Acceleration sensor

An acceleration sensor for detecting an acceleration caused by an object oscillated in an oscillation direction, comprising:

• a sensor casing having a center axis and to be positioned in coaxial alignment with said oscillation direction to receive said acceleration, said sensor casing including a cylindrical fixed case member having a supporting portion axially extending, and a cover assembly provided on said fixed case member to cover said fixed case member to define a closed space;
• an oscillation plate accommodated in said closed space of said sensor casing and having a central portion supported by said supporting portion of said fixed case member, and a peripheral portion integrally formed with said central portion and extending radially outwardly of said central portion to be freely movable with respect to said supporting portion of said fixed case member, said oscillation plate being partly oscillatable along said center axis with respect to said fixed case member, said oscillation plate having a first flat surface opposing and spaced apart along said center axis with respect to said fixed case member, and a second flat surface opposing and spaced apart along said center axis with respect to said cover assembly of said sensor casing;
• a first piezoelectric element having a first surface and a second surface, said first surface of said first piezoelectric element held in contact with said second flat surface of said oscillation plate to generate a voltage indicative of said acceleration when said acceleration is exerted on said sensor casing to have said oscillation plate partly oscillated along said center axis with respect to said sensor casing with said peripheral portion of said oscillation plate being deformed;
• a second piezoelectric element having a first surface and a second surface, said first surface of said second piezoelectric element held in contact with said first flat surface of said oscillation plate to generate a voltage indicative of said acceleration when said acceleration is exerted on said sensor casing to have said oscillation plate partly oscillated along said center axis with respect to said sensor casing with said peripheral portion of said oscillation plate being deformed, said first and second piezoelectric elements each having a plurality of electrodes having said voltage indicative of said acceleration to output therethrough, said electrodes including a first electrode provided on said second surface of said first piezoelectric element, and a second electrode provided on said second surface of said second piezoelectric element, and said oscillation plate and said first and second piezoelectric elements being integrally oscillatable within a range of effective oscillation frequencies;
• and
• at least one terminal pin extending through said cover assembly and terminating at an exterior of said cover assembly, said terminal pin electrically connected with said first and second electrodes;
• whereby said oscillation plate and said first and second piezoelectric elements are integrally oscillatable in two different modes consisting of:
• a first oscillation mode where said oscillation plate is irregularly deformed to have said peripheral portion oscillated with a single vector in said oscillation direction of said oscillation plate when said oscillation plate is oscillated with respect to said fixed case member at a resonance frequency f0;
• and a second oscillation mode where said oscillation plate is irregularly deformed to have two different half parts of said peripheral portion oscillated with respective different vectors opposite to each other in said oscillation direction of said oscillation plate when said oscillation plate is oscillated with respect to said fixed case member at a noise frequency f01, and said resonance frequency f0 and said noise frequency f01 are out of said range of effective oscillation frequencies.