Abstract:
The invention relates to an actuator comprising an actuator element movably supported at an actuator housing, a pyrotechnic pressure element to move the actuator element and a control means to control a force exerted onto the actuator element by the pressure element to move the actuator element.

Description:
FIELD OF THE INVENTION 
   The invention relates to an actuator comprising an actuator element movably supported at an actuator housing and a pyrotechnic pressure element to move the actuator element. 
   BACKGROUND OF THE INVENTION 
   An actuator of this type is generally known and is used, for example, to interrupt electrical connections or to trigger fast switching procedures, e.g. in the motor vehicle safety sector. 
   The pyrotechnic pressure element, which is also called a pyrotechnic igniter in the case of an electrical activation, has the advantage in addition to a particularly fast power development that the energy required to move the actuator element can be stored without pressure over a long period of time by means of suitable chemical substances and can be released as required by means of a comparatively small electrical or mechanical energy. 
   An activation of the pressure element triggers a conversion of the chemical substances and results in the generation of a pressure impulse by which the actuator element is moved relative to the actuator housing, e.g. is pushed out of it. Since the action on the actuator element takes place very abruptly, the actuator element is moved in a short time and in an uncontrolled manner from a starting position into an end position. 
   This fast and uncontrolled movement of the actuator element has proved to be disadvantageous in those applications in which the movement procedure of the actuator element should endure for a specific time and/or a bounce of the actuator element should be avoided, e.g. in locking or unlocking processes. 
   It is the underlying object of the invention to provide a pyrotechnic actuator, wherein the movement of the actuator takes place in a controlled manner. 
   An actuator having the features of claim  1  is provided to satisfy this object. 
   The actuator in accordance with the invention comprises an actuator element movably stored at an actuator housing, a pyrotechnic pressure element for the movement of the actuator element and a control means for the control of a force exerted onto the actuator element by the pressure element to move the actuator element. 
   The force exerted on the actuator element on a triggering of the pressure element can be set by the control means such that the movement of the actuator element takes place at a desired speed. The control means is in particular adjustable such that the movement of the actuator element takes place over a desired period and/or a bounce of the actuator element is avoided. A defined movement of the actuator element can therefore be pre-set by the control means and a matching of the actuator to its respective area of use is possible. 
   Advantageous embodiments of the invention can be seen from the dependent claims, from the description and from the drawing. 
   SUMMARY OF THE INVENTION 
   In accordance with a preferred embodiment, the control means is arranged between the pressure element and the actuator element. It is thereby achieved that the gas pressure generated by the pyrotechnic pressure element does not build up abruptly, but increasingly in front of a surface of the actuator element which is to be acted on. This contributes to a yet more controlled movement of the actuator element. 
   The control means advantageously includes a diaphragm. This represents a particularly simple form of a control means. On an activation of the pressure element, a high-pressure system is created in front of the diaphragm, i.e. on the pressure element side of the diaphragm, and a low-pressure system is created behind the diaphragm, i.e. on the actuator element side of the diaphragm. By a suitable selection of the diaphragm cross-section, the pressure build-up in the low-pressure system, i.e. the pressure increase gradient, and thus ultimately the resulting force acting on the actuator element, can be set. In other words, the cross-section of the diaphragm forms a control parameter of the control means. 
   The diaphragm is preferably integrated into a spacer means for the pressure element. The spacer means serves for the correct positioning of the pressure element in the actuator housing. The spacer means satisfies a dual function by the simultaneous integration of the diaphragm, whereby the number of the components is reduced and the design of the actuator is simplified. 
   In accordance with a further embodiment, grouting is provided for the pressure element. In the event of an activation of the pressure element, the grouting brings about a more uniform conversion of the chemical substances contained in the pressure element and thus results in a more uniform gas pressure. Ultimately, a more uniform action on the actuator element and consequently an even more controlled movement of the actuator element is thereby achieved. 
   In accordance with an advantageous embodiment, the actuator element is fixed in a starting position by a grouting element. The grouting element satisfies a dual function in that it forms grouting for the pressure element, on the one hand, and provides a fixing of the actuator element, on the other hand. The design of the actuator is thereby simplified even further. 
   The grouting element preferably has a shear section which cooperates with the actuator housing such that a substantial movement of the actuator element relative to the actuator housing is only possible after a shearing of the shear section off the grouting element. For example, the shear section can be supported at a shoulder of the actuator housing in a starting position of the actuator element. 
   Due to the shear section, the actuator element is not set in motion immediately on an activation of the pressure element, but a pressure must first build up at the side of the actuator element to be acted on, said pressure being sufficient to shear off the shear section of the grouting element. A force threshold is created in this manner below which no movement of the actuator element takes place. It is thereby ensured that the force which acts on the actuator element and which the actuator element can in turn apply is not lower than a minimum force. 
   In accordance with a further advantageous embodiment, a holding device is provided to hold the actuator element in an end position after a movement by the pressure element. The holding device has the effect that the actuator element cannot be simply returned back into its starting position from its end position after a triggering of the actuator. In other words, the movement of the actuator element is irreversible. 
   The holding device can include a knurling of the actuator element which is pressed into a bore of the actuator housing on a movement of the actuator element. Alternatively or additionally, the holding device can include a friction-retaining slope of the actuator housing in which the actuator element jams on its movement. Both variants represent a particularly simple form of a holding device for the actuator element and thus contribute to a simple design of the actuator. 
   The actuator element is preferably formed by a piston displaceably supported in the actuator housing. Generally, however, other designs of the actuator element are also conceivable; the actuator element could e.g. be made in the manner of a lever and could be pivoted in the event of a triggering of the pressure element. 

   
     DESCRIPTION OF THE DRAWINGS 
     The invention will be described in the following purely by way of example with reference to advantageous embodiments and to the enclosed drawing. There are shown: 
       FIG. 1  a cross-sectional view of a first embodiment of the actuator in accordance with the invention in a starting state; 
       FIG. 2  a cross-sectional view of the actuator of  FIG. 1  in a triggered state; 
       FIG. 3  a cross-sectional view of a second embodiment of the actuator in accordance with the invention in a starting state; 
       FIG. 4  a cross-sectional view of the actuator of  FIG. 3  in a triggered state; 
       FIG. 5  a cross-sectional view of a third embodiment of the actuator in accordance with the invention in a starting state; 
       FIG. 6  a cross-sectional view of the actuator of  FIG. 5  in a triggered state; 
       FIG. 7  a cross-sectional view of a fourth embodiment of the actuator in accordance with the invention in a starting state; and 
       FIG. 8  a cross-sectional view of the actuator of  FIG. 7  in a triggered state. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   A first embodiment of the pyrotechnic actuator in accordance with the invention is shown in  FIGS. 1 and 2 . 
   The actuator has an actuator housing  10  in which a pyrotechnic pressure element  12  is arranged. The pressure element  12  is held by a pressure element carrier  14  in a rear region, a lower region in the Figure, of the actuator housing  10 . 
   For the correct positioning of the pressure element carrier  14  in the actuator housing  10 , a beaker-shaped spacer cup  16  is provided whose open side faces the pressure element carrier  14  and which surrounds the pressure element  12  at least regionally. The pressure element carrier  14  is fixed to the actuator housing  10  by means of a clinching connection  18 . 
   Ignitable chemical substances are contained in the pyrotechnic pressure element  12  and can be brought to reaction, for example by electrical energy, on a triggering of the pressure element  12 . Pressure elements of this type and suitable ignition mechanisms are sufficiently known. 
   A gas pressure impulse is created in the pressure element  12  by a fast conversion of the chemical substances and opens a cylindrical sleeve  20  of the pressure element  12  projecting into the spacer cup  16 . Desired break points, e.g. in the form of stampings, are provided at the end face  22  of the sleeve  20  to ensure an opening of the sleeve  20  at the end face. 
   The pressure element  12  serves for the actuation of an actuator element  24  which is arranged in a front region, an upper region in the Figure, of the actuator housing  10 . The actuator element  24  has the shape of a piston which is supported displaceably in the axial direction in the actuator housing  10 . 
   The piston  24  includes a cylindrical main section  26  which is guided in a bore  30  provided at a front end face  28  of the actuator housing  10 . As  FIG. 1  shows, a front end face  32  of the piston  24  terminates in a flush manner with the front end face  28  of the actuator housing  10  in the starting state of the actuator. 
   In the region of the rear end of the main section  26 , the piston  24  has a disk-shaped head section  34  which is guided, in a starting position of the piston  24 , by a wall section  36  of the actuator housing  10  and terminates with it in a substantially gas-tight manner ( FIG. 1 ). 
   When the pressure element  12  is ignited, a gas pressure is built up in the pressure element  12  by the reaction of the chemical substances located in the pressure element  12  which results in an opening of the sleeve  20  of the pressure element  12 . The gas created can flow out of the pressure element  12  through the opening of the sleeve  20  and build up a gas pressure in a space  38  bounded by the spacer cup  16  and the pressure element  12  or the pressure element carrier  14 . 
   As  FIG. 1  shows, the piston head section  34  is disposed at a base  40  of the spacer cup  16  in the starting position of the piston  24 . An opening  42  is provided in the base  40  of the spacer cup  16  through which the gas generated can flow through and can act on the head section  34  of the piston  24 . The piston  24  is thereby moved away from the spacer cap  16  and pushed to the front out of the actuator housing  12 . 
   The base  40  and the opening  42  of the spacer cup  16  form a diaphragm on whose side facing the pressure element  12  a high-pressure system is formed and on whose side facing the piston  24  a low-pressure system is formed. The pressure build-up in the low-pressure system takes place in dependence on the diaphragm cross-section, i.e. on the diameter of the opening  42 . The diaphragm cross-section therefore represents a control parameter via which the pressure increase gradient in the low-pressure system, and thus ultimately the force acting on the piston  24 , can be set. 
   The displacement of the piston  24  is bounded by a shoulder  46  of the actuator housing  10  which forms an abutment for the head section  34  of the piston  24 .  FIG. 2  shows the piston  24  in an end position in which the piston  24  is maximally pushed out of the actuator housing  10  and the head section  34  abuts the shoulder  46  of the actuator housing  10 . 
   In  FIGS. 3 and 4 , a second embodiment of the actuator in accordance with the invention is shown which only differs from the first embodiment in that grouting is provided for the regularization of the conversion of the chemical substances of the pressure element  12  and of the gas pressure created in this process. 
   The grouting is achieved by a grouting element  48  which surrounds the main section  26  of the piston  24  like a sleeve. The grouting element  48  has an outwardly angled section  50  in the region of its front end facing away from the head section  34 . As  FIG. 3  shows, the grouting element  48  is dimensioned such that the angled section  50  cooperates with the shoulder  46  of the actuator housing  10  in the starting position of the piston  24  and is in particular supported at said shoulder. The grouting element  48  is therefore arranged between the head section  34  and the shoulder  46  viewed in the axial direction. The piston  24  is thereby fixed in the actuator housing  10  at its starting position and is prevented from a displacement relative to the actuator housing  10 . 
   The angled section  50  of the grouting element  48  forms a shear section which has to be sheared off to permit a displacement of the piston  24  out of the actuator housing  10 . The force required for the shearing off of the shear section  50  can be set by the selection of a corresponding material and/or of a corresponding geometry of the shear section  50 , e.g. of the thickness of the shear section  50  and/or of the arrangement of desired break notches. An optimum grouting force and a particularly uniform realization of the chemical substances can be achieved in this manner. This permits the setting of a defined gas pressure and thus ultimately of a defined ejection force of the piston  24 . 
     FIG. 4  shows the actuator in the triggered state, with the piston  24  being in its end position, i.e. being maximally pushed out of the actuator housing  10 . As can be seen from the Figure, the head section  34  of the piston  24  does not directly abut the shoulder  46  of the actuator housing  10  in this case, but only indirectly via the sheared off shear section  50  disposed therebetween. 
   So that the movement of the piston  24  in the axial direction is not blocked by the part of the grouting element  48  remaining at the piston  24 , the inner diameter of the section  52  of the actuator housing  10  disposed between the front end face  28  and the shoulder  46  has a width which is larger than an outer diameter of the grouting element  48  in the sheared-off state. 
   In  FIGS. 5 and 6 , a third embodiment of the actuator in accordance with the invention is shown which only differs from the second embodiment in that the main section  26  of the piston  24  is provided with a knurling  54 . 
   The knurling  54  is positioned in a region of the main section  26  in the center viewed in the axial direction such that it is pressed into the bore  30  of the front end face  28  of the actuator housing  10  on the ejection of the piston  24 . The knurling  54  is furthermore made such that an optimum pressing is present when the piston  24  has reached its end position, i.e. has been maximally pushed out of the actuator housing  10  ( FIG. 6 ). 
   The knurling  54  pressed into the bore  30  in a slight interference fit and prevents the piston  24  fully pushed out of the actuator housing  10  from being able to be pushed back into the actuator housing  10 . The actuator in accordance with the third embodiment therefore represents an irreversible system in which the piston  24  can admittedly be moved out of the actuator housing  10 , but cannot be pushed back into it. 
   The term “irreversible” in this connection is to be understood such that the movement of the piston  24  cannot be reversed at least when forces are applied which occur in the normal use of the actuator. Unlike with the actuators in accordance with the first and second embodiments, the piston  24  of the actuator in accordance with the third embodiment can therefore not easily be pushed back into its starting position. 
   In  FIGS. 7 and 8 , a fourth embodiment of the actuator in accordance with the invention is shown which only differs from the third embodiment in that, instead of the knurling  54 , a friction-retaining sloping surface  56  is provided in which the piston  24  jams when moving out. The sloping surface  56  is formed at the inner side of the actuator housing  10  in front of the shoulder  46 , when viewed in the ejection direction of the piston  24 , such that an optimal jamming of the head section  34  is achieved when the piston  24  has reached its end position, i.e. has moved maximally out of the actuator housing  10  ( FIG. 8 ). As in the third embodiment, the completely moved out piston  24  can no longer be moved back into the actuator housing  10  so that it is also an irreversible actuator in the fourth embodiment.