# Patent

## Title
Pressurized actuator

## Abstract

A linear actuator contains a housing having a first end and a second end. A hollow piston is positioned within the housing to slidably engage with an inner wall of the housing. A sealed gas chamber is formed within the hollow piston and contains stored gas for driving the piston upon activation of the actuator.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of U.S. Provisional Application Ser. No. 61/864,955 filed on Aug. 12, 2013.


TECHNICAL FIELD
The present invention relates generally to gas generating systems, and to an improved linear actuator.
BACKGROUND OF THE INVENTION
The present invention relates to vehicle occupant protection systems or other safety systems employing linear actuators to elevate a vehicle surface such as a hood, in the event of collision or impact with a pedestrian. Known linear actuators typically employ pyrotechnic means to activate a piston within an actuator. This increases the cost of manufacturing given that the gas generating composition must also be manufactured prior to insertion within the actuator. Further, shipping and handling may be more complex or complicated due to transportation and related regulatory requirements. Additionally, typical pyrotechnic compositions may exhibit untenable moisture sensitivity and increase the size of the actuator due to storage requirements within the actuator. It would therefore be an improvement to provide an alternative to the typical pyrotechnically actuated pistons.
SUMMARY OF THE INVENTION
A pyrotechnic actuator contains a housing having a first end and a second end. An ignition chamber is formed adjacent to the first end of the housing. The initiator is fixed at the first end in a known manner. A hollow piston or tube is positioned within the housing and substantially coextensive therewith, the piston having a third end and a fourth end, whereby the third end is proximate to the first end of the housing and the fourth end is proximate to the second end, the piston extending from the first end to the second end prior to activation of the actuator. A stored gas is contained within a hollow piston rod attached to the piston. A burst shim or seal may be fixed across a passage formed at the third end of the piston assembly, either external or internal of the piston rod or tube, thereby sealing the gas within the piston rod. Upon activation of the actuator, the initiator ruptures the burst shim, whereby gas exits the piston and concurrently drives the piston forward in a direction opposite of the gas release. In this manner the piston is propelled from the first end of the housing to the second end of the housing.
In sum, a piston assembly of the present invention contains a housing having a first end and a second end. A hollow piston rod is contained within the housing, wherein the piston rod has a third end and a fourth end, the third end proximate to the first end and the fourth end proximate to the second end. A sealed gas chamber filled with stored gas is formed within the hollow piston rod and substantially constitutes the interior of the hollow piston rod. An initiator is fixed at the first end near the third end of the piston rod, and is used to burst a seal on the piston rod thereby liberating the stored gas from the hollow chamber and propelling the piston rod from the first end to the second end of the housing.
A piston fixed to the piston rod may be defined by a first flange formed on the third end, the first flange having a first outer diameter slidably engaged with an inner wall or diameter of the housing upon activation of the actuator. A second flange may be formed on the third end, the second flange positioned closer to the initiator and the second flange having a second outer diameter smaller than the first outer diameter of the first flange. By virtue of the different sizes of the first and second diameters, an annular conduit is formed between the inner diameter or inner wall of the housing and the second flange. Gas may therefore be shunted through the conduit onto a surface area formed in an annular plenum created between the first and second flanges and an annular wall formed therebetween, thereby driving the piston assembly through the housing.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a pressurized pyrotechnic actuator in accordance with the present invention.
FIG. 1A illustrates a macro view of the ignition chamber and burst shim interface, as identified by region “A” in FIG. 1.
FIG. 2 illustrates a pre-activated pyrotechnic actuator in accordance with the present invention.
FIG. 3 illustrates a pyrotechnic actuator of FIGS. 1 and 2, after activation of the actuator.



DETAILED DESCRIPTION OF THE INVENTION
As shown in a first embodiment of FIG. 1, a linear actuator 10 contains a housing 12. The housing 12 contains a first end 14 and a second end 16. An initiator or igniter 18 is fixed within the first end 14 in a known manner, such as by a body bore seal for example. An ignition chamber 20 is formed proximate to the igniter 18. A burst shim or seal 22 may be fixed adjacent the chamber 20 thereby retaining the pressurized gas within the piston rod interior 30A tube or hollow piston rod 23 is contained within the housing 12 and extends from immediately adjacent the ignition chamber 20 to the second end 16 (prior to activation of the actuator). It will be appreciated that a portion 32 of a piston first end 26 may therefore have an outer diameter substantially equivalent to the inner diameter of the housing 12 as defined by the inner wall 25. An outer wall 23a of the piston 23 may be almost coextensive with the length of the housing 12. The portion or first piston, flange 32 of the piston 23 is fleshly fit against the annular inner wall 25 of the body 12, thereby sealing the flange 32 against the inner wall of the housing 12. First piston flange 32 has a first outer diameter 37 that slidably engages with the inner wall 25 of the housing 12. A front surface 32d is formed integral to first flange 32 and provides a stop of the forward action of the piston rod assembly 23 when actuator 10 is activated. An annular plenum 28 is formed within the first piston end 26, that as explained below, provides an annular gaseous force against a back portion 32e (integrally formed with the first piston flange 32), upon activation of the actuator 10.
A second piston flange 32b is formed on the first end 26 closer to the igniter 18 than the first flange 32, whereby the first flange 32 and the second flange 32b sandwich the plenum 28 formed therebetween. A surface area 32e is defined within the plenum 40 and operably communicates with the stored gas 33 once the actuator is activated, thereby driving the piston rod 23 through the housing 12. Second piston flange 32b has a relatively and slightly smaller second outer diameter 39 as compared to the first outer diameter of the first piston flange 32. By virtue thereof, an annular gap or plenum 40 is formed between the outer annular surface of the second flange 32b and the inner wall 25 of the housing 12, thereby permitting gas to flow between the second flange 32b and the inner wall 25 of the housing 12 upon activation of the actuator 10. As elaborated on below, as gas flows into the plenum 40, the piston rod assembly 23 is driven forward as the gas pressure increases and exerts a force against the surface area or back portion 32e of the first tangy 32.
A piston, cap, or plug 99 is fixed within the piston rod assembly first end 26, and contains and is generally defined by the first flange 32, the second flange 32b and a core wall 99a integrally formed with the first and second flanges. An annular gas passage 99b is defined within the core wall 99a and extends from a first end 99c through the piston 99 into the interior 30 of the piston rod assembly 23. The first annular end 99c is formed in the cap 99 proximate to the igniter and a second annular end 99d is formed in the cap 99 closer to the second end 16 of the housing 12. Upon activation of the actuator 10, the annular passage 99b provides an exit or conduit tier gas to expand out of interior 30 into chamber 20, through gap 40 and into plenum 28. The burst shim or seal 22 may be fixed to either first or second annular end 99c/99d, or both.
A mount 103 may be positioned and fixed about the periphery of housing 12 for mounting to a vehicle (not shown).
A second piston or cap 101 is welded, press-fit, or otherwise joined to and at least partially within a second piston end 27 thereby sealing the piston rod or tube 23 at the end 27. A junction 29 is formed at a point where a rounded portion of the housing 12 and the outer wall 23a of the piston 23 meet. A portion 101a of the piston cap 101 extends into the interior 30 at the second piston end 27. A second portion 101b of the piston cap 101 preferably has a greater diameter than portion 101a, that may be substantially equivalent to the diameter of the housing 12.
When manufacturing the actuator 10, stored gas 33 such as argon, nitrogen, helium, other inert gases, and combinations thereof; may be provided by preferably welding a “plug” bore seal assembly 99/22 under pressure. The piston rod would be filled with pressurized gas and then plug bore seal assembly 99, already having the burst shim or seal 22 installed, could be welded under pressure to the tube or piston rod 23. The welding pressure would of course not exceed the burst pressure of the shim 22. Accordingly, the tube or piston interior 30 may be filled under pressurized conditions wherein the burst shim 22 is fixed to the end 99c or 99d, respectively, and then the initiator 18 is fixed to the end 14 of housing 12 in a known manner, under ambient pressure conditions if desired. The piston rod 23 and the housing 12 may be metal-forged as known in the art, cold-drawn flat example; on the other hand, if the piston 23 and/or housing 12 is polymeric or plastic, the parts may be injection-molded or otherwise formed as known in the art. The initiator or igniter 18 may be any state-of-the-art initiator as known in the art. The gas may be provided by known suppliers such as Praxair, for example. In general, the various constituents of the actuator 10 are made as known in the art, but in a novel configuration as described above.
In operation, a sensor (not shown) built as known in the art senses a predetermined event, such as impending impact of an associated vehicle hood by a pedestrian, and thereby triggers the activation of the actuator 10 by providing an electronic stimulus to the igniter 18 or example. As the igniter 18 is activated, the ignition threes such as pressure and perhaps heat that is provided by the igniter 18 provide a force gnat enough to rupture the burst shim 22. Upon rupture of the burst shim, stored gas quickly exits gas passage 99b and enters chamber 20 and then plenum 28 as it passes through annular gap 40. The annular burst of gaseous pressure provided in the annular plenum 28 drives the piston rod assembly 23 forward as the gaseous force is biased against rear portion 32e of first flange 32. As the piston rod assembly 23 is driven forward, hint portion or piston stop 32d arrests and terminates the movement of the piston rod assembly 23 once piston stop 32d interfaces with or slams against the rounded housing wall 38e at junction 29.
Various aspects of the present actuator 10 may be modified to tailor the performance of the actuator 10. For example, the conduit or gas passage 99b may be increased or decreased in diameter to affect a change in the speed of the gas as it exits the interior 30 of piston 23 and travels into chamber 20. In the same way, the annular gap 40 may be increased or decreased depending on desired gas flow design criteria as it flows into plenum 28. Yet further, plenum 28 may be optimized by increasing or decreasing the volume of plenum 28 to affect a desired increase or decrease in the speed of the piston rod assembly 23. The type of gas used and the design pressure within the piston rod assembly 23 may also be modified as desired.
If desired, housing 12 may be perforated or contain gas exit apertures 12a (not shown) that may provide vents for the gas released into the housing 12 from the interior 30 of piston rod assembly 23. Accordingly, if gas exit apertures 12a are formed closer to end 16, the gas within housing 12 will not be vented until sealing first flange 32 passes the gas exit aperture 12a. As the first flange 32 passes the gas exit apertures 12a, the gas within housing 12 is permitted to vent thereby releasing the hood lift provided by the extended piston as shown in FIG. 3 for example. FIGS. 2 and 3 as shown, however, illustrate a non-vented or non-perforated housing 12, wherein gas is simply retained within housing 12 to retain the hood elevation or hood lift provided upon activation of actuator 10.
In operation, the present pressurized linear actuator 10 is activated when the igniter 18 receives a signal from a vehicle computer algorithm that responds to impact, deceleration, or other known appropriate sensor. As the pedestrian makes contact with the associated vehicle and/or vehicle hood, the algorithm senses the impact and signals the igniter to activate. Upon activation, heat and pressure products from the igniter 18 burst the burst shim 22 thereby releasing the pressurized gas and driving the piston first end 26 and piston rod 23 across the length of the body 12 to the second end 16. As the piston 99 and piston 23 are propelled within and along the length of the housing 12, the second end 16, larger in diameter than the rest of the piston, functions to elevate or raise the hood to mitigate the harm or injury to the pedestrian in contact therewith.
Again, it will be appreciated that the present actuator may be largely formed or manufactured as known in the art. For example, U.S. Pat. No. 6,568,184 generally teaches the basic structure of the first embodiment, and is herein incorporated by reference in its entirety. The body or housing 12 may be drawn or otherwise metal formed as known in the art. One difference would be that the present invention is charged with gas whereas the referenced known actuator is a pyrotechnic actuator. Additionally, it will be appreciated that gases known to be suitable for use in hybrid or stored gas inflators for airbags, are equally useful here. As such the gas may be any suitable inert gas such as argon, nitrogen, and mixtures thereof.
It should further be understood that the preceding is merely a detailed description of various embodiments of this invention and that numerous changes to the disclosed embodiments can be made in accordance with the disclosure herein without departing from the scope of the invention. The preceding description, therefore, is not meant to limit the scope of the invention. Rather, the scope of the invention is to be determined by the various equivalents as would be appreciated by those of ordinary skill in the art.

## Claims

1. A linear actuator containing:
a housing having a first end and a second end;
a hollow piston rod contained within said housing, said hollow piston rod containing an inner wall, said piston rod having a third end and a fourth end, the third end proximate to the first end and the fourth end proximate to the second end;
a sealed gas chamber defined by the inner wall of the hollow piston rod;
a pressurized gas contained within the sealed gas chamber prior to activation of the actuator; and
an initiator fixed at the first end and proximate to the third end of the piston rod, for releasing the pressurized gas upon activation of the actuator to thereby drive the piston rod.

2. The linear actuator of claim 1 further comprising:
a first plug fixed on said piston rod at said third end;
a surface area on said first plug in operable communication with said pressurized gas upon actuation of said linear actuator, for propelling said piston rod.

3. The linear actuator of claim 2 wherein said first plug comprises:
an inner wall formed on said housing, said inner wall having an inner diameter;
a first flange formed on said third end, said first flange having a first outer diameter slidably engaged with said inner diameter;
a second flange formed on said third end, said second flange positioned closer to said initiator and said second flange having a second outer diameter smaller than said first outer diameter; and
an annular conduit formed between said inner diameter and said second flange.

4. The linear actuator of claim 3 further comprising:
an outer annular wall formed between said first flange and said second flange of the first plug; and
an annular plenum formed between said first flange and said second flange and said outer annular wall.

5. The linear actuator of claim 1 further comprising a burst shim fixed to said hollow piston rod at said third end, for sealing said gas chamber.

6. A linear actuator containing:
a housing having a first end and a second end;
a hollow piston rod contained within said housing, said hollow piston rod defining an interior contained therein, said piston having a third end and a fourth end, the third end proximate to the first end and the fourth end proximate to the second end;
a sealed gas chamber formed as the interior of the hollow piston rod;
a pressurized gas contained within the sealed gas chamber prior to activation of the actuator;
an initiator fixed at the first end and proximate to the third end of the piston rod for releasing the pressurized gas upon activation of the actuator;
a first annular plug fixed on said piston rod at said third end;
a surface area on said first plug, said surface area in operable communication with said pressurized gas upon actuation of said linear actuator to drive said piston.

7. A linear actuator comprising:
a housing having a first end and a second end, and an inner wall;
a hollow piston rod having a third end and a fourth end, the third end proximate to the first end and the fourth end proximate to the second end, said hollow piston rod defining an interior;
a sealed gas chamber defined by the interior of the hollow piston rod;
a stored gas contained within the sealed gas chamber;
an initiator fixed at the first end and proximate to the third end of the piston rod for releasing the stored gas upon activation of the actuator;
a first flange formed on said third end, said first flange having a first outer diameter slidably engaged with said inner wall;
a second flange formed on said third end, said second flange positioned closer to said initiator and said second flange having a second outer diameter smaller than said first outer diameter; and
an annular conduit formed between said inner diameter and said second flange for passage of gas upon activation of said actuator.

8. The linear actuator of claim 7 wherein an annular plug is fixed to said third end and contains said first and second flanges.

9. The linear actuator of claim 8 further comprising:
an outer annular wall formed between said first flange and said second flange of the first plug; and
an annular plenum formed between said first flange and said second flange and said outer annular wall.

10. The linear actuator of claim 8 containing a burst shim fixed across said first annular plug prior to activation of said actuator.