Abstract:
A pyrotechnic actuator is provided for an active hood that encompasses an installation site for a gas generator, a cylinder incorporating a moving piston and a compressed gas line that joins the installation site with the cylinder. A filter body for trapping particles from the gas stream of the gas generator is arranged on the compressed gas line.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to German Patent Application No. 102008020087.5, filed Apr. 22, 2008, which is incorporated herein by reference in its entirety. 
       TECHNICAL FIELD 
       [0002]    The present invention relates to a pyrotechnic actuator for an active hood of a motor vehicle. 
       BACKGROUND 
       [0003]    A pyrotechnic actuator is known from DE 10 2006 008 900 A1, for example. The object of such an actuator is to lift the front hood of a motor vehicle involved in an accident in the shortest time possible by igniting a propellant charge to increase the distance between the hood and underlying parts of the engine block or other non-deformable components of the vehicle, thereby creating as expansive a delay zone as possible for any impacted pedestrian to lower the danger of serious injury. 
         [0004]    In practice, it turns out that the compressed gas supplied by the propellant charge is significantly encumbered with solid particles that get into the cylinder of the actuator upon its activation. As a result, the actuator can only be used a second time, if at all, if the particles are removed from the cylinder. This requires that the actuator go through a costly stay at the workshop each time it is triggered. 
         [0005]    In view of the foregoing, at least one object of the present invention is to provide a pyrotechnic actuator that can be reused with the lowest outlay. In addition, other objects, desirable features, and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background. 
       SUMMARY 
       [0006]    The at least one object, and other objects, desirable features, and characteristics, is achieved in a pyrotechnic actuator for an active hood with a gas generator, a cylinder incorporating a moving piston and a compressed gas line, which links the gas generator with the cylinder, and a filter body is arranged on the compressed gas line to trap particles contained in the compressed gas of the gas generator. 
         [0007]    Surprisingly, it was shown that a good filtering effect can be achieved with a filter body that covers a wall of the compressed gas line. 
         [0008]    It makes sense in particular to align an upstream section of the compressed gas line in such a way as to form a gas jet aimed against the covered wall. Because of their mass inertia, the particles contained in the gas jet penetrate more deeply into the material of the filter body than the gas, so that the gas can no longer entrain them once they come to rest in the filter body. 
         [0009]    In order to achieve this effect, it is not necessary for the gas stream to traverse the filter body; rather a downstream section of the compressed gas line preferably proceeds from a surface of the filter body receiving the stream. 
         [0010]    To efficiently separate out the particles, it is advantageous if the upstream and downstream section of the compressed gas line be aligned at a right angle to each other. 
         [0011]    A filter body that crosses the compressed gas line can also be provided. The design of the actuator is simplified by having the filter body covering the wall and the filter body crossing the compressed gas line in sections of one and the same filter body. 
         [0012]    Such an arrangement can be easily realized by designing the filter body as a hollow item, and having an inner cavity of the filter belong to the downstream section of the compressed gas line. 
         [0013]    In particular, the filter body can be tubular, and a first peripheral section of the tubular filter body covers the wall, and a peripheral section lying opposite the first peripheral section is adapted to cross the upstream line section. 
         [0014]    This filter body can be enveloped by an annular or sectoral cavity, which belongs to the upstream section of the compressed gas line. 
         [0015]    Several upstream line sections each originating with various gas generators advantageously hit various sections of the filter body. Since the cylinder is protected against particles by the preceding filter body, and can hence be used multiple times, the several gas generators for repeated use of the cylinder can already be integrated into the actuator from the start. This minimizes the repair outlay after an accident, since parts of the pyrotechnic actuator need only be replaced or enhanced once all gas generators have been expended. Because the line sections are aligned toward respectively different sections of the filter body, a different section of the filter body is used to filter out the particles each time the actuator is activated, so that the efficiency and permeability of the filter remains essentially unchanged over several activations. 
         [0016]    The actuator can be given an especially compact design by arranging the sections of the filter body crossing the compressed gas lines on a first half of the circumference of the filter body, and the sections covering the wall on a second half. 
         [0017]    Another configuration makes it possible to accommodate the filter body in a blind cavity that faces the upstream section. 
         [0018]    The piston can preferably be locked in the cylinder, and unlocked by the supply of compressed gas. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and: 
           [0020]      FIG. 1  is a partial longitudinal view through the socket area of a pyrotechnic actuator according to a first embodiment of the invention; 
           [0021]      FIG. 2  is an axial view through the socket area of an actuator according to a second embodiment of the invention; 
           [0022]      FIG. 3  is a radial section along the III-III plane from  FIG. 2 ; 
           [0023]      FIG. 4  is a section analogous to  FIG. 3  according to a third embodiment of the invention; 
           [0024]      FIG. 5  is an axial section according to a fourth embodiment of the invention; 
           [0025]      FIG. 6  is a section along the VI-VI plane from  FIG. 5 ; 
           [0026]      FIG. 7  is a radial section analogous to  FIG. 6  according to a fifth embodiment of the invention; 
           [0027]      FIG. 8  is a partial longitudinal section through the socket area of a pyrotechnic actuator according to a sixth embodiment of the invention; 
           [0028]      FIG. 9  is a section along the IX-IX plane from  FIG. 8 ; and 
           [0029]      FIG. 10  is a section along the X-X-plane from  FIG. 8 . 
       
    
    
     DETAILED DESCRIPTION 
       [0030]    The following detailed description is merely exemplary in nature and is not intended to limit application and uses. Furthermore, there is no intention to be bound by any theory presented in the preceding background and summary or the following detailed description. 
         [0031]      FIG. 1  shows a section through an actuator according to an embodiment of the invention along the longitudinal axis of its cylinder  1  only partially depicted on the figure. A sliding piston  2  inside the cylinder  1  is secured to an engine hood of a motor vehicle to be lifted by the actuator (not shown on the figure) by a piston rod  3  exiting at the upper end of the cylinder  1 . The entire actuator is mounted under the engine hood in the body structure of a motor vehicle. 
         [0032]    The piston  2  encompasses a hollow cylindrical piston sheath  4  rigidly connected with the piston rod  3  and open toward the bottom, and a slider  5  with an essentially cylindrical shape, the bottom side of which is enlarged by a continuous collar  6 , so that it fills out the free cross section of the cylinder  1  to the exclusion of a slight clearance. In the configuration shown, a top section  7  of the slider  5  holds a plurality of latching balls  8  securely in a position where some are accommodated in boreholes  28  in the jacket sheath  4 , and others engage a groove  9  on the inside of the cylinder  1 . The latching balls  8  keep the piston  2  locked firmly in place, so that the engine hood on the motor vehicle body remains securely anchored by the actuator. 
         [0033]    A compressed gas line  10  links the bottom side of the slider  5  with a plurality of gas generators  11 . When one of these gas generators  11  is fired, the compressed gas it supplies first streams against the bottom side of the slider  5 , forcing it upwards. As a result, a continuous groove  12  of the slider  5  moves to the level of the latching balls  8 , while the slider  5  simultaneously hits the jacket sheath  4 , and conveys the pressure of the gas to it. This causes the latching balls  8  to slip out of the groove  9  of the cylinder  1  and into the groove  12  of the slider  5 , releasing the lock of the piston  2 . The piston can now yield to the pressure of the gas and lift the hood. 
         [0034]    The compressed gas line  10  encompasses a plurality of boreholes incorporated into the massive metal socket of the cylinder  1 . Three parallel boreholes each form chambers, which incorporate gas generators  11 . They are interconnected by a collective borehole  13 , which is introduced from the bottom side of the socket and tightly sealed by a cover  14 . One of the three boreholes marked  15  that accommodates the gas generators  11  is lengthened up to the longitudinal axis of the cylinder  1  and a bit further beyond that. It crosses a borehole  16  that axially lengthens the chamber of the cylinder  1 . A filter body  17  comprised of a porous material is housed in a sack-like end section of the borehole  15  lying opposite the gas generator  11  on the other side of the borehole  16 . 
         [0035]    When one of the gas generators  11  is fired, the compressed gas ejected by it first shoots along the borehole  15  until deflected in the crossing zone of the boreholes  15 ,  16 . Particles entrained by the compressed gas cannot catch up with the directional change of the gas fast enough, are carried through the crossing area, and hit the opposing filter body  17 , where they remain stuck. The compressed gas that finally reaches the chamber of cylinder  1  is essentially free of particles. As a result, the actuator can be activated several times without having to be taken apart and cleaned after each time activated. 
         [0036]    A borehole  44  running through the piston  2  allows the compressed gas to seep out after the piston  2  has been released and lifted. As a result, after keeping the hood lifted for the time necessary for cushioning the pedestrian, the piston  2  can be pressed backs into the position shown on  FIG. 1  without exerting a lot of force, and be locked into that position once again. 
         [0037]      FIG. 2  shows an axial section through the socket area of a pyrotechnic actuator according to a second embodiment of the invention. The cylinder of the actuator itself and the piston accommodated therein are not shown; their structural design can be the same as described above with reference to  FIG. 1 . The collective borehole  13  is omitted in this embodiment; in its place, each of a total of three gas generators  11  is incorporated in a separate upstream borehole  15 , which runs in a radial direction toward the downstream axial borehole  16  and is lengthened a bit beyond the latter to form a receiving pocket for a filter body  17 . As readily evident in the radial section on  FIG. 3 , each gas generator  11  lies opposite a filter body  17 , which is flanked on both sides by the boreholes  15  of other gas generators  11 , and traps particles of the gas generator  11  opposite it. 
         [0038]    In a radial section along the same plane on  FIG. 3 ,  FIG. 4  shows a third embodiment of the actuator. In order to reduce the diameter of the actuator socket, the gas generators  11  are here accommodated in boreholes parallel to the piston axis, and hence visible in a top view on the figure. Upstream boreholes  15  into which the gas generators  11  release their respective compressed gas are oriented radially, perpendicular to the longitudinal axis of the cylinder  1 , and end in a shared axial parallel, downstream borehole  16  via nozzles  18 . The nozzles  18  bundle the ejected compressed gas on the filter body  17  lying respectively diametrically opposite the nozzle  18 . The respective filter body  17  is accommodated in a borehole  29  diametrically opposite the upstream borehole  15  of the allocated gas generator  11 , and both boreholes  15 ,  29  are each sealed to the outside by screwed-in stoppers  19 . 
         [0039]      FIG. 5  in turn shows an axial section through the socket area of an actuator according to a fourth embodiment of the invention. The arrangement of gas generators  11  is the same as described in reference to  FIG. 1 . The structural design of the cylinder  1  and the piston  2  is also identical to the one shown on  FIG. 1 , and hence not shown separately on  FIG. 5 . 
         [0040]    A hollow cylindrical or tubular filter body  17  is incorporated in a chamber in the crossing area of a radially oriented upstream borehole  15  and a downstream borehole  16  running on the cylindrical axis. In the present case, the chamber  20  is formed by a borehole with a large diameter, which is advanced from the bottom side of the socket and oriented coaxially to the borehole  16 , just as a collective borehole  13  that joins the gas generators  11  with the borehole  15 . The collective borehole  13  and chamber  20  are here sealed by a shared cover  21 . 
         [0041]    If required by the structure of the material comprising the filter body  17 , the filter body  17  can be stabilized against the pressure of the gas released by one of the gas generators  11  by having the journal  22  of the cover  21  extend a bit inside the cavity of the filter body  17  and/or an upper edge of the filter body  17  extend into a groove on the cover of the chamber  20 . 
         [0042]    As evident from the section on  FIG. 6 , the filter body  17  has two areas  23 ,  24  that act in respectively different ways on the gas stream of the gas generator  11 . The gas stream passes by the area  23  facing the gas generator  11 , catching a portion of the particles contained therein. Since the area  23  does not have to catch all particles, it can be highly porous, so that the pressure drop at area  23  can be kept low enough not to notably delay the raising motion of the hood, and not to load the filter material beyond its load-bearing limit. The convex bulging of the surface of the filter body  17  facing the gas generator  11  increases its load-bearing capacity further. 
         [0043]    Particles that were not trapped in the traversed area  23  of the filter body  17  pass through the inner cavity of the filter body  17 , and head to the area  24  on the opposite side, where they remain stuck. 
         [0044]      FIG. 7  shows an axial section through a fifth embodiment of the actuator, which combines the features of the second and fourth embodiment. Three radial boreholes  15  respectively fitted with a gas generator  11  empty via nozzles  18  into a cylindrical chamber  20 , which is equipped with a tubular filter body  17 . The filter body  17  has three sections  23 ,  24  that alternate in the peripheral direction. The sections  23  lying in front of a respective nozzle  25  carry the compressed gas from one of the gas generators  11  when fired; adjacent sections  24  trap the respective particles of another of the gas generators  11  that have passed the respectively diametrically opposing area  23  without being caught. Since separate areas  23  or  24  are allocated to each gas generator  11  in this embodiment, the gas from each gas generator  11  that is fired hits fresh sections of the filter body  17  not yet encumbered with the particles of other gas generators. For this reason, the efficiency of the filter body  17  remains essentially just as good when activating the third gas generator  11  as it was when generating the first. 
         [0045]    The sections  24  of the filter body do not have to completely abut a wall area of the chamber  20  that they cover. As denoted by a dashed line on  FIG. 7 , a well chamber  26  for particles can be recessed diametrically opposite to a respective borehole  15 . However, areas  27  of the wall should contact the filter body  17  between such a well chamber  26  and adjacent nozzles  24  to prevent an area  24  already loaded with particles from being flushed in the opposite direction when another gas generator  11  is activated, entraining particles trapped therein. 
         [0046]    A preferred embodiment of the pyrotechnic actuator according to an embodiment of the invention is described based on the axial section on  FIG. 8  and the two cross sections on  FIG. 9  and  FIG. 10 , which each show sections along the IX-IX or X-X planes on  FIG. 8 . Elements of this actuator that were already described with respect to the preceding embodiments are marked with the same reference numbers, and will only be elucidated below to the extent that there are differences relative to the other embodiments. 
         [0047]    The cylinder  1  of this actuator consists of at least two elements joined together, a long stretched-out pipe section  30  and a footing  31 . The footing  31  has a base plate  32  and a pipe fitting  33  projecting from the base plate  32 , into which the pipe section  30  is screwed. The groove  9  forms a border between the pipe section  30  and the footing  31 , so that both parts  30 ,  31  can be easily fabricated without back cuts. 
         [0048]    The footing  31  is housed in a pot-shaped casing  34 . The base plate  32  and a floor area of the casing  34  border a cavity  35 , which incorporates a molding  36  and, in a flat chamber  20  of the latter, an annular or tubular filter body  17 . A large opening  37  in the floor plate  33  joins the chamber of the cylinder  1  with the interior cavity of the filter body  17 . Three smaller openings  38  of the base plate  32  are joined with the outside of the filter body  17  by ditches  39  which are recessed in the molding  36 . 
         [0049]    Three sleeves  40  parallel to the axis of the cylinder  1  are embedded in a second molding  41  above the base plate  32 . A ring  42  screwed onto the upper edge of the casing  34  keeps a cover plate  43  pressed against the molding  41 . The respective gas generators  11  are positively secured to openings of the cover plate and in the sleeves  40 . 
         [0050]    The compressed gas ejected by one of the gas generators  11  passes through an opening in the floor of the sleeve  40  accommodating the generator, one of the openings  38  in the floor plate  33  and one of the ditches  39  and on to the filter body  17 . The sections  23  of the filter body  17  carrying gas from the three gas generators  11  extend roughly over half its periphery; the sections  24  where the compressed gas passing through the sections  23  is diverted and the residual particles of the compressed gas are trapped in the process form another half of the periphery of the filter body  17 . As evident, the fact that the gas generators  11  are oriented parallel to the cylindrical axis  1  and placed on the same half of the periphery of the filter  17  enables an especially compact design of the actuator. 
         [0051]    While at least one exemplary embodiment has been presented in the foregoing summary and detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims and their legal equivalents.