Gas flow rate measuring apparatus for minimizing temperature dependent errors

Patent metadata

Field	Value
Publication number	US-9297677-B2
Application number	US-201214240917-A
Country	US
Kind code	B2
Filing date	Aug 16, 2012
Priority date	Sep 30, 2011
Publication date	Mar 29, 2016
Grant date	Mar 29, 2016

Abstract

A gas flow rate measuring apparatus including a gas flow rate detection circuit configured to output a first analog signal of a gas flow rate of a gas; a gas temperature detection element configured to output a second analog signal of a temperature of the gas or a temperature of an integrated circuit; analog-to-digital converters for converting the analog signals into respective digital signals; a digital signal correction device comprising a map table and configured to correct a characteristic bend of the first digital signal based on the map table and the second digital signal, wherein the map table comprises correction constants arranged as lattice points, wherein a first number of lattice points in a first region of the characteristic bend of the gas flow rate signal is larger than a second number of lattice points of a second region outside the first region of the characteristic bend.

First claim

The invention claimed is:

1. A gas flow rate measuring apparatus including
a gas flow rate detection circuit configured to output a first analog signal of a gas flow rate of a gas flowing in a gas flow path;
a gas temperature detection element configured to output a second analog signal of a temperature of the gas in the gas flow path or a temperature of an integrated circuit;
a first analog-to-digital (AD) converter for converting the first analog signal from the gas flow rate detection circuit into a first digital signal;
a second AD converter for converting the second analog signal from the gas temperature detection element into a second digital signal;
a digital signal correction device comprising a map table and configured to correct a characteristic bend of the first digital signal based on the map table and the second digital signal, resulting in a gas flow rate measurement,
wherein the map table comprises correction constants arranged in a lattice pattern of lattice points;
a first number of lattice points in a first region of the characteristic bend of the gas flow rate signal is larger than a second number of lattice points of a second region outside the first region of the characteristic bend, wherein the first region and the second region are equal in size;
the gas flow rate is represented by Q and a value obtained by zero-span operation of an output characteristic of the gas flow rate detection signal which is a target after correction and an output of the gas flow rate detection signal is represented by ΔY;
a minimum value of a search region for the characteristic bend is represented by a, a maximum value of the search region for the characteristic bend is represented by b, and a division number between a and b is represented by n; and
a product of a value obtained by dividing a sum of ΔY and a gradient of Q for individual intervals obtained by the division between a and b and a value ΔYmax when ΔY is highest between a and b or a value ΔYmin when ΔY is lowest between a and b is represented by S,
the digital signal correction device configured to search for a location of the characteristic bend in accordance with a and b, calculate a magnitude of the characteristic bend on the basis of the magnitude of S, and correct, when the value of an absolute value |S| of S is equal to or higher than 0.005, the gas flow rate detection signal such that the value of |S| is equal to or lower than 0.055 in accordance with the values of a, b, and S.

2. The gas flow rate measuring apparatus according to claim 1 , wherein the digital signal correction device includes:
a first coordinate conversion table for moderating a non-linearity of the gas flow rate detection signal;
a second coordinate conversion table for moderating a non-linearity of the temperature detection signal; and
a correction table for carrying out correction on the basis of a signal obtained by the coordinate conversion.

3. The gas flow rate measuring apparatus according to claim 2 , wherein the first and second coordinate conversion tables are regular-interval tables of an arbitrary division number.

4. The gas flow rate measuring apparatus according to claim 2 , wherein the gas temperature detection signal used for the correction table is a gas temperature signal from the gas temperature detection element.

5. The gas flow rate measuring apparatus according to claim 2 , wherein the gas temperature detection signal used for the correction table is a temperature signal from a substrate temperature sensor provided in the integrated circuit.

6. The gas flow rate measuring apparatus according to claim 1 , wherein the integrated circuit is configured to generate output signals obtained by correcting the digital signals and output as analog signals the output signals obtained by correcting the digital signals.

7. The gas flow rate measuring apparatus according to claim 1 , wherein the gas flow rate measuring apparatus is configured to carry out a correction arithmetic process based on the digital signals input from the gas temperature detection signal and the gas flow rate detection signal from the gas flow rate detection circuit after individual conversion into digital signals.

Assignees

• Suzuki Kazunori
• Nakada Keiichi
• Sato Ryo
• Hitachi Automotive Systems Ltd

Inventors

• Suzuki Kazunori
• Nakada Keiichi
• Sato Ryo

Classifications

• G01F1/696 Primary

  Circuits therefor, e.g. constant-current flow meters · CPC title

• G01F5/00

  Measuring a proportion of the volume flow · CPC title

• G01F1/6965

  comprising means to store calibration data for flow signal calculation or correction · CPC title

• G01F1/64 Primary

  by measuring electrical currents passing through the fluid flow; measuring electrical potential generated by the fluid flow, e.g. by electrochemical, contact or friction effects (G01F1/58 takes precedence) · CPC title

• G01F1/6842

  with means for influencing the fluid flow · CPC title