 is to create a cavity 82, as seen in Figure 22, in the top of rotor 20. This cavity 82, which preferably is a relatively small cylindrical bore centrally located with rounded edges 84, creates an unsupported region 83 of rupture disk 22 over the cavity 82. In extreme close-up, shown in Figure 22, it can be expected that under normal conditions there will be a slight bulging out of unsupported region 83, providing a circular-shaped rupture disk. This small unsupported region 83 of rupture disk 22 will have a spontaneous rupture pressure. A flow exit path 79 which connects cavity 82 with the exterior region of rotor 20 could be provided if necessary to help pressurized fluid 14 flow to the exterior once unsupported region 83 has ruptured due to overpressure. It should be noted that the strength of rupture disk 22 in a circular geometry, as shown, is related to the ratio of its diameter to its thickness. Thus, it is quite reasonable that unsupported region 83 can be suitably dimensioned to withstand the normal storage pressure of pressurized fluid 14. With reference to Figure 1, for a sealed vessel such as pressure vessel 12, generally the only cause that leads to the need for self-relieving means is exposure of the pressurized fluid 14 to excessive temperature. Accordingly, although this is slightly less direct than the self-relieving means by overpressure explained above, another way to achieve self-relief is to automatically relieve the pressurized fluid 14 when the release mechanism 10 reaches a predetermined elevated temperature. As explained above, the protractor 42 used to selectively actuate release mechanism 10 contains a small quantity of explosive material. This explosive material has a characteristic auto-ignition temperature. Thus, when the release mechanism 10 reaches this auto-ignition temperature, the explosive material ignites releasing the pressurized fluid 14. Alternatively, suitable additives could be added to the explosive material such that its auto-ignition temperature can be adjusted to any predetermined value chosen with sound engineering judgement. Major Embodiment #2 With reference now to Figures 23-28, release mechanism 120, herein after known as the pin-and-drop embodiment, has many features in common with release mechanism 10, the spin-and-drop embodiment (shown in Figure 1). Release mechanism 120 is for use with a pressure vessel 121 which contains pressurized fluid 122. Pressure vessel 121 is generally cylindrical and necks down to a skirt 123 which has holes 124 for diffusing the pressurized fluid 122 into an airbag (not shown). The release mechanism 120 includes support member 125 which is a supporting means that supports rupture disk 126 but, unlike release mechanism 10, it does not have any rotational motion. The only motion of support member 125 is that it drops, or descends, along its axis 127 in direction 128. Support member 125 has an upper end 140 which contacts and supports rupture disk 126, a lower end 141 which operates like a piston, and a groove 142 around its circumference which receives pin 144. As is best seen in Figure 27, pin 144 which holds support member 125 in place, has a substantially cylindrical cross-section enabling it to fit within groove 142 of support member 125. Pin 144 is slidably positioned within channel 145 which is positioned in skirt 123. With continuing reference to Figures 23-28, release mechanism 120 operates in much the same manner as release mechanism 10 (shown in Figure 1) discussed above except that when protractor 146 extends piston 147, piston 147 slides pin 144 along channel 145 until support member 125 is no longer supported by pin 144. It should be noted that the alignment of piston 147 and pin 144 is off-center. By off-center it is meant that the longitudinal axis of piston 147 and the longitudinal axis of pin 144 are parallel but not precisely co-linear. This is illustrated in Figure 28 which shows the contact area 148 on pin 144 where piston 147 contacts pin 144 when activated. It can be clearly seen that contact area 148 is not concentric with pin 144. This off-center alignment is done so that when piston 147 is extended it does not interfere with the motion of support member 125. Once support member 125 is no longer supported by pin 144, it drops in direction 128, thus removing the support from rupture disk 126 allowing rupture disk 126 to rupture and begin releasing pressurized fluid 122 from pressure vessel 121. Similar to release mechanism 10 (shown in Figure 1), once support member 125 descends through a free descent stage, its lower end 141 contacts damping substance 150 located in holding region 151 where the continued descent of support member 125 is damped.

Claims: A mechanism (10) for releasing pressurized fluid from a pressure vessel having an opening, the mechanism comprising: a rupture disk (22) for sealing the opening of the pressure vessel; supporting means (125) for supporting said rupture disk; opening means (42) for selectively opening said rupture disk, said opening means selectively removing said supporting means; and, damping control means (50, 53) for damping motion of said supporting means, characterised in that said damping control means are configured such that the damping of the motion of said supporting means also regulates the release of pressurized fluid. The mechanism (10) of claim 1 wherein said supporting means (125) comprises a rotor (20) selectively rotatable about its axis, said rotor selectively moveable along its axis. The mechanism (10) of claim 2 wherein said rotor (20) has a lower end which operates like a piston. The mechanism (10) of claim 2 wherein said opening means (42) comprises actuation means (42), said actuation means selectively rotating said rotor (20). The mechanism (10) of claim 2 wherein said opening means (42) comprises a non-contained explosive device. The mechanism (10) of claim 1 wherein said damping control means comprises a damping substance (53), said damping substance damping the motion of said supporting means (125). The mechanism (10) of claim 6 wherein said damping control means further comprises: a damper body (50) having a cylinder with a cylindrical bore (26), said cylinder receiving said supporting means (125); a first collecting region (55) for collecting said damping substance (53); and, a first bleed hole (91), said first bleed hole connecting said cylinder to said first collecting region (55), said damping substance selectively flowable through said first bleed hole. The mechanism (10) of claim 6 wherein the pressure vessel and said damper body (50) form the boundaries of said first collecting region (55). The mechanism (10) of claim 6 wherein said damping control means further comprises: adjusting means for selectively adjusting the flow area of said first bleed hole (91). The mechanism (10) of claim 6 wherein said damping control means further comprises: a second bleed hole (92), said second bleed hole connecting said cylinder to said first collecting region (55), said damping substance (53) selectively flowable through said second bleed hole, said first and second bleed holes being selectively openable.

Inventors: DOSCH MICHAEL, MAHON GEOFFREY LAWRENCE, MATERNA PETER, MOAKES RICHARD, SOEMER JOHN, DOSCH, MICHAEL, MAHON, GEOFFREY LAWRENCE, MATERNA, PETER, MOAKES, RICHARD, SOEMER, JOHN
Applicants: BREED AUTOMOTIVE TECH, BREED AUTOMOTIVE TECHNOLOGY, INC.
Application year: 1998
Main classification: F16K31
IPC codes: F16K17, B60R21, F16K31, F17C13