Knock Sensor Resin Mold Gate Positioning for Crack Resistance
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Solution Overview
Problem
Conventional knock sensors suffer from resin mold cracking due to heat shock and moisture exposure, leading to weakened resin strength and potential failure of the piezoelectric element when cracks allow moisture ingress.
Innovation Solution
The knock sensor design relocates the injection gate for the resin mold to a position on the circumference excluding the connector section, forming a weld with reduced thermal stress and shortening the filling time to enhance junction strength, thereby improving resistance to cracks and ensuring reliable operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the injection gate is located on the circumference opposing the connector section, then the manufacturing process is simplified, but the weld strength at the junction is weakened due to prolonged cooling time
Solution Approach 1:
The injection gate is positioned asymmetrically at a specific angle (45° to 135°) relative to the center line connecting the through-hole and connector section centers, rather than at the symmetric opposing position. This asymmetric positioning optimizes the mold material flow path to reduce cooling time at the weld junction while maintaining manufacturing simplicity.
Solution Approach 2:
The problem is solved by introducing an angular dimension parameter (the angle between the injection gate position and the center line) as a new design variable. By controlling this angular parameter within the specified range, the mold material flow dynamics are optimized to achieve both ease of manufacture and adequate weld strength.
2Manufacturing precision
If the mold material fills the connector section after meeting at the junction, then the connector section is properly formed, but the resin strength remains weaker at the weld portion due to cooling and hardening time difference
Solution Approach 1:
The injection gate is positioned asymmetrically to create an optimized flow path where mold material reaches the connector section and weld junction in a balanced sequence. This prevents excessive cooling at the junction while ensuring complete filler section formation.
Solution Approach 2:
The angular position parameter of the injection gate is changed from the conventional opposing position to a specific angle range (45° to 135°). This parameter change alters the mold material flow characteristics, reducing the time difference between junction filling and connector section filling, thereby minimizing cooling-induced strength reduction at the weld.
3Reliability
If the resin mold is exposed to heat shock from engine operation, then the sensor functions in practical environments, but thermal stress causes cracks in the weld portion with reduced strength
Solution Approach 1:
The asymmetric injection gate positioning creates a weld junction with optimized geometry and reduced thermal stress concentration. This asymmetric design makes the weld portion more resistant to crack propagation under thermal cycling conditions while maintaining sensor functionality.
Solution Approach 2:
The injection gate positioning is designed in advance to preemptively reduce thermal stress concentration at the weld junction. By optimizing the flow path and junction geometry beforehand, the structure is cushioned against the harmful effects of subsequent thermal shock during engine operation.
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
This design enhances the resin mold's resistance to cracks and thermal stress, preventing abnormal outputs and ensuring a highly reliable knock sensor performance in practical use environments.
Implementation Method 1
converts the vibration into an electric signal by means of a piezoelectric element clamped in the sensor
Data Source
AI summary
A knock sensor includes a resin mold having a first cylindrical resin mold section that encloses a base, annular constituent parts and a pressing member of the knock sensor; and a connector section that protrudes from a side of the first mold section and is integrally injection-molded at one time with the first mold section; wherein an injection gate for resin mold is located on the first resin mold circumference excluding portions thereof opposing the connector section, and forms a predetermined angle (45° to 120°) with respect to the center line connecting the center of the connector section with that of a through-hole of the base.