# US 4,393,688 A · Piezoelectric knock sensor

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- Number: US 4,393,688 A
- Document ID: US4393688A
- Status: Granted
- Kind: A
- Application number: 06/322,989
- Filed: 1981-11-19
- Granted: 1983-07-19
- Earliest claimed: 1981-11-19
- Assignees: General Motors Corporation
- Inventors: Daniel U. Johnston; George A. Shinkle
- Web page: https://patentgrep.com/patent/US4393688A

## CPC

- G01L 23/222: {using piezoelectric devices}
- G01P 15/0922: {of the bending or flexing mode type}
- G01N 2291/02827: Elastic parameters, strength or force
- G01L: MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE (weighing G01G)
- G01P: MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT (measuring or recording blood flow A61B5/02, A61B8/06; monitoring speed or deceleration of electrically-propelled vehicles B60L3/00; vehicle lighting systems adapted to indicate speed B60Q1/54; determining position or course in navigation, measuring ground distance in geodesy or surveying G01C; combined measuring devices for measuring two or more variables of movement G01C23/00; measuring velocity of sound G01H; measuring velocity of light G01J7/00; measuring direction or velocity of solid objects by reception or emission of radiowaves or other waves and based on propagation effects, e.g. Doppler effect, propagation time, direction of propagation, G01S; measuring speed of nuclear radiation G01T; measuring acceleration of gravity G01V; {measuring or recording the speed of trains B61L23/00; speed indicators incorporated in motor vehicles B60K35/00; measuring frequency or phase G01R; traffic control G08G})
- G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q)

## Abstract

A piezoelectric knock sensor has a case comprising a mounting stud, flexing plate and cover. The flexing plate has a surface provided with a plurality of raised radial ridges. A piezoelectric disk is affixed to the surface with an adhesive and abuts the ridges for improved strain transmission and reliable electrical ground contact. A spring contact further biases the disk against the ridges during assembly bonding of the adhesive; and excess adhesive can flow radially outward between the ridges.

## Claims

### Claim 1

A knock sensor for an internal combustion engine comprising, in combination:
a mounting element adapted for rigid attachment to the engine;
a flexing plate supported on the mounting element and adapted to execute plate vibrations in response to knock events in the engine, the plate having a surface comprising a plurality of raised radial ridges;
a piezoelectric disk affixed to the surface of the plate for flexure with vibrations thereof in abutment with the radial ridges by means of an adhesive substance between the raised radial ridges, said ridges providing internal electrical ground contact for one surface of the piezoelectric disk through the plate, mounting element and engine, as well as strain transmission between the plate and the disk;
a cover affixed to the periphery of the plate, the cover including an electric output terminal; and
spring means compressed between the cover and the other surface of the piezoelectric disk, said spring means being in electrical contact with the electric output terminal, the radial arrangement of said ridges permitting radial outflow of excess adhesive to permit the spring means to force the piezoelectric element into contact with said ridges, whereby good internal electrical ground contact in the sensor is assured.

### Claim 2

A knock sensor for an internal combustion engine comprising, in combination:
a mounting element adapted for rigid attachment to the engine;
a flexing plate supported on the mounting element and adapted to execute plate vibrations in response to knock events in the engine, the plate having a surface comprising a plurality of radial grooves with a raised radial ridge on each side thereof;
a piezoelectric disk affixed to the surface of the plate for flexure with vibrations thereof in abutment with the radial ridges by means of an adhesive substance between the raised radial ridges, said ridges providing internal electrical ground contact for one surface of the piezoelectric disk through the plate, mounting element and engine as well as strain transmission between the plate and the disk;
a cover affixed to the periphery of the plate, the cover including an electrical output terminal; and
spring means compressed between the cover and the other surface of the piezoelectric disk, said spring means being in electrical contact with the electric output terminal, the radial arrangement of said ridges permitting radial outflow of excess adhesive to permit the spring means to force the piezoelectric element into contact with said ridges, whereby good internal electrical ground contact in the sensor is assured.