JP4089657B2 - Air flow sensor - Google Patents

Description

The present invention relates to air flow sensors, in particular, it relates to suitable air flow sensor for detecting an intake air flow rate of the engine.

[Conventional technology]
Conventionally, a thermal air flow sensor has been used to detect an air flow rate such as an intake air flow rate of an engine. A thermal air flow sensor (hereinafter referred to as a sensor) includes a Wheatstone bridge circuit in which an air flow detection element (hereinafter referred to as a detection element) is incorporated in one of the wirings. This detection element is usually a resistor that has a positive resistance temperature coefficient and generates heat when energized.

  The sensor adjusts the amount of current supplied to the detection element to balance the heat generated by the current supply and the heat removal by the air flow, etc., and adjust the temperature of the detection element to a predetermined value, and the voltage at the low potential side terminal of the detection element. Is output as an electrical signal corresponding to the air flow rate. The ECU or the like calculates the air flow rate by using the output value of the electrical signal, thereby measuring the air flow rate.

[Problems with conventional technology]
However, according to this sensor, when the air flow rate is reduced, the amount of electricity supplied to the detection element is reduced together with the amount of heat generated by the detection element, so that the voltage as an electric signal is also reduced. For this reason, at a low air flow rate, the influence of noise or the like on the electric signal becomes large, and the influence of measurement error on the true value becomes large.

As a technique for improving the conventional detection element, two resistors are electrically connected in parallel, and these resistors are arranged from the upstream side to the downstream side along the air flow to improve the responsiveness. (For example, see Patent Document 1), a material whose resistance temperature coefficient is improved by forming a resistor with a doped silicon semiconductor thin film (for example, see Patent Document 2), and a material having a high resistivity. There is one that improves the heat capacity of the resistor by forming the resistor so that the resistance value is about 1 kΩ, and can cope with a higher air flow rate (see Patent Document 3).
However, the effect of measurement errors at low air flow rates has not been improved sufficiently.
JP 9-126850 A JP 2001-194202 A Japanese Patent No. 2880651

  The present invention has been made to solve the above-described problems, and it is an object of the present invention to provide an air flow rate detecting element and an air flow rate sensor that can reduce the influence of measurement errors at a low air flow rate.

[Means of Claim 1]
The air flow rate sensor according to claim 1 has a first resistance temperature coefficient having a positive resistance temperature coefficient, and a second resistance body having a negative resistance temperature coefficient having a positive resistance temperature coefficient and temperature sensing. Thus, an air flow rate detecting element is formed by connecting them in parallel. The second resistor is disposed on the downstream side of the first resistor with respect to the air flow, and is heated by the air flow heated to remove the heat of the first resistor and raise the temperature.
As a result , both the resistance values of the first and second resistors are reduced, so that the amount of energization of the entire detection element is increased and the voltage at the low potential side terminal of the detection element is increased. As a result, it is possible to reduce the influence of noise or the like on the electric signal, so that measurement errors can be reduced.

The air flow sensor of the best mode 1 includes a first resistor that has a positive resistance temperature coefficient and generates heat when energized, and a second resistor that has a negative resistance temperature coefficient and senses temperature. Are connected in parallel to form an air flow rate detecting element. The second resistor is disposed on the downstream side of the first resistor with respect to the air flow, and is heated by the air flow heated to remove the heat of the first resistor and raise the temperature.

[Configuration of Example 1]
A configuration of an air flow rate sensor (hereinafter referred to as a sensor) 1 according to the first embodiment will be described with reference to FIGS. 1 and 2. The sensor 1 is used, for example, for measuring an intake air amount of an engine (not shown).

  As shown in FIG. 1, an air flow rate detection element (hereinafter referred to as a detection element) 2 of the sensor 1 has a positive resistance temperature coefficient, a first resistor 3 that generates heat when energized, and a negative resistance temperature coefficient. The second resistor 4 having the above is formed by electrically connecting in parallel. And the sensor 1 is attached to a predetermined position so that the 2nd resistor 4 may be arrange | positioned in the downstream of the 1st resistor 3 with respect to the flow of air.

The first resistor 3 is made of a material having a positive temperature coefficient of resistance, and is made of a metal such as platinum, gold, copper, aluminum, chromium, nickel, tungsten, and permalloy.
The second resistor 4 is made of a material having a negative resistance temperature coefficient, and is made of, for example, a semiconductor material such as silicon or gallium arsenide, or a metal oxide such as manganese, cobalt, or nickel.

  As shown in FIG. 2, the sensor 1 includes a detection element 2, a temperature compensation resistor 5 that is disposed in the air flow path together with the detection element 2, and a fixed resistance body 6, 7 that has a constant resistance value. , 8 incorporated therein, a Wheatstone bridge circuit (hereinafter referred to as a bridge circuit) 9 is included.

  In the bridge circuit 9, the detection element 2 is incorporated in the wiring 12, and the temperature compensation resistor 5 and the fixed resistor 6 are incorporated in series in the wiring 13. The fixed resistor 7 is incorporated in the wiring 14 in series with the wiring 12, and the fixed resistor 8 is incorporated in the wiring 15 in series with the wiring 13.

  A contact a between the wiring 12 and the wiring 14 is connected to a non-inverting input terminal of the operational amplifier 18, and a contact b between the wiring 13 and the wiring 15 is connected to an inverting input terminal of the operational amplifier 18. Further, a wiring 20 for outputting the voltage Va of the contact a as an electric signal branches from the wiring 19 connecting the contact a and the non-inverting input terminal, and an ECU (not shown) for calculating the air flow rate is connected. It is connected to the terminal c. Note that a well-known amplifier 22 is incorporated in the wiring 20 to amplify an electric signal.

  The output terminal of the operational amplifier 18 is connected to the base terminal of the transistor 24. Further, the collector terminal of the transistor 24 is connected to a connection terminal d of a power source (not shown) that supplies power to the bridge circuit 9, and the emitter terminal is connected to a contact point e between the wiring 12 and the wiring 13. The contact f between the wiring 14 and the wiring 15 is grounded.

[Features of Example 1]
The characteristics of the sensor 1 according to the first embodiment will be described. The sensor 1 is operated by the operational amplifier 18 and the transistor 24 so that the amount of heat generated by the first resistor 3 is balanced with the amount of heat removed by the air flow and the like, so that the first resistor 3 is maintained at a predetermined temperature. Constant temperature type. Further, the sensor 1 detects and amplifies the voltage Va as an electric signal corresponding to the air flow rate, and then outputs it to the ECU. Then, the ECU calculates the air flow rate using the output value of this electrical signal.

  The first resistor 3 generates heat when energized and is removed by an air flow. When the air flow rate increases and the amount of heat removed from the first resistor 3 due to the air flow increases, the sensor 1 maintains the temperature of the first resistor 3 at a predetermined value, and the amount of heat generated by the first resistor 3 ( That is, it acts in the direction of increasing the energization amount). For this reason, as shown by the correlation line A in FIG. 3, the energization amount of the first resistor 3 increases as the air flow rate increases.

  On the other hand, the second resistor 4 is heated by the air flow that has been heated by heat removal from the first resistor 3. When the air flow rate is increased and the amount of heat removed from the first resistor 3 is increased, the amount of heating of the second resistor 4 by the heated air flow is also increased. Here, since the second resistor 4 has a negative resistance temperature coefficient, when the temperature is increased by increasing the heating amount, the resistance value decreases and the energization amount increases. For this reason, as shown by the correlation line B in FIG. 3, the energization amount of the second resistor 4 also increases as the air flow rate increases.

  As described above, as indicated by the correlation line C in FIG. 3, the energization amount of the detection element 2 that is the sum of the energization amount of the first resistor 3 and the energization amount of the second resistor 4 increases as the air flow rate increases. . As a result, the voltage Va increases as the air flow rate increases, so that the output value to the ECU also increases as the air flow rate increases as shown by the correlation line D in FIG. Further, the gradient of the correlation line D, that is, the rate of increase of the output value with respect to the air flow rate (hereinafter referred to as sensitivity) is larger than the correlation line E when the detection element 2 is configured by only the first resistor 3.

[Operation of Example 1]
The operation of the sensor 1 according to the first embodiment will be described.
For example, when the voltage Va becomes higher than the voltage Vb of the contact b, the output voltage becomes the high voltage VH because the input voltage of the non-inverting input terminal is higher than the input voltage of the inverting input terminal in the operational amplifier 18. As a result, the voltage applied to the base terminal increases, so that the power supplied from the power source to the bridge circuit 9 increases. For this reason, the energization amount in the detection element 2 is increased, and the first resistor 3 is heated by increasing the heat generation amount, so that the resistance value of the first resistor 3 is increased. As a result, the voltage Va decreases and eventually the voltage Va becomes smaller than the voltage Vb.

  When the voltage Va becomes smaller than the voltage Vb, the input voltage at the non-inverting input terminal in the operational amplifier 18 becomes smaller than the input voltage at the inverting input terminal, so that the output voltage becomes the low voltage VL. As a result, the voltage applied to the base terminal is reduced, and the power supplied from the power source to the bridge circuit 9 is reduced. For this reason, the energization amount in the detection element 2 decreases, and the first resistor 3 decreases in temperature because the heat generation amount decreases, so that the resistance value of the first resistor 3 decreases. As a result, the voltage Va increases and eventually the voltage Va becomes higher than the voltage Vb.

  Thus, since the voltage Va becomes larger than the voltage Vb, the output voltage from the operational amplifier 18 becomes the high voltage VH again, and the same operation is repeated. Thereby, the sensor 1 can respond to the fluctuation | variation of an air flow rate, and can change the voltage Va to the value according to the air flow rate.

[Effect of Example 1]
In the sensor 1 according to the first embodiment, the detection element 2 includes a first resistor 3 having a positive resistance temperature coefficient and generating heat when energized, and a second resistor 4 having a negative resistance temperature coefficient. Are connected in parallel. And the sensor 1 is attached to a predetermined position so that the 2nd resistor 4 may be arrange | positioned in the downstream of the 1st resistor 3 with respect to the flow of air.
As a result, the second resistor 4 is heated and heated by the air flow that has been removed by removing heat from the first resistor 3, and the resistance values of the first and second resistors 3 and 4 both decrease. To do. Further, the decrease in the resistance value of the second resistor 4 is significant at a low air flow rate. For this reason, in particular, the energization amount of the entire detection element 2 increases and the voltage Va increases at a low air flow rate. As a result, as shown in FIG. 4, when the detection element 2 is configured with the first and second resistors 3 and 4, rather than when the detection element 2 is configured with only the first resistor 3 (correlation line E). (Correlation line D) improves sensitivity at a low air flow rate.

  As a result, the influence of the measurement error on the true value of the air flow rate can be significantly reduced at a low air flow rate. That is, the output of the electric signal is uniformly affected by noise and the like regardless of the sensitivity and the output value. For this reason, the output value increases, for example, by the deviation ε uniformly, and a measurement error occurs. However, when the sensitivity is improved, for example, the measurement error for the same true value X1 decreases from the value ΔXE to the value ΔXD. Thus, if the sensitivity is improved, it is possible to reduce the influence of the measurement error due to noise or the like on the true value.

(Example 1) which is a block diagram of an air flow rate detection element. (Example 1) which is a circuit diagram of an air flow sensor. (Example 1) which is a correlation diagram of the energization amount of an air flow rate detection element, and an air flow rate. (Example 1) which is a correlation diagram of the output value from an air flow sensor and an air flow rate.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Air flow sensor 2 Air flow detection element 3 1st resistor 4 2nd resistor

Claims (1)

In the air flow sensor that detects the air flow rate,
A first resistor having a positive resistance temperature coefficient and generating heat upon energization;
Have a negative temperature coefficient of resistance, and a second resistor for temperature sensing,
By connecting electrically in parallel, an air flow rate detecting element is formed,
The second resistor is disposed on the downstream side of the first resistor with respect to an air flow, and is heated by an air flow that has been heated to remove heat from the first resistor, and the temperature is raised. Air flow sensor.

Images