Electrical transmission or interconnection systems – Vehicle mounted systems – Automobile
Reexamination Certificate
2000-06-09
2001-05-01
Ballato, Josie (Department: 2836)
Electrical transmission or interconnection systems
Vehicle mounted systems
Automobile
C280S735000, C180S274000
Reexamination Certificate
active
06225707
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The invention relates to a method for operating a firing circuit which is configured to actuate at least one firing cap of a firing system, in particular of a vehicle occupant protection system of a motor vehicle. The circuit has at least one firing capacitor for storing the energy necessary to fire the firing cap, and contains a switch which controls the connection between the at least one firing capacitor and the firing cap. The firing cap has a certain internal resistance and it requires, in order to be fired, a current which is at least as high as a predefined minimum current value for at least a specific minimum time period (T).
Firing circuits of this type are used to fire one or more firing caps when necessary, i.e., when it is desired that a pyrotechnic charge be ignited. Such firing circuits can generally be used to trigger explosive processes, but in the present invention they are preferably used in vehicle occupant protection systems of motor vehicles, in particular for securing systems, for example seat belt pretensioning systems or airbag systems.
U.S. Pat. No. 3,949,357 discloses a firing circuit in which the firing cap is arranged in series with two switches which are closed when the vehicle is subject to a collision. In other words, the switches serve as crash sensors. The firing circuit is fed by a battery which makes available the necessary firing energy.
U.S. Pat. No. 5,554,890 (German published patent application DE 44 09 019 A1) discloses a firing circuit that is provided with its own firing capacitor array which is charged to a predefined charge voltage during the normal operation of the motor vehicle, by a voltage or current generator which is fed from the motor vehicle battery. The firing capacitor array is composed in the simplest case of a single firing capacitor which is connected in parallel with the voltage or current generator, but it can also contain two or more firing capacitors which are connected in parallel or in series.
U.S. Pat. No. 5,929,535 (German patent DE 196 24 357 C1) discloses a firing circuit for an airbag in which either current is drawn from an energy accumulator in an unregulated fashion or in a regulated fashion with a regulated and limited output current mode.
The firing cap - also referred to as a squib - which is to be fired when the vehicle is in a collision is provided at the manufacturing end with specific specifications which define the minimum current value necessary for reliable firing and the minimum necessary period for which current must flow.
When the firing cap or firing caps have fired, there remains a residual quantity of energy which has not been consumed in the firing capacitor or capacitors. That residual quantity of energy cannot be utilized, but it makes it necessary for the firing capacitor or capacitors to be overdimensioned and thus be of a corresponding size.
SUMMARY OF THE INVENTION
The object of the invention is to provide an igniter circuit and a method of operating the same, which overcome the above-noted deficiencies and disadvantages of the prior art devices and methods of this kind, and which makes possible a compact design of the firing circuit, and good utilization of energy.
With the above and other objects in view there is provided, in accordance with the invention, a method of operating a firing circuit configured to actuate a firing cap of a firing system, such as trigger circuit in a motor vehicle occupant protection system. The firing circuit includes a firing capacitor for storing energy necessary to fire the firing cap, and a switch connected between the firing capacitor and the firing cap. The firing cap has a given internal resistance and is fired with a current having a value at least as high as a predefined minimum current value and a duration of at least a given minimum time period. The method comprises the following method steps:
charging the firing capacitor to a charge voltage of 2.0 to 2.4 times a product of the internal resistance of the firing cap and the current supplied to the firing cap during a firing operation;
limiting the current, during the firing operation, to a value corresponding to 1.0 to 1.2 times the minimum current value; and
setting a capacitance of the firing capacitor to a capacitance value corresponding to 1.0 to 1.2 times the given minimum time period divided by the internal resistance of the firing cap.
With the above and other objects in view there is also provided, in accordance with the invention, a firing circuit for firing a firing cap having a predefined internal resistance and, for firing, requiring a supply of current having a value at least equal to a predefined minimum current value and a duration of at least a predefined minimum time period. The firing circuit comprises:
at least one firing capacitor;
a voltage or current source connected to and charging the firing capacitor to a specific charge voltage;
a switch for connecting the firing capacitor to the firing cap during a firing operation; and
a current limiter limiting a current flowing to the firing cap during the firing operation to 1.0 to 1.2 times a minimum current value specified for the firing cap;
the firing capacitor having a charge voltage set to 2.0 to 2.4 times a product of the limited current flowing to the firing cap and an internal resistance of the firing cap; and
the firing capacitor having a capacitance set to 1.0 to 1.2 times the minimum time period divided by the internal resistance of the firing cap.
In accordance with another feature of the invention, the current limiter is integrated into the switch.
The firing circuit outlined above permits particularly good utilization of firing energy and a compact circuit design.
In the invention, the current flowing into the firing cap (or firing caps) in the case of firing is limited to the minimum current necessary for the firing cap or to a current which is selected to be of a defined somewhat greater magnitude, and the charge voltage of the firing capacitor or capacitors is calculated as a function of the defined firing current and the internal resistance of the firing cap and set. Furthermore, the capacitance value of the firing capacitor or capacitors is calculated selectively as a function of the minimum period of current flow necessarily for the firing cap or caps, divided by the internal resistance of the firing cap or caps, and correspondingly dimensioned.
This procedure enables the energy which remains unused in the firing capacitor or capacitors after a firing operation and the energy which is consumed at the firing cap switch or in the current limiter to be selectively minimized. In this way, the method and the firing circuit are configured in such a way that the firing energy which is stored in the firing capacitor or capacitors is used for the firing procedure in an optimum fashion so that the capacitance value, and thus the magnitude of the firing capacitor or capacitors, can be set to an optimally small value. In this way, the utilization of energy and the charge voltage can be optimized and at the same time the dimensions of the firing circuit can be minimized owing to the use of a relatively small firing capacitor. The charge voltage and the capacitance value can be set here to the respective necessary minimum values. For safety reasons, it is, however, also possible to provide for the charge voltage and/or the capacitance value selected to have a safety threshold of, for example, 20%, preferably 10%, above the calculated values.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a firing circuit and method for operating it, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, h
Ballato Josie
DeBeradinis Robert L
Greenberg Laurence A.
Lerner Herbert L.
Siemens Aktiengesellschaft
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