DE102011106513A1 - Pyrotechnic actuator for vehicle safety device, has exhaust that is designed such that flow connection is blocked in end section of piston, where piston is arranged in cylinder tube with longitudinal axis and is displaced in axial direction - Google Patents

Abstract

The pyrotechnic actuator (10) has an exhaust that is designed such that flow connection is blocked in the end position of piston (32). The piston is arranged in a cylinder tube (12) with a longitudinal axis, and is displaced in the axial direction from a starting position to an end position through an intermediate position. A pressure chamber in the cylinder tube is formed between a gas generator and the piston, and is actuated by the pressurized propellant combustion. The piston after reaching the end position against the resistance of a trapped gas is displaced to the intermediate position.

Description

The invention relates to a pyrotechnic actuator, in particular for a vehicle safety device.

In pyrotechnic actuators, which are designed as a linear drive, a guided in a cylinder tube piston is driven by the expansion of a gas generated by a gas generator, such as a pyrotechnic lighter gas. The piston is thus displaceable in the cylinder tube and reaches after such a displacement an end position, in some cases, a later provision of the piston may be desired. The gas trapped between the gas generator and the piston must be discharged to the outer environment of the cylinder tube. For this purpose, various venting concepts are known.

One of these concepts, as for example the publication DE 103 05 685 54 describes, provides radial vent holes in the cylinder tube or in the piston. In these solutions, however, it is conceivable that gas can escape even before reaching the end position of the piston, which reduces the efficiency or the performance of the drive. For most applications, it must also be ensured that the piston can hold its end position for a certain period of time while withstanding a certain counterforce. To achieve this, more gas would have to be generated over a longer period, and / or the vent holes would have to be so small that after reaching the end position not all the gas can escape too quickly. However, the production of such small radial vent holes, in particular by punching or drilling, is difficult, even if in a series product tight tolerances in terms of reliability and reproducibility are observed. In addition, the radial bores must be secured over the entire life of the actuator against the entry of contaminants and moisture with additional components (sealing plug, dam o. Ä.). These components must then reliably release the vent holes at a predetermined opening pressure. In a series production in particular the compliance with the correct orientation of the vent hole (s) increases the assembly effort to a considerable extent.

The object of the invention is therefore to improve a pyrotechnic actuator with respect to the holding of the end position and the recoverability of his piston.

This object is achieved according to the invention by a pyrotechnic actuator having the features of claim 1. Advantageous and expedient embodiments of the pyrotechnic actuator according to the invention are specified in the subclaims.

The pyrotechnic actuator according to the invention comprises a gas generator having a fuel, a cylinder tube having a longitudinal axis, a piston arranged in the cylinder tube, which is displaceable from an initial position, via an intermediate layer, in an end position in the axial direction, in the cylinder tube between the gas generator and the pressure chamber formed by the piston, which is acted upon by combustion of the fuel with pressure, and a vent, which is at least in the intermediate position of the piston, a flow connection between the pressure chamber and the outer environment of the cylinder tube produced. According to the invention, the vent is designed so that the flow connection is blocked in the end position of the piston. Under an intermediate position of the piston is to be understood in this context, a position of the piston between the starting position and the end position.

The invention is based on a different concept than the solutions known from the prior art. Although it is a vent provided, but this is ineffective in the end position of the piston. Thus, in the end position of the piston, no gas can escape from the expanded pressure chamber, and the piston remains safely in the extended position.

The actuator according to the invention is characterized in particular by a very simple structure, which manages without additional components. In contrast to known actuators with radial ventilation holes, no particular orientation must be observed when installing the actuator. There are also no additional measures to protect against ingress of dirt and moisture during the life of the actuator necessary.

The inventive construction of the pyrotechnic actuator also allows a provision of the piston. For this purpose, it is provided that the piston is displaceable after reaching the end position against the resistance of the gas in the pressure chamber in the intermediate layer in which the vent is effective. In the intermediate layer thus the gas can be removed, and the resistance to the provision of the piston is eliminated, at least greatly minimized. The invention allows by appropriate design of the flow connection in particular embodiments in which the piston is pressed only by a short distance linearly into the cylinder tube, so does not need to be rotated in order to achieve the intermediate position.

Immediately after reaching the end position of the piston, the resistance for a return movement of the piston in the intermediate layer is still very large, so that a desired support function of the actuator, such as the setting up of a hood to protect a pedestrian, is reliably maintained. However, with decreasing gas temperature in the pressure chamber, the resistance gradually decreases, and it is easier to manually push the piston into the intermediate layer.

The preferred embodiment of the invention provides that the vent has a groove formed on the inner wall of the cylinder tube and / or that the vent has a cylinder tube area with extended inside diameter. A groove manufacturing technology is relatively easy to manufacture, especially since due to the inventive concept basically no tight tolerances must be met. For a basic function "venting on / off", it is only necessary that gas can flow past the groove at the piston seal at all.

In the simplest embodiment of the venting according to the invention, the groove or the cylinder tube region extends with an expanded inner diameter linearly and preferably in the axial direction.

The flow connection between the pressure chamber and the outer periphery of the cylinder tube can advantageously be automatically blocked in the end position of the piston by the groove is axially spaced from a stop for the piston, which defines the end position of the piston, and the piston in the end position of the pressure chamber seals to the outside. In this case, no further components for the desired interruption of the flow connection in the end position of the piston are necessary. The stop may be formed by a tapered section of the cylinder tube or a stop element mounted in the cylinder tube or at the cylinder tube end.

In order to ensure the most efficient drive of the piston in the starting phase and to prevent as sure as possible that in the end position of the piston gas can flow past this, the piston preferably has a seal which in the starting position, in the intermediate position and in the End position is in contact with the inner wall of the cylinder tube. Such seals are also in known actuators in use. It is advantageous that this piston seal in the actuator according to the invention can also be used to block the flow connection between the pressure chamber and the outer environment of the cylinder tube.

To ensure that in the end position of the piston, the gas, the piston seal can not pass through the groove, the groove should end at an axial distance before the stop, which is greater than the axial distance between the stop and the seal in the end position of the piston , The size of this distance determines how far the piston has to be moved back into the cylinder tube for its return in order to start the vent.

The groove should extend at least over an axial length greater than the axial dimension of the seal. In practice, the axial longitudinal extent but be designed to be larger, so that the piston is not accidentally pushed so far that the groove can no longer act as overflow. The axial longitudinal extent of the groove namely determines the range of possible intermediate layers (positions) in which a venting of the actuator is possible.

So that the piston does not have to be pressed too far into a venting intermediate layer in the case of a desired return (the greater the distance the greater the resistance of the gas enclosed in the pressure chamber), it is recommended that the groove in the distal with respect to the gas generator axial Half, preferably in the distal third and more preferably in the distal quarter of the cylinder tube to order.

A development of the invention provides that the venting of the pyrotechnic actuator has a plurality of grooves.

At least some of the grooves may differ in axial position, length, cross section and / or shape.

On the number and the said parameters of the grooves, an adaptation of the ventilation concept according to the invention to a wide variety of requirements is possible.

According to a particular embodiment of the pyrotechnic actuator according to the invention, the vent on one or more spirally extending grooves. This can be advantageous for influencing the outflow behavior of the gas.

Further features and advantages of the invention will become apparent from the following description and from the accompanying drawings, to which reference is made. In the figures show in perspective view:

1 a conventional pyrotechnic actuator;

2 a sectional view of a cylinder tube of a pyrotechnic actuator according to the invention;

3 a further sectional view of the cylinder tube with a piston in an end position; and

4 a further sectional view of the cylinder tube with the piston in an intermediate position.

In 1 is an example of a pyrotechnic actuator 10 ' represented according to the prior art. The actuator 10 ' includes an elongated cylinder tube 12 ' and one in the cylinder tube 12 ' slidable piston (not visible), from which a piston rod 14 having a smaller diameter than the piston in the longitudinal direction (axial direction). The piston is equipped with a seal, z. B. an O-ring, provided, which is the inner wall of the cylinder tube 12 touched.

At a first end portion 16 ' of the cylinder tube 12 ' is mounted a (not shown here) gas generator with a fuel. The opposite second end portion 18 ' of the cylinder tube 12 ' is tapered, the step between the tapered second end section 18 ' and the adjoining middle section 20 ' of the cylinder tube 12 ' , which has a constant inside diameter, forms a stop 22 ' for the piston.

1 shows the pyrotechnic actuator 10 ' in an initial state, in which the piston and the piston rod 14 ' completely in the cylinder tube 12 ' are included. In the activation case, the fuel is ignited in the gas generator and burns off. The resulting gas abruptly increases the pressure in a pressure chamber formed between the gas generator and the piston, more precisely, the seal of the piston. The pressurization ensures that the piston moves from its initial position in the axial direction into a remote from the gas generator end position in which the piston rod 14 ' from the cylinder tube 12 ' protrudes. The movement is stopped by the piston at the stop 22 ' comes to a standstill.

The pyrotechnic actuator 10 ' has a vent in the form of a radial vent hole 24 ' on, extending completely through the wall of the cylinder tube 12 ' extends through. The axial position of the vent hole 24 ' is determined so that the piston, in particular its seal, the vent hole 24 ' completely before he takes his final position. This ensures that the gas in the expanded pressure chamber passes through the vent hole 24 ' can escape into the environment.

2 shows a cylinder tube 12 a pyrotechnic actuator according to the invention 10 with the exception of the vent as well as the previously described actuator 10 ' is constructed. Instead of the vent hole 24 ' here is a groove 26 provided in 2 is shown only schematically. The groove 26 is on the inside wall 28 of the cylinder tube 12 formed and extends in the illustrated embodiment linearly in the axial direction of the cylinder tube 12 or the actuator 10 , The groove 26 is located in relation to the gas generator distal quarter of the cylinder tube 12 but not enough 22 , More precisely, the groove ends 26 before the stop 22 at a certain distance, which is defined more precisely below. The axial longitudinal extent of the groove 26 is significantly larger than the axial dimension of the seal 30 of the piston 32 ,

The piston 32 of the actuator according to the invention 10 is driven in the same way as in the previously described actuator 10 ' , When the piston 32 at the stop 22 comes to a stop and takes its final position, seals the piston 32 , more precisely its seal 30 , the expanded pressure chamber to the outside. The piston 32 but not wedged or jammed in the final position, and he is not prevented in any other way by a mechanical device to a return movement.

The axial distance of the groove 26 from the stop 22 is sized so that the groove 26 in the piston end position not to the seal 30 of the piston 32 reaches as in 3 that the piston 32 in the final position shows, can be seen. The gas generated by the gas generator thus has no possibility to escape from the expanded pressure chamber. The piston 32 holds in this condition alone due to the enclosed gas in the pressure chamber of an application-specific predetermined counterforce, ie the end position of the piston 32 is stable.

So that through the groove 26 formed vent can exert its effect, the piston must 32 against the resistance of the gas in the pressure chamber as far back into the cylinder tube 12 be pressed until the groove 26 the seal 30 of the piston 32 covered. 4 shows an example of one of many liners of the piston 32 that meets this requirement.

In the intermediate position of the piston 32 forms the groove 26 an overflow channel, and the gas can pass through the groove 26 at the seal 30 and on the piston 32 passing through the tapered second end portion 18 of the cylinder tube 12 emanate into the environment. Important for the function of the actuator 10 is that the seal 30 of the piston 32 in the initial position and in the end position of the piston 32 in contact with the inner wall of the cylinder tube 12 stands.

The groove 26 thus puts in the intermediate position of the piston 32 a flow connection between the expanded pressure chamber and the outer periphery of the cylinder tube 12 ago. In the end position of the piston 32 is this However, fluid communication is deliberately blocked to prevent unwanted return of the piston 32 to prevent.

Of course, several grooves 26 be provided to meet the above-mentioned requirements for the axial position and the axial extent. The grooves 26 may differ in length, cross section and / or course within these requirements. It is also an embodiment with one or more spiraling grooves 26 possible.

By suitable choice of the number, the course, the length, the cross-sectional size and shape as well as further parameters of the grooves 26 in coordination with the axial piston length, the outflow behavior of the gas can be influenced in such a targeted manner that a large number of application-specific requirements can be covered.

So place the position and the axial length of the grooves 26 determines at which piston strokes gas can flow out of the pressure chamber. The number and cross section of the grooves 26 determine the volume flow (amount per unit time) of the outflowing gas. Also by a special course or a special shape of the grooves 26 (eg spiral instead of straight, axial course; different length of several grooves 26 ; progressive cross section change in the axial direction; etc.), the volume flow of the escaping gas can be set in the desired manner.

In particular, the grooves can 26 be positioned and designed so that at the beginning of the piston movement escapes no or only a negligible proportion of the gas.

Instead of the groove or grooves 26 In general, this can also be an area of the middle section 20 of the cylinder tube 12 have an extended inner diameter. For the axial position and extent of this range, the same requirements apply as for the grooves 26 ,

LIST OF REFERENCE NUMBERS

10, 10

pyrotechnic actuator

12, 12 '

cylinder tube

14, 14 '

piston rod

16, 16 '

first end section

18, 18 '

second end section

20, 20 '

midsection

22, 22 '

attack

24 '

vent hole

26

groove

28

inner wall

30

poetry

32

piston

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 1030568554 [0003]

Claims (9)

Pyrotechnic actuator, with a gas generator having a fuel, a cylinder tube ( 12 ) with a longitudinal axis, one in the cylinder tube ( 12 ) arranged piston ( 32 ), which is displaceable from an initial position, via an intermediate layer, into an end position in the axial direction, one in the cylinder tube ( 12 ) between the gas generator and the piston ( 32 ) pressure chamber which can be acted upon by combustion of the fuel, and a vent, by means of which at least in the intermediate position of the piston ( 32 ) a flow connection between the pressure chamber and the outer environment of the cylinder tube ( 12 ) can be produced, characterized in that the vent is designed so that the flow connection in the end position of the piston ( 32 ) is blocked. Pyrotechnic actuator according to claim 1, characterized in that the piston ( 32 ) is displaced after reaching the end position against the resistance of the gas enclosed in the pressure chamber in the intermediate layer. Pyrotechnic actuator according to claim 1 or 2, characterized in that the vent one on the inner wall ( 28 ) of the cylinder tube ( 12 ) formed groove ( 26 ) and / or that the vent has a cylinder tube area with an expanded inner diameter. Pyrotechnic actuator according to claim 3, characterized in that the groove ( 26 ) or the cylinder tube area extends with extended inner diameter linearly and preferably in the axial direction, and / or characterized in that a stop for the piston ( 32 ), the end position of the piston ( 32 ), whereby the groove ( 26 ) is axially spaced from the stop and the piston ( 32 ) seals in the end position, the pressure chamber to the outside. Pyrotechnic actuator according to claim 5, characterized in that the piston ( 32 ) a seal ( 30 ), which in the starting position, in the end position and in the intermediate layer in contact with the inner wall ( 28 ) of the cylinder tube ( 12 ) stands. Pyrotechnic actuator according to claim 6, characterized in that the groove ( 26 ) terminates at an axial distance before the stop, which is greater than the axial distance between the stop and the seal ( 30 ) in the end position of the piston ( 32 ). Pyrotechnic actuator according to claim 6 or 7, characterized in that the groove ( 26 ) extends over an axial length which is greater than the axial dimension of the seal ( 30 ), and / or characterized in that the groove ( 26 ) in the distal relative to the gas generator axial half, preferably in the distal third and more preferably in the distal quarter of the cylinder tube ( 12 ) is arranged. Pyrotechnic actuator according to one of claims 3 to 9, characterized in that the venting a plurality of grooves ( 26 ) having. Pyrotechnic actuator according to claim 10, characterized in that at least some of the grooves ( 26 ) in the axial position, length, cross-section and / or course, and / or characterized in that the venting one or more spiral grooves ( 26 ) having.

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