DE19702899C1 - Pyrotechnical ignition device control method for motor vehicle airbag gas generator - Google Patents

Abstract

The method involves feeding an ignition voltage (Uzund) to a pyrotechnical ignition unit (1) via a switching element (S) from an autonomous capacitor (C) parallel to the voltage supply (UB). Immediately after ignition of the unit the switching element returns to the open, non-conducting state. The potential drop across the capacitor is used to determine the time at which the switching element is driven into the open state.

Description

The invention relates to a method for the electrical control of pyro technical ignition devices according to the preamble of the patent claim 1.

Such an electrically controllable, pyrotechnic ignition device is known from DE-OS 37 38 862 A1. It has an electrically triggered one Ignition unit with an igniter and an igniter. By The ignition device is triggered when an ignition voltage is applied.

It is also known that to ensure the ignition voltage for Ignition timing an autarky capacitor is used, which he one hand the ignition voltage even if the operating voltage is briefly lost maintains and on the other hand the ignition energy in whole or in part includes. The disadvantage of these circuit arrangements is that in and after Ignition timing a high load on the source of the company supply tension occurs. This can be intensified if the Ignition device due to the high mechanical or thermal Load a short circuit of the two ignition electrodes or on one of the both occurs against the ground.

DE-OS 37 38 862 A1 therefore proposes that the state of self-sufficiency Capacitor checked and if a defect is found this is separated. In addition, the trigger means, i.e. the pyro technical ignition devices, a predetermined time for their activation permanently connected to the operating supply source. This is what the DE-OS 37 38 862 A1 an evaluation device connected to timing elements. This time-controlled procedure is to be supplemented by the evaluations device monitors the amount of energy supplied to the release means and determines whether a sufficiently large amount of energy has been supplied.  

Such energy quantity monitoring has already been described in DE-OS 37 38 862 A1 even in the prior art as difficult and expensive realize characterized. In addition, the time-controlled process should adapted to the ambient temperature by means of a temperature sensor and thus ensure that the pyrotechnic ignition devices the required amount of energy has been made available.

The object of the invention is a method for electrical control of pyrotechnic ignition devices to show which is simple The source of the operating supply voltage should be as low as possible burdened and at the same time ensures that a sufficiently large energy quantity was supplied.

The task was accomplished through the characteristic features of the patent Claim 1 solved.

Immediately after the pyrotechnic ignition device has burned down, this becomes Switching element switched back in the open state by the Drop in ignition voltage across the self-sufficiency capacitor as a measure of that Determine when to use. On the one hand, this becomes a long-term earth short circuit over the possibly short-circuited Avoided electrodes of the ignition devices and on the other hand the Self-sufficiency capacitor, if present, only partially discharged, so that the Source the operating supply voltage to the capacitor by only one reloads small amount. The source of the operating supply voltage is thus significantly relieved, which on the one hand significantly improves operational safety increases and on the other hand offers the possibility to lower the source dimension and thus save costs. There is also surveillance that of the ignition voltage can easily be implemented via the self-sufficient capacitor and does not require a complex evaluation device.

Advantageous developments of the inventive method show the Claims 2 to 4.

Claim 2 teaches that to determine the switch-off time the ignition voltage drop this advantageously with a reference voltage is compared, which forms a threshold at which Falling below the switching element again in the open state is controlled.  

This further development is made possible by an easily implementable method steps, in particular without measuring devices within the ignition direction, the time after the ignition device has burned down can be seen because the ignition voltage is clearly due to the ignition current falls off.

The use of this method proves to be particularly advantageous in a BUS system for individual control of pyrotechnic Ignition devices for vehicle safety devices, in particular airbag Gas generators, belt tensioners or similar. These BUS systems allow individual and therefore also to trigger individual safety systems with a time delay. Therefore But it must be ensured that after the first triggering a Ignition device the BUS system continues to work safely and others Ignition devices can possibly be triggered later. By the extensive relief of the source of the operating supply voltage it is ensured that this does not fail prematurely and also at several already triggered ignition devices for the other of the required nominal amount of the operating supply voltage for communication cation is present. Relief of the source of the Operating supply voltage in a BUS system, if the source is next the operating supply voltage also modulated data, e.g. B. the Zünd transmits signal data, since here with a high ohmic capacitance Load from the first triggered ignition devices from the source on the one hand no longer apply the level for the power supply and on the other hand, no longer the required slope for the modulated ones Can ensure data pulses.

The invention is explained in more detail below on the basis of exemplary embodiments with reference to FIGS. 1 to 5.

Show it:

Fig. 1 block diagram of an electrically controllable ignition device,

Fig. 2 block diagram of an electrically controllable ignition device with an evaluation of the ignition voltage across the capacitor,

Fig. 3 circuit arrangement for driving an ignition device with a comparison circuit for resetting the switching element,

Fig. 4 level scheme before process-related variables; during and after ignition of the ignition device,

Fig. 5 BUS system with several ignition devices and a combined data and supply line.

Fig. 1 shows in the form of a block diagram the basic structure of a pyrotechnic ignition device. The poles of the ignition unit ( 1 ) are connected to ground, the other to the first pole of the switching element (S). At the second pole of the switching element (S) the supply voltage (U _B ) and the self-sufficiency capacitor (C) are connected on the one hand via a diode (D) and a decoupling resistor (R _e ). The self-sufficiency capacitor (C) is connected to ground and is charged by the supply voltage (U _B ) or kept in the charged state. The ignition voltage (U _Zünd ) is thus tapped across the capacitor (C). Even if the supply voltage (U _B ) drops briefly, the ignition voltage (U _Zünd ) can thus be kept ready. If the control unit ( 2 ) receives a safety-critical signal via the data line (Data-In) or the command to trigger the ignition device, the control unit ( 2 ) closes the switching element (S). After a certain time, which according to the invention is only so large that the ignition unit can ignite, the switching element (S) is reset. Basically, this can be done by various mechanisms, e.g. B. by specifying a fixed time, a level threshold or the like.

The execution of the electrically controllable switching element are available Various possible technical variants open, e.g. B. as a magnet switch, switching transistor or the like. It is crucial for the invention that Switching element is not only switchable, but also resettable.

In FIG. 2, the control unit ( 2 ) from FIG. 1 is replaced by an expanded control unit ( 3 ) which, in addition to the data input (Data-In), also has a tap of the ignition voltage (U _Zünd ). The ignition voltage (U _Zünd ) is evaluated in the control unit ( 3 ). This is symbolized as area ( 3.1 ) of the extended control unit ( 3 ). If the ignition voltage (U _Zünd ) falls below a predetermined threshold value, the switching element (S) is opened again or cannot be closed. In addition, the extended control unit ( 3 ) carries out the functions of the control unit ( 2 ) from FIG. 1, as shown as area ( 3.2 ) of the extended control unit ( 3 ), quasi identical to the control unit ( 2 ) in FIG. 2 is.

Fig. 3 shows a circuit arrangement for performing the method according to claim 4. The switching element (S) is designed as a MOSFET (n-channel enhancement type). The ignition unit ( 1 ) is connected to the source output. On the drain side is the self-sufficient capacitor C, which receives a pulsed voltage signal from the supply voltage (U _B ) via a decoupling resistor (R _E ) and a diode (D), which prevents the capacitor from discharging in the direction U _B. This pulse-shaped voltage signal is also received by the evaluation unit ( 4 ), preselected via the comparators (K₁ and K₂). The comparison voltages (U₃, U₄) of the comparators (K₁, K₂) are chosen so that they are each between the levels of the pulse-shaped signal (U₀, U₁, U₂), so U₀ <= U₃ <= U₁ <= U₄ <= U₂). The evaluation unit ( 4 ) processes the data and, after receiving the trigger information, sets the first switching signal S 1 to "high". In normal operation, the capacitor (C) is charged with a voltage approximately the upper level (U₂) of the operating supply voltage (U _B ). Since the level of the reference voltage (U _ref ) is significantly below the level (U₂), but still above the signal level (U₁), the second switching signal (S₂) will be "High" when the capacitor (C) is charged. In the logical "AND" element ( 5 ) the final switching signal (S _e ) is formed when the first switching signal (S₁) and the switching signal (S₂) lying in normal operation at "High" and the gate connection of the switching element (S ) placed. As a result, the drain-source channel becomes conductive and the ignition current (i _Zünd ) can flow; the ignition is triggered.

If the voltage across the capacitor (C), ie the ignition voltage (U _Zünd ), _drops after a few milliseconds below the threshold value which defines the reference voltage (U _ref ), the second switching signal (S₂) automatically becomes "Low". The final switching signal (S _e ) follows this due to the logic operation (AND gate 5 ), so that the gate connection is de-energized and the drain-source channel becomes non-conductive again.

The circuit has thus independently over-discharging the capacitor (C) or a permanent short to ground of the operating supply source (U _b ) due to a short circuit in the ignition unit ( 1 ) avoided. The signal transmission via the pulses of the supply voltage remains ensured. Other modules can still be controlled.

Fig. 4 shows a prior level procedural schemes relevant variables, during and after ignition of the ignition device.

In detail, these are:

FIG. 4a) of the operating level of the supply voltage,

FIG. 4b) symbolic of the signal at the data input (Data In) is a function that t the transfer of the trigger information as Chrash- level from the time _{a crash} describes

Fig. 4c) of the temporal course of the ignition current (i _ignition) upon the occurrence of the short circuit,

Fig. 4d) of the temporal course of the ignition voltage U _ignition, which is identical to the capacitor voltage is in normal operation and a cyclic loading of the capacitor indicated by the pulses of the operating power supply voltage,

Fig. 4e) Abbrandverlauf,

Fig. 4f) the switching phases of the switching element.

The embodiment in Fig. 4 has a pulsed operating supply voltage U _b ( Fig. 4a), which is used in particular in the combined transmission of data by means of the operating supply voltage. Even at fixed levels of the operating supply voltage, the application of the invention makes sense, since these sources must not be overloaded. However, loads on the operating supply voltage source are even more critical if they are also to be used to transmit data.

The ignition voltage (U _Zünd ) in Fig. 4d, which is identical to the capacitor voltage, shows a cyclical loading of the capacitor (C) and a slight drop in the respective pulse pauses in normal operation. As shown symbolically in function b 4, at time t _crash, the triggering information (crash level) to the data input (Data-In), where the control unit. Then the switching element (S) is switched on ( Fig. 4f). The ignition current I _Zünd increases suddenly ( FIG. 4c) and triggers the burnup ( FIG. 4e). The ignition voltage (U _Zünd ) across the capacitor drops. The load on the source of the operating supply voltage (U _b ) is so great that the quality of the pulses in amplitude and slope steeply decreases significantly (see. Fig. 4a). In addition, a possibly occurring short-circuit current (I _{short-circuit} ) is shown in FIG. 4c, which can arise between the electrodes due to the uncontrollable erosion of the ignition material. Due to the high loads falls at time t _from the ignition voltage (U _ignition) across the capacitor falls below the predetermined threshold value (U _S), whereupon the switching element (S) is set to "OFF / OPEN". If this were not done, the capacitor voltage would first drop even further and would have to be recharged via the source (U _b ). The pulses of the operating supply voltage remained weak and dirty or the source (U _b ) fails. If additional ignition devices are now fired, the load increases further and the risk of the source or the BUS system failing.

The use of this method in a BUS system which controls a plurality of ignition devices (ZE) is shown in FIG. 5. This embodiment example again shows the advantageous use for BUS systems with a combined supply and data source (U _b ). The circuit arrangement of each ignition device (ZE) corresponds to that shown in FIG. 3.

A pulse-shaped voltage signal is generated via the source (U _B ), which on the one hand holds the voltage across the capacitor (C) in a certain level range and on the other hand transports data. Using the data information, the individual addressing and command transmission to the individual ignition devices (ZE _i ) can take place. A section of a pulse sequence of the operating supply voltage source (U _B ) has sequences in which information for the individual ignition devices (ZE _i ) is transmitted. So follows a pulse sequence for charging the capacitor (level U₁ → U₂), a first information sequence (level (U₀ → U₂) for the first ignition device (ZE _i ), after another charging pulse sequence (level U₁ → U₂), a second information sequence, this or for the second ignition sequence, for example for the second ignition device (ZE _{i + 1} ) It is also conceivable that a group of ignition devices is addressed with one ignition sequence.

It becomes clear once again how important it is for the operation to be so safe safety-relevant bus systems is that the source of the company supply voltage as low as possible and the data transmission continues is ensured, even if one of the ignition devices already is ignited.

Claims (4)

1. A method for the electrical control of pyrotechnic ignition devices, in particular igniters of airbag gas generators, in which an ignition voltage (U _Zünd ) from an operating voltage _source (U _b ) and in an autarky capacitor (C) for triggering by means of a switching element (S) ) provided parallel to the operating supply voltage (U _b ) and applied to a pyrotechnic ignition unit ( 1 ), characterized in that immediately after the pyrotechnic ignition unit ( 1 ) has burned down, the switching element (S) is again controlled into the open, non-conductive state by the Drop in the voltage across the self-sufficiency capacitor (C) is used to determine the time at which the switching element (S) is controlled again in the open, non-conductive state. 2. The method according to claim 1, characterized in that the voltage across the self-sufficient capacitor (C) is compared with a threshold-forming reference voltage (U _ref ). 3. The method according to any one of the above claims, characterized records that it is in a BUS system for the individual control of Automotive security devices are used. 4. The method according to any one of the above claims, characterized records that it ver for a combined supply voltage source is used in which the voltage for the purpose of data transmission is pulse-shaped.