JPS61104225A - Apparatus for thermally measuring flow amount of air - Google Patents

Abstract

PURPOSE:To enhance detection sensitivity, by raising the temp. of the temp.- sensitive element arranged in an air stream to be measured to specific one by applying power with definite voltage to said temp. sensitive element and measuring the power applying time at this time. CONSTITUTION:A temp.-sensitive element 12 and an auxiliary temp.-sensitive element 13, both of which have a temp. resistance characteristic, are arranged in a pipe 11 and constitute a bridge circuit along with fixed resistors 14, 15. A transistor 16 is brought to a continuity state by FF18 set by a current supply start signal and a power source +B is connected. When the temp. of the temp.- sensitive element 12 reaches a specific value, a comparator 17 is operated and FF18 is reset to cut off the power source +B. Because the connection time of the power source +B corresponds to the flow amount of air, the pulse width output of FF18 is taken in a control unit 19 through a driver circuit 20 and an interface circuit 25 and used as a flow amount signal. By this method, output with high detection sensitivity is obtained by a simple circuit.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention can be effectively used as a sensor mechanism for detecting the operating state of an engine, for example, when electronically controlling the air-fuel ratio of the engine. The present invention relates to a thermal air flow measuring device that detects the amount of intake air flowing into an intake pipe.

[Background Art] When electronically controlling the air-fuel ratio of an engine, the operating state of the engine is constantly monitored and a signal corresponding to the operating state is detected, and based on this detection signal, for example, the amount of fuel injection IJJ for the engine, It calculates the ignition timing, etc., and executes fuel injection amount control and ignition timing control based on the calculation results.

As a means of monitoring the operating condition of such an engine,
There are sensors for detecting engine rotation speed, engine cooling water temperature, throttle opening, etc., but these sensors directly depend on the operating state of the engine.

Directly related to this are air flow measuring devices that measure and detect the amount of intake air.

As a means for measuring the amount of intake air, a thermal air flow rate measuring device that utilizes the heat dissipation effect of airflow is known, for example, as disclosed in Japanese Patent Laid-Open No. 55-104538. In other words, a temperature-sensing element made of a resistor whose resistance value changes depending on temperature is set in the intake pipe, and a heating current is supplied to this temperature-sensing element to measure its temperature change state. The heating current is feedback-controlled so that the temperature of the temperature sensing element is controlled to a specified temperature state. Therefore, the amount of air flowing into the intake pipe can be measured from the state of this heating current.

However, in the case of a thermosensor configured to heat the thermosensor to a constant temperature using an analog-controlled current, the measurement output varies even though the air flow rate changes by a factor of 100, for example. It only changes by about twice, and its measurement sensitivity is extremely low. Therefore, in order to use this air flow rate sensor for engine control, it becomes necessary to provide an offset processing means for the detection signal amplification circuit, and the control means therefor tends to become complicated.

In addition, when configuring an engine control device using a microcomputer, it is necessary to convert analog output signals from sensors into digital signals, and in this case, high-precision A/D conversion is required. must be carried out. That is, a high-resolution A/D converter and an extremely high-precision reference voltage power source for this A/D converter are required.

[Problems to be Solved by the Invention] This invention has been made in view of the above-mentioned points. In addition to ensuring sufficient measurement detection sensitivity, the detection signal can be obtained under conditions that best match the operating conditions of the engine, and a circuit system that requires particularly high precision is not required. The present invention aims to provide a thermal air flow rate measuring device.

Furthermore, when the measurement signal from the air flow rate measurement section is supplied to the engine control unit, the noise component is effectively removed and the measurement signal is outputted via the interface circuit. The purpose is to ensure that engine control is executed stably by outputting the engine in an accurate state.

Means for Solving Problem E] That is, in the thermal air flow measuring device according to the present invention, a temperature sensing element having temperature characteristics is set in the air flow to be measured, and a standard is set for this temperature sensing element. In response to the voltage signal from the voltage power supply, the heating power whose voltage standard is set is set to be supplied at a specified period, and the temperature sensing element is heated to a specified temperature state. The heating power to the temperature sensing element is controlled to be interrupted so that a pulsed signal having a pulse time width corresponding to the supply width of the heating power to the temperature sensing element is generated as a measurement signal. Then, this measurement signal is supplied to an interface circuit via a driver circuit, and the output signal from this interface circuit is set to be supplied as an air flow signal to, for example, an engine control unit. is constituted by a reference voltage power source that sets the voltage of the heating power to the temperature sensing element as a reference. The interface circuit includes a filter function for removing noise components contained in the measurement signal.

[Function] In the thermal air flow rate measuring device configured as described above, a measurement output signal with a time width corresponding to the intake air flow rate flowing into the intake pipe is generated, and this time width is It comes to be handled as digital data. In addition, when outputting a signal with this time width, it is supplied to an interface circuit set on the input side of a microphone, for example, in a state that accurately reproduces the time width. This can be effective for executing engine control with high precision.

[Example J Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows its configuration, in which a temperature sensing element 12 made of, for example, platinum wire or the like having temperature resistance characteristics is set inside an intake pipe 11 that supplies intake air to an engine (not shown). There is. Further, an auxiliary temperature sensing element 13 configured in the same manner as the temperature sensing element 12 is set inside the intake pipe 11 as an element for measuring the temperature of the air flowing inside the intake pipe 11. , the temperature sensing element 12 and the auxiliary temperature sensing element 13 have their one ends connected in common, and are connected to fixed resistors 14 and 15, respectively.
A bridge circuit is constructed by connecting the terminal to ground through the terminal. Then, the temperature sensing element 12 and the holding temperature sensing element 13
A power supply +8 is connected to the connection point with the transistor 16 which acts as a switching element.

The voltage signal at the connection point between the temperature sensing element 12 and the resistor 15 is supplied to the inverting input terminal of the comparator 11, and the voltage signal at the connection point between the temperature sensing element 12 and the resistor 15 is supplied to the non-inverting input terminal of the comparator 11. A connection point voltage signal with the resistor 15 is set to be supplied. That is, when the temperature of the temperature sensing element 13 is raised to a high temperature state specified with respect to the air temperature measured by the auxiliary temperature sensing element 13, the output from the comparator 17 rises. The output signal from this comparator 17 is then transmitted to a flip-flop circuit 18.
is supplied as a reset command.

The flip-flop circuit 18 is set and controlled by, for example, an energization start signal generated from the engine control unit 19. Here, the above-mentioned energization start signal is composed of a pulse signal that is generated periodically. For example, if it is composed of a signal that is synchronized with the rotation of the engine, it can be effectively used for fuel injection amount calculation control, etc. Become.

Therefore, the flip-flop circuit 18 is
is set by the power start signal, and the comparator 18
The pulse-like signal corresponding to this set and reset operation is
It is supplied as a measurement signal to the driver circuit 20 and also controls the transistor 21.

This transistor 21 is set to control the base circuit of the transistor 16, and the transistor 16 is set to a conductive state when a signal in the set state is generated from the flip-flop circuit 18. Then, heating power is set to be supplied from the power supply to the bridge circuit including the temperature sensing element 12.

In this case, the base circuit of the transistor 16 is controlled by the output signal from the differential amplifier 23 which detects the voltage signal of the heating power to the temperature sensing element 12 and compares it with the reference voltage from the reference voltage power supply 22. , the voltage value of the heating power is controlled at a constant voltage in accordance with a reference voltage.

The driver circuit 20 has a push-pull configuration with a pair of transistors 20a and 20b, and if! for this driver circuit 20! is the group t
The power amplifier circuit 24 is configured to correspond to the voltage power supply 22.

Here, the driver circuit is used to accurately output the pulse width of the pulse-shaped measurement signal to the interface circuit, and is configured, for example, by a push-pull type circuit, and is configured to output the pulse width of the pulse-shaped measurement signal to the interface circuit. By matching the rise time and fall time, a signal with a highly accurate pulse width is output. In this case, in order to prevent malfunctions due to noise in the control unit, the interface circuit is configured to include a filter function, and when the rising and falling portions of the pulsed measurement signal are set, respectively. It is designed to integrate according to a constant.And,
A threshold level is set corresponding to each of the rising and falling portions, and a pulsed output signal having a time width corresponding to the measurement signal is reproduced from the integrated waveform. In this case, by appropriately selecting the threshold levels corresponding to the rise and fall of the measurement signal, it is possible to obtain output pulse-like signals that are delayed by times tIJ and t2 from the rise and fall of the measurement signal, respectively. By setting [t1=t2J, the pulse width of the measurement signal and the pulse width of the interface output signal can be matched.

However, if the measurement output signal is taken out through such an interface circuit, the correspondence between the threshold levels will change depending on the power supply voltage set to be supplied to the driver circuit. If the correspondence between the threshold levels changes, the times t1 and t2 mentioned above will also change, and the state of [tl-t2J] cannot be set, and the pulse time width of the measurement signal will be output. It cannot be reproduced by the pulse time width of the signal. That is, the air flow measurement signal supplied to the engine control unit becomes inaccurate, making it difficult to accurately control the engine.

FIG. 2 shows a specific configuration example of the power amplifier circuit 24 that supplies power to the driver circuit 20 in consideration of such points. The signal is configured to be supplied to the power supply circuit of the circuit 20, and the base circuit of the transistor 24a is controlled by the output signal of the differential amplifier 24b.

The input terminal section of the differential amplifier is supplied with the voltage signal on the output side of the transistor 24a and the reference voltage signal from the reference voltage power supply 22, and the output from the driver circuit 24. The voltage of the power supply is set as a standard.

Then, the pulse-like signal from the driver circuit 20 having a set pulse time width corresponding to the setting and resetting of the flip-flop circuit 18 is supplied to the interface circuit 25 to eliminate noise components contained in the pulse-like signal. In the removed state, it is supplied to the engine control unit 19 as an air flow signal.
'Here, the power supply circuit 26 is used as a power supply for driving the comparator 17 and the seven-lip-flop circuit 18.'

FIG. 3 shows a specific circuit example of the interface circuit 25. The output signal from the driver circuit 20 is integrated by an integrating circuit consisting of a resistor 25a and a capacitor 25b, and is supplied to the inverting input terminal of the comparator 25c. do. A comparison voltage set by resistors R1, R2, and R3 is set to the non-inverting input terminal of the comparator 25C.

That is, in the air flow measuring device configured as described above, heat radiation from the temperature sensing element 12 is controlled by the air flow flowing through the intake pipe 11. Therefore, the heat dissipation effect of the temperature sensing element 12 is set by the air flow rate inside the intake pipe 11, and when heating power set at a voltage is supplied to the temperature sensing element 12, the temperature of the temperature sensing element 12 is The rising speed is influenced by the air flow rate.

That is, when the heating power to the temperature sensing element 12 rises in response to the 111m start signal, the temperature sensing element 12 rises to a temperature state specified with respect to the air temperature measured by the auxiliary temperature sensing element 13. The time required to do so will correspond to the air flow rate. Therefore, the time width of the output signal from the flip-flop circuit 18, which is set by the energization start signal and reset by the output of the comparator 17, corresponds to the amount of air flowing into the intake pipe 11.

Such a pulse-like signal with a pulse time width set corresponding to the measured air flow rate is supplied to the driver circuit 20, and the driver circuit is shaped into a waveform as shown in FIG. 4(A), for example. It is output from 20. With this waveform, tw is set to a time width corresponding to the air flow rate. This waveform signal is supplied to the interface circuit 25, and its rising and falling portions are integrated to obtain the state shown in FIG. 4(B). (2) By setting L to an appropriate value, the output waveform of the comparator 25c becomes as shown in FIG. 4(C). That is, tl and t2 at the leading and trailing edges of the waveform, respectively.
A signal having a time width tw' with a time delay of 2 is output. By setting the threshold levels VH and Vt so as to equalize t1 and t2, Tw of the waveform shown in figure (A) and tw' shown in figure (C) are made the same. It is something that you will be able to do.

However, in a normal configuration, the power for such a driver circuit is supplied from the power supply circuit 26 in the same way as the comparator 17, the flip-flop circuit 18, etc., and therefore, as shown in FIG. (A
The voltage value vp of the output pulse waveform from the driver circuit 20 shown in > cannot be set to a stable state. If this Vp changes, the delay times t1 and t2 will change. Specifically, as Vp increases, tl becomes shorter, and [tw'> tvr J. Conversely, when Vp becomes low, [tw'<twJ, and the pulse time width of the output pulse-like signal of the driver circuit 20 is not expressed by the pulse time width of the output pulse waveform of the interface circuit 25.

Since this pulse time width corresponds to the air flow measurement data, an accurate air flow measurement output signal will not be provided to the engine control unit in this state.

On the other hand, in the device shown in the above embodiment, the power supply voltage of the driver circuit 20 is set to the reference voltage voltage 122 used to stably set the heating power supplied to the temperature sensing element 12. Since the peak voltage Vp of the pulse-like waveform shown in (A> in FIG. 4) is always set as a reference in a stable state, it is applied from the power amplifier circuit 24. The times t1 and t2 are always set in a stable state, and by appropriately selecting the threshold levels Vo and VL, the output pulse width tw of the driver circuit 20 and the output pulse width tw' of the interface circuit 25 can be adjusted to This allows the settings to be made to match reliably.

In the above embodiment, only for the driver circuit 20,
') Although shown as supplying a power supply with a reference voltage set, it goes without saying that the output power from the power amplifier circuit 24 may be used as the operating power supply for the comparator 17, the flip-flop circuit 18, and the like.

[Effects of the Invention] As described above, according to the thermal air flow measuring device according to the present invention, when a pulse-like measurement signal with a set time width corresponding to the air flow rate is generated, the wave height of the measurement signal is The voltage value is set to a reference voltage state. Therefore, even if such a measurement signal is supplied to, for example, an engine control unit via an interface circuit equipped with a filter function for removing noise, the pulses of the output signal of this interfunication circuit The time width ensures that it matches the pulse time width of the measurement signal, and the air flow data corresponding to this time width is supplied to, for example, an engine control unit, so that the engine control can adjust the engine operation at that time. It is executed in accordance with the exact situation.

[Brief explanation of drawings]

Fig. 1 is a circuit configuration diagram illustrating a thermal air flow rate measuring device according to an embodiment of the present invention, Fig. 2 is a diagram showing an example of a power amplifier circuit used in the above embodiment≦, and Fig. 3 is the same. FIGS. 4(A) to 4(C) showing the intertooth circuit are signal waveform diagrams illustrating the operation of the interface output portion of the measurement waveform of the above embodiment, respectively. 12... Temperature sensing element, 13... Auxiliary temperature sensing element, 16.
... Transistor (heating power switching), 17... Comparator, 18... Flip-flop circuit, 19...
Engine control unit, 20...driver circuit, 22
...Reference voltage power supply, 23...Differential amplifier, 24...
-Power amplifier circuit, 25...interface circuit. Applicant's representative Patent attorney Takehiko Suzue Figure 1 Figure 2 Figure 3 Figure 4 Procedure? m Official document (method) 1. Indication of the case Japanese Patent Application No. 59-225323 2. Name of the invention Thermal air flow rate measuring device 3. Person making the amendment Relationship to the case Patent applicant (426) Nippondenso Co., Ltd. 4 , Agent No. 17 Mori Building, 1-26-5 Toranomon, Minato-ku, Tokyo
105 Telephone 03 (502) 3181 (main representative) 4
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a configuration diagram illustrating a thermal air flow 11 measuring device according to an embodiment of the present invention, and FIG. 2 is a diagram illustrating an example of a power amplifier circuit used in the above embodiment. , FIG. 3 is a diagram showing the interface and circuit, and FIG. 4 is a signal waveform diagram illustrating the operation of the interface output portion of the measurement waveform of the above embodiment.

Claims (1)

[Claims] a temperature sensing element having a temperature resistance characteristic set in an air flow to be measured; and means for controlling the rise of heating power supplied to the temperature sensing element in accordance with a specified period;
means for detecting a state in which the temperature of the temperature sensing element has increased to a specified temperature state with respect to the temperature of the air, and controlling and interrupting the heating power in this detection state; and a means for specifying the voltage state of the heating power. A reference voltage power source for controlling the voltage settings; The driver circuit includes a driver circuit that generates a measurement output signal, and an interface circuit configured to include a filter function that removes noise components contained in the pulsed output signal output from the driver circuit, and a power source for the driver circuit. A thermal air flow measuring device characterized in that it is constructed by the reference voltage power supply described above.