JPH03118421A - Method and apparatus for controlling temperature of heated measuring resistor - Google Patents

Abstract

PURPOSE: To improve the accuracy and the resolution of a measurement result by changing the operating temperature of a measurement resistor to a different value according to a reference amount and considering the operating temperature when processing the measurement result. CONSTITUTION: A measurement resistor RH heated to a specific operating temperature TB by current flow is cooled according to each air flow rate (m). As a result, the resistance changes so that a bridge is detuned, a signal is generated at an output 8 of an operational amplifier 7, the operating temperature is adjusted via a conductor 10, and the resistor RH is maintained at an original temperature TB. The difference in the temperature in sucked air flow may affect a measurement result, but a temperature-sensitive resistor RK arranged in the air flow similarly can compensate for the influence. Also, the value of a variable resistor R2 can be changed, thus causing a temperature TB of the resistor RH to change also, thus adjusting temperature to a high value TB and increasing a voltage change width regardless of whether the change in air flow rate is small in a measurement voltage U.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method and apparatus for controlling the temperature of a heated measuring resistor, and more particularly to a measuring resistor for detecting the flow rate of a fluid, and in particular for a measuring resistor that detects the flow rate of a fluid during measurement. The present invention relates to a method and apparatus for controlling the temperature of a measuring resistor such as a hot wire of an air amount measuring device for an internal combustion engine that is heated to an operating temperature higher than that of the internal combustion engine.

BACKGROUND OF THE INVENTION In automotive technology, measuring resistors, in particular hot wires or thin films, whose temperature is controlled by passing an electric current through them, are used to detect the amount of air drawn in by an internal combustion engine. The inlet air flow passes through the heated hot wire. This hot wire preferably forms part of an electrical bridge circuit and is maintained at a constant operating temperature above the intake air temperature, preferably by passing an electric current through it. Based on this principle, the amount of air drawn in by the internal combustion engine can be determined using the required heating current. The heating current is converted into a voltage signal by the resistance of the bridge, which voltage signal is used by the control unit of the internal combustion engine as an input variable for adjusting the optimum operating point. If the surface of the hot wire becomes dirty, the measurement results will be erroneous, so after the internal combustion engine is shut off, the current is increased to scorch the hot wire to remove as much dirt as possible. When the exhaust gas value and load value of an internal combustion engine are low, it is necessary to accurately detect the relevant parameters at each combustion point.
Since the optimum output cannot be produced, it is necessary to improve the accuracy of this type of air quantity measuring device and the resolution of the measurement results.

[Problem to be Solved by the Invention] The present invention has been proposed to solve the above-mentioned drawbacks and provides a heated measuring resistor of the type mentioned at the beginning, which makes it possible to improve the accuracy and the resolution of the measurement results. The object of the present invention is to provide a temperature control method and device.

[Means for Solving the Problems] The above problems are solved in the method of the present invention by the features set forth in claim 1.

[Operation] According to the method of the present invention having the features set forth in claim 1, high resolution measurement results can be obtained when the amount of intake air is small, especially in the idle link and partial load regions. Therefore, the measuring resistor has characteristics that allow it to be used even in the low load range of the internal combustion engine and at low air flow rates. This is particularly important when the air quantity measuring device is arranged in the bypass path of the internal combustion engine. Furthermore, the measurement area for detecting the intake air volume can be widened, so that a high resolution can be obtained.The advantage of this is that the operating temperature of the measuring resistor can be varied to different values according to at least one reference quantity. , by processing the measurement results taking into account changes in the operating temperature accordingly.The operating temperature therefore changes automatically during the measurement operation.This change is preferably effected by changing the current flowing through the measuring resistor. The change in operating temperature is performed according to at least one reference quantity, and an amount corresponding to each operating state can be used as the reference quantity.Since the measurement result also changes depending on the change in operating temperature, the present invention According to , when processing measurement results, an adaptation process is performed taking into account changes in the operating temperature.

Preferably, the operating temperature is changed stepwise or continuously. In that case, an appropriate adaptation process must be performed when processing the measurement results.

Preferably, an amount determined by measurement is used as the reference amount. The operating temperature of the measuring resistor is therefore set according to the value of the quantity determined by measurement.

Preferably, the rotational speed of the internal combustion engine is used as the reference variable. The operating temperature of the measuring resistor is continuously adjusted according to the measured rotational speed. Further, if the measured rotational speed exceeds a predetermined threshold value, the rotational speed can be adjusted in stages. The same applies when the throttle valve angle of the internal combustion engine is used as the reference quantity. In particular, it is also possible to use the measurement result itself (measured voltage) to adjust the operating temperature of the measuring resistor. In that case as well, it is possible to adjust stepwise or continuously.

If the operating temperature of the measuring resistor is set to a high temperature, a large voltage range can be obtained as a measurement result even with a small change in the air flow rate. Even if the operating temperature of the measuring resistor is low, a large measuring area can be used. can.

Therefore, it is preferable to set the operating temperature accordingly in order to obtain optimal measurement results. If a predetermined variation width (particularly voltage variation width) is required in the measurement results in order to obtain accurate measurement results, the operating temperature is set according to this required amount.

The invention further relates to a temperature control device for a measuring resistor for detecting the flow rate of a fluid, in particular a measuring resistor such as a hot wire of an air flow measuring device of an internal combustion engine, which is heated by a current to an operating temperature higher than the temperature of the fluid during measurement. The operating temperature is varied to different values according to at least one reference quantity, and the variation in the operating temperature is taken into account when processing the measurement result (measured voltage) accordingly. In particular, a bridge circuit with two bridge branches configured as a voltage divider is used, in which a measuring resistor and a variable resistor with a variable resistance for adjusting the operating temperature are provided6. Adjustments are made according to the aforementioned reference quantities.

[Example] Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 1 is a block circuit diagram showing the principle of hot-wire air flow measurement ml for detecting the air flow rate of an internal combustion engine (not shown) of an automobile. The hot wire air amount measurement Ht has a bridge circuit 2,
The bridge circuit is provided with two bridge branches 3 and 4 formed as voltage dividers.The voltage divider of the six bridge branches 3 is formed by a series circuit of a resistor R1, a temperature-sensitive resistor RK, and a variable resistor R2. ing. The voltage divider of bridge branch 4 is formed by measuring resistor RH and resistor R3. The measuring resistor RH is a hot wire or a hot thin film of the hot wire air flow meter l.The voltage taps 5 and 6 of the voltage divider are connected to the two input terminals of the operational amplifier 7. The output 8 of the operational amplifier 7 is connected to a terminal 9 and further connected to a measuring resistor RH and a resistor RK via a conductor IO. Terminal 11 is connected to ground 12 and to resistors R2 and R3. The measurement result, in particular the measurement voltage U, can be taken out between terminals 9 and 11. The measuring resistor RH (hot wire) and the temperature-sensitive resistor RK are provided inside the intake pipe 13 of the internal combustion engine. The intake pipe 13 has an air flow rate m [kg/h].

Next, the operation of such a configuration will be explained.

The measuring resistor (RH), which has been heated to a predetermined operating temperature TB by passing an electric current, is cooled in accordance with the air flow, the size of which is 1 m, respectively. This changes the resistance value and thus detunes the bridge.

As a result, a signal is generated at the output 8 of the operational amplifier 7 which causes an adjustment of the operating temperature via the line IO and maintains the measuring resistor RH at the original operating temperature TO. Differences in the temperature of the sucked airflow are used to affect the measurement results, but
This effect can be compensated for by a temperature-sensitive resistor RK which is likewise arranged in the air stream. The measured voltage U between terminals 9 and 11 indicates the magnitude of the air flow im.

In the present invention, since the value of the variable resistor R2 can be changed, the operating temperature TB of the measuring resistor RH can be changed. As a result, according to the invention, it is possible, for example, to adjust to a high operating temperature TH and to make the voltage change width as large as possible despite the small change Δm in air flow rate at the measured voltage U. In that case, of course, the measuring range that can be made in this way is relatively small, but according to the means of the invention, the operating temperature TB of the measuring resistor RH can be varied (in this example reduced) during the measurement and adjusted individually. be able to. For example, if a predetermined air flow E1m is exceeded during measurement,
Automatically the measuring resistor RH is switched to the lower operating temperature TB, thereby expanding the measuring range, so that the generated voltage change width ΔU spans a larger air flow range Δm, improving the resolution. That is, the resolution is much greater than if the operating temperature TB of the measuring resistor RH did not change.

This situation is illustrated in FIG. In the figure, the measured voltage U is shown as a function of the air flow Jim. Curve a shows the case where the operating temperature TB of the measuring resistor RH is high,
Curve b shows the state when the operating temperature TB is low. In region I where the air flow rate m is relatively small (this applies in particular to idle-link drive or part-load drive of the internal combustion engine), a relatively large range of change in the measured voltage U is obtained. If the air flow rate m exceeds a predetermined threshold value (which means that the measured voltage U exceeds a predetermined value), a switch is automatically made to curve b, which has a slope smaller than curve a. Therefore, even in region II where the air flow rate m is relatively large, a fairly large variation range for the measured voltage U can be obtained, so that a large resolution is guaranteed in both regions I and II. As already explained, in this embodiment the switching from curve a to curve b takes place in accordance with the magnitude of the measured voltage U itself. For this purpose, various processing circuits, not shown and well known to those skilled in the art, are used.

In the embodiments described above, an example is shown in which the operating temperature TB changes stepwise. However, instead of operating temperature T
B may be changed continuously. In that case, other curves are obtained.

As already explained, the operating temperature TB of the measuring resistor RH is adjusted according to the measurement result, ie the measured voltage. Therefore (in this embodiment) the operating temperature is dependent on a predetermined reference quantity G determined by measurement. According to various embodiments of the invention, different quantities are used as the reference quantity G. That is, it is also possible to use the rotational speed of the internal combustion engine as the reference amount G instead of the measurement result (measured voltage). For example, it is also possible to set the throttle valve angle of the internal combustion engine to the reference ff1G.

A detailed explanation of how to adjust the variable resistor R2 (eg, mechanically) will be omitted. There are several methods well known to those skilled in the art, in which case the resistance value of the variable resistor R2 can be varied by varying the reference quantity.

As described above, this change in resistance value is performed stepwise or continuously when a predetermined threshold value is exceeded.

Therefore, according to the present invention, a hot wire type air amount measuring device is obtained in which the temperature of the hot wire is variable during the measurement operation. This is because it is assumed that if the operating temperature TB of the hot wire changes, the measurement results should be processed accordingly6, because otherwise the measured quantity would be distorted. Not only does the operating temperature TB of the measuring resistor RH change due to a change in the reference NG, but the value obtained from the measurement result also changes accordingly. Various hardware methods can be considered to compensate for this, but since they are all well known to those skilled in the art, detailed explanations will not be provided.

[Effects of the Invention] As is clear from the above description, the present invention provides a temperature control method for a heated measuring resistor of the type mentioned at the beginning, which can improve the accuracy and resolution of measurement results, and its implementation. You can get equipment to do that.

[Brief explanation of drawings]

FIG. 1 is a block circuit diagram showing the principle of a hot wire air flow rate measuring device configured with a bridge circuit, and FIG. 2 is a line section showing the relationship between air flow rate and measurement results. ■...Hot wire air flow meter 2...Bridge circuit 3.4...-Bridge branch 5.6...Voltage extraction tap 7...-Operation amplifier fan>

Claims (1)

[Claims] 1) A method for controlling the temperature of a measuring resistor that detects the flow rate of a fluid, particularly a measuring resistor such as a hot wire of an air flow measuring device for an internal combustion engine that is heated to an operating temperature higher than the temperature of the fluid by a current during measurement. A heated measuring resistor, characterized in that the operating temperature (TB) of the measuring resistor is varied to different values according to the reference quantity (G), and the variation in the operating temperature (TB) is taken into account when processing the measurement results. temperature control method. 2) A method according to claim 1, characterized in that the operating temperature (TB) is changed stepwise or continuously. 3) The method according to claim 1 or 2, characterized in that the reference amount (G) is an amount obtained by measurement. 4) According to any one of claims 1 to 3, wherein the reference amount (G) is the rotational speed of the internal combustion engine, the throttle valve angle of the internal combustion engine, or the measurement voltage (U) of the flow rate. the method of. 5) A method according to any one of claims 1 to 4, characterized in that the operating temperature (TB) is varied according to the measurement area. 6) A method according to any one of claims 1 to 5, characterized in that the operating temperature (TB) is changed in accordance with the range of change in the measured voltage. 7) A method according to any one of claims 1 to 6, characterized in that the operating temperature (TB) is varied according to the measurement resolution. 8) In a temperature control device for a measuring resistor that detects the flow rate of a fluid, especially a measuring resistor such as a hot wire of an air quantity measuring device of an internal combustion engine that is heated to an operating temperature higher than the temperature of the fluid by the current during measurement, the operating temperature (TB ) to different values according to at least one reference quantity (G), and taking into account changes in the operating temperature when processing the measurement results. 9) Two bridge branches (3) configured as voltage dividers
, 4), and a variable resistor (R2) with a variable resistance value used for adjusting the measuring resistor (RH) and the operating temperature (TB) is provided in the bridge branch path. 9. Apparatus according to claim 8, characterized in that: