Air Mass Sensor Grate Geometry for Vibration-Stable Flow
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Solution Overview
Problem
Existing sensor arrangements for determining intake air mass in internal combustion engines face issues with non-uniform airflow, leading to signal noise and increased pressure drop due to flow separations and structural vibrations, which affect measurement reproducibility and accuracy.
Innovation Solution
A specially designed grid with varying radial thicknesses and strut dimensions is implemented in the flow tube to optimize airflow uniformity and reduce structural vibrations, featuring a circular ring structure with grid rings and struts that taper in thickness from the center to the edge, and from upstream to downstream, to guide intake air smoothly and minimize vibrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a grid is positioned upstream of the probe to homogenize the velocity profile and eliminate swirl, then airflow uniformity is improved, but high-frequency structural vibrations occur which adversely affect measurement behavior
Solution Approach 1:
The grid rings are designed with non-uniform thickness distribution, where each grid ring has a different thickness in different radial sections. Specifically, the grid ring closer to the central axis has a smaller thickness in the radial direction than the adjacent grid ring closer to the grid edge. This local variation in thickness allows different parts of the grid to perform different functions: inner rings provide flow guidance while outer rings provide structural support, thereby reducing vibrations while maintaining flow homogenization
Solution Approach 2:
The grid structure employs asymmetric thickness distribution rather than uniform thickness. The grid rings have varying thicknesses that create an asymmetric geometry optimized for both flow control and vibration reduction. This asymmetric design allows the grid to effectively dampen high-frequency vibrations while maintaining its flow homogenization function
2Ease of manufacture
If the grid rings have uniform thickness, then manufacturing is simplified, but structural vibrations are not adequately reduced
Solution Approach 1:
Instead of uniform thickness throughout, each grid ring is designed with specific local thickness variations. The thickness is optimized at different radial positions to achieve vibration reduction while maintaining manufacturability through systematic design patterns
3Strength
If the grid struts have large thickness, then structural strength is increased, but airflow resistance and pressure drop increase
Solution Approach 1:
The grid struts are designed with non-uniform thickness distribution along their length. The thickness varies to provide adequate structural strength at critical locations while minimizing obstruction to airflow in other regions, thereby reducing pressure drop while maintaining grid integrity
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 significantly reduces high-frequency structural vibrations and enhances airflow uniformity, resulting in improved measurement reproducibility and reduced signal noise, thereby enhancing the accuracy of air mass determination.
Implementation Method 1
The grid's function is to homogenize the velocity profile in the flow tube and eliminate any swirl that may be present in the flow
Implementation Method 2
Such hot-film air mass meters are generally based on a sensor chip, in particular a silicon sensor chip, with a measuring surface that is permeable to the flowing fluid medium. The sensor chip comprises a heating element and at least two temperature sensors, which are arranged, for example, on the measuring surface of the sensor chip. An asymmetry in the temperature profile detected by the temperature sensors, which is influenced by the flow of the fluid medium, allows conclusions to be drawn about the mass flow and/or volume flow of the fluid medium
Implementation Method 3
the aforementioned special grid geometry ensures that high-frequency structural vibrations are significantly reduced
Data Source
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AI summary
The invention relates to a sensor assembly for determining the intake air mass of an internal combustion engine, the sensor assembly (1) comprising: an insertion sensor (10), which is arranged in a flow pipe (20) and has a sensor element (13) for determining the intake air flowing in a main flow direction (S) in the flow pipe (20); and at least one grate (30), which is arranged upstream of the insertion sensor (10) in the main flow direction (S), wherein: the grate (30) is in the shape of a circular ring around a center axis (2) of the flow pipe (20), which center axis extends in the direction of the main flow direction (S); the grate (30) has grate rings (31) and grate struts (32), which extend radially with respect to the center axis (2) and the grate rings (31); the grate rings (31) and the grate struts (32) form passages (33) therebetween for the intake air flowing in the main flow direction (S); the grate rings (31) are arranged around the center axis (2) and coaxial to each other and are separated from each other by the grate struts (32); the grate (30) has an outer grate edge (34) facing the flow pipe (20) and an innermost grate ring (311), which is closest to the center axis (2). The aim of the invention is to reduce structural oscillations of the flow in the flow pipe. This aim is achieved, according to the invention, in that each grate ring (31) arranged closer to the center axis (2) than a grate ring (31) which is adjacent to said grate ring (31) and which is arranged closer to the grate edge (34) has a smaller grate ring thickness (RD1; RD2; RD3) in the radial direction in a sectional plane (SE1; SE2) extending perpendicularly to the center axis (2) through the grate (30) than the adjacent grate ring (31) arranged closer to the grate edge (34).