JP4914226B2 - Gas flow meter - Google Patents

Description

  The present invention relates to a flow meter for measuring a flow rate of gas, and more particularly to a flow meter suitable for detecting an air flow rate taken into an automobile engine.

  As a conventional example of an automotive engine intake air flow meter, a heating control current value of a heating resistor as described in Patent Document 1 is detected and converted into an air flow rate. There is known a system that detects a thermal effect on a temperature-sensitive resistor arranged downstream as a temperature difference signal and captures it as a voltage of a bridge circuit.

Here, when detecting the intake air flow rate of an automobile engine, a flow meter having a characteristic that can be stably detected under any use conditions is required in consideration of the following conditions and environment.
(1) Consider the influence of fouling substances caused by water vapor, oil, gasoline, etc.
(2) Consideration that ambient temperature change is severe (environment from below freezing to 100 ° C or higher).

  As a prior art with respect to said subject, there exist some which are described in patent document 2, for example. In Patent Document 2, a gas having a second heating resistor, a means for judging the degree of fouling from the resistance value of the second heating resistor, and correcting the output value obtained from the first heating resistor is disclosed. A flow measuring device is disclosed.

  Moreover, it is known that the above fouling substances can be burned off by placing them in a temperature environment above the boiling point.

JP 2003-185481 A JP-T 2005-181096

  In the prior art disclosed in Patent Document 2, it is necessary to newly provide a separate second heating resistor, and to provide a temperature detection element, a heating temperature calculation means, and a correction means. It was.

  The fouling substances adhering to the heating resistor can be baked by heating to a temperature above the boiling point, but the terminal part supporting the heating resistor is close to the air temperature, so it burns completely. It is difficult. Furthermore, the heat transfer from the surface of the heating resistor to the gas is dominant in the overall heat dissipation of the heating resistor, but the heat transferred to the terminal that supports the heating resistor by heat conduction is transferred to the gas. There are also paths that are released, and the temperature of this part decreases, so that the contamination progresses. To maintain the measurement accuracy over a long period of time, it is insufficient to raise the temperature of the heating resistor.

  The present invention relates to a gas flowmeter that measures a gas flow rate based on a heating current in a gas flowmeter that causes a heating current to flow through the heating resistor and measures a gas flow rate based on a heat radiation amount to the gas. A second heating resistor installed in the vicinity of the first heating resistor, and a temperature-sensitive resistor for detecting the air temperature, wherein the first heating resistor and the second heating resistor are Each of them is configured to be controlled so that the temperature difference from the gas temperature detected by the temperature sensitive resistor becomes a substantially constant value.

  Second, the first heating resistor and the second heating resistor are controlled by a single control bridge circuit so that the temperature difference between the gas temperature detected by the temperature-sensitive resistor and the gas temperature is substantially constant. It is characterized by that.

  Third, the heating resistor and the second heating resistor are controlled so that the temperature difference from the gas temperature detected by at least one temperature-sensitive resistor becomes a substantially constant value. .

  Fourthly, the heating control circuit is composed of a heating resistor and at least one temperature sensing resistor, and controls the heating current of the first heating resistor so that the temperature difference from the temperature sensing resistor is substantially constant. A second heating resistor is connected to the current supply end, and the temperature of the second heating resistor is controlled so that the temperature difference from the gas temperature detected by the temperature-sensitive resistor becomes a substantially constant value. It is a feature.

  Fifth, it has a fixed resistance connected in parallel with the heating resistor.

  Sixth, the heating current of the second heating resistor changes according to the output of the control circuit that controls the heating current of the heating resistor.

  Seventh, in the gas flowmeter that measures the gas flow rate based on the amount of heat released to the gas by supplying a heating current to the heating resistor, the second is for measuring the gas flow rate based on the heating current on the diaphragm on which the substrate is processed. A first heat generating resistor, a second heat generating resistor disposed in the vicinity of the first heat generating resistor, and a temperature sensitive resistor for detecting an air temperature, the first heat generating resistor and the first heat generating resistor Each of the two heating resistors is controlled so that the temperature difference from the gas temperature detected by the temperature-sensitive resistor becomes a substantially constant value.

  The gas flowmeter of the present invention is very simple because the difference between the air temperature and the heating resistance of the two heating resistors is controlled to a constant value by one bridge circuit and one temperature sensing resistor that detects the air temperature. Thus, the present invention is effective in preventing characteristic deterioration due to contamination at low cost. In addition, even if the heat dissipation characteristics of the first heat generating element and the second heat generating element are different, the heating temperature based on the flow rate value can be controlled to a substantially constant value, so that there is an advantage that high accuracy can be achieved.

  Several embodiments of the present invention in which the effects of fouling are reduced with a simple control circuit are described below.

A first embodiment of the present invention will be described with reference to FIGS.
FIG. 1 shows a detection circuit of a gas flow meter according to a first embodiment of the present invention. A bridge circuit including a first heating resistor (hereinafter referred to as “heater”) 1, a gas temperature detection element (hereinafter referred to as “temperature sensor”) 2, fixed resistors 4 and 5, an operational amplifier 7, and a transistor 8 causes gas to flow. The flow rate detection circuit 16 is configured. Both the heater 1 and the temperature sensor 2 are made of a material whose resistance value changes with temperature, for example, a platinum wire. The heater 1 is supplied with heating current from the power source 9 by the operational amplifier 7 and the transistor 8 so that the bridge balance is maintained when the temperature becomes higher than the temperature sensor 2 by a certain value or more. When the flow rate of the gas changes and the amount taken away from the heater 1 by heat transfer changes, the heating current changes so that this bridge balance is maintained. When the gas flow rate is Q, the heating current is Ih, the heater resistance is Rh, and the temperature difference between the heater and the temperature sensor is ΔTh, the relationship between the gas flow rate Q and the heater heating current Ih is as follows: Holds.

  Here, A and B are constants. The heating current Ih is converted into a voltage signal by the fixed resistor 4 and input to the output adjustment circuit 17. The output adjustment circuit 17 is adjusted to a predetermined characteristic by an offset adjustment circuit composed of the reference voltage source 11 and the fixed resistors 12 and 13 and a sensitivity adjustment circuit composed of the operational amplifier 10 and the fixed resistors 14 and 15 and is output. The The gas flow rate can be detected by the configuration as described above.

  Here, a circuit composed of the second heating resistor 3 (hereinafter referred to as “sub-heater”) and the fixed resistor 6 is added between the heating current supply end in the flow rate detection circuit 16 and the ground. The heater 1 and the sub-heater 3 together constitute a gas flow rate detection element 18. Here, during the heating operation of the heater 1 and the sub heater 3, the value of the fixed resistor 6 is set so that the relationship of the following equation (2) is established.

  Here, Rsh is a resistance value during operation of the sub-heater, Rh is a resistance value during operation of the heater, and R4 and R6 are resistance values of the fixed resistors 4 and 6, respectively.

  With the above configuration, the heater 1 and the sub heater 3 can be controlled to be heated to a constant temperature with respect to the temperature sensor 2 by one gas detection element and one bridge circuit.

  FIG. 2 shows a state in which the gas flow meter according to the first embodiment of the present invention is attached to the internal combustion engine. The component parts of the gas flow meter include a housing member 25 containing a circuit board 24 constituting a drive circuit, a sub air passage constituent member 28 formed by a non-conductive member, and the like. The gas flow rate detection element 18 in which the heater 1 for detecting the air flow rate and the sub-heater 3 are integrated, and the gas temperature detection element 2 are connected to each other through terminals 20, 21, 22 formed of conductive members. It arrange | positions so that it may electrically connect with the board | substrate 24. FIG.

  The housing 25, the circuit board 24, the auxiliary air passage 23B, the gas flow rate detecting element 18, the temperature sensor 2, and the like are configured as an integrated module of the gas flow meter. A hole 26A is formed in the wall surface of the main air passage constituting member 27 constituting the intake pipe, and the auxiliary air passage 23B of the gas flow meter is inserted from the outside through the hole 26A, and the wall surface of the auxiliary air passage constituting member 28 is inserted. And the housing member 25 are fixed with screws, an adhesive or the like. A sealing material 26B is attached between the auxiliary air passage constituting member 28 and the main air passage constituting member 27 to maintain the airtightness inside and outside the intake pipe.

  The measured gas flow rate flows in through the main air passage 23A from the direction of the arrow 29 and detects the amount of the main air passage 23A that flows through the sub air passage 23B.

  FIG. 3 shows a detection element of the gas flow meter according to the first embodiment of the present invention. Sub-heaters 3A and 3B are connected to both ends of the heater 1 via leads 30 and 31 made of a conductive member. The leads 30 and 31 are electrically connected to terminals 20A, 20B, 21A and 21B made of conductive members, respectively, and are held in the gas flow path.

  Here, since the temperature of the lead between the sub-heaters 3A and 3B and the terminal is lowered, the heat transfer amount taken from the lead portion to the gas varies depending on the amount of contamination of the lead portion. However, since the lead portions connected to both ends of the heater 1 are sandwiched between the sub-heaters 3A and 3B, the temperature is kept high, so that no fouling occurs. For this reason, the amount of heat transferred to the gas from the heater 1 that detects the gas flow rate does not change depending on the presence or absence of fouling.

  FIG. 4 shows a system configuration when the gas flowmeter according to the first embodiment of the present invention is applied to an automobile engine. The intake air 57 sucked from the air cleaner 43 is sucked into the engine cylinder 52 through an intake manifold 49 including a gas flow meter body 44, an intake duct 45, a throttle body 48, and an injector 50 to which fuel is supplied. On the other hand, the exhaust gas 53 generated in the engine cylinder 52 is discharged through the exhaust manifold 54.

  The intake air temperature signal from the intake air temperature sensor 41, the air flow signal output from the circuit module 42 of the gas flow meter, the intake air temperature signal from the temperature sensor, and the throttle valve output from the throttle angle sensor 47 of the idle air control valve 46 An angle signal, an oxygen concentration signal output from an oxygen concentration meter 55 provided in the exhaust manifold 54, an engine rotation speed signal output from the engine rotation speed meter 51, and the like are supplied to the engine control unit 56.

  The control unit 56 sequentially calculates these signals to obtain an optimal fuel injection amount and an idle air control valve opening, and controls the operations of the injector 50 and the idle control valve 46 using the values.

  The gas flowmeter of the present invention is applied to the engine control system as described above, and can always measure an accurate air flow rate even during engine operation or after long-term use. This contributes to the realization of highly accurate engine control.

FIG. 5 shows a detection circuit according to the second embodiment of the present invention.
In the second embodiment, a fixed resistor 19 is connected in parallel with the sub heater 3 in particular. With this configuration, even when the temperature dependence of the resistance values of the main heater 1 and the sub heater 3 is different, the resistance temperature characteristic on the sub heater side can be adjusted by the value of the fixed resistance. For this reason, the heating temperature of the sub heater 3 can be controlled even by a combination of a heater and a sub heater having different structures.

FIG. 6 shows a detection circuit according to the third embodiment of the present invention.
In the third embodiment, the circuit for controlling the heating of the sub-heater 3 includes the operational amplifier 60, the voltage source 9, the transistor 61, and the fixed resistors 6 and 19, and the detection signal of the gas flow rate detection bridge circuit is the non-inverting input terminal of the operational amplifier 60. It is connected to the. With this circuit configuration, the heating current of the sub-heater can be made variable according to the gas flow rate detection signal. For this reason, even if the heat dissipation characteristics due to heat transfer to the gas flow rate of the main heater 1 and the sub-heater 3 are different, the heat dissipation characteristics on the sub-heater side can be adjusted by the value of the fixed resistance, and the sub-heater 3 can be adjusted more accurately. The heating temperature can be controlled.

  FIG. 7 shows a planar structure of the detection element of the gas flow meter of Example 4 of the present invention, and FIG. 8 shows a cross-sectional view at the AA portion.

  The detection element 71 is made of a silicon substrate or the like, and is formed with an air flow rate detection diaphragm 80 processed by an etching process using an alkali solvent or the like from the back side, and includes a heater 72, upstream temperature sensitive resistors 76 and 77, and downstream side. Temperature sensitive resistors 78 and 79 are arranged. On the substrate around the diaphragm 80, fixed resistors 73 and 74 and a resistance temperature detector 75 are formed. Further, sub-heaters 95 (95A, 95B) are formed on the diaphragm 80 so that the temperature sensitive resistors 76, 77, 78, 79 are sandwiched between the heaters 72. These resistors are made of a platinum film or a polysilicon film whose resistance value changes with temperature. Further, these elements are connected to the outside by terminals 82 to 94, 96A, 96B, 97A, 97B, 98A, and 98B.

  FIG. 9 shows the circuit configuration of the gas flow meter of Example 4 of the present invention. FIG. 9A shows the heater control circuit (the power supply is omitted), and FIG. Shows the temperature difference detection circuit.

  In the heater control circuit shown in FIG. 9A, a bridge circuit is configured by the heater 72, the side temperature resistor 75, and the fixed resistors 73 and 74, and the operational amplifier 105 controls the terminals 88 and 93 to have the same potential. The heating current supplied to the heater 72 is feedback controlled. For this reason, it operates so that the temperature difference between the gas temperature detected by the resistance temperature detector 75 and the heater 72 becomes a substantially constant value.

  In the temperature difference detection circuit shown in FIG. 9B, the temperature-sensitive resistors 76 and 77 that are arranged on the upstream side of the heater 72 and change in resistance value due to the heat effect from the heater 72 are arranged on the downstream side. A voltage is supplied from the power source 106 to the bridge circuit formed by the temperature sensitive resistors 78 and 79, and a differential signal corresponding to the air flow rate is detected from the terminal 84 (or 90) and the terminal 92 (or 85). . This differential signal is adjusted to a predetermined characteristic by the air flow signal adjusting unit 107 and output as an air flow signal.

  In the gas flow meter having this configuration, a circuit including the sub heater 95 and the fixed resistor 99 is added between the heating current supply terminal 87 (or 82) and the ground.

FIG. 10 shows a mounting cross-sectional schematic diagram in a state where the gas flowmeter of the present invention is actually used.
The gas flow meter 119 is mounted so as to be inserted into the air passage tube 120, and is fixed to the air passage tube by the flange 118. A circuit board 115 on which the detection element 111 and the circuit element 116 are mounted is mounted on the housing 117. A part of the air flow 121 flowing in the intake pipe is diverted into the air flow meter by the air intake 112, bypasses the detection element 111 through the bypass passage 113, and returns to the main passage pipe from the bypass outlet 114. .

  With the above configuration, the gas flow direction can be detected, and the heater 72 and the sub-heater 95 can be controlled to be heated to a constant temperature with respect to the resistance temperature detector 75. A direction detection type gas flow meter can be configured.

  The gas flowmeter of the present invention can be applied not only to detect the intake air amount of the internal combustion engine described above but also to the detection of the exhaust gas flow rate of the internal combustion engine. It can be widely used as a gas flow meter for measuring the flow rate of various gases.

  It can be used for a device that detects air flow rate and air temperature, for example, an airplane or a ship, or a medium other than air, for example, a flow rate detection device such as exhaust gas or hydrogen, which requires high reliability.

It is the figure which showed the detection circuit of the gas flowmeter of Example 1 of this invention. It is explanatory drawing which shows the state with which the gas flowmeter of Example 1 of this invention was attached to the internal combustion engine. It is explanatory drawing which shows the detection element of the gas flowmeter of Example 1 of this invention. It is explanatory drawing which shows the system structure at the time of applying the gas flowmeter of Example 1 of this invention to the engine of a motor vehicle. It is explanatory drawing which shows the detection circuit of the gas flowmeter of Example 2 of this invention. It is explanatory drawing which shows the detection circuit of the gas flowmeter of Example 3 of this invention. It is explanatory drawing which shows the detection element of the gas flowmeter of Example 4 of this invention. It is explanatory drawing which shows the cross-section of the gas flowmeter of Example 4 of this invention. It is explanatory drawing which shows the detection circuit of the gas flowmeter of Example 4 of this invention. It is the mounting cross-sectional schematic diagram which shows the attachment structure of the gas flowmeter of Example 4 of this invention.

Explanation of symbols

  1 heater, 2 gas temperature detection element (temperature sensor), 3, 3A, 3B sub-heater, 4, 5, 6 fixed resistance, 7 operational amplifier, 8 transistor, 9 power supply, 10 operational amplifier, 11 reference voltage source, 12, 13, 14, 15, 19 Fixed resistance, 16 Flow rate detection circuit, 17 Output adjustment circuit, 18 Gas flow rate detection element, 20, 20A, 20B, 21, 21A, 21B, 22 Terminal, 23A Main air passage, 23B Sub air passage, 24 Circuit board, 25 housing member, 26A auxiliary air passage insertion hole, 26B sealing material, 27 main air passage constituting member, 28 auxiliary air passage constituting member, 29 air flow, 30, 31 lead, 41 intake air temperature sensor, 42 circuit module, 43 Air cleaner, 44 body, 45 Air intake duct , 46 Idle air control valve, 47 Throttle angle sensor, 48 Throttle body, 49 Intake manifold, 50 Injector, 51 Tachometer, 52 Engine cylinder, 53 Exhaust, 54 Exhaust manifold, 55 Oxygen meter, 56 Control unit, 57 Inhalation Air flow, 60 operational amplifier, 61 transistor, 71 sensing element, 72 heater, 73,74 fixed resistance, 75 resistance temperature detector, 76,77 upstream temperature sensing resistor, 78,79 downstream temperature sensing resistor, 80 diaphragm 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94 terminals, 95A, 95B sub-heater, 96, 96A, 96B, 97, 97A, 97B, 98, 98A, 98B 99, 99A, 99B fixed resistor, 105 operational amplifier, 106 reference voltage source, 107 air flow signal adjustment unit, 111 detection element, 112 air intake port, 113 bypass passage, 114 bypass outlet, 115 circuit board, 116 circuit element, 117 housing, 118 flange, 119 gas flow meter, 120 air passage tube, 121 air flow

Claims (6)

In the gas flowmeter that flows the heating current to the heating resistor and measures the gas flow rate based on the amount of heat released to the gas,
A first heating resistor fixedly supported on the lead material and measuring a gas flow rate based on a heating current;
A second heating resistor disposed on opposite sides of said first heating resistor,
Has a temperature sensitive resistor for detecting gas temperature level, the,
The first first temperature difference between the second gas temperature detected by the temperature and the temperature sensitive resistor of the heating resistor and the gas temperature detected by the temperature and the temperature sensitive resistor of the heating resistor second and the temperature difference, the gas flow meter, wherein the benzalkonium is controlled to substantially respectively constant values with. The gas flowmeter according to claim 1,
Gas flow meter, characterized in that one temperature difference the first by the control bridge circuit and the second temperature difference is controlled to be constant value I GENERAL, respectively. The gas flowmeter according to claim 1,
The first temperature difference is approximately the second heating resistor to the current supply terminal of the heating control circuit for controlling the heating current of the to be constant first heating resistor is connected, the second gas flow meter, characterized in that the temperature difference is generally controlled to be a constant value. The gas flowmeter according to claim 1,
A gas flowmeter comprising a fixed resistor connected in parallel with the second heating resistor. The gas flowmeter according to claim 1,
A gas flowmeter configured to change the heating current of the second heating resistor according to the output of a control circuit for controlling the heating current of the first heating resistor. In the gas flowmeter that flows the heating current to the heating resistor and measures the gas flow rate based on the amount of heat released to the gas,
A first heating resistor provided on a diaphragm on which a substrate is processed and for measuring a gas flow rate based on a heating current;
A second heating resistor disposed on the upstream side and the downstream side of the gas flow to the first heat generating resistor,
It has a temperature sensitive resistor for detecting the gas temperature and,
The first first temperature difference between the second gas temperature detected by the temperature and the temperature sensitive resistor of the heating resistor and the gas temperature detected by the temperature and the temperature sensitive resistor of the heating resistor second and the temperature difference, the gas flow meter, wherein the benzalkonium is controlled to substantially respectively constant values with.

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