Abstract:
A vehicle is provided having an active bonnet and a pyrotechnic actuator configured to lift the active bonnet a plurality of times without having to perform maintenance on the pyrotechnic actuator. The pyrotechnic actuator includes a cylinder having an inlet opening, a first chamber and a second chamber that are separated by a central region; a piston that is configured to be displaced through the central region of the cylinder between a first position in the first chamber and a second position in the second chamber; and a carrier having first and second gas generators each being coupled to the inlet opening. The first gas generator is configured to be ignited to lift the active bonnet a first time, and the second gas generator is configured to be ignited independently of the first gas generator to lift the active bonnet a second time.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a divisional of U.S. Application Ser. No. 12/091,893, filed Sep. 26, 2008, which is a U.S. National-Stage entry under 35 U.S.C. §371 based on International Application No. PCT/EP2006/009540, filed Oct. 2, 2006, which was published under PCT Article 21(2) and which claims priority to German Application No. DE 10 2005 051 657.2, filed Oct. 28, 2005, which are herein incorporated in their entirety by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to a pyrotechnic actuator for an active bonnet of a motor vehicle. 
       BACKGROUND 
       [0003]    An active bonnet is taken to mean a bonnet which is automatically raised in the event of an accident by one or more actuators to increase the spacing between the bonnet and parts of the motor vehicle which are located therebelow and are difficult to deform, and to thus provide a pedestrian possibly impacting against the bonnet with an extended braking path. This is intended to avoid the pedestrian colliding against the non-deformable body parts at a speed which may lead to life-threatening injuries. 
         [0004]    Various pyrotechnic actuators have already been proposed for this purpose which use gas generators, such as are also known from airbags, to drive the bonnet movement. These pyrotechnic actuators have an advantageously short response time as they are generally electrically ignited and therefore solid parts do not have to be accelerated in a time-consuming manner to activate them, and they achieve a powerful acceleration of the bonnet so it reaches its raised position in the shortest time. However, it is disadvantageous that the conventional pyrotechnic actuators are not reversible. In other words, they are only suitable for a single use and then have to be exchanged. A faulty triggering of the actuators therefore makes an expensive stay in a workshop necessary every time. As it is hardly possible to avoid triggering of the actuators in the event of an accident, if the bonnet is unaffected by the events of the accident, the cost of repair of a vehicle equipped with pyrotechnic actuators is generally higher after an accident than those of a vehicle without these actuators. 
         [0005]    A reversible actuator for a motor vehicle is known from DE 103 08140 B3, which is driven mechanically by spring force. An actuator of this type makes it apparently simple, after it has been triggered, to bring the bonnet back into its normal position from which a renewed triggering can take place, but the spring has to have large dimensions because of the very short lifting times so reversal of the spring is possible only with the aid of a gearing down mechanism. A further problem emerges from the fact that the tensioned springs press with a high force against an obstacle which, on activation of the actuator has to be moved extremely rapidly. A high pressure of the spring against the obstacle makes a correspondingly high driving force to remove the obstacle necessary, the build up of which severely delays the actuating movement of the actuator. 
         [0006]    A further problem of conventional active bonnets is that the known actuators are in a position to sharply accelerate the bonnet but, as soon as the actuators reach their stop, the bonnet is decelerated still more abruptly than it was previously accelerated, and made to strongly vibrate. If a pedestrian impacts against a region of the bonnet between two actuators while said region is deflected downward, the spacing between this region of the bonnet and hard parts of the vehicle located below is sharply reduced, and there is a risk that the distance available for the deceleration of the pedestrian is not sufficient to avoid a collision against these hard vehicle parts. 
         [0007]    In view of the foregoing, at least one object of the present invention is to provide an actuator for an active bonnet which is suitable for driving a plurality of lifting movements of the bonnet without making a stay in a workshop necessary after each of these lifting movements, and which thus avoids the disadvantages of a mechanical drive. In addition, other objects, desirable features, and characteristics will become apparent from the subsequent summary, detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background. 
       SUMMARY 
       [0008]    The at least one object, desirable features and characteristics, are achieved by a pyrotechnic actuator with a cylinder, a piston which can be displaced in the cylinder under the influence of a propellant gas and a plurality of gas generators which can be ignited independently of one another. 
         [0009]    The actuator preferably also has an electronic ignition circuit, which, upon external ignition commands, ignites the gas generators in each case individually and sequentially. 
         [0010]    A further object of the invention is to provide an actuator which is in a position once the bonnet has been lifted to prevent or at least limit undesired vibrations thereof 
         [0011]    This object is achieved in that, in a pyrotechnic actuator with a cylinder, a piston which can be displaced in the cylinder under the influence of a propellant gas and a first gas generator for producing the propellant gas, the cylinder has two chambers on either side of the piston, which can be charged with propellant gas from the gas generator. If, in a normal position of the actuator, the first of these chambers is significantly smaller than the second, a small quantity of gas fed into the first chamber is sufficient to build up a high pressure therein, which drives the movement of the piston. This movement inevitably continuously reduces the volume of the second chamber, so a counter-pressure building up in this second chamber gradually decelerates the movement of the piston and, with it, the movement of a bonnet driven by the actuator. A hard stopping of the piston at the end of this adjustment path that would excite strong vibrations of the bonnet is thus avoided. 
         [0012]    In order to avoid an unnecessarily early build up of a counter-pressure in the second chamber, the second chamber can preferably be charged with the propellant gas after the first chamber. A sequence of this type can be structurally ensured in a simple manner in that the second chamber can be charged with the propellant gas through the first chamber. With an arrangement of this type, the second chamber only receives propellant gas to a significant extent when the latter has built up sufficient pressure in the first chamber, in order to penetrate from there into the second chamber. 
         [0013]    In order to delay the supply of the second chamber with propellant gas, an inlet passage for propellant gas into the second chamber is preferably blocked in a rest position of the piston and is only open when the piston is deflected from the rest position. 
         [0014]    In order to ensure an effective support of the bonnet in the raised state by the gas pressure prevailing in the first chamber of the actuator, the inlet passage should expediently also be blocked when the piston is in an end position opposite to the rest position. 
         [0015]    A throttled transfer of propellant gas from the first chamber into the second can be implemented in a simple manner if the inside width of the cylinder in a central region of the cylinder is greater than in at least one of its end regions. 
         [0016]    If a pedestrian impacts against the bonnet this will generally lead to the actuator piston moving back, during which movement work is carried out against the pressure of the propellant gas in the first chamber, so the pedestrian is decelerated. In order to keep the pressure of the propellant gas in the first chamber during this downward movement, the piston expediently comprises a central piece connected to a piston rod and an apron surrounding the central piece and axially displaceable thereon. 
         [0017]    The axial displaceability of the apron against the central piece should be limited in both directions by stops to ensure that the apron follows a movement of the central piece. 
         [0018]    To facilitate the gas transfer into the second chamber during the upward movement of the bonnet, the apron may be provided with local through openings. 
         [0019]    The spacing of the through openings from one end of the apron is preferably larger than the length of the central region to ensure that a transfer of propellant gas from the first chamber into the second chamber substantially only takes place during an upward movement of the bonnet, but not during a downward movement. 
         [0020]    A throttle point, by means of which the second chamber communicates with the surroundings, prevents a counter-pressure decelerating the piston movement from building up earlier than necessary in the second chamber. 
         [0021]    The embodiments of the invention also relates to a motor vehicle with an active bonnet which is held on a frame of the motor vehicle by means of actuators of the type defined above. As the actuators themselves can yield in each case upon an impact, a bonnet held by them may be flexible over its entire surface, so a pedestrian is effectively protected regardless of on which location of the bonnet he impacts. 
         [0022]    In one embodiment, a pyrotechnic actuator is configured to lift the active bonnet a plurality of times without having to perform maintenance on the pyrotechnic actuator. The pyrotechnic actuator includes a cylinder having an inlet opening, a first chamber and a second chamber that are separated by a central region; a piston that is configured to be displaced through the central region of the cylinder between a first position in the first chamber and a second position in the second chamber; and a carrier having first and second gas generators each being coupled to the inlet opening. The first gas generator is configured to be ignited to lift the active bonnet a first time, and the second gas generator is configured to be ignited independently of the first gas generator to lift the active bonnet a second time. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and 
           [0024]      FIG. 1  shows a motor vehicle with a bonnet held by actuators in a raised position; 
           [0025]      FIG. 2  shows a perspective exploded view of an actuator according to the invention; 
           [0026]      FIG. 3  shows a schematic section through an actuator cylinder according to the present invention in the normal position; 
           [0027]      FIG. 4  shows the actuator cylinder from  FIG. 3  with a raised piston; 
           [0028]      FIG. 5  shows a schematic section through an actuator cylinder according to a second configuration of the invention in the normal position; 
           [0029]      FIG. 6  shows an actuator cylinder during the raising of the bonnet; 
           [0030]      FIG. 7  shows an actuator cylinder with a maximally raised bonnet; 
           [0031]      FIG. 8  shows the actuator cylinder at a first instant during a downward movement of the bonnet driven by the impact of a pedestrian; and 
           [0032]      FIG. 9  shows a section through the actuator cylinder at a second, later instant of the downward movement. 
       
    
    
     DETAILED DESCRIPTION 
       [0033]    The following detailed description of the invention is merely exemplary in nature and is not intended to limit embodiments of the invention or the application and uses. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description. 
         [0034]      FIG. 1  schematically shows a motor vehicle with an engine bonnet  1 , which is held in a raised position compared to a normal position, in which it is flush with adjacent body parts  6 , by actuators  5 ,  3  arranged adjacent to the front or rear edge of the bonnet  4 ,  2 . The bonnet  1  is supported exclusively by the actuators  3 ,  5 . 
         [0035]      FIG. 2  shows a perspective exploded view of one of these actuators  3 ,  5 . It comprises an elongated cylinder  7 , which carries two fastening flanges  8  for the assembly of the cylinder  7  on a rigid frame of the motor vehicle. A gas inlet flange  9  with an inlet opening  10  is arranged between the fastening flanges  8 . A gas generator carrier  11  is provided to be fastened in a gas tight manner on the inlet flange  9 . The gas generator carrier  11  has chambers for three gas generators  12  which are connected to the inlet opening  10 . A destructible partition, not shown in the Figure, may be attached in the gas generator carrier  11  in a passage between each chamber and inlet opening  10 , in each case, which partition tears open when the gas generator  12  is ignited in the chamber associated with it, but protects a gas generator  12  accommodated in the chamber associated with it from also being ignited by the explosion of a gas generator  12  in an adjacent chamber. 
         [0036]    A cover  13  to be assembled on the side of the gas generator carrier  11  remote from the cylinder  7  contains an electric ignition circuit which, on receipt of an ignition command by way of a signal cable  14 , in each case ignites one of the gas generators  12 . 
         [0037]    The actuator of  FIG. 2  is therefore in a position to drive three lifting movements of the bonnet  1 , before it is used up and has to be exchanged. 
         [0038]    It is obvious that more or less than three gas generators  12  may also be accommodated in the gas generator carrier  11 . The number of gas generators will generally, however, not greater than five or six, as the number of the bonnet lifting movements to be expected during the service life of a motor vehicle is limited. 
         [0039]    Basically, a gas generator carrier with a single gas generator would also be a possibility and would then have to be exchanged each time after a lifting of the bonnet  1  while the cylinder itself could remain in the vehicle. An exchange of the generator carrier which would then be necessary after each lifting of the bonnet  1 , would, however, require considerable safety precautions which can only be ensured with difficulty in a motor vehicle workshop. 
         [0040]      FIG. 3  shows a schematic section through the cylinder  7  of the actuator according to a first configuration of the invention in the normal state. A displaceable piston  15  divides the interior of the cylinder  7  into two chambers, a lower chamber  16 , the volume of which is minimal in the normal position shown, and an upper chamber  17 , which takes up almost the entire interior of the cylinder  7 , and through which a piston rod  18  extends, to the upper end of which, not shown, the bonnet  1  is fastened. A gas line  19  extends from the inlet opening  10  into the lower chamber  16 . 
         [0041]    The wall of the cylinder  17  is subdivided in the longitudinal direction into three portions  20 ,  21 ,  22 . The cross-section of the lower portion  20  and the upper portion  22  corresponds to that of the piston  15 , so the latter, in these portions, substantially rests closely against the cylinder wall. In the central portion  21 , the inside width of the cylinder is slightly larger than in the portions  20 ,  22 , so when the piston  15  has been raised into the section  21  by propellant gas flowing into the gas chamber  16  by way of the gas line  19 , part of the propellant gas can flow past the piston  15  into the upper chamber  17 , as indicated by arrows  23 . When the piston  15  reaches the upper portion  22  in the course of its further upward movement, it again closely adjoins the cylinder wall and the gas in the upper chamber  22  is compressed. The counter-pressure resulting therefrom decelerates the piston  15  and, with it, the bonnet  1 , so the piston  15  does not, or at most only gently, strikes against the upper wall of the cylinder  7 . 
         [0042]    In this upper wall, a throttle passage  24  is shown, through which gas compressed in the chamber  17  can escape into the open. The free passage cross-section between the piston  15  and cylinder wall in the portion  21  and the passage cross-section of the throttle passage  24  are expediently adapted to one another such that the counter-pressure in the chamber  17  brings the upward movement of the piston to a standstill immediately before it impacts against the upper wall of the cylinder  7 . The throttle passage  24 , which is shown here as an opening spaced apart from the piston rod  18  in the upper wall of the cylinder, may, of course, also be formed by a gap between the piston rod  18  and the upper wall of the cylinder surrounding it. 
         [0043]    In  FIGS. 3 and 4 , the central portion  21  is shown cylindrically, with a slightly enlarged diameter compared to the portions  20 ,  22 . Obviously, the inside width in the portion  21  could also be enlarged only on a part of its periphery, for example by one or more grooves extending in the direction of the hollow axis of the cylinder  7  over the length of the portion  21 , between which extend wall portions which are flush with the portions  20 ,  22  and also precisely guide the piston  15  in the central portion  21 . 
         [0044]    A further-developed configuration of the actuator is explained with the aid of  FIGS. 5 to 9 . The cylinder  7  has substantially the same configuration as that considered above. The piston  15  is subdivided into a flat cylindrical central piece  25  rigidly connected to the piston rod  18  and a sleeve  26  surrounding the central piece  25 . The sleeve  26  has, at its upper and lower end, an inwardly directed peripheral web  27 , in each case, which forms a stop for the central piece  25 . A plurality of through openings  28  is formed at a distance from the upper edge of the sleeve  26 , which is not greater than the thickness of the central piece  25 . A lower portion  29  of the sleeve  26  which is free of openings is at least as long as the central portion  21  of the cylinder  7 . 
         [0045]    If the central piece  25  of the piston is driven out of the normal position shown in FIG.  5  by propellant gas flowing in by way of the gas line  19 , it firstly rises inside the sleeve  26 , which, due to inertia, remains at rest. Only when the central piece  25  strikes against the upper web  27  is the sleeve  26  entrained and the piston  15  reaches the position shown in  FIG. 6 , in which a passage of gas out of the lower chamber  16  into the upper chamber  17  takes place by way of the through openings  28 . 
         [0046]    In the course of the further upward movement of the piston, as shown in  FIG. 7 , the latter is gradually decelerated by gas pressure building up in the upper chamber  17 . In the position in which the piston comes to rest, the openings have passed the portion  21 , so no further gas can pass through them. 
         [0047]    If a downward movement of the bonnet then starts under the pressure of an impacting passenger, initially only the central piece  25  moves; the sleeve  26  only follows as soon as the central piece  25  has reached the lower web  27  of the sleeve  26 , as shown in  FIG. 8 . Although the central piece  25  is now in the portion  21  of the cylinder  7 , since the through openings  28  have remained in the portion  22 , propellant gas cannot pass to a significant extent from the lower chamber  16  into the upper chamber  17 , so that to force the piston down work has to be carried out which is taken from the impact energy of the pedestrian. 
         [0048]      FIG. 9  shows the stage of downward movement of the piston in which the through openings  28  reach the central portion  21  of the cylinder. At this instant, the central piece  25  and the lower edge of the sleeve  26  have already reached the portion  21 , so no gas can overflow into the upper chamber  17  here either. Thus the pedestrian is effectively decelerated over the entire stroke of the piston  15  and optimally protected. 
         [0049]    While at least one exemplary embodiment has been presented in the foregoing 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 of the invention in any way. Rather, the foregoing 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 of the invention as set forth in the appended claims and their legal equivalents.