JP4222202B2 - Thermal air flow detector - Google Patents

Description

  The present invention relates to a thermal air flow rate detection device that detects the flow rate of air flowing in an air flow path and outputs an air flow rate signal corresponding to the air flow rate, and in particular, a semiconductor having a polycrystalline structure as a heating resistor. The present invention relates to a thermal air flow rate detection device using the above.

  In recent years, automobile engines equipped with electronically controlled fuel injection devices have been widely used in order to reduce pollution and fuel consumption. For example, fuel injection control that enables optimization of the amount of fuel injected into intake air by accurately detecting the air flow rate of intake air is performed by the electronically controlled fuel injection device. A thermal air flow rate detection device that uses a heating resistor to detect such an air flow rate is considered suitable for an automobile engine because it can directly detect the mass air flow rate.

  For example, it comprises two sets of bridge circuits composed of four resistors including a heating resistor, and a differential amplifier circuit that amplifies the differential voltage between the terminal voltages of each heating resistor in each bridge circuit. The output voltage is an air flow signal corresponding to the air flow rate, and the forward / reverse direction of the air flow is detected based on the positive / negative of the output voltage, and erroneous detection of the intake air flow rate due to the reverse air flow is prevented. As an example of a conventional thermal air flow rate detection device, there is a “thermal air flow rate detection device” disclosed in Patent Document 1. In addition, the heating resistor and temperature sensitive resistor that make up such a bridge circuit are made of temperature sensitive platinum, tungsten, etc. whose resistance changes in response to temperature changes. As an example of a relatively inexpensive configuration, a “thermal air flow sensor and internal combustion engine control device” disclosed in Patent Document 2 has been proposed.

  Such a thermal air flow rate detection device includes, for example, a housing main body 102 formed in a substantially rectangular flat box shape, as in the thermal air flow rate detection device 100 shown in FIG. The sensor housing 104 is formed in a cylindrical shape with a protruding slit and the sensor board 110 accommodated in the sensor housing 104, and the air flow path formed by the intake duct IM of the automobile engine The sensor housing 104 can be attached. A sensor circuit is configured on the sensor substrate 110.

  For example, the two sets of bridge circuits shown in FIG. 7 are composed of a first bridge circuit comprising a heating resistor Rha, a temperature sensitive resistor Rka, a first fixed resistor R1a, a second fixed resistor R2a, and an operational amplifier OPa, and a heating resistor Rhb. And a second bridge circuit composed of a temperature sensitive resistor Rkb, a first fixed resistor R1b, a second fixed resistor R2b and an operational amplifier OPb, and the difference voltage between the terminal voltages of the heating resistors Rha and Rhb in these bridge circuits Is constituted by an operational amplifier OPc and resistors R91 and R92. In FIG. 7, the heating resistors Rha and Rhb are surrounded by broken lines to indicate that the resistance value can vary depending on the air flow rate due to thermal coupling. Moreover, the arrows attached to the symbols of the heating resistors Rha and Rhb indicate that the resistance values of the heating resistors Rha and Rhb vary depending on the air flow rate, and the inclination of the arrow indicates the degree of influence thereof.

  With this configuration, air flowing from the slit of the sensor housing 104 contacts the heating resistors Rha and Rhb and the temperature sensitive resistors Rka and Rkb on the sensor substrate 110, so that the air according to the flow rate of the air A flow rate signal is output from the output terminal (Out) of the operational amplifier OPc via the terminal 106 of the housing body 102.

In each bridge circuit shown in FIG. 7, the output of the operational amplifier OPa is directly connected to the heating resistor Rha and the temperature sensing resistor Rka, and the output of the operational amplifier OPb is directly connected to the heating resistor Rhb and the temperature sensing resistor Rkb. In practice, however, the operational amplifier and the heating resistor are connected via a current drive transistor (not shown) controlled by the output currents of these operational amplifiers OPa and OPb (Patent Document 1). See FIG. 3). Therefore, a direct current voltage (control voltage) controlled by the operational amplifiers OPa and OPb is applied to the heating resistors Rha and Rhb. The voltage follower circuit constituted by the operational amplifier OPd receives the output from the first bridge circuit with high impedance so as not to affect the first bridge circuit due to the impedance fluctuation on the differential amplifier circuit side.
JP-A-8-43162 (pages 2-8, FIGS. 1-5) JP 2002-048616 A (2nd to 7th pages, FIGS. 1 to 11)

  However, in the conventional thermal air flow rate detection device 100 constituted by a bridge circuit and a differential amplifier circuit as shown in FIG. 7, the heating resistors Rha and Rhb are operational amplifiers OPa constituting the first and second bridge circuits. , OPb is controlled so as to have a predetermined heat generation temperature with respect to the air temperature in the intake duct IM, and when the air temperature becomes high, the heat generating resistors Rha and Rhb are controlled to generate heat at a higher temperature. Is done. Therefore, if the heating resistors Rha and Rhb are made of polycrystalline silicon, the structure of the polycrystalline structure whose atomic structure is not constant compared to the single crystal structure is likely to cause structural fluctuations due to high-temperature heat generation (for example, 300 ° C.). Variations in the electrical properties of the body can occur. On the other hand, at a low temperature, since the surface of the heat generating resistor placed in the flow path is also frozen, there is a demand for increasing the heat generating temperature as much as possible.

  That is, in a thermal air flow rate detection device that detects the air flow rate using heat generated from a heating resistor, when a polycrystalline semiconductor (for example, polycrystalline silicon) is used as the heating resistor, the crystal structure When heat generation control is performed so as to reach a high temperature that causes such fluctuations, it is difficult to obtain stable heat generation characteristics even after that. For this reason, such heat generation control not only affects the electrical characteristics of the heating resistor, but also has a problem that the reliability of the air flow signal obtained thereby can be reduced.

  The present invention has been made in order to solve the above-described problems, and an object of the present invention is to provide heat that can suppress a decrease in the reliability of an air flow signal even when a polycrystalline semiconductor is used as a heating resistor. An object of the present invention is to provide an air flow rate detection device.

In order to achieve the above object, the means described in claim 1 described in claims is adopted. According to this means, a heating resistor that can be provided in the air flow path made of a polycrystalline semiconductor, a control circuit unit that controls the current flowing through the heating resistor to control the heat generation of the heating resistor, and the heating resistor An amplifying circuit unit that amplifies an electrical signal based on heat generated by the body and outputs an air flow rate signal, and the control circuit unit has a temperature characteristic that has a negative slope with respect to a change in the ambient temperature of the heating resistor. line heat generation control of the heating resistor Utame, the heating resistor Rh, the temperature-sensitive resistor Rk that resistance value based on the ambient temperature is connected at one end to one end of the heating resistor Rh varies, the heating resistor A first fixed resistor R1 having one end connected to the other end of the body Rh, and a second fixed connected between the other end of the first fixed resistor R1 and the other end of the temperature sensitive resistor Rk. A bridge circuit comprising a resistor R2, and the heating resistor A predetermined control voltage is applied between a connection end a of Rh and the temperature sensitive resistor Rk and a connection end b of the first fixed resistor R1 and the second fixed resistor R2, and the heating resistor Rh and the first A control circuit for controlling the predetermined control voltage so that a potential difference between the connection end c of the first fixed resistor R1 and the connection end d of the temperature sensitive resistor Rk and the second fixed resistor R2 is zero. The temperature coefficient of the heating resistor Rh is TCRh, the temperature coefficient of the temperature sensing resistor Rk is TCRk, the temperature coefficient of the first fixed resistor R1 is TCR1, the temperature coefficient of the second fixed resistor R2 is TCR2, and the heat generation The resistance value of the resistor Rh at normal temperature is Rh0, the resistance value of the temperature sensitive resistor Rk is Rk0, the resistance value of the first fixed resistor R1 is R10, and the second fixed resistor R2 is normal temperature. Resistance value of R20 The heating temperature of the heating resistor Rh represented by “TCTh≈TCRh−ΔTCR / (1−γ)” where “TCRh + TCR2−TCRk−TCR1” is ΔTCR and “Rh0 × R20 / Rk0 / R10” is γ. Controlling the heat generation of the heating resistor Rh so that the coefficient TCTh is negative;
The amplifier circuit unit amplifies the electrical signal so as to have a temperature characteristic that has a positive slope with respect to a change in the ambient temperature of the heating resistor, and therefore inputs the potential of the connection end c or the connection end d. And an amplification circuit that amplifies the electrical signal with an amplification degree determined by a ratio of the resistance Rg and the resistance Rr, the temperature coefficient of the resistance Rg is TCRg, the temperature coefficient of the resistance Rr is TCRr, and the resistance Rg When the resistance value at room temperature of Rg0 is Rg0 and the resistance value of the resistor Rr at room temperature is Rr0, “TCR1-ΔTCR × γ / 2 / (1-γ) + Rg0 / (Rg0 + Rr0) × (TCRg−TCRr) = The electric signal is amplified by setting the temperature coefficient TCRg of the resistor Rg and the temperature coefficient TCRr of the resistor Rr so that “0” is established. The “normal temperature” is a temperature when heating and cooling are not performed, and normally 25 ° C. is assumed (the same applies hereinafter).

As a result, the heating resistor is controlled by the control circuit unit so as to have a temperature characteristic that has a negative slope with respect to a change in the ambient temperature of the heating resistor. For example, the ambient temperature of the heating resistor is Even if the temperature rises, it is possible to prevent the heat generation from being controlled at a higher temperature. That is, since the heat generation resistor Rh is controlled by the control circuit so that the heat generation temperature coefficient TCTh is negative, for example, even if the ambient temperature of the heat generation resistor Rh increases, It is possible to prevent the heat from being controlled.
In addition, even if the heating resistor is controlled to have a temperature characteristic that has a negative slope with respect to changes in the ambient temperature of the heating resistor, the amplification circuit unit is positive for the ambient temperature change of the heating resistor. Since the electric signal is amplified so as to have a temperature characteristic that has a slope of, the negative temperature characteristic with respect to the change in the ambient temperature of the heating resistor given to the electric signal is changed by the positive temperature characteristic by the amplification circuit unit. Can be countered. That is, even when the heat generation is controlled by the control circuit so that the heat generation temperature coefficient TCTh of the heat generation resistor Rh becomes negative, the negative signal included in the electric signal which is the potential of the connection end c or the connection end d output thereby. The temperature coefficient “Rg0 / (Rg0 + Rr0) × (TCRg−TCRr)” that cancels the temperature coefficient “TCR1−ΔTCR × γ / 2 / (1−γ)” is included in the amplification degree of the amplifier circuit. The negative temperature characteristic can be canceled by the positive temperature characteristic included in the amplification degree.

By adopting the means according to claim 2 , at least one of the temperature-sensitive resistor Rk constituting the bridge circuit, the resistor Rg constituting the amplifier circuit, and the resistor Rr is the resistance of the resistor. Since part or all of the semiconductor is composed of a polycrystalline semiconductor forming the heating resistor Rh, for example, in the manufacturing process of the polycrystalline semiconductor forming the heating resistor Rh, the temperature sensitive resistance Rk, the resistance Rg, A resistor Rr can be generated. Thereby, since these resistors can be manufactured by the manufacturing process of the heating resistor Rh, the manufacturing cost can be reduced and the product can be reduced in size and weight.

By adopting the means described in claim 3 , the heating resistor is polycrystalline silicon, so that the thermal air flow rate detecting device having the above-described features, functions, and effects is provided. Manufacturing cost can be reduced. Further, in the manufacturing process of the heating resistor Rh, by generating the temperature sensitive resistance Rk, the resistance Rg, and the resistance Rr (Claim 2 ), the manufacturing cost can be further reduced and the product can be reduced in size and weight.

  In the first aspect of the invention, the heating resistor is controlled by the control circuit unit so as to have a temperature characteristic that has a negative slope with respect to a change in the ambient temperature of the heating resistor. Even if the ambient temperature rises, it is possible to prevent the heat from being controlled so as to generate heat at a higher temperature. In addition, even if the heating resistor is controlled to have a temperature characteristic that has a negative slope with respect to changes in the ambient temperature of the heating resistor, the amplification circuit unit is positive for the ambient temperature change of the heating resistor. Since the electric signal is amplified so as to have a temperature characteristic that has a slope of, the negative temperature characteristic with respect to the change in the ambient temperature of the heating resistor given to the electric signal is changed by the positive temperature characteristic by the amplification circuit unit. Can be countered. Therefore, even if a polycrystalline semiconductor is used as the heating resistor, a decrease in the reliability of the air flow signal can be suppressed.

In the invention of claim 2 , since the temperature sensitive resistor Rk, resistor Rg, and resistor Rr can be manufactured by the manufacturing process of the heating resistor Rh, the manufacturing cost can be reduced and the product can be reduced in size and weight. Therefore, even if a polycrystalline semiconductor is used as the heating resistor, the reliability of the air flow rate signal can be suppressed, and the thermal air flow detection device can be realized at low cost and in small size and light weight.

In the invention of claim 3 , since the heating resistor is polycrystalline silicon, it is possible to reduce the manufacturing cost of the thermal air flow rate detecting device having the above-described features, functions, and effects. Further, in the manufacturing process of the heating resistor Rh, by generating the temperature sensitive resistance Rk, the resistance Rg, and the resistance Rr (Claim 2 ), the manufacturing cost can be further reduced and the product can be reduced in size and weight. Therefore, even if polycrystalline silicon is used as the heating resistor, the reliability of the air flow rate signal can be suppressed, and the thermal air flow detection device can be realized at a lower cost and with a smaller size and weight.

  Hereinafter, an embodiment of a thermal air flow detection device of the present invention will be described with reference to the drawings. First, a schematic configuration of the thermal air flow detection device 20 according to the present embodiment will be described with reference to FIG.

  As shown in FIG. 6, the thermal air flow rate detection device 20 includes a housing body 22, a sensor housing 24, a terminal 26, a sensor substrate 30, and the like, similar to the conventional thermal air flow rate detection device 100 described above, It can be attached in the middle of the intake pipe IM of the engine. As will be described later, since the sensor circuit other than the sensor circuit configured on the sensor substrate 30 is the same as that of the thermal air flow rate detection device 100 described above, detailed description thereof will be omitted here.

  As shown in FIG. 1, the sensor circuit configured on the sensor substrate 30 includes, for example, a first bridge circuit including a heating resistor Rha, a temperature sensitive resistor R11, a first fixed resistor R1a, a second fixed resistor R2a, and an operational amplifier OPa. And a second bridge circuit comprising a heating resistor Rhb, a temperature sensitive resistor R12, a first fixed resistor R1b, a second fixed resistor R2b and an operational amplifier OPb, and an operational amplifier OPc and resistors R21 and R22. It comprises a differential amplifier circuit that amplifies the differential voltage between the terminal voltages of the resistors Rha and Rhb, and a voltage follower circuit using an operational amplifier OPd. In FIG. 1, components that are substantially the same as those of the thermal air flow rate detection device 100 described above are denoted by the same reference numerals.

  The first bridge circuit and the second bridge circuit may correspond to the “control circuit unit” recited in the claims, and the operational amplifiers OPa and OPb are included in the “control circuit” recited in the claims. It can be equivalent. The differential amplifier circuit may correspond to the “amplifier circuit unit” and the “amplifier circuit” recited in the claims, and the resistor R22 is the “resistor Rg” recited in the claims. The resistor R21 can respectively correspond to “resistor Rr” recited in the claims.

  Here, the basic principle of the heating resistor Rha, Rhb control circuit shown in FIG. 1, that is, the heating resistor control circuit, will be described with reference to FIGS. For example, the simplest heating resistor control circuit is shown in FIG. In the circuit shown in FIG. 2, the following equation (1) is established. In the following description with reference to FIGS. 2 and 3, the heating resistor Rh as a general concept of the heating resistors Rha and Rhb shown in FIG. 1, and the temperature sensitive resistor Rk as a general concept of the temperature sensitive resistors R11 and R12. As a general concept of the first fixed resistors R1a and R1b, the first fixed resistor R1, as a general concept of the second fixed resistors R2a and R2b, and as a general concept of the operational amplifiers OPa and OPb, the operational amplifier OPx is used, respectively. And Further, “a” shown in FIGS. 2 and 3 can correspond to “connection end a” recited in the claims. Similarly, “b”, “c”, and “d” shown in FIG. 2 and FIG. 3 respectively correspond to “connecting end b”, “connecting end c”, and “connecting end d” described in the claims. It can be equivalent.

Ih ² · Rh = (α + β√G) · Th (1)
Rh · R2 = R1 · Rk (2)

Equation (1) is obtained by calculating the heating power (Ih ² · Rh) of the heating resistor Rh obtained from the air flow rate signal current Ih that is the heating resistor current flowing through the heating resistor Rh and the resistance value Rh of the heating resistor Rh. The heat radiation (α · Th) escaping to the structure such as the sensor substrate 30 forming the heating resistor Rh and the heat radiation (β√G · Th) due to the air flow contacting the heating resistor Rh Show. In the formula (1), α and β are constants depending on the shape of the structure around the heating resistor, G is the air flow rate, and Th is the heating temperature of the heating resistor Rh.

  Expression (2) is a control relational expression of the operational amplifier OPx, and the operational amplifier OPx controls so that the relation of the expression (2) is established at an arbitrary temperature. Then, the following equation (3) is derived from the equation (2).

  Rh0 · (1 + TCRh · ΔT + TCRh · Th) · R20 · (1 + TCR2 · ΔT) = R10 · (1 + TCR1 · ΔT) · Rk0 · (1 + TCRk · ΔT) (3)

  In the formula (3), R * 0 (* is “h”, “k”, “1”, “2”, the same shall apply hereinafter) indicates the room temperature value of each subscript resistor, and TCR * is The temperature coefficient of each index resistor is shown. Further, ΔT represents a temperature difference between the ambient temperature of the sensor circuit and normal temperature (25 ° C.). From these equations, the heating temperature Th of the heating resistor Rh and the air flow rate signal current Ih are expressed by the following equations (4) and (5).

Th = {R10 · (1 + TCR1 · ΔT) · Rk0 · (1 + TCRk · ΔT) / R20 / (1 + TCR2 · ΔT) −Rh0 · (1 + TCRh · ΔT)} / Rh0 / TCRh (4)
Ih = √ (α + β√G) / √ (Rh0 · TCRh) · √ {1-R20 · (1 + TCR2 · ΔT) · Rh0 · (1 + TCRh · ΔT) / R10 / (1 + TCR1 · ΔT) / Rk0 / (1 + TCRk · ΔT )} …(Five) .

  Here, since the temperature change amount (R * 0 · TCR * · ΔT) of each resistor is smaller than the normal temperature value (R * 0) of each resistor, the equations (4) and (5) can be simplified. The following equations (4) ′ and (5) ′ are obtained.

Th≈ (1 + TCRh · ΔT) / TCRh · [1 / γ · {1+ (TCR1 + TCRk−TCR2−TCRh) · ΔT} −1] ≈ (1-γ) / γ / TCRh · [1+ {TCRh−ΔTCR / (1 −γ)} · ΔT] (4) ′
Ih≈√ (α + β√G) · √ (1-γ) / √Rh0 / √TCRh · {1-γ · ΔTCR / 2 / (1-γ) · ΔT} (5) ′.

  In the formulas (4) ′ and (5) ′, γ represents Rh0 · R20 / Rk0 / R10, and ΔTCR represents TCRh + TCR2−TCRk−TCR1.

  Therefore, the temperature coefficient (heat generation temperature coefficient) TCTh of the heat generation temperature Th of the heat generation resistor Rh and the temperature coefficient TCVs of the air flow rate signal voltage Vs (= R1 · Ih) are expressed by the following equations (6) and (7). Equation (6) may correspond to “TCTh≈TCRh−ΔTCR / (1−γ)” described in the claims.

TCTh≈TCRh−ΔTCR / (1−γ) (6)
TCVs≈TCR1-ΔTCR · γ / 2 / (1-γ) (7)

  Here, the temperature coefficient of each resistor constituting the heating resistor control circuit shown in FIG. 2 is normally 0 (zero) for the first fixed resistor R1 and the second fixed resistor R2, and the temperature coefficient of the heating resistor Rh. And the temperature coefficient of the temperature sensitive resistance Rk are set to be equal to each other, that is, as shown in the following equation (8).

  TCR1 = TCR2 = 0, TCRk = TCRh (8)

  In this case, since ΔTCR = TCRh + TCR2−TCRk−TCR1 becomes ΔTCR = 0 (zero), the above equations (6) and (7) are expressed by the following equation (9).

  TCTh≈TCRh, TCVs≈0 (9)

  From this equation (9), it can be seen that instead of the air flow rate signal voltage Vs having no temperature characteristic, the heating resistor current Ih has a temperature characteristic of + TCRh. That is, when the temperature coefficient of each resistor is set so as to satisfy the relationship of equation (8) in the heating resistor control circuit shown in FIG. 2, the heating resistor temperature is set equal to the ambient temperature as shown in FIG. It has a positive slope (positive temperature coefficient) with respect to the slope (characteristic by the broken line and the alternate long and short dash line shown in FIG. 4) (characteristic by the thin solid line shown in FIG. 4). This is because, as shown in the equation (9), the air flow rate signal voltage Vs is set so as not to have temperature dependency (no temperature characteristic).

  From the above, when the temperature coefficient of each resistor constituting the heating resistor control circuit is set according to the equation (8) based on the equations (6) and (7), as shown by the thin solid line in FIG. As a temperature characteristic of Rh, a temperature characteristic (positive temperature characteristic) that tends to increase with respect to the ambient temperature is obtained. For this reason, the heating resistor Rh further increases the heating temperature at normal temperature as the ambient temperature rises. For example, when the ambient temperature reaches + 100 ° C., the heating resistor Rh has a heating temperature exceeding the ambient temperature + 200 ° C. Since the heating resistor control is performed, the heating temperature of the heating resistor Rh exceeds 300 ° C. As a result, as described in the section “Problems to be Solved by the Invention”, when the heating resistor Rh is composed of a semiconductor having a polycrystalline structure (for example, polycrystalline silicon), the characteristics of the polycrystalline structure are used. The structure is likely to change, and the electrical characteristics of the heating resistor Rh (heating resistor) may change.

  Therefore, in the present embodiment, “the heating resistor control circuit (control circuit unit, control circuit) has a temperature characteristic that has a negative slope with respect to a change in the ambient temperature of the heating resistor Rh (heating resistor). Heat generation resistance of the heating resistor Rh is controlled, and the detection signal amplification circuit (amplification circuit unit, amplification circuit) has an air flow rate signal voltage so as to have a temperature characteristic that has a positive slope with respect to a change in ambient temperature of the heating resistor Rh. “Vs (electric signal) amplification is performed”. A basic configuration example is shown in FIG. In FIG. 3, the heating resistor control circuit (control circuit unit, control circuit) for controlling the heat generation of the heating resistor Rh includes a heating resistor Rh, a combined temperature sensing resistor Rs, a first fixed resistor R1, and a second fixed resistor. The detection signal amplification circuit (amplification circuit unit, amplification circuit) is composed of an operational amplifier OPy and resistors Rg and Rr.

  Specifically, for example, as shown in FIG. 3, the temperature coefficient TCTh of the heating resistor Rh is made negative by setting the temperature coefficient of the combined temperature sensing resistor Rs smaller than the temperature sensing resistor Rk shown in FIG. (Characteristic by thick solid line shown in FIG. 4). For example, the combined temperature-sensitive resistor Rs is configured by combining a resistor having a temperature coefficient TCRh and a resistor having a temperature coefficient TCR = 0 at a resistance value ratio of 1: 1. As a result, TCRk becomes (TCRh / 2), and when both the temperature coefficient TCR1 of the first fixed resistor R1 and the temperature coefficient TCR2 of the second fixed resistor R2 are set to 0 (zero), (7) becomes the following formulas (10) and (11).

TCTh≈ (1-2 · γ) / 2 / (1-γ) · TCRh (10)
TCVs≈γ / 4 / (1-γ) · TCRh (11).

  Further, when γ is converted into the heating resistor heating temperature Th0 at room temperature (25 ° C.) using the above formula (3), the following formula (12) is obtained, so the above formulas (10) and (11) are Furthermore, the following equations (13) and (14) are obtained.

γ = 1 / (1 + TCRh · Th0) (12)
TCTh ≒ (TCRh-1 / Th0) / 2 (13)
TCVs≈−1 / 4 / Th0 (14).

  For example, when TCRh is set to 2000 ppm / ° C. and Th 0 is set to 200 ° C., from formulas (13) and (14), TCTh≈−1500 ppm / ° C. and TCVs≈−1250 ppm / ° C. The heating temperature of the heating resistor is + 220 ° C. to + 178 ° C. with respect to the ambient temperature −40 ° C. to + 100 ° C.

  Thus, when the heat generation temperature coefficient TCTh of the heat generating resistor Rh is set to be negative with respect to the change in the ambient temperature of the heat generating resistor Rh (characteristic by the bold solid line shown in FIG. 4), the temperature characteristic negative to the air flow signal voltage Vs. Will occur. That is, as described above, without setting the temperature coefficient so as to satisfy the relationship of TCRk = TCRh according to the above equation (8), for example, the temperature sensitive resistance of the temperature coefficient TCRh and the fixed resistance of the temperature coefficient TCR = 0 Since the temperature coefficient is set in a relationship of TCRk <TCRh in which 1: 1 is combined, the air flow signal voltage Vs has temperature dependence (temperature characteristics). For this reason, in the present embodiment, the amplification factor A of the amplifier circuit by the operational amplifier OPy can have a positive temperature coefficient that cancels the negative temperature characteristic of the air flow rate signal voltage Vs.

  For example, by combining the resistance Rg / resistor Rr (ratio of the resistance Rg and the resistance Rr) that can set the amplification degree A by the operational amplifier OPy, the amplification degree A can have a positive temperature characteristic. In the amplifier circuit centered on the operational amplifier OPy shown in FIG. 3, the amplification factor A is given by the following equation (15), and the temperature characteristic TCA of the amplification factor A is given by the following equation (16).

A = Rg0 · (1 + TCRg · ΔT) / Rr0 / (1 + TCRr · ΔT) +1 (15)
TCA = Rg0 / (Rg0 + Rr0) · (TCRg−TCRr) (16).

  Therefore, for example, the resistance Rr sets its temperature coefficient TCRr to 0 (zero), and the resistance Rg sets its temperature coefficient to 1250 ppm / ° C. by a combination of TCR = 0 and TCRh (= 2000 ppm / ° C.). In this case, a combined temperature-sensitive resistor Rg is configured by combining a resistor having a temperature coefficient TCR = 0 and a resistor having a temperature coefficient TCRh (2000 ppm / ° C.) at a resistance value ratio of 3.75: 6.25. Here, the same material (for example, polycrystalline silicon) as that of the heating resistor Rh is used as a material of the resistance necessary for the combination, but this also forms a resistor having the temperature coefficient in the process of forming the heating resistor Rh. This is because the advantage of the manufacturing process that it can be taken into consideration. Note that the temperature coefficient TCRr of the resistor Rr may be set to be negative.

  From the above, by setting the heating temperature coefficient TCTh of the heating resistor Rh according to the above equation (6) to be negative, the air flow rate signal voltage Vs output from the bridge circuit has a negative temperature coefficient according to the equation (7). TCVs (<0) are generated. Therefore, in order to cancel the temperature characteristic due to the negative temperature coefficient TCVs included in the air flow signal voltage Vs, TCRg and TCRr are combined so that TCVs + TCA = 0 holds. That is, TCRg and TCRr that satisfy the following expression (17) are selected. The equation (17) may correspond to “TCR1−ΔTCR × γ / 2 / (1−γ) + Rg0 / (Rg0 + Rr0) × (TCRg−TCRr) = 0” described in the claims. .

  TCR1−ΔTCR · γ / 2 / (1−γ) + Rg0 / (Rg0 + Rr0) · (TCRg−TCRr) = 0 (17).

  Thus, the heat generation resistor Rh is controlled in heat generation by the heat generation resistor control circuit so that the heat generation temperature coefficient TCTh is negative. For example, even if the ambient temperature of the heat generation resistor Rh rises, Therefore, it can be controlled to generate heat at a higher temperature. Even if the heat generation resistor control circuit controls the heat generation of the heat generation resistor Rh so that the heat generation temperature coefficient TCTh of the heat generation resistor Rh becomes negative, the potential of the connection end c or the connection end d output thereby A temperature coefficient “Rg0 / (Rg0 + Rr0) × (TCRg−TCRr)” that cancels a negative temperature coefficient “TCR1-ΔTCR × γ / 2 / (1-γ)” included in a certain air flow signal voltage Vs (electrical signal) Since it is included in the amplification degree A of the detection signal amplification circuit, the negative temperature characteristic included in the air flow rate signal voltage Vs can be canceled by the positive temperature characteristic included in the amplification degree A. Therefore, even if, for example, polycrystalline silicon is used for the heating resistor Rh, a decrease in the reliability of the air flow rate signal can be suppressed. It should be noted that various combinations of resistances with temperature coefficients are possible as long as the above-described equations (6), (7), (16), and (17) are satisfied.

  Here, returning to FIG. 1, the sensor substrate 30 of the thermal air flow rate detection device 20 according to the present embodiment (see FIG. 6) has a heating resistor Rha, a temperature sensitive resistor R11, a first resistor as a control circuit unit. A first bridge circuit comprising a fixed resistor R1a and a second fixed resistor R2a, a second bridge circuit comprising a heating resistor Rhb, a temperature sensitive resistor R12, a first fixed resistor R1b and a second fixed resistor R2b, and a first bridge circuit An operational amplifier OPa (control circuit) that applies a predetermined control voltage to the second bridge circuit, and an operational amplifier OPb (control circuit) that applies a predetermined control voltage to the second bridge circuit. As described above, the heating temperature coefficient TCTh of the heating resistors Rha and Rhb (Rh) represented by the above formula (6) is negative with respect to the first and second bridge circuits. The heat generation of the heating resistors Rha and Rhb (Rh) is controlled. The reason for providing two bridge circuits like the first and second bridge circuits is to make it possible to detect the flow rate of air flowing through the intake duct IM as an air flow path in both forward and reverse directions.

  In addition, as an amplifier circuit section, the air by the difference voltage between the air flow rate signal voltage Vsa input from the first bridge circuit via the voltage follower by the operational amplifier OPd and the air flow rate signal voltage Vsb input from the second bridge circuit. It has an operational amplifier OPc (amplifier circuit) that amplifies the flow rate signal by the amplification degree determined by the resistor R22 / resistor R21 (ratio of the resistor R22 and the resistor R21). When the temperature coefficient of the resistor R22 is TCRg, the temperature coefficient of the resistor R21 is TCRr, the resistance value of the resistor R22 at room temperature is Rg0, and the resistance value of the resistor R21 at room temperature is Rr0, the above equation (17) is obtained. The air flow rate signal is amplified by setting the temperature coefficient TCRg of the resistor R22 and the temperature coefficient TCRr of the resistor R21 so as to be established.

  Thus, the heating resistors Rha and Rhb (Rh) are controlled in heat generation by the operational amplifiers OPa and OPb so that the heating temperature coefficient TCTh is negative. For example, the heating resistors Rha and Rhb (Rh) ) Can be prevented from being controlled to generate heat at a higher temperature even if the ambient temperature increases. Further, even if the heat generation is controlled by the operational amplifiers OPa and OPb so that the heat generation temperature coefficient TCTh of the heat generation resistors Rha and Rhb (Rh) becomes negative, the negative values included in the air flow rate signal voltages Vsa and Vsb output thereby. The temperature coefficient “Rg0 / (Rg0 + Rr0) × (TCRg−TCRr)” that cancels the temperature coefficient “TCR1-ΔTCR × γ / 2 / (1-γ)” is included in the amplification factor of the operational amplifier OPc. The negative temperature characteristic included in the voltages Vsa and Vsb can be canceled by the positive temperature characteristic included in the amplification degree. Therefore, even if, for example, polycrystalline silicon is used for the heating resistors Rha and Rhb, a decrease in the reliability of the air flow rate signal output from the operational amplifier OPc can be suppressed. Further, since the heat generation temperature at a low temperature is higher than that of the conventional one, it is possible to improve the freezing removal ability.

  Similarly, as shown in FIG. 5 (A), the present invention can also be applied to a circuit provided with a bridge circuit for air flow rate detection in addition to the bridge circuit for heating resistor control. That is, in the prior art, as shown in FIG. 5 (B), a bridge circuit for controlling a heating resistor composed of a fixed resistor R101, a temperature sensitive resistor R102, a fixed resistor R103, and a temperature sensitive resistor R104, to which a power supply voltage is applied, The operational amplifier OPe that causes a heat generation control current to flow through the heat generating resistor R105 that is thermally coupled to the temperature sensitive resistor R102 so that the difference between the potentials at both ends of the temperature sensitive resistor R102 and the temperature sensitive resistor R104 is 0 (zero). And a heating resistor control circuit comprising a heating resistor R105. A bridge circuit for air flow detection configured to be thermally coupled to the temperature sensitive resistor R102 and the heat generating resistor R105 is provided with temperature sensitive resistors R111 (small influence), R112 ( By arranging alternately the large influence), R113 (small influence), and R114 (large influence), the air flow rate can be detected by the potential difference output from the non-equilibrium state of the resistance value of the bridge circuit. For this reason, the difference between the both-end potential of the temperature-sensing resistor R112 and the both-end potential of the temperature-sensing resistor R114 is configured to be input to the detection signal amplification circuit by the operational amplifier OPg. The amplification factor of the detection signal amplification circuit by the operational amplifier OPg is set by the resistor R121 / resistor R122. The potential at both ends of the temperature sensitive resistor R112 is input to the detection signal amplifier circuit through an operational amplifier OPf that forms a voltage follower circuit.

  When the present invention is applied to the conventional configuration shown in FIG. 5 (B), as shown in FIG. 5 (A), it is connected in series with a temperature sensitive resistor R104 constituting a bridge circuit for controlling a heating resistor. Is provided with a fixed resistor R51 having no temperature characteristic, that is, having a temperature coefficient of 0 (zero). Thereby, the temperature sensing resistor R104 and the fixed resistor R51 constitute the synthesized temperature sensing resistor Rs described with reference to FIG. On the other hand, in the detection signal amplifying circuit, a fixed resistor R52 having a temperature coefficient of 0 (zero) is inserted in series with a resistor R122 that sets the degree of amplification by the ratio with the resistor R121. Thereby, the synthetic | combination temperature sensitive resistance Rg demonstrated with reference to FIG. 3 is comprised.

  In addition to the heating resistor control bridge circuit, an air flow rate detection bridge circuit that has been separately described with reference to FIG. 1 is configured as shown in FIG. 5 (A). It becomes possible to obtain the same operation and effect as the above.

  As described above, according to the thermal air flow detection device of the present embodiment, the heating resistor Rh that is made of polycrystalline silicon and can be provided in the intake duct IM, and the current Ih that flows through the heating resistor Rh is controlled. An operational amplifier OPx that controls the heat generation of the heat generating resistor Rh (heat generating resistor Rh, synthetic temperature sensitive resistor Rs, first fixed resistor R1, second fixed resistor R2, operational amplifier OPx) and the heat generation of the heat generating resistor Rh And an operational amplifier OPy that amplifies the air flow signal voltage Vs and outputs an air flow signal (synthetic temperature sensitive resistor Rg, resistor Rr, operational amplifier OPy). The operational amplifier OPx and the like change the ambient temperature of the heating resistor Rh. The heat generation resistor Rh is controlled to have a negative temperature characteristic, and the operational amplifier OPy or the like has a positive temperature characteristic with respect to a change in the ambient temperature of the heat generation resistor Rh. To amplify the air flow rate signal voltage Vs to have.

  As a result, the heating resistor Rh is controlled by the operational amplifier OPx or the like so as to have a temperature characteristic that has a negative slope with respect to a change in the ambient temperature of the heating resistor Rh. Even if the ambient temperature rises, it is possible to prevent the heat from being controlled so as to generate heat at a higher temperature. Further, even if the heat generation control of the heating resistor Rh is performed so as to have a negative temperature characteristic with respect to the change in the ambient temperature of the heating resistor Rh, the change in the ambient temperature of the heating resistor Rh by the operational amplifier OPy or the like. Since the air flow rate signal voltage Vs is amplified so as to have a positive temperature characteristic, the negative temperature characteristic with respect to the change in the ambient temperature of the heating resistor Rh given to the air flow rate signal voltage Vs. It can be canceled by the positive temperature characteristic by the operational amplifier OPy or the like. Therefore, even if polycrystalline silicon is used as the heating resistor Rh, a decrease in the reliability of the air flow rate signal can be suppressed.

  In the above-described embodiment, a fixed resistance having a temperature coefficient of 0 (zero) and a temperature sensitive resistor having a temperature coefficient other than 0 (zero) are connected in series as the “temperature resistance Rk” described in the claims. However, the present invention is not limited to this, and one temperature sensitive resistor having a required temperature coefficient may be configured. Further, in the above-described embodiment, the “resistance Rg” described in the claims includes a fixed resistance having a temperature coefficient of 0 (zero) and a temperature-sensitive resistance having a temperature coefficient of not 0 (zero) connected in series. The temperature resistance Rg is illustrated as an example, but the present invention is not limited to this, and one temperature-sensitive resistance having a required temperature coefficient may be configured. Further, in the above-described embodiment, the “resistance Rr” described in the claims is exemplified by using the fixed resistance Rr having a temperature coefficient of 0 (zero), but the present invention is not limited to this. A temperature sensitive resistor having a required temperature coefficient is used together with the resistor Rg, or a fixed resistor having a temperature coefficient of 0 (zero) is used for the resistor Rg, while a temperature sensitive resistor having the required temperature coefficient is used for the resistor Rr. It may be configured. Furthermore, in the above-described embodiment, the “heat generating resistor made of a semiconductor having a polycrystalline structure” described in the claims is exemplified by using polycrystalline silicon. However, the present invention is not limited to this. For example, a thermistor or a diffused resistor may be used. In any of these configurations, it is possible to obtain the same operation and effect as the above-described embodiment.

It is a circuit diagram which shows the electrical constitution of the thermal type air flow rate detector which shows one Embodiment of this invention. It is a circuit diagram which shows the basic composition of the heating resistor control circuit which comprises a thermal type air flow rate detection apparatus. It is a circuit diagram which shows the basic composition of the heating resistor control circuit and detection signal amplifier circuit which concern on this embodiment. It is a characteristic view which shows the fluctuation characteristic of the heating resistor temperature with respect to the ambient temperature of the heating resistor. FIG. 5 (A) is a circuit diagram showing the electrical configuration of a thermal air flow rate detector provided with a bridge circuit for air flow rate detection in addition to the bridge circuit for heating resistor control. FIG. FIG. 5B is a circuit diagram of a conventional example. It is explanatory drawing which shows the schematic structural example of a thermal-type air flow rate detection apparatus. It is a circuit diagram which shows the electrical structural example of the conventional thermal type air flow rate detection apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 20 ... Thermal air flow detection apparatus 30 ... Sensor board IM ... Intake duct (air flow path)
OPa, OPb ... operational amplifier (control circuit)
Rh, Rha, Rhb ... exothermic resistors Rk, R11, R12 ... temperature sensitive resistors R1, R1a, R1b ... first fixed resistors R2, R2a, R2b ... second fixed resistors Rg, R21 ... resistors Rr, R22 ... resistors

Claims (3)

A thermal air flow rate detection device that detects the flow rate of air flowing in an air flow path and outputs an air flow rate signal corresponding to the air flow rate,
A heating resistor that can be provided in the air flow path, made of a polycrystalline semiconductor,
A control circuit unit for controlling the current flowing through the heating resistor to control the heat generation of the heating resistor;
An amplification circuit unit that amplifies an electrical signal based on the heat generated by the heating resistor and outputs the air flow rate signal;
Wherein said control circuit unit, the heating line of the heating control of the heating resistor so as to have the temperature characteristics as a negative slope with respect to changes in the ambient temperature of the resistor Utame,
A resistance value fluctuates based on the heating resistor Rh and the ambient temperature, one end side is connected to one end side of the heating resistor Rh, and one end side is connected to the other end side of the heating resistor Rh. A bridge circuit comprising a first fixed resistor R1 and a second fixed resistor R2 connected between the other end side of the first fixed resistor R1 and the other end side of the temperature sensitive resistor Rk;
A predetermined control voltage is applied between the connection end a of the heating resistor Rh and the temperature sensitive resistor Rk and the connection end b of the first fixed resistor R1 and the second fixed resistor R2, and the heating resistor A control circuit for controlling the predetermined control voltage so that a potential difference between the connection end c of Rh and the first fixed resistor R1 and the connection end d of the temperature sensitive resistor Rk and the second fixed resistor R2 becomes zero. And having
The temperature coefficient of the heating resistor Rh is TCRh, the temperature coefficient of the temperature sensitive resistor Rk is TCRk, the temperature coefficient of the first fixed resistor R1 is TCR1, the temperature coefficient of the second fixed resistor R2 is TCR2, and the heating resistor The resistance value of Rh at room temperature is Rh0, the resistance value of the temperature sensing resistor Rk at room temperature is Rk0, the resistance value of the first fixed resistor R1 at room temperature is R10, and the resistance of the second fixed resistor R2 is room temperature. When the value is R20, “TCRh + TCR2−TCRk−TCR1” is ΔTCR, and “Rh0 × R20 / Rk0 / R10” is γ, the heating resistance expressed by “TCTh≈TCRh−ΔTCR / (1−γ)” Controlling the heat generation of the heating resistor Rh so that the heat generation temperature coefficient TCTh of the body Rh becomes negative,
The amplification circuit unit amplifies the electrical signal so as to have a temperature characteristic having a positive slope with respect to a change in the ambient temperature of the heating resistor .
An amplification circuit that amplifies the electric signal input as a potential of the connection end c or the connection end d with an amplification degree determined by a ratio of a resistor Rg and a resistor Rr;
When the temperature coefficient of the resistor Rg is TCRg, the temperature coefficient of the resistor Rr is TCRr, the resistance value of the resistor Rg at room temperature is Rg0, and the resistance value of the resistor Rr at room temperature is Rr0, “TCR1−ΔTCR × The temperature coefficient TCRg of the resistor Rg and the temperature coefficient TCRr of the resistor Rr are set so that “γ / 2 / (1−γ) + Rg0 / (Rg0 + Rr0) × (TCRg−TCRr) = 0” holds. A thermal air flow rate detector for amplifying a signal . At least one of the temperature-sensitive resistor Rk constituting the bridge circuit, the resistor Rg constituting the amplifier circuit, and the resistor Rr is a semiconductor having a polycrystalline structure in which a part or all of the resistor forms the heating resistor Rh. The thermal air flow rate detection device according to claim 1, comprising: The heating resistor, thermal air flow detecting device according to claim 1 or 2, characterized in that a polycrystalline silicon.

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