JP2006170804A - Gas flow meter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a highly reliable gas flowmeter capable of preventing stains from adhering to a heating sensor element. <P>SOLUTION: In the gas flowmeter for detecting the mass flow of gas to be measured by heating a heating element part, the heating sensor element is constituted of the heating element part made of a heating resistor having a protective coating on its surface and formed in a ceramic bobbin; lead parts electrically connected to both sides of the heating element part; and fixing parts for fixing the lead parts in a gas channel and electrically connected to an external circuit. The lead parts are divided into two in the vicinity of joints to the heating element and arranged in such a way that leads in the downstream side may not be directly exposed to a gas flow. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a gas flow meter for measuring a mass flow rate of gas such as engine intake air and exhaust gas.

  In recent years, exhaust gas recirculation (EGR) that reduces NOx by returning a part of exhaust gas to the intake system has been widely used. The recirculation amount (EGR amount) needs to be accurately controlled so as to be compatible with the stability of combustion and the like, and particularly when applied to a diesel engine, if excessive EGR occurs, the generation of smoke increases. Therefore, highly accurate EGR control according to the driving situation is required.

  Incidentally, as a conventional EGR control, there is JP-T-2003-516696. This conventional example is composed of a gas flow meter for measuring the amount of fresh air taken into the intake passage and a gas flow meter for measuring the amount of EGR gas provided in the exhaust gas recirculation path. Control is performed based on the EGR rate (= EGR gas amount / (fresh air intake amount + EGR gas amount)) from the fresh air intake air amount and the EGR gas amount measured by the meter. In order to control the EGR rate with high accuracy, a gas flow meter that accurately detects the fresh air intake air amount and the EGR gas amount is required.

  A gas flow meter places a heat sensor element heated to a constant high temperature in the flow of intake air or exhaust gas, and flows to keep the heat sensor element cooled by the intake air or exhaust gas at a constant temperature at all times. The mass flow rate of intake air or exhaust gas is calculated by measuring the current value. Therefore, the heat generation sensor element is always exposed to the flow of intake air or exhaust gas.

  The intake air passes through the heat cleaner element after passing through the air cleaner. However, since it contains dust, exhaust gas, etc., dirt adheres to the heat sensor element. On the other hand, the exhaust gas has a problem that a large amount of oil, carbon, etc. in the exhaust gas adheres. When dirt is attached to the heat generation sensor element, the heat generation sensor element does not directly touch the intake air or the exhaust gas, so that there is a problem that an error occurs in the measurement of the mass flow rate.

  In order to solve the problem, the conventional example has been devised to prevent dirt from adhering to the heat generation sensor element. For example, Japanese Patent Laid-Open No. 59-206714 describes a method of volatilizing oil or the like adhering to a heat generation sensor element by increasing the temperature of the heat generation sensor element.

  In the heat sensor element 1 of the conventional example, as shown in FIGS. 9 and 10, a heat generating element portion 2 formed by winding a platinum wire 7 as a heat generating resistor around a ceramic bobbin 6 and protecting the surface with a protective glass 9. The lead portions 3a and 3b which are electrically connected to both sides of the heat generating element portion 2 are connected to the ceramic bobbin 6 by the adhesive glass 8, and the lead portions 3a and 3b are fixed portions 4a for electrically connecting to an external circuit. , 4b are fixed in the gas flow path.

In the conventional heat generating sensor element 1 configured as described above, when it is exposed to the intake air or the exhaust gas 5, as shown in FIG. Although it is possible to prevent adhesion of carbon or the like, lead portions 3a connected to both sides of the heating element portion 2,
Since the temperature of the 3b and the fixing parts 4a and 4b is lowered, a large amount of dirt 10 such as carbon with oil or the like adhering thereto remains, causing a problem of generating an error in the measurement of the mass flow rate of the gas.

That is, since the heating element unit 2 is controlled to be higher than the temperature of the intake air or the exhaust gas 5 by a certain temperature (170 to 300 ° C.), oil and the like adhering to the heating element unit 2 is volatilized. Is not a problem. However, since the lead portions 3a, 3b and the fixing portions 4a, 4b are not heated to such an extent that the oil component is volatilized, the oil components etc. adhere to the lead portions 3a, 3b and the fixing portions 4a, 4b, and further, dirt 10 such as carbon remains for a long time. It adheres and accumulates over time.

  In particular, when dirt 10 such as carbon adheres to the A part of the lead parts 3a and 3b, the dirt 10 exhibits a thermal insulation effect between the lead part and the intake air or the exhaust gas 5 in a high flow rate region, thereby reducing heat dissipation and generating heat. The current value required to keep the temperature of the sensor element 1 constant decreases, and a negative error occurs in the mass flow rate. On the other hand, in the low flow rate region, the dirt 10 reduces the thermal resistance between the heating element part 2 and the fixing parts 4a and 4b, and heat conduction (heat leakage) from the heating element part 2 to the fixing parts 4a and 4b increases. Therefore, the current value increases and a positive error occurs in the mass flow rate.

  In Patent Document 1 of another conventional example for preventing the adhesion of the dirt 10, one of the lead portions 3 a and 3 b is lengthened and folded back from the fixing portion 4 to the upstream side of the heat generating element portion 2 to provide a shielding effect against the dirt 10. Proposals have been made.

  However, since the shielding portion is provided on the upstream side of the heating element portion 2 in this way, a turbulent flow is generated in the flow of the intake air or the exhaust gas 5 to affect the heating element portion 2. There is a problem that generates an error.

  Further, as a conventional example for preventing the adhesion of the dirt 10, there is JP-A-7-120288. In this conventional example, as shown in FIG. 12, the heat generating sensor element includes a heat generating element portion 2 in which a platinum wire 7 is wound around a ceramic bobbin 6 and the surface is coated with glass, and lead portions connected to both sides of the heat generating element portion 2. The heat insulating member 11 is formed on the surfaces of the lead portions 3a and 3b.

  With this configuration, since the heat insulating member 11 is formed on the outer periphery of the lead portions 3a and 3b, there is almost no heat dissipation from the lead portion, and the dirt 10 is attached to the lead portion. It is assumed that the influence of the heat generation sensor element is almost the same as in the case of not being present.

  However, the conventional example configured as described above has no effect of reducing the dirt 10 adhering to the lead portion, and if the dirt 10 adheres in a large amount, an error occurs in the measurement of the mass flow rate. Further, since the heat insulating member 11 is formed on the outer periphery of the lead portions 3a and 3b, the effective sectional area of the lead portion is increased, the thermal resistance between the heating element portion 2 and the fixing portions 4a and 4b is reduced, and the heating element portion 2 is formed. There is a problem that power consumption increases because heat conduction (heat leakage) from the first to the fixed portions 4a and 4b increases.

JP-A-6-94499

  The present invention has been made to solve the above problems, and provides a highly reliable gas flow meter that prevents an error from occurring in the measurement of the mass flow rate of the gas due to dirt adhering to the heat generation sensor element. The purpose is to do.

(Means for Solving Claim 1)
In the gas flowmeter for detecting the mass flow rate of the gas based on the current value flowing through the heat generation sensor element arranged in the flow of the gas to be measured,
The heat generating sensor element includes a heat generating element formed by forming a heat generating resistor on a ceramic bobbin and protecting the surface, a lead part electrically connected to both sides of the heat generating element part, and the lead part in the gas flow path. It consists of a fixed part for fixing and electrical connection with an external circuit,
The lead portions at both ends branch into two in the vicinity of the joint portion with the heat generating element portion to constitute a set of a first lead portion and a second lead portion and a set of a third lead portion and a fourth lead portion, respectively. The other end of the lead portion is connected and fixed to a fixing portion corresponding to each lead portion,
The second and fourth lead portions are arranged upstream of the gas flow of the first lead portion and the third lead portion, respectively, so that the first lead portion and the third lead portion are not directly exposed to the gas flow,
By energizing the first lead part and the third lead part and heating the heating element part to measure the mass flow rate of the gas to be measured,
The first lead part and the third lead part related to the measurement are hidden downstream of the second and fourth lead parts, so that direct hit of the gas flow is avoided, and the carbon attached to the first lead part and the third lead part, etc. Therefore, the mass flow rate can be measured with high reliability.

(Means for Solving Claim 2)
At an appropriate time before and after the measurement period of the gas flow meter, branch so that a part of the heating current flows from the first lead part to the third lead part via the second lead part. It is possible to measure the mass flow rate with higher reliability by providing circuit means to remove the deposits attached to the second and fourth lead parts by forming and heating the second and fourth lead parts. It becomes.

(Means for Solving Claim 3)
In the gas flow meter, as a branching means that a part of the heating current reaches the second and fourth lead parts, a switching element and an adjustment resistor are connected in series between the fixed parts of the second and fourth lead parts,
The switching element is turned on by a predetermined timing signal, and the heating current flows from the fourth lead part to the third lead part via the second lead part from the first lead part by the adjusting resistor, and the first lead part. Adjust the ratio of the heating current flowing from the heating element part to the third lead part to a predetermined value,
Since the second and fourth lead portions are heated to remove the deposits attached to the second and fourth lead portions, the mass flow rate can be measured with high reliability.

(Means for Solving Claim 4)
When the gas to be measured is intake air and exhaust gas in an internal combustion engine, a gas flow meter that can more effectively prevent dirt adhering to the lead portion and prevent occurrence of errors in mass flow measurement. Can be realized.

(Means for Solving Claim 5)
The heating resistor is formed by winding a platinum wire, and the protective coating is made of a glass material, so that a highly accurate gas flow meter can be realized.

(Means for Solving Claim 6)
The heat generating element portion maintains an average temperature of the heat generating element portion at 400 ° C. or higher so that carbon or the like is not deposited, thereby further preventing contamination of carbon or the like adhering to the lead portion. The flow rate can be measured.

(Means for Solving Claim 7)
A gas temperature sensor element for detecting a gas temperature is further provided in the flow of the gas to be measured, and the temperature of the heat generation sensor element is controlled to be higher than the temperature of the gas temperature sensor element by a predetermined temperature. By configuring so that the mass flow rate of the gas is detected based on the value of the current flowing through the gas, a highly accurate gas flow meter can be realized.

(Means for Solving Claim 8)
A gas temperature sensor element for detecting the temperature of the gas is further provided in the flow of the gas to be measured, and the temperature of the heat generation sensor element is controlled to a constant temperature, and the gas is measured based on the current value flowing through the heat generation sensor element. By detecting the mass flow rate of the gas and correcting the mass flow rate of the gas based on the gas temperature detected by the gas temperature sensor element, it is possible to further prevent contamination such as carbon adhering to the lead portion and to have high reliability. Measurement of mass flow rate is possible.

  According to the present invention described above, a highly reliable gas flow meter that prevents measurement errors in the gas mass flow rate due to dirt adhering to the heat generation sensor element can be provided, so that highly accurate EGR control of the internal combustion engine can be performed, and smoke and NOx An excellent effect is achieved in that reduction is achieved.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 2 shows an EGR control apparatus using a gas flow meter which is an embodiment to which the present invention is applied, and the configuration will be described below.

  This EGR control device includes an internal combustion engine 12, an intake passage 16 in which an air cleaner 14 and a throttle valve 15 are installed to supply intake air 13 to the engine 12, and an exhaust gas catalyst 19 for cleaning exhaust gas 20. An exhaust pipe 18 for exhausting the exhaust gas, an EGR valve 23 provided in an exhaust gas recirculation path 24 for recirculating (recirculating) the exhaust gas, an EGR cooler 22 for cooling the exhaust gas and increasing cylinder suction efficiency, and an intake passage 16, a gas flow meter 17 for measuring the amount of intake air, a gas flow meter 25 for measuring the amount of recirculated exhaust gas provided in the exhaust gas recirculation path 24, an EGR valve 23, and a throttle valve according to operating conditions 15 and a control unit 21 for operating the fuel injection injector 26.

  The exhaust gas recirculation passage 24 is connected to the exhaust passage 18 and the intake passage 16 so as to short-circuit them. The EGR valve 23 and the throttle valve 15 are connected to the control unit 21, and a part of the exhaust gas flowing through the exhaust passage 18 is joined to the intake passage 16 according to the opening degree, and is returned to the engine 12. Yes.

Gas flow meters 17 and 25, which are embodiments to which the present invention is applied, are arranged in the intake passage 16 and the exhaust gas recirculation passage 24, respectively, and measure the intake air amount and the recirculated exhaust gas amount to measure the EGR rate (= EGR gas amount). / (Fresh air intake amount + EGR gas amount)) is realized to achieve highly accurate EGR control according to the operating condition of the engine to reduce smoke and NOx of exhaust gas.

  FIG. 3 shows the configuration of the gas flowmeters 17 and 25 according to the first embodiment to which the present invention is applied. FIG. 1 shows the heat generation sensor element 1 constituting the gas flowmeters 17 and 25. Is.

  First, the principle of operation of the gas flow meters 17 and 25 will be described with reference to FIG. In FIG. 3, 16 and 24 are an intake passage and an exhaust gas recirculation passage, and the heat generation sensor element 1 and the gas temperature sensor element 27 are arranged in the passages 16 and 24. 3a, 3c, 3b and 3d have resistance values at the first, second, third and fourth lead portions of the heat generation sensor element 1, respectively. 30 is a power source, 28 is a transistor for supplying a heating current to the heat generation sensor element 1, and 33 is a switching element (transistor) in which the adjustment resistor 32c is connected in series between the second lead portion 3c and the fourth lead portion 3d. 32a and 32b are resistors, 29 is a differential amplifier, and 21 is a control unit.

  Here, the heat generation sensor element 1 forms a bridge circuit including the gas temperature sensor element 27 and the resistors 32a and 32b via the first lead portion 3a and the third lead portion 3b. At the time of normal gas flow rate measurement, the switching element 33 is turned off, and the second lead portion 3c and the fourth lead portion 3d are open with no current flowing. The voltage at the terminals 31a and 31b of the bridge circuit is input to the differential amplifier 29, and the temperature (Th) of the heat generation sensor element 1 is a certain temperature (ΔTh == the temperature of the gas temperature sensor element 27 corresponding to the gas temperature). The resistance values 32 a and 32 b are set so as to be higher than Th−Te) and at 400 ° C. or higher at which no oil or carbon in the gas adheres, and feedback control is performed by the differential amplifier 29.

  For measuring the intake air amount and the recirculated exhaust gas amount, the voltage of the terminal 31a of the resistor 32a corresponding to the heating current flowing through the heat generating sensor element 1 is input to the control unit 21 and measured. That is, when the intake air amount and the recirculated exhaust gas amount increase, the heat generation sensor element 1 is cooled by the heat transfer effect of the gas, and feedback control is performed so that the heat generation sensor element 1 becomes a constant temperature (ΔTh = Th−Te). Therefore, the heating current (terminal voltage of 31a) flowing through the heat generation sensor element 1 increases and can be detected as a mass flow rate.

  The relationship between the heat radiation power Ph of the heat generation sensor element 1 and the mass flow rate Qe of the gas to be measured is expressed by the following king equation.

Ph = (a + b√ (Qe)) ΔTh (1)
Here, the first term (a) of the equation (1) is a contribution due to the heat conduction effect, and the second term (b) is a contribution due to the heat transfer effect due to the gas to be measured.

  On the other hand, after the measurement period of the gas flow meter is over or at an appropriate time before the measurement, the second and fourth lead portions 3c and 3d are heated and attached to the second and fourth lead portions 3c and 3d. Remove the kimono.

  The switching element 33 is turned on by a predetermined timing signal from the control unit 21, and the heating current flows from the fourth lead portion 3d to the third lead portion 3b via the first lead portion 3a, the second lead portion 3c, and the adjusting resistor 32c. The second and fourth lead portions 3c and 3d are heated to remove the deposits adhering to the second and fourth lead portions 3c and 3d.

  At this time, the adjustment resistor 32c is set so that the ratio of the heating current flowing in the branch to the heating current flowing from the first lead portion 3a to the third lead portion 3b via the heating element portion 2 becomes a predetermined value. Adjusting and appropriately heating the second and fourth lead portions to remove the adhering matter adhering to the second and fourth lead portions 3c and 3d enables highly reliable mass flow rate measurement.

  The heat generation sensor element 1 of FIG. 1 includes a heat generation element portion 2 formed by forming a heat generation resistor on a ceramic bobbin and having a protective coating on the surface, and lead portions 3a, 3b, 3c, 3d electrically connected to both sides of the heat generation element portion 2. In addition, the lead portions are fixed in the gas flow passages 16 and 24, and are configured by fixing portions 4a, 4b, 4c, and 4d for electrical connection with an external circuit.

  The lead portion divides into two in the vicinity of the joint portion with the heat generating element portion 2, and constitutes a set of the first lead portion 3a and the second lead portion 3c and a set of the third lead portion 3b and the fourth lead portion 3d. The other ends of the respective lead portions are connected and fixed to fixing portions 4a, 4b, 4c, 4d corresponding to the respective lead portions, and the second and fourth lead portions 3c, 3d are respectively connected to the first lead portion. The first lead portion and the third lead portions 3a, 3b are arranged on the upstream side of the gas flow of the third lead portions 3a, 3b so as not to be directly exposed to the exhaust gas 5.

One end of each of the fixing portions 4a, 4b, 4c, 4d and the lead portions 3a, 3b, 3c, 3d is fixed by welding. The other ends of the lead portions 3a, 3b, 3c, and 3d are the first lead portion 3a and the second lead portion 3c, and the third lead portion 3b and the fourth lead portion 3d in the vicinity of the joint portion with the heating element portion 2. Each set is welded and has a structure that branches into two from the welded portion toward the fixed portion. Further, at the joint portion between the welded portion and the heat generating element portion 2, the lead portions 3 c and 3 d are fixed via the ceramic bobbin 6 and the adhesive glass 8 as in the conventional example of FIG. 10. Yes.

  The fixing parts 4a, 4b, 4c, 4d are made of a conductive metal such as stainless steel, for example. The lead portions 3a, 3b, 3c, 3d are made of a conductive wire material such as a platinum-based alloy having a diameter of 150 μm. For the platinum wire 7, a current flows through the fixing portions 4 a and 4 b and the lead portions 3 a and 3 b when measuring a normal gas flow rate.

  One end of the platinum wire 7 is welded from the welded portion of the lead portions 3a and 3c to the surface of the lead portion 3c in the vicinity of the ceramic bobbin 6. The platinum wire 7 with one end welded is wound around the outer periphery of the ceramic bobbin 6 at a constant interval to form the heating element portion 2. The other end of the platinum wire 7 is wound around the lead portion 3d inside the welded portion of the lead portions 3b and 3d for two or three turns and then welded to the surface of the lead portion 3d. The diameter of the platinum wire 7 of this embodiment is 20μ.

  A protective glass film 9 is formed on the surface of the platinum wire 7. In this embodiment, the protective glass film 9 is composed of a heat-dissipating glass coating having a thickness of several μm to several tens of μm. The glass coating is formed up to a portion where the platinum wire 7 of the lead portions 3c and 3d is wound. The purpose of the glass coating is to fix the platinum wire 7 to the ceramic bobbin 6 to prevent the platinum wire 7 from loosening and to protect the platinum wire 7.

  In the gas flow meter according to the first embodiment of the present invention configured as described above, the second and fourth lead portions 3c and 3d are upstream of the gas flows of the first lead portion and the third lead portions 3a and 3b, respectively. Since the first lead portion and the third lead portions 3a and 3b are arranged on the side so as not to be directly exposed to the exhaust gas 5, dirt such as oil and carbon in the exhaust gas 5 is contaminated by the second and fourth lead portions. Since it is trapped by 3c and 3d and does not adhere to the first lead portion and the third lead portions 3a and 3b used for measurement, it is possible to accurately measure the mass flow rate.

  In addition, oil and carbon dirt once attached to the second and fourth lead portions 3c and 3d may be removed after the measurement period of the gas flow meter is finished or at an appropriate time before the measurement. The deposits adhering to the second and fourth lead portions 3c and 3d can be removed by heating 3c and 3d.

  The effects of the gas flow meter according to the first embodiment of the present invention will be described below with reference to the drawings.

  FIG. 4 shows the heat sensor element 1 constituting the gas flowmeter according to the first embodiment of the present invention. Oil, carbon, etc. after being placed in the intake passage 16 or the exhaust gas recirculation passage 24 of the internal combustion engine and operated for a long time. This shows how the dirt 10 adheres. Since the heating element portion 2 is heated to a high temperature of 400 ° C. or higher, there is no adhesion of the dirt 10. Further, a heating current flows through the first lead portion and the third lead portions 3a and 3b used for measuring the gas flow rate as indicated by 34 in order to heat the heating element portion 2. Dirt 10 adheres to the second and fourth lead portions 3c and 3d because they are directly hit by oil or carbon in the exhaust gas 5, but the first lead portion and the third lead used for measuring the gas flow rate. The portions 3a and 3b can be trapped by the second and fourth lead portions 3c and 3d on the upstream side to prevent the dirt 10 from adhering.

  FIG. 5 is an explanatory diagram of a method for removing the deposits attached to the second and fourth lead portions 3c and 3d. The dirt such as oil or carbon once adhering to the second and fourth lead portions 3c, 3d is removed after the measurement period of the gas flow meter is finished or at an appropriate time before the measurement. The adhering matter adhering to the second and fourth lead portions 3c and 3d is removed by heating 3d.

  When the switching element 33 is turned on by a predetermined timing signal from the control unit 21, the direction from the first lead portion 3a to the second lead portion 3c in the direction of the arrow 34 shown in FIG. A part of the heating current flows through the lead portion 3b. Further, a heating current flows through the heating element portion 2 in parallel along the route indicated by 35. The heating currents of both routes 34 and 35 are appropriately adjusted according to the resistance ratio between the adjusting resistor 32c and the heating element portion 2, and the second and fourth lead portions 3c and 3d are heated to remove the deposit 10.

  FIG. 6 shows the temperature distribution of the second and fourth lead portions 3c and 3d and the heating element portion 2. 36 is a temperature distribution when no heating current flows through the second and fourth lead portions 3c and 3d in the measurement period of the gas flow meter, and 37 is the second and fourth lead portions before and after the measurement period. This is a temperature distribution when a heating current is branched and supplied to 3c and 3d. Although the temperature is the same at the center of the heating element portion 2, there are differences in the temperatures of the lead portions 3c and 3d. When the heating current is branched and supplied to the second and fourth lead portions 3c and 3d, the temperature is high in all regions of the lead portions 3c and 3d, and the temperature rises greatly particularly in the A portion.

  As described above, since the temperature becomes high in the entire region of the lead portions 3c and 3d, the dirt 10 such as oil or carbon once adhered to the second and fourth lead portions 3c and 3d is measured by the gas flow meter. It can be removed after the period is over or at an appropriate time before the measurement.

  In FIG. 6, the temperature of the heating element portion 2 when the heating current is branched and supplied to the second and fourth lead portions 3c and 3d before and after the measurement period is the same as that before the branching. In order to enhance the effect of removing the dirt 10 such as, it is also possible to set it higher than before branching. In this case, the adjustment resistor 32c may be adjusted to an appropriate resistance in the circuit configuration of FIG. 3, and the voltage of the power supply 30 may be boosted by the switching circuit in synchronization with the switching element 33.

FIG. 7 shows the measurement error of the mass flow rate of the exhaust gas 5 after being placed in the intake passage 16 or the exhaust gas recirculation passage 24 of the internal combustion engine and operating for a long time. In the figure, 38 is a conventional example,
39 is a measurement result of the heat generation sensor element 1 of the present invention. The conventional example of 38 shows a large error which is positive in the low flow region and negative in the high flow region, but there is almost no change in the heat generation sensor element 1 of the present invention.

Regarding the measurement of the mass flow rate, the output is expressed by the above-mentioned King equation (1), and in particular, ΔTh =
It is proportional to (Th-Te). Accordingly, in the heat generation sensor element 1, the high temperature portion of the heat generation element portion 2 and the A portion of the lead portions 3a and 3b particularly affects the output. The fixed part 4a having a low temperature,
4b, 4c, 4d and the lead portions in the vicinity thereof do not significantly affect the output. In the heat generating sensor element 1 of the present invention, the dirt 10 such as oil or carbon does not adhere to the heat generating element portion 2 and the A portion of the lead portions 3a and 3b, so that there is almost no change in output and the output is stable.

  FIG. 8 shows the configuration of gas flow meters 17 and 25, which are a second embodiment to which the present invention is applied. In this embodiment, the temperature control of the heat generation sensor element 1 is different from that in the first embodiment.

  The heat generation sensor element 1 and the gas temperature sensor element 27 are disposed in the passages 16 and 24 in the figure. In the first embodiment of FIG. 3, the heat generation sensor element 1 forms a bridge circuit with the gas temperature sensor element 27, but in this embodiment, the gas temperature sensor element 27 is replaced with a resistor 32d. Therefore, in the first embodiment, feedback is performed so that the temperature (Th) of the heat generation sensor element 1 is higher than the temperature (Te) of the gas temperature sensor element 27 corresponding to the gas temperature by a certain temperature (ΔTh = Th−Te). Although controlled, in this embodiment, it is controlled to a constant heater temperature (Th) regardless of the gas temperature (Te).

  Thus, by controlling the temperature (Th) of the heat generation sensor element 1 to be constant, the temperature (Th) becomes constant even when the temperature change of the gas temperature (Te) changes greatly. 1 can be prevented from being heated without being heated. Further, the temperature (Th) of the heat generation sensor element 1 is always controlled to a constant value of 400 ° C. or higher regardless of the gas temperature (Te), thereby preventing the attachment of floating substances such as carbon and realizing a highly reliable configuration. .

  On the other hand, when controlled to a constant temperature (Th), the output of the mass flow rate strongly depends on the gas temperature (Te). For this reason, the gas temperature sensor element 27 is disposed in the passages 16 and 24, the gas temperature (Te) output is taken into the control unit 21 from the terminal 31c, and the heating current flowing through the heat generation sensor element 1 (= terminal voltage of 31a). Perform output correction.

  Also in this embodiment, the operation of the switching element 33, the adjustment resistor 32c, etc. is the same as that of the first embodiment, and the oil and carbon etc. once adhered to the second and fourth lead portions 3c, 3d. 10 can be removed after the measurement period of the gas flow meter is over or at an appropriate time before the measurement.

  Although the present invention has been described with respect to several embodiments, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the spirit of the present invention.

1 is a heat generation sensor element according to a first embodiment of the present invention. It is explanatory drawing of an EGR control apparatus. It is composition explanatory drawing of the gas flowmeter which is a 1st Example. It is explanatory drawing of the heat_generation | fever sensor element which is a 1st Example. It is explanatory drawing of the heat_generation | fever sensor element which is a 1st Example. It is explanatory drawing of the temperature distribution of an exothermic sensor element. It is explanatory drawing of an output characteristic. It is composition explanatory drawing of the gas flowmeter which is a 2nd Example. This is a conventional heat generation sensor element. It is sectional drawing of the exothermic sensor element which is a prior art example. It is explanatory drawing of the heat-generation sensor element which is a prior art example. It is explanatory drawing of the heat-generation sensor element which is a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Heat generation sensor element, 2 ... Heat generation element part, 3a, 3b, 3c, 3d ... Lead part, 4a,
4b, 4c, 4d ... fixed part, 5 ... exhaust gas, 6 ... ceramic bobbin, 7 ... platinum wire, 8 ... adhesive glass, 9 ... protective glass.

Claims (12)

In a gas flow meter that detects the mass flow rate of a gas based on the value of a current flowing through a heat generation sensor element arranged in the flow of the gas to be measured,
The heating sensor element is a heating element formed by forming a heating resistor on the bobbin and protecting the surface, a lead part electrically connected to both sides of the heating element part, and the lead part fixed in the gas flow path And is composed of a fixed part for electrical connection with an external circuit,
The lead portions at both ends branch into two in the vicinity of the joint portion with the heat generating element portion to constitute a set of a first lead portion and a second lead portion and a set of a third lead portion and a fourth lead portion, respectively. The other end of the lead portion is connected and fixed to a fixing portion corresponding to each lead portion,
The second and fourth lead portions are arranged upstream of the gas flow of the first lead portion and the third lead portion, respectively, so that the first lead portion and the third lead portion are not directly exposed to the gas flow,
A gas flow meter configured to measure the mass flow rate of the gas to be measured by energizing the first lead portion and the third lead portion to heat the heating element portion. In the gas flowmeter according to claim 1, at an appropriate time before and after the measurement period,
A branch is formed so that a part of the heating current flows from the fourth lead part to the third lead part via the second lead part from the first lead part, and the second and fourth lead parts are heated to A gas flow meter comprising circuit means for removing deposits adhering to the second and fourth lead portions. 3. The gas flowmeter according to claim 2, wherein a switching element and an adjustment resistor are provided between the fixed portions of the second and fourth lead portions as branching means that a part of the heating current reaches the second and fourth lead portions. Connected in series,
The switching element is turned on by a predetermined timing signal, and the heating current flows from the fourth lead part to the third lead part via the second lead part from the first lead part by the adjusting resistor, and the first lead part. Adjust the ratio of the heating current flowing from the heating element part to the third lead part to a predetermined value,
A gas flowmeter characterized in that the second and fourth lead portions are heated to remove deposits attached to the second and fourth lead portions.   4. The gas flow meter according to claim 1, wherein the gas to be measured is intake air and exhaust gas in an internal combustion engine.   5. The gas flow meter according to claim 1, wherein the heating resistor is a wire wound with a platinum wire, and the protective coating is made of a glass material.   6. The gas flowmeter according to claim 1, wherein an average temperature of the heating element portion is maintained at 400 ° C. or higher so that carbon or the like is not deposited on the heating element portion.   7. The gas flowmeter according to claim 1, further comprising a gas temperature sensor element for detecting a gas temperature in the flow of the gas to be measured, and measuring the temperature of the heat generation sensor element with the gas temperature sensor. A gas flow meter configured to detect a mass flow rate of a gas based on a current value flowing through the heat generation sensor element by controlling the temperature of the element higher by a certain temperature.   7. The gas flowmeter according to claim 1, further comprising a gas temperature sensor element for detecting a gas temperature in the flow of the gas to be measured, and controlling the temperature of the heat generation sensor element to a constant temperature. And a gas flowmeter that detects a mass flow rate of the gas based on a current value flowing through the heat generation sensor element and corrects the mass flow rate of the gas based on a gas temperature detected by the gas temperature sensor element. In a gas flow meter that detects the mass flow rate of a gas based on the value of a current flowing through a heat generation sensor element arranged in the flow of the gas to be measured,
The heating sensor element is a heating element formed by forming a heating resistor on the bobbin and protecting the surface, a lead part electrically connected to both sides of the heating element part, and the lead part fixed in the gas flow path And is composed of a fixed part for electrical connection with an external circuit,
The lead portion is divided into two at least in the vicinity of the joint with the heat generating element portion, and is composed of a set of a first lead portion and a second lead portion and an opposite third lead portion, and the other end of each lead portion Are connected and fixed to the fixing portions corresponding to the respective lead portions,
The first lead portion and the third lead portion are energized to heat the heating element portion and measure the mass flow rate of the gas to be measured.
A gas flowmeter characterized in that an electric current is passed from the first lead portion via the second lead portion to remove deposits attached to the first lead portion. The gas flowmeter according to claim 1, further comprising a fourth lead portion branched from the vicinity of the heating element of the third lead portion,
A branch is formed so that a part of the heating current flows from the fourth lead part to the third lead part via the second lead part from the first lead part, and the second and fourth lead parts are heated to A gas flowmeter characterized by removing deposits adhering to the second and fourth lead portions. The gas flow meter according to claim 10, wherein a switching element and an adjusting resistor are provided between the fixed portions of the second and fourth lead portions as branching means that a part of the heating current reaches the second and fourth lead portions. Connected in series,
The switching element is turned on by a predetermined timing signal, and the heating current flows from the fourth lead part to the third lead part via the second lead part from the first lead part by the adjusting resistor, and the first lead part. Adjust the ratio of the heating current flowing from the heating element part to the third lead part to a predetermined value,
A gas flowmeter characterized in that the second and fourth lead portions are heated to remove deposits attached to the second and fourth lead portions. 12. The gas flow meter according to claim 9, wherein the gas to be measured includes exhaust gas in an internal combustion engine.

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