Pyrotechnic actuator

Abstract

Pyrotechnic actuator (1) comprising a tubular housing (2) having a pyrotechnic detonator (21) at one end, and further comprising a piston with piston tip (4a) and piston rod (4), wherein the piston tip (4a) is displaceable in the housing (2) by the detonator (21) from an initial position adjacent to the detonator (21) to an end position distant from the detonator (21), and wherein a one-piece sealing element (5) is provided at the end of the housing (2) facing away from the detonator (21) between the piston rod (4) and the housing (2), wherein the piston rod (4) passes through the sealing element (5) and has a step (14) in the region of the sealing element (5), wherein the outer diameter (13) of the piston rod (4) on the side of the step (14) facing away from the detonator (21) is smaller than the outer diameter (12) on the side facing the detonator (21). (21) side facing the step (14), characterized in that the sealing element (5) has a corresponding opposing step (27),so that the sealing element (5) sits on the step (14) of the piston rod (4).

Description

Technical field

[0001] The present invention relates to a pyrotechnic actuator comprising a tubular housing which has a pyrotechnic detonator at one end, and which further comprises a piston with a piston tip and piston rod, wherein the piston tip in the housing can be displaced by the detonator from an initial position adjacent to the detonator to an end position distant from the detonator, and wherein a one-piece sealing element is provided at the end of the housing facing away from the detonator between the piston rod and the housing, wherein the piston rod passes through the sealing element and has a step in the region of the sealing element, wherein the outer diameter of the piston rod on the side of the step facing away from the detonator is smaller than the outer diameter on the side of the step facing the detonator. State of the art

[0002] Pyrotechnic actuators for raising a car hood in the event of a collision with a pedestrian or cyclist are widely used in automotive safety technology, particularly in Europe, Japan and, in the future, also in China.

[0003] Pyrotechnic actuators are well known, including from GB 2375329 A, DE 102008039168 A, WO 2015 / 072293 A, US 2018038393 A, EP 2546531 A and US 2015175496 A

[0004] The basic design of such an actuator is shown in AT 511500 B by Hirtenberger. The actuator typically comprises a housing, a connection to the vehicle body, a movable piston with a piston tip and piston rod, and a gas generator to move the piston tip and thus the piston rod. The challenge is to use these known components to achieve the desired functionality—that is, to generate a specific force / displacement curve for actuating the hood against its inertia—as cost-effectively as possible. However, in the solution described in the aforementioned document, the sealing element is relatively complex: it consists of a turned part with a groove into which an O-ring is inserted.

[0005] A simpler and therefore more cost-effective solution is known from EP 2699455 B (corresponding to WO 2012 / 144939 A) by Autoliv. According to this document, a one-piece seal achieves both the sealing of the piston rod and the guidance of the piston rod within the tubular housing. However, the cap-like design of the seal shown there also has disadvantages. On the one hand, the contact area of ​​the piston on the hinge is limited to the diameter of the piston rod. This leads to poor results with larger manufacturing tolerances between the hinge and the piston rod, and also with hinges that have an unfavorable contact area, for example, with release elements in elongated holes. On the other hand, for each desired actuator length, not only the length of the piston rod but also the length of the housing must be changed, which increases manufacturing costs.

[0006] Another simpler and more cost-effective solution is known from the generic WO 2011 / 138553 A. This involves using a one-piece seal for both sealing and securing the piston rod to the housing. However, this solution also requires changes to both the piston rod length and the housing length for each desired actuator length. Furthermore, the piston rod is guided by a separate component, which increases manufacturing costs. Description of the invention

[0007] The object of the present invention is to overcome these disadvantages and to create an actuator in which the striking surface can be enlarged and in which different lengths of the piston rod can be realized with one and the same housing, without increasing the manufacturing effort, in particular without using turned parts for guiding and sealing the piston rod.

[0008] This problem is solved according to the invention by a pyrotechnic actuator of the type mentioned above in that the sealing element has a corresponding counter-step, so that the sealing element sits on the step of the piston rod.

[0009] In contrast to the aforementioned EP 2699455 B, the sealing element is not designed as a cap, but as an essentially tubular sealing element through which the piston rod passes. An actuator according to the invention thus has an essentially tubular sealing element with two inner diameters, which sits on a step of the piston rod.

[0010] Because the piston rod passes through the sealing element, it is possible for the piston rod to protrude beyond the sealing element, and the extent of this protrusion depends on the required actuator length. Therefore, only the piston needs to be changed if a different actuator length is required.

[0011] Furthermore, a disc-shaped component can be fixed to the end of the piston rod furthest from the igniter. This component has a diameter larger than the smaller outer diameter of the piston rod, and preferably also larger than the larger outer diameter. This increases the effective area accordingly.

[0012] In this case, it is advantageous if the sealing element has a cross-sectional expansion on its outer side at the end furthest from the igniter. This provides an additional seal between the disc-shaped component and the housing.

[0013] If the sealing element has a circumferential sealing rib on its area furthest from the igniter, this seal is further improved.

[0014] It is preferred that the sealing element is axially preloaded against the housing when installed. This axial preload serves, on the one hand, to prevent ringing noises and, on the other hand, to compensate for the different thermal expansions of the materials used.

[0015] Furthermore, this design allows for a radial gap between the sealing element and the housing on the side of the stage facing the detonator. This significantly simplifies actuator assembly because the piston rod with the attached sealing element (or the sealing element alone) can be inserted from the detonator side without friction hindering the process. When the detonator is then inserted, it exerts an axial force on the piston tip and thus on the piston rod, creating axial preload on the sealing element against the housing and thereby achieving the sealing effect.

[0016] On the other hand, it is advantageous if there is an interference fit between the sealing element and the piston rod on the side of the stage facing the igniter; that is, the inner diameter of the sealing element (preferably the larger inner diameter) is smaller than the corresponding outer diameter of the piston rod before assembly. Since the sealing element is made of an elastic material, it holds itself in place on the piston rod once it has been slid onto it, which facilitates assembly.

[0017] According to one embodiment of the invention, the sealing element can expand when the actuator is triggered, thus releasing the piston rod. In this case, the step should ideally have no sharp edges, but rather be as rounded as possible; a continuous change in diameter is also possible.

[0018] As is the case according to EP 2699455 B, which has already been mentioned several times, it can also be provided in the present invention that the sealing element is torn apart when the actuator is triggered, so that the piston rod can be pushed out.

[0019] Tearing is facilitated if the angle of the sealing element's step to the inner surface in the direction of the detonator is a maximum of 90°. The sealing element can easily tear at such a sharp angle, especially if the cross-section of the sealing element is also reduced in this area.

[0020] Furthermore, it is advantageous to have a circumferential projection in the area of ​​the sealing element's step. Such a projection can be deformed more easily than the entire sealing element, thus increasing the travel required to achieve a specific axial preload. This prevents minimal piston displacements from negatively affecting the axial preload. Additionally, a depression, a kind of groove, inevitably forms next to the projection, where the sealing element is particularly prone to tearing.

[0021] The tearing of the sealing element can be further facilitated by the fact that the step of the piston rod has a sharp edge or an undercut.

[0022] Suitable materials for the sealing element include rubber, TPE, or silicone. Using such materials ensures that the sealing element has a hardness of 50-90 Shore A and an elastic elongation of at least 0.4 mm perpendicular to the longitudinal axis, meaning it can withstand an increase in diameter of at least 0.4 mm without breaking.

[0023] To fix the piston rod in its initial position, it is advantageous if the sealing element has a penetration force for the piston rod of at least 200 N; a penetration force of at least 300 N is particularly advantageous.

[0024] A particularly simple design results when the sealing element has two essentially cylindrical sections with different inner diameters. In this case, the piston rod can also be cylindrical on both sides of the stage. Brief description of the drawings The present invention is explained in more detail with reference to the accompanying drawings. They show: Fig. 1 an actuator according to the invention in perspective view; Fig. 2 the same in longitudinal section; Fig. 3 the excerpt III of Fig. 2 on an enlarged scale; and Fig. 4 the sealing element on the same scale as in Fig. 3. Best way to implement the invention

[0025] How to make Fig. 1 detects that the pyrotechnic actuator 1 has a housing 2 that is firmly connected to a holder 3. In Fig. Figure 2 shows this pyrotechnic actuator 1 in longitudinal section, with detail III in Fig. Figure 3 is shown enlarged. It should be noted that the sealing element 5 is shown in its initial (undeformed) position and therefore overlaps with other components. This serves to illustrate where the sealing element 5 is deformed; in reality, the sealing element rests against the adjacent component in these overlapping areas with a certain pressure (due to the elasticity of the sealing element) without actually overlapping.

[0026] In Fig. 2 and Fig. Figure 3 shows that the housing 2 has a taper 19 and subsequently a tapered area 18, onto which the holder 3 was slid until it abutted the taper 19. Then the housing 2 was bent outwards in area 18a, so that a firm connection exists between the housing 2 and the holder 3.

[0027] How to make Fig. As can be seen from the housing 2, a gas generator 20 is located at the opposite end of the housing 2. This gas generator 20, as is typical, includes an igniter 21 with electrical connections 22 and a propellant charge 23. This gas generator 20 has an annular disk 25 that projects slightly outwards. On both sides of this disk 25, the housing 2 is pressed together in the areas 26, so that the gas generator 20 is reliably fixed within the housing 2.

[0028] Following the gas generator 20, a piston is provided in the housing 2, which has a piston tip 4a that transitions into a piston rod 4. This piston rod 4 extends through the entire housing 2 and protrudes from it at its end. At this end, a tapered section 15 is provided, onto which a disc-shaped component 16 was slid. The tapered section 15 was then plastically deformed, for example by riveting (riveted area 17) or by crimping. The disc-shaped component 16 is thus reliably fixed to the end of the piston rod 4.

[0029] A sealing element 5 is provided between the piston rod 4 and the housing 2 (see also Fig. 4), which is particularly designed according to the invention. First, it is externally adapted to the contour of the housing 2, i.e., it has a region with a larger outer diameter 8 and a region with a reduced outer diameter 9, which lies in the tapered region 18 of the housing 2. The piston rod 4 (see Fig. 2 and Fig. 3) has a region with a larger outer diameter 12 and a region with a reduced outer diameter 13, with a step 14 located between these regions. Accordingly, the sealing element 5 (see Fig. 4) a region with a larger inner diameter 7 and a region with a smaller inner diameter 6, between which a step 27 is located. When the gas generator 20 is now ignited, the step 14 of the piston rod 4 cuts through the sealing element 5, so that the piston rod 4 can then extend unhindered.

[0030] In the illustrated embodiment, the sealing element 5 has a cross-sectional expansion 10 outside the housing 2 with a sealing rib 11. The sealing rib 11 lies against the disc-shaped component 16 (see Fig. 2 and Fig. 3) so that sealing also takes place here.

[0031] To allow the sealing element 5 to be easily inserted from the gas generator side, its larger outer diameter 8 is slightly smaller than the inner diameter of the housing 2. To ensure a reliable seal nonetheless, the sealing element 5 is axially pre-tensioned. This is achieved during manufacturing by inserting the gas generator 20 not only until it rests against the piston tip 4a, but a little further, so that the sealing element 5 is pre-tensioned and presses against the tapered section 19. The gas generator 20 is then fixed in this position by reducing the diameter of the housing 2 in the areas 26 on both sides of the disk 25.

[0032] To ensure that this pre-tensioning of the sealing element 5 does not require too much force, in the area of ​​stage 27 (see Fig. 4) A circumferential projection 28 is provided, which is directed towards the detonator. This projection 28 acts as a kind of spring; it can be easily and relatively far compressed and thus exerts a force in the direction against the taper 19 (see Fig. 2 and Fig. 3) safely over a very long period of time.

[0033] Should the piston nevertheless move towards the igniter 21, the cross-sectional expansion 10 of the disc-shaped component 16 will be pressed against the bent area 18a of the housing 2, so that a seal against the outside world is also provided in this case.

[0034] The assembly process is as follows:

[0035] First, the tapered section 18 of the housing 2 is inserted into the holder 3 until it rests against the tapered section 19, and section 18a is bent outwards so that the housing 2 and holder 3 are firmly connected. Then, the sealing element 5 is inserted into the housing 2 from the gas generator side until the cross-sectional expansion 10 protrudes from the housing 2. This is easily achieved due to the elasticity of the sealing element 5, as it is tubular and the cavity in the middle is free, allowing the inner diameters 6 and 7 to be slightly reduced. Finally, the piston, with the piston rod 4 leading, is inserted into the housing 2 from the gas generator side until the piston rod 4 contacts the sealing element 5. Since this has an inlet slope 5a, it is easy to guide the piston rod 4 into the axial cavity of the sealing element 5 and to push the piston tulip 4a further until the piston rod 4 emerges from the sealing element 5.The sealing element 5 is now fixed by the piston rod 4, i.e., on both sides of the tapered area 18 there is material of the sealing element 5, thus axially fixing the sealing element 5.

[0036] Next, a punch is used to press down on the piston tip, thus pushing the piston, or more precisely the piston rod 4, slightly further out of the housing 2 (whereby the sealing element 5 is pre-tensioned in the area of ​​the narrowing 19 of the housing 2). The disc-shaped component 16 is then placed onto the narrowed section 15 of the piston rod 4, and the protruding portion of the narrowed section 15 is riveted, resulting in the riveted section 17. The force required for riveting (several kN) must be absorbed by the punch. Other methods, such as crimping or welding, are also possible instead of riveting. When the punch is then removed, the sealing element 5 relaxes and moves the piston back slightly, thus pre-tensioning the sealing element 5 in the area of ​​the sealing rib 11. This creates an additional seal due to the cross-sectional expansion 10, which is further reinforced if the piston rod 4 moves towards the igniter 21.

[0037] Finally, the gas generator 20 is inserted and used to push the piston slightly further into the housing 2 (though less far than previously with the plunger), thereby pressing the sealing element 5 from the step 14 against the reduction 19, so that the sealing element 5 is again axially pre-tensioned. In this state, the diameter of the housing 2 is now reduced in the areas 26.

[0038] If the sealing element 5 does not have a cross-sectional expansion 10, assembly can be simplified. Instead of first sliding the sealing element 5 into the housing 2, it can be slid directly onto the piston rod 4, and then the piston, together with the sealing element 5, can be inserted into the housing 2 from the gas generator side.

[0039] However, a similar assembly is possible even with the cross-sectional expansion 10 present. In this case, the sealing element 5 is only placed onto the piston rod 4 until the step 14 of the piston rod 4 rests against the inlet chamfer 5a. This is possible because the larger inner diameter 7 of the sealing element 5 is slightly smaller in its relaxed state than the larger outer diameter 12 of the piston rod 4. In this state, the piston, together with the sealing element 5, is inserted into the housing 2 from the gas generator side. In this state, the axial cavity of the sealing element 5 is free in the area of ​​the cross-sectional expansion 10, allowing the sealing element 5 to be slightly compressed there. The piston, together with the sealing element 5, can then be inserted until the sealing element 5, with its cross-sectional expansion 10, protrudes from the housing 2. In this state, the sealing element 5 rests against the reduction 19 and therefore cannot be inserted any further.If pressure is applied further to the piston tulip 4a, the step 14 passes over the inlet chamfer 5a into the area of ​​the sealing element 5 with the larger inner diameter 7, until the step 14 abuts the step 27 of the sealing element 5. The assembly then proceeds as described above.

[0040] The sealing element 5 centers the piston rod 4 in the housing 2, and when the gas generator 20 is ignited, the sealing element 5 guides the piston rod 4 as it extends.

[0041] In the example shown, the piston nozzle 4a is not sealed against the housing 2, meaning that the pressure around the piston rod 4 is approximately the same as between the gas generator 20 and the piston nozzle 4a. The effective force is therefore calculated by multiplying this pressure by the cross-sectional area of ​​the piston rod 4 (and not the cross-sectional area of ​​the piston nozzle 4a).

[0042] Since the gas pressure of the gas generator 20 prevails around the piston rod 4 when the gas generator 20 is triggered, a seal should also exist between the piston rod 4 and the housing 2. The seal between the sealing element 5 and the piston rod 4 is automatically provided because the sealing element 5 rests elastically against the piston rod 4. After the sealing element 5 breaks off, there appears to be no longer a seal between the sealing element 5 and the housing 2 because the step 14 of the piston rod 4 no longer presses against the sealing element 5. However, this is not a problem because the gas pressure wave strikes the end face 29 of the sealing element 5, thereby axially loading it and pressing it against the tapered section 19. Reference symbol list: 1 actuator 2 cases 3 holders 4 piston rod 4a Piston tulip 5 Sealing element 6 smaller inner diameter of 5 7 larger inner diameter of 5 8 larger outer diameter of 5 9 smaller outer diameter of 5 10 Cross-sectional widening from 5 11 Sealing rib 12 larger outer diameters of 4 13 smaller outer diameter of 4 14th grade between 12 and 13 15 tapered section of 4 16 disc-shaped component 17 riveted area 18 tapered area of ​​2 18a Area of ​​2, bent outwards 19 Rejuvenation of 2 20 Gas generator 21 detonators 22 electrical connections 23 propellant charge 25 slices out of 20 26 range of 2 by 25 27th level 28 lead 29 Front surface QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] GB 2375329 A

[0003] DE 102008039168 A

[0003] WO 2015 / 072293 A

[0003] US 2018038393 A

[0003] EP 2546531 A

[0003] US 2015175496 A

[0003] AT 511500 B

[0004] EP 2699455 B [0005, 0009, 0018] WO 2012 / 144939 A

[0005] WO 2011 / 138553 A

[0006]

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