Acceleration sensor

Details Acceleration sensor Acceleration sensor

1996-06-28

1998-03-31

Williams, Hezron E.

Measuring and testing

Speed, velocity, or acceleration

Acceleration determination utilizing inertial element

73493, 73654, 310329, 29 2535, 296211, G01P 1509, H01L 4108, H04R 1700

Patent

active

057341079

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The present invention relates to an acceleration sensor and more specifically an acceleration sensor having a piezoelectric sensor element which is supported as a flexural resonator in a holding module.


BACKGROUND INFORMATION

Acceleration sensors are generally known. They are employed in motor vehicles, for example, to detect specific accelerative forces acting on the motor vehicle and to provide a control signal as a function of these forces. The control signals are used, e.g., to quickly trigger safety devices, such as airbags, seatbelt tighteners or the like. To this end, the acceleration sensors are equipped with a sensor element, which responds very sensitively to an acceleration occurring in a specific direction. Piezoelectric sensor elements designed as flexural resonators which deflect in response to an occurring acceleration are known. This deflection produces a polarization in the piezoelectric sensor element because of the piezoelectric effect, i.e., a displacement of positive and negative charge carriers leads to the generation of a voltage between two electrodes of the sensor element. These voltage signals can be tapped off and fed to an evaluation circuit. To produce the necessary voltage signals, the piezoelectric sensor elements are comprised of two oppositely poled layers of a piezoceramic material placed in a holding module, which, under the influence of an acceleration, permits a deformation of the sensor element. The disadvantage associated with the known acceleration sensors is that the devices used to accommodate the sensor element and for its electrical contacting are quite complex and, thus, expensive to manufacture. Moreover, it is quite difficult to distinctly specify a sensing direction for the sensor element. This requires auxiliary devices which hold the sensor element in a specific position in relation to a mounting surface.


SUMMARY OF THE INVENTION

In contrast, the acceleration sensor according to the present invention offers the advantage of enabling a precise alignment of the sensor element in a specific sensing direction running, in particular, parallel to a mounting or reference surface and, at the same time, of permitting a mechanical and electrical coupling of the sensor element. Because the module is preferably made of two separate retaining means, which are connected to the evaluation circuit and consist of an electrically conductive material, it is advantageously possible to use these retaining means to mechanically fix the piezoelectric sensor element in position and, at the same time, to electrically contact it. Separate additional measures for stabilizing the position of and for aligning the sensor element, i.e., for tapping off the voltage signals are not needed. Thus, the holding module is able to be produced very simply and cost-effectively.
Additionally, the present invention provides for the holding module to be formed as a blank, which obtains the final shape of the holding module by means of a bending-shaping process, additional mechanical auxiliary stop means, initially joined to the holding module, being available for the assembly operation while the sensor element is introduced into the holding module. The sensor elements are, therefore, able to be introduced quite advantageously in a self-adjusting assembly process into the holding module, it being possible to precisely align the sensor elements in an x-y-z direction and to exactly repeat such alignment during a large-scale production because of the design of the mechanical auxiliary stop means. Thus, acceleration sensors can be produced in a useful, low-cost manufacturing process, so that, under a same acceleration, sensor signals within a narrowly limited scatter range can be expected because of the exact same alignment of the sensor element in each case as a result of the exact same bending bar design. Thus, on the one hand, the interchangeability of the acceleration sensors is facilitated, since they each provide the same signals within narrow tolerance ranges. On the o

REFERENCES:
patent: 5226325 (1993-07-01), Komurasaki et al.
patent: 5239869 (1993-08-01), Uemura et al.
patent: 5452612 (1995-09-01), Smith et al.

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