Knock Sensor Partial Electrode Design for Noise Suppression

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Solution Overview

Problem

Existing knock sensors face issues with changing output sensitivity without altering the sensor's outer shape and suffer from noise generation due to temperature changes, leading to erroneous signal detection.

Innovation Solution

A knock sensor design featuring partial electrodes on the piezoelectric element with a specific radial interval and thickness ratio (L/d < 80) to prevent dielectric breakdown and suppress noise, allowing for adjustable sensitivity without changing the sensor's shape.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If electrode layers are partially formed on the piezoelectric element to change output sensitivity without changing the sensor's outer shape, then sensitivity adjustability is improved, but a gap is created between the piezoelectric element and electrode plates causing dielectric breakdown and noise

Engineering Contradiction:

Improveoutput sensitivity adjustabilityVSAvoidsignal accuracy

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

An insulating sheet is introduced as an intermediary component between the piezoelectric element and the electrode plates. This insulating sheet fills the gap created by partial electrode formation, preventing dielectric breakdown while allowing the partial electrodes to maintain sensitivity adjustability. The insulating sheet acts as a mediator that resolves the conflict between sensitivity adjustment and signal reliability.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Ease of manufacture

If the radial interval L and electrode thickness d are not properly controlled, then manufacturing is easier, but dielectric breakdown occurs causing noise and erroneous signal detection

Engineering Contradiction:

Improveelectrode formation simplicityVSAvoiddielectric breakdown noise

Core Design Contradiction:

Ease of manufactureVSObject-affected harmful factors

Solution Approach 1:

The patent establishes specific parameter relationships (L/d < 80) that control the geometry of partial electrodes. By defining this critical ratio between radial interval L and electrode thickness d, the invention transforms the manufacturing process from one requiring complex quality control to one with clear, quantifiable design criteria. This parameter control prevents dielectric breakdown while maintaining manufacturing feasibility.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If electrode layers are formed on the entire surface of the piezoelectric element, then electrical connection is ensured, but output sensitivity cannot be adjusted without changing the sensor's outer shape

Engineering Contradiction:

Improveelectrical connection stabilityVSAvoidoutput sensitivity adjustability

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The electrode layers are segmented into partial electrodes rather than covering the entire surface. This segmentation allows specific regions of the piezoelectric element to be activated, enabling sensitivity adjustment through selective electrode placement. The segmented electrode structure maintains reliable electrical connection in the activated regions while providing the flexibility to adjust output sensitivity without altering the sensor's outer dimensions.

Inventive Principle:

Principle #1Segmentation

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The solution enables stable output signals by preventing noise superimposition from temperature changes, allowing for accurate knocking signal detection and adjustable sensitivity without altering the sensor's outer dimensions.

Implementation Method 1

adapted to convert, when a knocking vibration is generated in the internal combustion engine, the knocking vibration into an electric signal through the use of a piezoelectric element

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

The annular piezoelectric element is polarized in the direction of thickness thereof

Methodology Applied

Scientific EffectPolarization: Polarisation

Data Source

PatentUS7449819B2Knock sensor

Publication Date: 2008.11.11 MITSUBISHI ELECTRIC MOBILITY CORP

AI summary

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.