Measuring and testing – Instrument proving or calibrating – Speed – velocity – or acceleration
Reexamination Certificate
1998-12-28
2001-09-04
Noland, Thomas P. (Department: 2856)
Measuring and testing
Instrument proving or calibrating
Speed, velocity, or acceleration
Reexamination Certificate
active
06282941
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to an impact detection device, in particular for a motor vehicle, including at least one micromechanical acceleration switch having a contact element to be moved as a function of acceleration and a counter-contact element. A monitoring circuit, which is electrically conductively connected to a terminal of the contact element and to a terminal of the counter-contact element, has a controllable voltage source and an evaluation device. The impact detection device has an operating state for detecting an impact, in which a voltage is fed to the terminals by the voltage source.
European Patent Application 0 567 938 A1, corresponding to U.S. Pat. No. 5,610,337, has disclosed an impact detection device which has at least one acceleration switch that has a micromechanical structure. Such an acceleration switch essentially contains a contact element which can be moved as a function of acceleration, as well as a counter-contact element. When a defined acceleration is exceeded, the contact of the acceleration switch closes. A monitoring circuit is electrically conductively connected to terminals of the contact elements. A voltage is fed to the terminals in order to detect an impact (see FIG. 1c of European Patent Application 0 567 938 A1, corresponding to U.S. Pat. No. 5,610,337).
In order to test and reset the micromechanical switch, a test electrode is provided which is electrically connected through a separate conductor to the monitoring circuit and which is driven by the monitoring circuit (see FIG. 3a of European Patent Application 0 567 938 A1, corresponding to U.S. Pat. No. 5,610,337). In particular, if the monitoring circuit and the acceleration switch are spatially separated from one another, a line with at least three conductors is necessary between the acceleration switch and the monitoring circuit. The line is provided, on one hand, in order to be able to detect an acceleration-dependent closure of the acceleration switch in the monitoring circuit and, on the other hand, in order to be able to test or reset the acceleration switch through the use of the monitoring circuit.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide an impact detection device, in particular for a motor vehicle, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and which, in particular, reliably detects a switching operation of an acceleration switch and permits the acceleration switch to perform a self-test with little complexity in terms of circuitry and wiring.
With the objects of the invention in view there is also provided an impact detection device, in particular for a motor vehicle, comprising at least one micromechanical acceleration switch carrying a measurement signal, the acceleration switch having a contact element to be moved as a function of acceleration and having a counter-contact element, the elements each having a respective terminal; a monitoring circuit electrically conductively connected to the terminal of the contact element and to the terminal of the counter-contact element, the monitoring circuit having a controllable voltage source and an evaluation device evaluating the measurement signal tapped at the acceleration switch; the voltage source feeding a first voltage to the terminals in a first operating state of the impact detection device for detecting an impact, the first voltage having a first absolute value; and the voltage source feeding a second voltage to the terminals in a second operating state of the impact detection device for testing the acceleration switch by deflecting the contact element with an electrostatically acting force, the second voltage having a second absolute value greater than the first absolute value.
Therefore, in order to test the acceleration switch, the higher second voltage is fed to the terminals of the contact elements of the acceleration switch by the controllable voltage source of the monitoring circuit. The movable contact element is significantly deflected through the use of the second voltage on the basis of electrostatically acting forces. As a result, the switching contact is closed, with the proviso that the acceleration switch is operationally capable.
The movable contact element and counter-contact element are constructed in this case in such a way that the feeding of the high voltage causes significant deflection of the movable contact element. Small circuit structures of micromechanical acceleration switches are a prerequisite for this deflection. The movable contact element and the counter-contact element are both used as capacitor plates in the test. The electrostatic force of attraction between the movable contact element and the counter-contact element depends in particular on the distance between the two contact elements and on the surface of the contact elements.
In accordance with another feature of the invention, instead of contact elements that are constructed with large surfaces, the acceleration switch has a test electrode which is electrically connected to the counter-contact element, is a large electrode surface, for example, and interacts electrostatically with the movable contact element. The test electrode is connected to the counter-contact element near the acceleration switch so that in all cases only two conductors are necessary between the monitoring circuit and the acceleration switch.
In order to detect an impact in the operating state, the first voltage which is fed by the voltage source and is supplied between the contact elements or contact element and the test electrode is not under any circumstances of such a size that the contact elements are deflected by the electrostatic force of attraction until the acceleration switch closes. The absolute value of the second voltage which is necessary for the induced closure of the acceleration switch in this case is greater than the absolute value of the first voltage.
The measurement signal which is tapped at the acceleration switch is evaluated in the evaluation device of the monitoring circuit. The measurement signal permits conclusions to be drawn regarding, inter alia, the operational capability of the acceleration switch during the test operation and the action of a sufficiently large acceleration on the acceleration switch during the operation for detecting an impact.
The invention has the great advantage that only two conductors are necessary for each acceleration switch, to connect it to the monitoring circuit. Through the use of this impact detection circuit with minimized wiring complexity it is possible to detect acceleration-dependent switching of the acceleration switch and to carry out a self-test of the acceleration switch. The complexity of circuitry in the monitoring circuit is likewise kept extremely small by virtue of the impact detection system according to the invention. These advantages are of particular benefit when connecting a plurality of acceleration switches to the monitoring circuit and, in particular, when there is a spatial separation between the acceleration switch and monitoring circuit. The invention significantly reduces the number of conductors in a cable harness of a motor vehicle.
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 an impact detection device, in particular for a motor vehicle, 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, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.
REFERENCES:
patent: 5506454 (1996-04-01), Han
Greenberg Laurence A.
Lerner Herbert L.
Noland Thomas P.
Siemens Aktiengesellschaft
Stemer Werner H.
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