Thermal Air Flow Sensor Self-Diagnosis via Electrode Segmentation
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Solution Overview
Problem
Conventional thermal flow rate sensors fail to accurately detect short circuits between adjacent electrode pads, which can occur due to voids in the resin seal, leading to undetected abnormalities and potential dangerous driving conditions, as the output changes fall within the normal range and are not recognized by the engine control unit.
Innovation Solution
The thermal flow rate sensor is designed with a specific arrangement of electrode pads and a self-diagnosis mechanism that ensures output values outside the normal range when a short circuit occurs, allowing for accurate detection of abnormalities, including the use of A/D converters and operational amplifiers to convert input voltages to digital values and set self-diagnosis outputs outside the normal range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a resin seal is used to protect electrode pads and gold wires from engine intake air contaminants, then protection against water, sulfur gas, and oil is improved, but voids may form inside the resin seal that can cause short circuits between adjacent gold wires
Solution Approach 1:
The electrode pads are divided into different potential groups (first group with first potential, second group with second potential) and spatially separated in the arrangement, so that even if a void forms in the resin seal, short circuits are prevented due to the potential difference and physical separation of adjacent pads
Solution Approach 2:
Adjacent electrode pads are set to different electrical potentials (first potential and second potential), creating an equipotential arrangement where no two adjacent pads share the same potential, thereby preventing short circuit detection failures and enabling reliable self-diagnosis
2Difficulty of detecting and measuring
If conventional short circuit detection using comparators is used for electric power source potential and ground potential, then detection of such short circuits is improved, but short circuits between midpoint potentials in bridge circuits are not detected
Solution Approach 1:
The self-diagnosis mechanism is designed to universally detect all types of short circuits including power source potential, ground potential, and midpoint potentials by comparing potentials between adjacent electrode pads, making the detection system multi-functional and comprehensive
Solution Approach 2:
The self-diagnosis mechanism provides feedback signals to the ECU indicating the normal or abnormal state of the flow rate detection element, enabling continuous monitoring and detection of short circuits between any electrode pads including midpoint potentials
3Area of stationary object
If electrode pads are arranged adjacently for compact design, then device size is reduced, but short circuits between adjacent pads become more likely due to voids in resin seal
Solution Approach 1:
Electrode pads are segmented into different potential groups and arranged in a compact pattern where adjacent pads have different potentials, maintaining small device size while preventing short circuits through potential differentiation and spatial arrangement
Solution Approach 2:
The electrode pads are arranged asymmetrically with different potentials assigned to adjacent pads, creating an asymmetric potential distribution that prevents short circuit formation while maintaining compact geometry
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
Enables the thermal flow rate sensor to perform self-diagnosis effectively even when short circuits occur between adjacent electrode pads, ensuring accurate detection of abnormalities and preventing dangerous driving conditions by setting output values outside the normal range.
Implementation Method 1
a bridge circuit with heat resistors Rh and upstream and downstream side temperature resistors Ru and Rd, to convert a voltage difference between upstream and downstream sides of the heat resistor Rh into an output signal
Implementation Method 2
heat resistors Rh and upstream and downstream side temperature resistors Ru and Rd
Data Source
Figure 1~2
Figure 3
Figure 4~5
AI summary
The purpose of the present invention is to provide a thermal flow-rate sensor that is capable of self-diagnosis. Provided is a thermal flow-rate sensor provided with a semiconductor element that detects a flow rate and that is equipped with electrode pads for electrical conduction with the outside, wherein at least two of the electrode pads are provided, and other electrode pads proximate to the electrode pads are arranged and have an electric potential beyond the scope of output to be used at the time of flow rate detection.