JP2000205915A - Flow rate detection apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the accuracy of detecting flow rate by making it possible to accurately detect the flow rate of intake air or the like even if high frequency pulsations occur in the intake air, etc. SOLUTION: First and second flow rate detection circuits 11, 13 constitute a bridge circuit having temperature sensing resistors 7, 9 and a differential amplifying circuit 15 is connected to the output side thereof. The differential amplifying circuit 15 outputs a flow rate detection signal V3 which matches a difference between first and second flow rate voltages V1, V2 outputted from the first and second flow rate detection circuits 11, 13. A gain compensating circuit 16 is connected to the output side of the differential amplifying circuit 15 and the flow rate detection signal V3 having a frequency between first and second predetermined frequencies is amplified by the gain compensating circuit 16 in proportion to that frequency. The gain compensating circuit 16 thus compensates a decrease in the flow rate detection signal V3 resulting from the heat-time constant of the temperature sensing resistors 7, 8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal type flow rate detecting device suitably used for detecting a flow rate of intake air from, for example, an automobile engine.

[0002]

2. Description of the Related Art Generally, an automobile engine or the like burns a mixture of fuel and intake air in a combustion chamber of an engine body, and obtains a rotational output of the engine from the combustion pressure. It is an important factor in calculating the intake air flow rate to calculate the intake air flow rate. For this reason, a thermal type flow detecting device is known as a flow detecting device for detecting an intake air amount of an engine (Japanese Patent Application Laid-Open No. 57-57).
No. 22563).

Such a flow rate detecting device according to the prior art is constituted by a bridge circuit or the like including a temperature-sensitive resistor, and calculates a flow rate detection signal corresponding to the flow rate of the fluid to be measured based on the resistance value of the temperature-sensitive resistor. It comprises a flow rate calculating means and a gain compensating means for amplifying a flow rate detection signal by the flow rate calculating means and compensating for a gain lowered by a thermal time constant of the temperature sensitive resistor.

[0004] The flow rate detecting device according to the prior art is
The temperature of the temperature sensitive resistor in the bridge circuit rises and falls according to the intake air amount, and the resistance value of the temperature sensitive resistor rises and falls according to the temperature. At this time, the resistance value of the temperature-sensitive resistor is output as, for example, a voltage signal, and a flow rate detection signal corresponding to the flow rate is calculated using the voltage signal.

In such a flow rate detecting device according to the prior art, since the temperature-sensitive resistor or the like has a heat capacity, this heat capacity acts as a first-order lag element. As a result, the response of the flow rate detection device to the change in the intake air flow rate is delayed, and the flow rate detection signal may be lower than the intake air flow rate. For this reason, in the conventional flow rate detection device, the decrease in the flow rate detection signal is compensated by the gain compensating means.

[0006]

In the above-mentioned prior art, the gain compensating means compensates for a decrease in the flow rate detection signal due to the time constant of the temperature-sensitive resistor or the like. here,
In the thermal type flow rate detection device, since the heat capacity of the temperature sensing resistor or the like acts as a first-order lag element, that is, a low-pass filter, the flow rate detection signal tends to decrease as the flow rate pulsates at a higher frequency. On the other hand, the conventional flow rate detecting device compensates for a decrease in the flow rate detection signal by increasing only the falling portion of the flow rate detection signal.
As a result, since the flow rate detection signal is converted into a signal of a lower frequency, there is a problem that the flow rate when pulsating at a high frequency cannot be accurately detected.

The present invention has been made in view of the above-mentioned problems of the prior art, and the present invention can accurately detect an intake air flow rate even when a high-frequency pulsation occurs, and can improve the flow rate detection accuracy. It is an object of the present invention to provide a flow detecting device as described above.

[0008]

In order to solve the above-mentioned problems, the present invention has a temperature-sensitive resistor provided in a fluid to be measured, and the fluid to be measured is determined by the resistance value of the temperature-sensitive resistor. And a gain compensating means for amplifying the flow rate detection signal by the flow rate computing means and compensating for the gain reduced by the thermal time constant of the temperature sensitive resistor. Applies to equipment.

A feature of the structure adopted in the first aspect of the present invention is that the gain compensating means is provided so that a flow rate detection signal having a frequency lower than a predetermined frequency determined by a thermal time constant of the temperature sensitive resistor is substantially constant. And a flow rate detection signal having a frequency higher than the predetermined frequency is amplified with a gain corresponding to the frequency.

Accordingly, when the flow rate pulsates at a frequency lower than the predetermined frequency, the flow rate detection signal output from the flow rate calculating means has a value substantially corresponding to the flow rate pulsation. At this time, the gain compensating means amplifies the flow rate detection signal with a predetermined constant gain. On the other hand, when the flow rate pulsates at a frequency higher than the predetermined frequency, the flow rate detection signal output from the flow rate calculation means decreases due to the heat capacity of the temperature-sensitive resistor. At this time, the gain compensator amplifies the flow rate detection signal with a gain corresponding to the frequency.

According to a second aspect of the present invention, the gain compensating means includes a flow rate detection signal having a frequency lower than a first predetermined frequency determined by a thermal time constant of the temperature-sensitive resistor. The flow rate detection signal in a range of a frequency higher than the first predetermined frequency and lower than a predetermined second predetermined frequency is amplified by a second gain corresponding to the frequency, and is amplified by the second gain. The flow rate detection signal having a frequency higher than the predetermined frequency is amplified with a substantially constant third gain which is larger than the second gain.

Thus, when the flow rate pulsates at a frequency lower than the first predetermined frequency, the flow rate detection signal has a value substantially corresponding to the flow rate pulsation. At this time, the gain compensator amplifies the flow rate detection signal with a constant first gain. When the flow rate pulsates in a frequency range higher than the first predetermined frequency and lower than a predetermined second predetermined frequency, the flow rate detection signal decreases due to the heat capacity of the temperature-sensitive resistor. At this time, the gain compensator amplifies the flow detection signal with the second gain corresponding to the frequency. further,
When the flow rate pulsates at a frequency higher than the second predetermined frequency, the gain compensator amplifies the flow rate detection signal with a third gain that is larger than the second gain and is substantially constant.

According to a third aspect of the present invention, the gain compensating means sets the first predetermined frequency to a frequency at which the flow rate detection signal starts to attenuate, and sets the second predetermined frequency to a flow rate at which gain compensation is required. That is, the highest frequency of the detection signal is set.

Thus, when the flow rate pulsates at a higher frequency than the frequency at which the flow rate detection signal starts to attenuate, the gain compensation means can amplify the flow rate detection signal with a gain corresponding to the frequency. In addition, since the second predetermined frequency is set to the highest frequency of the flow detection signal requiring the gain compensation, the flow detection signal requiring the gain compensation can be surely amplified.

Further, the invention according to claim 4 is characterized in that the gain compensating means comprises: an operational amplifier; a reference gain resistor connected to an inverting input terminal of the operational amplifier for setting a reference gain;
A compensation gain resistor connected in parallel to the reference gain resistor for compensating for the gain of the flow rate detection signal, and a thermal time constant of the temperature sensitive resistor together with the reference gain resistor connected in series to the compensation gain resistor. It is constituted by a capacitor for setting the predetermined frequency and a negative feedback resistor connected between an output terminal and an inverting input terminal of the operational amplifier.

Thus, the reference gain resistor sets an almost constant reference gain, and the compensation gain resistor sets a gain for compensating the flow rate detection signal. Further, a predetermined frequency can be set by the reference gain resistor and the capacitor, and a negative feedback amplifier circuit can be constituted by the negative feedback resistor.

According to a fifth aspect of the present invention, the flow rate calculating means includes a heater that generates heat at a constant temperature, a first temperature-sensitive resistor provided upstream of the heater, and a downstream side of the heater. A second temperature sensing resistor provided; first flow rate detection means for detecting a first flow rate signal based on a change in resistance value of the first temperature sensing resistor; A second flow rate detecting means for detecting a second flow rate signal based on a change in resistance value; a first flow rate detecting signal output from the first flow rate detecting means and a second flow rate detecting signal output from the second flow rate detecting means. And a flow detection signal output means for calculating a difference between the flow detection signal and the flow detection signal and outputting a flow detection signal.

Thus, the flow rate detection signal output means determines the difference between the first flow rate detection signal output from the first flow rate detection means and the second flow rate detection signal output from the second flow rate detection means. Calculate and output the flow rate detection signal. Then, the gain compensation means, when the flow rate detection signal from the flow rate detection signal output means decreases due to the heat capacity of the temperature sensitive resistor,
Compensate for that gain.

The invention according to claim 6 is that the flow rate detecting means is constituted by a bridge circuit including the temperature-sensitive resistor.

Thus, the bridge circuit outputs a change in the resistance value of the temperature-sensitive resistor as a flow rate detection signal. The gain compensating means compensates for the gain when the flow rate detection signal from the flow rate detection signal output means decreases due to the heat capacity of the temperature sensitive resistor.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a flow detecting device according to an embodiment of the present invention will be described in detail with reference to FIGS.

First, a first embodiment of the present invention will be described with reference to FIGS. Reference numeral 1 denotes a cylinder serving as a flow path through which a fluid to be measured such as air flows. The cylinder 1 is connected in the middle of an intake pipe (not shown) of the engine. During operation of the engine, intake air drawn into the combustion chamber of the engine body from the outside through the intake pipe flows in the cylinder 1 in the direction of arrow A.

Reference numeral 2 denotes a casing which forms the outer shape of the flow rate detecting device. The casing 2 includes a flange-shaped connector portion 2A attached to the cylindrical body 1, and a housing 2B extending from the connector portion 2A into the cylindrical body 1. It is constituted by. The casing 2 houses a flow rate detection element 3 and a detection circuit 9 described later.

Reference numeral 3 denotes a flow rate detecting element.
As shown in FIG. 2, a silicon substrate 4 having a trapezoidal concave portion 4A formed on the back side, and an insulating film 5 formed on the front side of the silicon substrate 4 by, for example, an oxide film, a nitride film, or the like.
A heater 6 formed at a position corresponding to the concave portion 4A on the silicon substrate 4 via the insulating film 5;
The first and the first films formed in the same manner as the heater 6 are located in the vicinity.
The second temperature-sensitive resistors 7 and 8 are provided. The heater 6 and the first and second temperature-sensitive resistors 7 and 8 include:
Electrode portions 6A, 7A, 8A for connection to reference resistors 12, 14 and the like described later are attached.

Here, the heater 6 is formed by depositing a platinum film on the silicon substrate 4 to a thickness of, for example, about 0.2 μm using a means such as print printing, sputtering or the like. The current value of the heater 6 is controlled by a current control transistor (not shown), and the heater 6 generates heat so as to keep the temperature at a constant temperature (for example, about 240 ° C.).

On the other hand, the first temperature-sensitive resistor 7 is formed on the upstream side of the heater 6 so as to have a resistance value RT1, and the second temperature-sensitive resistor 8 is formed on the downstream side of the heater 6. Is formed to have a resistance value RT2.

When the air flows in the direction indicated by the arrow A, the flow rate detecting element 3 detects the flow rate by utilizing the change in the resistance value of the temperature-sensitive resistors 7 and 8 cooled by the air flow. .

Reference numeral 9 denotes a detection circuit housed in the housing portion 2B of the casing 2. The detection circuit 9 is a heater control circuit (not shown) mounted on an insulating substrate made of, for example, a ceramic material or the like. It comprises a flow rate calculation circuit 10, a gain compensation circuit 16, and the like. Then, the heater control circuit always keeps the heater 6 at a constant temperature (for example, 240 ° C.).

Reference numeral 10 denotes a flow rate calculation circuit as flow rate calculation means. The flow rate calculation circuit 10 includes first and second flow rate detection circuits 11 and 13 which are bridge circuits to be described later, and the first and second flow rate detection circuits.
A differential amplifier 1 for differentially amplifying the first and second flow voltages V1 and V2 output from the second flow detection circuits 11 and 13.
5. And the flow rate calculation circuit 1
0 outputs a flow detection signal V3 corresponding to the flow Q.

Reference numeral 11 denotes a first flow detection circuit, which is constituted by connecting a first temperature-sensitive resistor 7 having a resistance value RT1 and a reference resistance 12 in series. ing. The first flow rate detection circuit 11 is connected between the battery voltage Eb set to a voltage of, for example, about 5 V and the ground, and is connected by a connection point a on the battery voltage Eb side and a connection point b on the ground side. 2 flow rate detection circuit 13
Are connected in parallel. For this reason, the first and second flow rate detection circuits 11 and 13 constitute a bridge circuit in which the resistance values of the opposing sides are equal.

The first temperature-sensitive resistor 7 and the reference resistor 12
Is connected to a non-inverting input terminal of a differential amplifier 15 described later. Then, the first flow rate detection circuit 11 detects a change in the resistance value RT1 of the first temperature-sensitive resistor 7
Is output as the flow voltage V1.

Reference numeral 13 denotes a second flow rate detection circuit. The second flow rate detection circuit 13 includes a second temperature-sensitive resistor 8 having a resistance value RT2 and a reference resistance value substantially similar to the first flow rate detection circuit 11. 1
4 are connected in series, and together with the first flow rate detection circuit 11, constitute a bridge circuit.

The second flow rate detecting circuit 13 is connected between the battery voltage Eb and the ground, and a connection point d between the second temperature sensitive resistor 8 and the reference resistor 14 is a differential amplifier. It is connected to the inverting input terminal of the circuit 15. And the second
The flow rate detection circuit 13 of the second embodiment has a resistance value R of the second temperature-sensitive resistor 8.
The change in T2 is output as the second flow voltage V2.

Reference numeral 15 denotes a differential amplifier circuit as a flow rate detection signal output means.
The connection points c and d of the second flow detection circuits 11 and 13 are connected, and a gain compensation circuit 16 described later is connected to the output side. The differential amplifier 15 calculates the difference between the first and second flow voltages V1 and V2, and outputs a flow detection signal V3 corresponding to the difference as a signal indicating the flow Q of the intake air.

Numeral 16 denotes a gain compensating circuit as gain compensating means. The gain compensating circuit 16 includes an operational amplifier 17 and a resistance R1 for setting a reference gain connected to an inverting input terminal of the operational amplifier 17. A reference gain resistor 18 having
The flow rate detection signal V3 connected in parallel to the reference gain resistor 18
A compensating gain resistor 19 having a resistance value R2 for compensating for the gain, a capacitor 20 connected in series with the compensating gain resistor 19 and having a capacitance C that determines the frequency characteristic together with the reference gain resistor 18, and the operational amplifier 17 And a negative feedback resistor 21 having a resistance value R3 connected between the output terminal and the inverting input terminal.

The non-inverting input terminal of the operational amplifier 17 is connected to the output terminal of the differential amplifier circuit 15, and the inverting input terminal is connected to the reference gain resistor 18 or the compensation gain resistor 19.
And a capacitor 20 to the reference voltage Es. The resistance value R1 of the reference gain resistor 18 is sufficiently larger than the resistance value R3 of the compensation gain resistor 19 (R
1 >> R3).

The product of the resistance value R1 of the reference gain resistor 18 and the capacitance C of the capacitor 20 is set to be substantially equal to the thermal time constant τ of the temperature-sensitive resistors 7, 8 as shown in the following equation (1). Is set to

[0038]

[Expression 1] τ = CR1

Then, as shown by the characteristic line 22A in FIG. 4, the gain compensating circuit 16 substantially suppresses the flow rate Q pulsating at a frequency f lower than the first predetermined frequency f1 shown in the following equation (2). The first gain G1 is set to be a constant first gain G1 shown in Expression 3. Further, as shown by the characteristic line 22B in FIG. 4, the gain compensating circuit 16 controls the flow rate pulsating at a frequency f higher than the first predetermined frequency f1 and lower than the second predetermined frequency f2 shown in the following Expression 4. Q is set to have a second gain G2 substantially proportional to the frequency f.
Further, as shown by the characteristic line 22C in FIG. 4, the gain compensation circuit 16 operates at a frequency f higher than the second predetermined frequency f2.
Is set so as to have a constant third gain G3 substantially as shown in equation (5).

[0040]

(Equation 2)

[0041]

(Equation 3)

[0042]

(Equation 4)

[0043]

(Equation 5)

Here, the first predetermined frequency f1 is determined by the thermal time constant τ of the temperature-sensitive resistors 7, 8, etc., and indicates the frequency at which the flow rate detection signal V3 starts to attenuate. That is, the first predetermined frequency f1 indicates the cutoff frequency of the low-pass filter when acting as a low-pass filter on the flow rate detection signal V3 due to the heat capacity of the temperature-sensitive resistors 7, 8, etc. It is. Also, the second predetermined frequency f2
Is the resistance value R2 of the compensation gain resistor 19 and the capacitor 20.
Indicates the highest frequency of the flow rate detection signal V3 for which gain compensation is required.

The gain compensating circuit 16 calculates the following equation (6).
As shown in the figure, for a flow rate pulsating at a frequency f between the first and second predetermined frequencies f1 and f2, the gain becomes a value between the gains G1 and G3 substantially in proportion to the frequency f. It amplifies the detection signal V3 (see the characteristic line 22 in FIG. 4).

[0046]

(Equation 6)

Therefore, when the flow rate detection signal V3 decreases as the frequency increases, the gain of the gain compensation circuit 16 increases.
To output an output signal Vout corresponding to the flow rate Q regardless of the frequency.

Reference numeral 23 denotes a controller.
3 stores a map indicating the relationship between the flow rate Q and the flow rate detection signal V3, as indicated by the characteristic line 24 in FIGS. Here, when the flow rate Q is small, the flow rate detection signal V3 due to the non-linear response of the temperature-sensitive resistors 7 and 8
Is large, and when the flow rate Q is large, it has a non-linear characteristic such that the change in the flow rate detection signal V3 becomes small.

The flow rate detecting device according to the present embodiment has the above-described configuration. Next, the operation of detecting the flow rate of the intake air will be described.

First, when the intake air flows in the direction of the arrow A, the first air located upstream on the silicon substrate 4
Is cooled by this flow of air, and the second temperature-sensitive resistor 8 located downstream receives heat from the heater 6. As a result, the resistance values RT1 and RT2 of the first and second temperature sensing resistors 7 and 8 change, so that a potential difference occurs between the flow voltages V1 and V2 from the first and second flow detection circuits 11 and 13. The differential amplifier circuit 15 outputs a flow rate detection signal V3 corresponding to the potential difference (V1 -V2).

When the flow rate Q1 is pulsating at a frequency f lower than the predetermined frequency f1 as shown by a characteristic line 25 in FIG. 5, the flow rate detection signal V3 becomes as shown by a characteristic line 26 in FIG. It changes according to the change in the flow rate Q1. At this time, the gain compensation circuit 16 amplifies the flow rate detection signal V3 with a predetermined constant gain G1. Next, the controller 23 calculates a flow rate calculation value Q1 'substantially equal to the characteristic line 25 in FIG. 5 from the flow rate detection signal V3 using the map shown in the characteristic line 24 in FIG. Finally, the controller 23 calculates an average value Q1av of the calculated flow rate values Q1 'obtained by the calculation and outputs the calculated value as the flow rate of the intake air.

On the other hand, when the flow rate Q2 is pulsating at a frequency f higher than the predetermined frequency f1 as shown by the characteristic line 27 in FIG. 6, the heat capacity of the silicon substrate 4, the temperature-sensitive resistors 7, 8 and the like becomes primary. Since it acts as a delay element, as shown by the characteristic line 28 in FIG. 6, the flow rate detection signal V3 cannot change in accordance with the change in the flow rate Q2, and its amplitude decreases. The flow rate detection signal V3 is represented by a characteristic line 29 in FIG.
Is close to the average value of the ideal output signal VA that should be output as shown in FIG.

At this time, when the gain compensation circuit 16 is not provided, the flow rate Q is determined based on the average value of the ideal output signal VA.
Is calculated. The average value QA of the flow rate calculated based on the average value of the output signal VA is smaller than the average value Q2av of the original flow rate Q2 due to the non-linear response of the temperature sensitive resistors 7 and 8.

However, in the present embodiment, a gain compensation circuit 16 is connected to the output side of the differential amplifier circuit 15. When the pulsation frequency f is higher than the predetermined frequency f1, the gain compensation circuit 16 is configured to increase the gain more than the gain G1 substantially in proportion to the frequency f. For this reason, the gain compensation circuit 16 outputs the flow rate detection signal V3
Is amplified with a gain larger than the gain G1, and an output signal Vout having an amplitude substantially equal to the ideal output signal VA is output as shown by a characteristic line 30 in FIG.

Then, the controller 23 calculates the flow rate calculation value Q2 'which is substantially equal to the characteristic line 27 in FIG. 6 based on the output signal Vout using the map shown in the characteristic line 24 in FIG. For this reason, the controller 23 calculates the average value Q2av of the calculated flow rate value Q2 'obtained by the calculation and outputs the calculated average value Q2av as the flow rate of the intake air. Therefore, it is necessary to detect the accurate flow rate Q irrespective of the pulsation frequency f. Can be.

Thus, according to the present embodiment, the gain compensating circuit 16 outputs the flow rate detection signal having a frequency f lower than the first predetermined frequency f 1 determined by the thermal time constant τ of the temperature sensitive resistors 7 and 8. V3 is amplified with a substantially constant gain G1, and the flow rate detection signal V3 having a frequency f higher than the predetermined frequency f1 is amplified with gains G2 and G3 corresponding to the frequency f.

Thus, when the flow rate Q pulsates at a frequency f lower than the predetermined frequency f1, the flow rate detection signal V3 has a value substantially proportional to the pulsation of the flow rate Q. At this time, since the gain compensation circuit 16 amplifies the flow rate detection signal V3 with a constant gain G1, the gain compensation circuit 16
And outputs an output signal Vout which is substantially proportional to the pulsation.

When the flow rate Q pulsates in a range of a frequency f higher than the first predetermined frequency f1 and lower than the second predetermined frequency f2, the flow detection signal V3 is output from the temperature-sensitive resistors 7, 8, etc. Its value is reduced by heat capacity. At this time, since the gain compensation circuit 16 amplifies the flow detection signal V3 with the gain G2 substantially proportional to the frequency f, the gain of the flow detection signal V3 that attenuates as the frequency f becomes higher can be compensated. For this reason, the gain compensation circuit 16 operates at the frequency f
, An output signal Vout corresponding to the flow rate Q can always be output.
Can be calculated.

Further, since the gain compensation circuit 16 is configured to amplify the flow rate detection signal V3 having a frequency f higher than the predetermined frequency f2 on the high frequency side with a substantially constant gain G3, the detection of the flow rate has almost no effect. Is not amplified more than necessary. Therefore, errors due to the flow rate detection signal V3 on the high frequency side can be eliminated, and the detection accuracy of the flow rate Q can be improved.

On the other hand, the gain compensation circuit 16 is
7, the reference gain resistor 18, the compensation gain resistor 19, the capacitor 20, and the negative feedback resistor 21
The predetermined frequency f1 can be set by the capacitor 20, and the predetermined frequency f1 can be easily set in accordance with the thermal time constant τ of the temperature-sensitive resistors 7 and 8.

Next, FIG. 8 shows a second embodiment according to the present invention. The feature of this embodiment is that a bridge circuit including a temperature-sensitive resistor whose resistance changes in accordance with temperature while generating heat is provided. To constitute the flow rate calculation means. The same components as those in the above-described first embodiment are denoted by the same reference numerals, and description thereof will be omitted.

Reference numeral 31 denotes a flow rate calculation circuit as flow rate calculation means for outputting a flow rate detection signal V4.
Reference numeral 1 includes a temperature-sensitive resistor 32, a resistance value of which changes in accordance with the temperature while generating heat, a temperature compensation resistor 33, a reference resistor 34, a flow rate adjustment resistor 35, and the like. It is configured using a bridge circuit 36. A connection point a 'between the temperature-sensitive resistor 32 and the temperature compensation resistor 33 is connected to the collector side of a current control transistor 39, which will be described later.
Is connected to the ground.

The flow rate calculation circuit 31 includes a temperature compensation resistor 33 and a flow rate adjustment resistor 35, a temperature sensitive resistor 32 and a reference resistor 3.
4 are connected in series, and each connection point c ',
d 'is connected to the input terminal of the differential amplifier circuit 37, and is connected to a connection point d' via a connection resistor 38 to a gain compensation circuit 40 described later.

The signal output from the differential amplifier circuit 37 becomes the current control voltage V0 of the current control transistor 39 for controlling the applied current of the flow rate operation circuit 31. On the other hand, from the connection point d 'of the flow rate operation circuit 31, the reference resistance 3
A flow rate detection signal V4 is output as a voltage between both ends of the resistor 4, and the flow rate detection signal V4 indicates the degree to which the temperature-sensitive resistor 32 is cooled by the flow rate.

Reference numeral 39 denotes a current control transistor. The current control transistor 39 has an emitter connected to the battery voltage Eb, a base connected to the output of the differential amplifier circuit 37, and a collector connected to the flow rate calculation circuit 31. It is connected to the connection point a '. The current control transistor 39 is connected to the current control voltage V0 from the differential amplifier circuit 37.
The collector current is controlled by changing the base current. Thus, the current control transistor 39 is connected to the temperature-sensitive resistor 3
Feedback control is performed to control the value of the current flowing to the second and the like and keep the temperature of the temperature-sensitive resistor 32 constant.

Reference numeral 40 denotes a gain compensation circuit according to the present embodiment. The gain compensation circuit 40 is substantially the same as the gain compensation circuit 16 according to the first embodiment, and includes an operational amplifier 17, a reference gain resistor 18, and a compensation gain. It comprises a resistor 19, a capacitor 20, and a negative feedback resistor 21. However, the point that the inverting input terminal of the operational amplifier 17 is connected to the ground via the reference gain resistor 18 or the compensation gain resistor 19 and the capacitor 20 is different from the gain compensation circuit 16 according to the first embodiment. Are different.

Thus, in the flow rate detecting device of the present embodiment having the above-described structure, the flow rate of the intake air can be accurately determined even when a high-frequency pulsation occurs, as in the first embodiment. Can be detected.

[0068]

As described above in detail, according to the first aspect of the present invention, the gain compensating means is provided so that the flow rate detection signal having a frequency lower than the predetermined frequency determined by the thermal time constant of the temperature-sensitive resistor is almost equal. Since the flow rate detection signal amplified at a constant gain and having a frequency higher than the predetermined frequency is amplified at a gain corresponding to the frequency, the flow rate detection signal is output when the flow rate pulsates at a frequency lower than the predetermined frequency. Is substantially proportional to the pulsation of the flow rate, and the gain compensating means amplifies the flow rate detection signal with a constant gain. On the other hand, when the flow rate pulsates at a frequency higher than the predetermined frequency, the value of the flow rate detection signal decreases due to the heat capacity of the temperature sensitive resistor or the like, and the gain compensation means amplifies the flow rate detection signal with a gain corresponding to the frequency. I do. For this reason, the gain compensating means can compensate for the gain of the flow rate detection signal that attenuates as the frequency increases, and always outputs an output signal corresponding to the flow rate regardless of the frequency, and can detect an accurate flow rate. it can.

According to the second aspect of the present invention, the gain compensating means is configured to set the predetermined frequency higher than the second predetermined frequency higher than the first predetermined frequency determined by the thermal time constant of the temperature-sensitive resistor. Since the flow rate detection signal is amplified with a substantially constant gain, the flow rate detection signal on the high frequency side, which hardly affects the flow rate detection, is not amplified more than necessary. For this reason, errors due to the flow rate detection signal on the high frequency side can be eliminated, and the flow rate detection accuracy can be improved.

According to the third aspect of the present invention, the first predetermined frequency set by the gain compensating means is set to a frequency at which the flow detection signal starts to attenuate, and the second predetermined frequency is set to a flow rate at which gain compensation is required. Since the highest frequency of the detection signal is set, the gain compensator can amplify the flow detection signal with a gain corresponding to the frequency when the flow pulsates at a higher frequency than the frequency at which the flow detection signal starts to attenuate.
In addition, since the second predetermined frequency is set to the highest frequency of the flow detection signal requiring the gain compensation, the flow detection signal requiring the gain compensation can be surely amplified.

According to the fourth aspect of the present invention, the gain compensating means is constituted by the operational amplifier, the reference gain resistor, the compensation gain resistor, the capacitor and the negative feedback resistor. The gain for a flow detection signal having a lower frequency can be set, and the gain for a flow detection signal having a frequency higher than a predetermined frequency can be set by a compensation gain resistor. Since the predetermined frequency can be set by the capacitor, these values can be easily set according to the time constant of the temperature-sensitive resistor.

According to the fifth aspect of the present invention, the flow rate calculating means includes a heater that generates heat at a constant temperature, a first temperature-sensitive resistor provided upstream of the heater, and a downstream side of the heater. A second heater, a first flow rate detecting means for detecting a first flow rate signal by a change in resistance value of the first temperature sensitive resistor, and a resistance value of the second temperature sensitive resistor. Second flow rate detection means for detecting a second flow rate signal by a change;
A flow rate detection signal for calculating a difference between a first flow rate detection signal output from the first flow rate detection means and a second flow rate detection signal output from the second flow rate detection means and outputting a flow rate detection signal; The flow rate detection signal output means is composed of the first flow rate detection signal output from the first flow rate detection means and the second flow rate detection signal output from the second flow rate detection means.
Then, a difference from the flow rate detection signal is calculated to output a flow rate detection signal. Therefore, the flow rate can be detected using the flow rate detection signal.

According to the sixth aspect of the present invention, since the flow rate detecting means is constituted by a bridge circuit including the temperature-sensitive resistor, the flow rate detecting means detects a change in the resistance value of the temperature-sensitive resistor by a flow rate detection signal. And the flow rate can be detected using the flow rate detection signal.

[Brief description of the drawings]

FIG. 1 is a vertical sectional view showing a state in which a flow detecting device according to a first embodiment is attached to an intake pipe.

FIG. 2 is a perspective view showing a heater, a first temperature-sensitive resistor, and a second temperature-sensitive resistor formed on a silicon substrate.

FIG. 3 is a circuit diagram illustrating a flow calculation circuit, a gain compensation circuit, and the like of the flow detection device according to the first embodiment.

FIG. 4 is a characteristic diagram showing a relationship between gain and frequency of a gain compensation circuit.

FIG. 5 is a characteristic diagram showing a relationship between a flow rate and a flow rate detection signal when the flow rate pulsates at a frequency lower than a first predetermined frequency.

FIG. 6 is a characteristic diagram showing a relationship between a flow rate and a flow rate detection signal when the flow rate pulsates at a frequency higher than a first predetermined frequency.

FIG. 7 is a characteristic diagram showing a relationship between time, a flow rate detection signal, and an output signal.

FIG. 8 is a circuit diagram illustrating a flow rate calculation circuit, a gain compensation circuit, and the like of a flow rate detection device according to a second embodiment.

[Explanation of symbols]

 7, 8, 32 Temperature-sensitive resistor 10, 31 Flow rate calculation circuit (flow rate calculation means) 11, 13 Flow rate detection circuit 15 Differential amplification circuit (flow rate detection signal output means) 16, 40 Gain compensation circuit (gain compensation means) 17 Operational amplifier 18 Reference gain resistor 19 Compensation gain resistor 20 Capacitor 21 Negative feedback resistor 36 Bridge circuit

Claims (6)

[Claims] And a flow rate calculating means for calculating a flow rate detection signal corresponding to a flow rate of the fluid to be measured based on a resistance value of the temperature sensitive resistor. A gain compensating means for amplifying a flow rate detection signal by the flow rate computing means and compensating for a gain reduced by a thermal time constant of the temperature-sensitive resistor. A flow detection signal having a frequency lower than a predetermined frequency determined by a constant is amplified with a substantially constant gain, and a flow detection signal having a frequency higher than the predetermined frequency is amplified with a gain corresponding to the frequency. A flow rate detecting device characterized by the above-mentioned. And a flow rate calculating means for calculating a flow rate detection signal corresponding to the flow rate of the fluid to be measured based on a resistance value of the temperature sensitive resistor. A gain compensating means for amplifying a flow rate detection signal by the flow rate computing means and compensating for a gain reduced by a thermal time constant of the temperature-sensitive resistor. A flow rate detection signal having a frequency lower than a first predetermined frequency determined by a constant is amplified with a substantially constant first gain, and a frequency higher than the first predetermined frequency and lower than a predetermined second predetermined frequency. Is amplified by the second gain corresponding to the frequency,
The flow rate detection device according to claim 1, wherein the flow rate detection signal having a frequency higher than the second predetermined frequency is amplified with a substantially constant third gain larger than the second gain. 3. The gain compensating means sets a first predetermined frequency to a frequency at which the flow detection signal starts to attenuate, and sets a second predetermined frequency to the highest frequency of the flow detection signal requiring gain compensation. The flow rate detection device according to claim 2, wherein the flow rate detection device is set. 4. The gain compensating means includes: an operational amplifier; a reference gain resistor connected to an inverting input terminal of the operational amplifier for setting a reference gain; and a flow rate detector connected in parallel to the reference gain resistor. A compensating gain resistor for compensating a signal gain, a capacitor connected in series with the compensating gain resistor, and a capacitor for setting the predetermined frequency determined by a thermal time constant of the temperature-sensitive resistor together with the reference gain resistor; 4. The flow detection device according to claim 1, wherein the flow detection device is constituted by a negative feedback resistor connected between an output terminal of the amplifier and an inverting input terminal. 5. The flow rate calculating means includes: a heater that generates heat at a constant temperature; a first temperature-sensitive resistor provided upstream of the heater; and a second sensor provided downstream of the heater. A temperature resistor, first flow rate detecting means for detecting a first flow rate signal based on a change in the resistance value of the first temperature sensitive resistor, and a second flow rate detecting means for detecting a second flow rate signal based on a change in the resistance value of the second temperature sensitive resistor; A second flow rate detection means for detecting a flow rate signal, and a difference between a first flow rate detection signal output from the first flow rate detection means and a second flow rate detection signal output from the second flow rate detection means. The flow rate detection device according to claim 1, 2, 3 or 4, comprising flow rate detection signal output means for calculating and calculating a flow rate detection signal. 6. The flow rate detecting means is constituted by a bridge circuit including the temperature-sensitive resistor.
The flow rate detection device according to 3 or 4.