Ammunition and explosives – Igniting devices and systems – Ignition or detonation circuit
Reexamination Certificate
2000-05-11
2001-08-28
Jordan, Charles T. (Department: 3641)
Ammunition and explosives
Igniting devices and systems
Ignition or detonation circuit
C102S218000, C102S206000
Reexamination Certificate
active
06279479
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a method for firing a firing cap of a vehicle occupant protection system of a motor vehicle. Furthermore, the invention is directed at a firing circuit of the vehicle occupant protection system of the motor vehicle. The firing circuit contains a firing switch connected in series with the firing cap and can be actuated by a firing pulse. The circuit further contains at least two capacitors for energizing the firing cap.
Because the vehicle occupant protection system of the motor vehicle must reliably trigger in the event of an accident (crash) even if a connection to the vehicle electrical system happens to be interrupted, one or more firing capacitors are usually provided. The firing capacitors are charged during normal operation of the motor vehicle and make available the power that is necessary to fire the firing cap or caps of the vehicle occupant protection system. The firing caps are connected to the firing capacitors via a firing switch that can be provided with a current limiter. Because a minimum voltage has to be maintained at the firing cap during the entire firing period in order to ensure that there is a current which does not drop below a specific minimum value, a relatively large part of the power usually remains stored uselessly in the capacitors. The quantity of power that remains must be greater here than the quantity of power consumed. Therefore, relatively large firing capacitors with a high capacitance value and high charge value have to be made available which require large amounts of space and therefore constitute an obstacle to a more compact configuration of the firing circuit. Because the firing caps have to be/are to be fed with a constant current, a current limiter, which consumes a large part of the power, is used.
Published, Non-Prosecuted German Patent Application DE 44 09 019 A1 discloses a firing circuit for a vehicle occupant protection device in a motor vehicle in which two firing capacitors make available sufficient power. Here, only the first firing capacitor is discharged within a first time period starting from the firing before only the second firing capacitor is discharged after a defined time period starting from the firing.
International Patent Disclosure WO 93/17893 discloses a method for triggering a vehicle occupant protection system and a firing circuit. In the known firing circuit, two or more firing capacitors are provided which are connected in parallel with one another and with the motor vehicle battery during normal operation of the motor vehicle, with the result they are each charged to the voltage of the vehicle electrical system. The object of this publication is, in the event of an accident, to supply the firing cap immediately with a voltage that lies significantly above the voltage of the vehicle electrical system, so that the triggering process can reliably start. For this purpose when an accident is sensed, the firing capacitors are immediately connected in series and the firing switch is closed so that the firing cap is supplied with a voltage which is twice as high as the voltage of the vehicle electrical system or is even higher when a plurality of capacitors are used.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method and a firing circuit for triggering a vehicle occupant protection system which overcome the above-mentioned disadvantages of the prior art methods and devices of this general type, which permits reliable firing of the firing cap using relatively small firing capacitors.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for firing a vehicle occupant protection system, which includes:
activating a firing circuit having a firing cap and a firing switch connected in series with the firing cap and the firing switch activated by a firing pulse, the firing circuit further having at least two firing capacitors connected in parallel with one another before a firing process, the firing capacitors can be charged by one of a voltage source and a current source and discharge a stored charge simultaneously into the firing cap in response to the firing pulse; and
maintaining the firing capacitors to remain connected in parallel at a start of the firing pulse and connected in series after a time delay after the start of the firing pulse.
The invention is distinguished by the possibility of using relatively small firing capacitors without the reliability of the correct triggering of the vehicle occupant protection system being adversely affected.
In the invention, a firing process is thus started using firing capacitors that are connected in parallel, the firing capacitors then being, however, switched over from the parallel connection to a series connection during the still persistent firing pulse. This procedure provides the following advantages. At the start of the firing process, the firing cap is supplied only with the simple charge voltage of the firing capacitors so that a firing current flows which has the value which is sufficient to activate the firing cap, but is not higher than the current limiting value. This permits a power loss caused by the current limitation to be avoided. Such a power loss could otherwise occur if the process is begun with a significantly higher excitation voltage provided by an initial series connection of the firing capacitors. However, during the firing process the charge stored in the firing capacitors is reduced so that the flow of current could then drop below the minimum required value. This tendency is counteracted according to the invention by the fact that the firing capacitors are switched over from the parallel connection to the series connection during the firing pulse. The composite voltage which then results being (at least) twice as high as the individual voltage of the firing capacitors which have been connected in parallel until then. The composite voltage is sufficient to maintain the flow of current at or above the minimum current value for a relatively long time without current limitation being performed on the current. With the invention it is thus possible to use a current limiter which is configured for a low power loss.
The switching over from the parallel connection to the series connection is carried out preferably if the voltages at the firing capacitors are approximately halved, i.e. after approximately half of the firing time or in the center of the firing pulse. However, the switching over can also take place earlier or later, preferably between 30% and 70% of the duration of the firing pulse. The switching over can take place after expiry of a specific time interval from the start of the firing pulse. Alternatively, there may also be provision for the voltage and/or the current of the firing pulse to be measured and for the switching over when the voltage and/or the current drops to be carried out to or below a predefined limiting value. In particular, there may also be provision for the firing capacitor voltage to be measured and for the switching over to take place when the voltage drops to or below a predefined limiting value.
After the switching over to series connection, the current can continue to flow across the firing cap until the voltages at the firing capacitors are halved again. Owing to this configuration, only approximately a quarter of the original power remains in the firing capacitors. As a result of this, the overall capacitance of the firing capacitors can be reduced by approximately 25% compared with a procedure without the series connection, with the result that more compact firing capacitors can be used and accordingly the dimensions of the firing circuit can be reduced. The size of the chip area of the current limiter can also be reduced.
It is also possible to use more than two firing capacitors which initially remain connected in parallel at the start of the firing pulse and are then either all connected in series or else merely connected in series to a cert
Greenberg Laurence A.
Jordan Charles T.
Lerner Herbert L.
Semunegus Lulit
Siemens Aktiengesellschaft
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