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EP0078427A2
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Air flow meter
Assignee: Hitachi Ltd
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Filing: 1982-10-14
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Granted: —
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Expires: 2002-10-14
Abstract
Abstract A temperature-dependent resistor (10) for sensing air flow rate is placed in the air flow, and another resistor (16) for detecting a current flowing through the above resistor (10) is connected in series therewith. The current is controlled so that the temperature-dependent resistor (10) is kept at a predetermined temperature higher than surrounding temperature. As the resistance of the temperature-dependent resistor (10) would vary in accordance with the air flow rate, the current varies with the flow rate. Accordingly, the air speed can be obtained by measuring the current. In such an air flow meter, when a key switch of an engine is turned on to put a power supply to work, a short circuit is formed between both ends of the current detecting resistor (16) to cause a large current to flow through the temperature-dependent resistor (10). Accordingly, the air flow rate can be measured immediately after the power supply has been turned on.
Inventors
- 👤 Yutaka Nishimura
- 👤 Yoshishige Ohyama
- 👤 Noboru Sugiura
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-08 22:37
CPC Classifications
G; G01; G01F; G01F1/00; G01F1/68; G01F1/696; G01F1/698
Claims Analysis
Total Claims: 12
Claim 1
Independent Claim
99 words
An air flow meter including a first resistor (10) whose resistance varies with temperature, a second resistor (16) connected in series with said first resistor, and control means (12, 14, 18, 20, 26) for controlling a current flowing through said first resistor so that said first resistor has a predetermined temperature, to measure the flow rate of air by said current flowing through said first resistor, said air flow meter characterized by means (36, 38) for forming a short circuit between both ends of said second resistor (16) for a predetermined time, when said air flow meter is energized.
Claim 2
Dependent Claim
99 words
An air flow meter including a first resistor (10) whose resistance varies with temperature, a second resistor (16) connected in series with said first resistor, and control means (12, 14, 18, 20, 26) for controlling a current flowing through said first resistor so that said first resistor has a predetermined temperature, to measure the flow rate of air by said current flowing through said first resistor, said air flow meter characterized by means (36, 38) for forming a short circuit between both ends of said second resistor (16) for a predetermined time, when said air flow meter is energized.
Claim 3
Dependent Claim
63 words
An air flow meter according to Claim 1, wherein said means for forming a short circuit are characterized by means (38) for generating a pulse having a predetermined time width when said air flow meter is energized, and means (36) receiving said pulse for forming said short circuit between both ends of said second resistor for a time equal to said time width.
Claim 4
Dependent Claim
46 words
An air flow meter according to Claim 2, wherein the pulse width of said pulse generated by said pulse generating means (38) varies with a supply voltage (VB), and the pulse width of said pulse is large as the supply voltage (V B ) is lower.
Claim 5
Dependent Claim
115 words
An air flow meter according to Claim 1, wherein said control means are characterized by a third resistor (12) having a resistance varying with temperature for detecting ambient temperature and a fourth resistor (18) connected in series with said third resistor (12) to form a bridge circuit using said first, second, third and fourth resistors, and includes means (20) for generating an output so that a voltage at a junction (B) of said first and second resistors becomes equal to a voltage at a junction (C) of said third and fourth resistors, and means (26) for changing said current flowing through said first resistor in accordance with said output of said output generating means (20).
Claim 6
Dependent Claim
55 words
An air flow meter according to Claim 4, characterized by means (30, 32, 34, 35) for applying a predetermined voltage to said junction of said first and second resistor, and means (44) for forming a short circuit between both ends of said fourth resistor for a predetermined time, when said air flow meter is energized.
Claim 7
Dependent Claim
38 words
An air flow meter according to Claim 4, characterized by means (46, 48) for maintaining said output of said output generating means (20) at a predetermined value for a predetermined time, when said air flow meter is energized.
Claim 8
Dependent Claim
99 words
An air flow meter according to Claim 1, wherein said control means are characterized by means (50, 52) for dividing a voltage developed across said first resistor (10) into two voltage parts, a third resistor (12) having a resistance varying with temperature for detecting ambient temperature, means (20) for generating an output so that one of said two voltage parts obtained by said voltage dividing means becomes equal to a voltage developed across said third resistor, and means (26) for changing said current flowing through said first resistor (10) in accordance with said output of said output generating means.
Claim 9
Dependent Claim
55 words
An air flow meter according to Claim 7, further characterized by means (30, 32, 34, 35) for applying a predetermined voltage to the output side of said third resistor (12), and means (44) for grounding a voltage dividing point of said voltage dividing means for a predetermined time, when said air flow meter is energized.
Claim 10
Dependent Claim
39 words
An air flow meter according to Claim 7, further characterized by means (46, 48) for maintaining said output of said output generating means (20) at a predetermined value for a predetermined time, when said air flow meter is energized.
Claim 11
Dependent Claim
221 words
An air flow meter characterized by: a flow rate sensing probe (10); a resistor (16) connected in series with said flow rate sensing probe; a power supply for applying a voltage to a series combination of said flow rate sensing probe and said resistor; a voltage dividing circuit (50, 52) for dividing a voltage developed across said flow rate sensing probe into two voltage parts; a temperature compensation probe (12); means (20) for comparing one of said voltage parts obtained by said voltage dividing means with a voltage developed across a temperature compensation circuit to generate an output in accordance with a difference between said voltage part and said voltage developed across said temperature compensation circuit; means (26) for controlling a current supplied from said power supply to said series combination; means (28) detecting a voltage at a junction of said flow rate sensing probe (10) and said resistor (16) for outputting said detected voltage as a flow rate indicating signal; a key switch for permitting or preventing the supply of a voltage from said power supply to said series combination; means (38) for outputting a pulse having a predetermined width in response to the turning-on of said key switch; and means (36) receiving said pulse for grounding said junction of said flow rate sensing probe (10) and said resistor (16).
Claim 12
Dependent Claim
221 words
An air flow meter characterized by: a flow rate sensing probe (10); a resistor (16) connected in series with said flow rate sensing probe; a power supply for applying a voltage to a series combination of said flow rate sensing probe and said resistor; a voltage dividing circuit (50, 52) for dividing a voltage developed across said flow rate sensing probe into two voltage parts; a temperature compensation probe (12); means (20) for comparing one of said voltage parts obtained by said voltage dividing means with a voltage developed across a temperature compensation circuit to generate an output in accordance with a difference between said voltage part and said voltage developed across said temperature compensation circuit; means (26) for controlling a current supplied from said power supply to said series combination; means (28) detecting a voltage at a junction of said flow rate sensing probe (10) and said resistor (16) for outputting said detected voltage as a flow rate indicating signal; a key switch for permitting or preventing the supply of a voltage from said power supply to said series combination; means (38) for outputting a pulse having a predetermined width in response to the turning-on of said key switch; and means (36) receiving said pulse for grounding said junction of said flow rate sensing probe (10) and said resistor (16).
References Cited (Backward Citations)
No citation records indexed.
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