A knock sensor includes: a base including an annular flange portion and a cylindrical portion, an annular piezoelectric element fitted onto the cylindrical portion, electrode portions oppositely formed on front and rear surfaces of the annular piezoelectric element, first and second terminal plates in contact with the electrode portions, an annular weight, a first insulating sheet interposed between the first terminal plate and the flange portion, a second insulating sheet interposed between the second terminal plate and the weight. The electrode portions include annular partial electrodes each having a width narrower than a radial width of the piezoelectric element. The annular partial electrode has a thickness d satisfying: L/d<80 where L is a radial dimension of outer circumferences of the front and rear surfaces where the electrode portions are not arranged.
1. A knock sensor, comprising:
a base including an annular flange portion and a cylindrical portion that is axially extended from the flange portion, the base being provided with a through hole axially penetrate the flange portion and the cylindrical portion;
an annular piezoelectric element fitted onto the cylindrical portion;
electrode portions oppositely formed on front and rear surfaces of the annular piezoelectric element;
first and second terminal plates fitted onto the piezoelectric element, and being in close contact with the electrode portions to draw output signals from said piezoelectric element;
an annular weight fitted onto the cylindrical portion to supply an excitation force to the piezoelectric element;
a first insulating sheet interposed between the first terminal plate and the flange portion to electrically insulate the first terminal plate from the flange portion;
a second insulating sheet interposed between the second terminal plate and the weight to electrically insulate the second terminal plate from the weight; and
a holding unit that holds a laminated body of the first insulating sheet, the first terminal plate, the piezoelectric element, the second terminal plate, the second insulating sheet and the weight, such that the laminated body is clamped between the flange portion and the holding unit;
wherein each of the electrode portions includes a corresponding one of annular partial electrodes respectively formed to an outer circumference of the front and rear surfaces of the piezoelectric element, each of the annular partial electrodes having a width narrower than a radial width of the piezoelectric element; and
the annular partial electrodes have a thickness d that satisfies the following inequality: L/d<80 where L is a radial dimension of outer circumferences of the front and rear surfaces where the electrode portions are not arranged.
2. The knock sensor according to claim 1 ,
wherein each of the first and second terminal plates has an annular portion formed into an annular shape whose inside diameter is larger than an inside diameter of the partial electrode and whose outside diameter is substantially equal to an outside diameter of the piezoelectric element; and
the annular portions are stacked to be in close contact with an entirety of surfaces of each of the partial electrodes.
3. The knock sensor according to claim 2 ,
wherein a space between a region, in which no partial electrodes are formed, of each of the front and rear surfaces of the piezoelectric element and each of the first and second insulating sheets is filled with an insulating resin.
4. A knock sensor, comprising:
a base including an annular flange portion and a cylindrical portion that is axially extended from the flange portion, the base being provided with a through hole axially penetrate the flange portion and the cylindrical portion;
an annular piezoelectric element fitted onto the cylindrical portion;
electrode portions oppositely formed on front and rear surfaces of the annular piezoelectric element;
first and second terminal plates fitted onto the piezoelectric element, and being in close contact with the electrode portions to draw output signals from said piezoelectric element;
an annular weight fitted onto the cylindrical portion to supply an excitation force to the piezoelectric element;
a first insulating sheet interposed between the first terminal plate and the flange portion to electrically insulate the first terminal plate from the flange portion;
a second insulating sheet interposed between the second terminal plate and the weight to electrically insulate the second terminal plate from the weight; and
a holding unit that holds a laminated body of the first insulating sheet, the first terminal plate, the piezoelectric element, the second terminal plate, the second insulating sheet and the weight, such that the laminated body is clamped between the flange portion and the holding unit;
wherein each of the electrode portions includes a corresponding one of annular partial electrodes respectively formed to an outer circumference of the front and rear surfaces of the piezoelectric element, each of the annular partial electrodes having a width narrower than a radial width of the piezoelectric element; and
the annular partial electrodes have a thickness d that satisfies the following inequality: L/d<50 where L is a radial dimension of outer circumferences of the front and rear surfaces where the electrode portions are not arranged.
5. The knock sensor according to claim 4 ,
wherein each of the first and second terminal plates has an annular portion formed into an annular shape whose inside diameter is larger than an inside diameter of the partial electrode and whose outside diameter is substantially equal to an outside diameter of the piezoelectric element; and
the annular portions are stacked to be in close contact with an entirety of surfaces of each of the partial electrodes.
6. The knock sensor according to claim 5 ,
wherein a space between a region, in which no partial electrodes are formed, of each of the front and rear surfaces of the piezoelectric element and each of the first and second insulating sheets is filled with an insulating resin.