JPH063388B2 - Thermal air flow measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention measures, for example, an intake air flow rate of an engine,
The present invention relates to a thermal air flow measuring device which can be effectively used for electronic control of an engine in an electronic engine control unit.

BACKGROUND ART For example, in an engine mounted on an automobile or the like, the fuel injection amount, the ignition timing, etc. are controlled by an electronic control unit using a microcomputer. When performing such electronic engine control, the operating state of the engine is electronically monitored, the monitoring data is supplied to the control unit, and the control unit controls the fuel based on the monitoring data. Engine control data such as injection amount is calculated.

There are various means for monitoring the operating state of the engine for controlling the engine.
For example, the state of the intake air flow rate of the engine is always monitored and measured as being directly related to the operating state of the engine.

As a means for measuring such an intake air flow rate, for example, as shown in JP-A-55-98621, temperature-
Air flow rate measuring means for setting a temperature sensitive element having a resistance characteristic in an intake pipe is known. That is, heating power is supplied to the temperature-sensitive element to control heat generation, the temperature state of the temperature-sensitive element is monitored, and from the heating power amount required to maintain the temperature in the specified temperature state, The air flow rate is calculated.

However, in such a measuring device, since the measurement output signal is analog data such as a current value, it is converted into digital data by a high-precision A / D converter, and then converted by the engine control unit. Need to be used. That is, highly accurate circuit elements are required for signal processing, and it is difficult to obtain highly accurate air flow rate measurement data.

In consideration of such a point, the present applicant has proposed a thermal type air flow rate measuring device in which the air flow rate is expressed by a time width. That is, constant-voltage-controlled heating power is supplied to the temperature-sensitive element, and the time width required for the temperature-sensitive element to rise to a specific temperature state is expressed by a pulse signal. That is,
By counting the pulse time width of this pulse-shaped signal with the clock signal, digital air flow rate data can be obtained.

Further, when such a pulse-shaped signal is subjected to waveform shaping by the output circuit, the pulse time width may not be accurately expressed due to the instability of the voltage. Considering such a point, it is considered that one pulsed output signal is expressed by a pair of pulse signals and an output circuit is configured to measure the period width of the pair of pulse signals.

FIG. 4 shows an example of an output circuit for expressing the pulse time width of a pulse signal by a pair of pulse signals.
As the input signal a, a signal having a pulse width T as shown in FIG. 5 (A) is supplied. In addition, in this output circuit, the capacitor 12 whose charge is controlled via the constant current circuit 11 is used.
In the absence of an input signal, the capacitor 12 is set to a discharging state via a switch 14 controlled to be closed by the output of the inverter 13. In this case, a constant current circuit 15 is provided in this discharge circuit.

Therefore, the capacitor 12 is charged with the time constant specified through the constant current circuit 11 because the switch 14 is opened at the rising edge of the input signal a, and its charging potential is (B) in FIG. ). Then, when this charging potential exceeds the potential Vth set by the reference power source 16, the output of the comparator 17 is inverted and the output of the inverter 18 rises as shown in FIG. 5 (C). This inverter
The output signal from 18 is supplied to the exclusive OR circuit 19 together with the above input signal. Therefore, the output signal from this exclusive OR circuit 19 rises at the rising edge of the input signal, and the output of the comparator 17 The first pulse signal as indicated by I in FIG. Then, in this state, the capacitor 12 is charged to the power supply voltage state.

Then, when the input signal shown in FIG. 5 (A) falls, the switch 14 is closed and the capacitor 12 is discharged through the constant current circuit 15, and the terminal voltage of this capacitor 12 becomes the reference power source 16 The output of the comparator 18 is inverted in the state where the output voltage of the comparator 18 drops below the voltage of. Then, the exclusive OR circuit 19 obtains the pulse signal II shown in FIG. 5 (D) which rises at the falling edge of the input signal.

That is, the first and second pulse signals I and II corresponding to the rising edge and the falling edge of the input pulse signal are obtained, and the time interval between these two pulse signals expresses the time width T. Become.

However, when such an output circuit is used, for example, the sixth
When the pulse time width of the input pulsed signal becomes extremely small as shown in (A) of the figure, as shown in (B) of the figure, before the capacitor 12 is sufficiently charged, The falling edge arrives. In this case, when the discharge start of the capacitor 12 is controlled by the falling edge of the input signal,
Since the terminal potential of 12 has not risen sufficiently, the terminal potential becomes the reference voltage state of the comparator 17 and the output of the comparator 17 is inverted in a very short time. Therefore,
The output signal of the inverter 18 is as shown in FIG. 6 (C), and the output signal obtained from the exclusive OR circuit 19 is
It becomes as shown in FIG.

That is, in such a state, the first pulse signal I corresponding to the rising edge of the input signal is generated in the normal state of the time width t1, but the second pulse signal II corresponding to the falling edge of the input signal is The state is in a very small time width t2.
Therefore, in the pulse width of the measurement output signal in such a state, particularly the pulse width of the second pulse signal, there is a possibility that a state in which the time width required for measurement cannot be set may occur.

[Problems to be Solved by the Invention] The present invention has been made in view of the above points, and when the air flow rate measurement signal is composed of a pulse-like signal expressing a time width, the expression of the pulse-like signal The time width is effectively represented by the first and second pulse signals, and in particular, the pulse widths of the first and second pulse signals are set to a state that can be reliably measured by the control unit or the like. SUMMARY OF THE INVENTION The present invention seeks to provide a thermal air flow measurement device that effectively allows the air flow measurement signal to be electronically used in control.

[Means for Solving Problems] That is, in the air flow rate measuring device according to the present invention, a temperature sensitive element having a temperature-resistance characteristic is set in the air flow to be measured, and this temperature sensitive element is used. On the other hand, the heating power is controlled to be supplied so that the time width required for the temperature of the temperature sensitive element to rise to the specified temperature state is taken out as a pulse-shaped signal expressed by the pulse width. This measurement signal is supplied to an output circuit that generates a first pulse signal and a second pulse signal that rise at the rising edge and the falling edge, respectively. In this output circuit, both edges are detected and at a predetermined time constant. A capacitor for starting charging and discharging is provided, and the first and second pulses are controlled to fall when the potential of the capacitor exceeds a set level, and further the capacitor is rapidly charged or discharged. It is what

[Operation] In the air flow rate measuring device as described above, when a pulsed signal is input to its output circuit, the first and second pulse signals are generated in response to rising and falling of the signal, respectively. It will stand up. In this case, the capacitor is charged or discharged with a predetermined time constant, and the first and second pulses are controlled to fall while the terminal potential of the capacitor exceeds the set level. . In this case, since the charge or discharge is rapidly controlled in the state where the potential of the capacitor exceeds the set level, the potential of this capacitor waits for the next operation in the state where the first and second pulses are generated. The charge and discharge is rapidly controlled to the potential of the state, and therefore the first
The pulse width of the second pulse signal is set to a stable state, and the control unit or the like can effectively measure and read the pulse width.

[Embodiment of the Invention] An embodiment of the present invention will be described below with reference to the drawings.
FIG. 1 shows the configuration, and shows an example of measuring the intake air flow rate of the engine. That is,
A temperature sensing element 22 and a temperature measuring element 23 are set in the intake pipe 21, and the temperature sensing element 22 and the temperature measuring element 23 are set to change their resistance values depending on the temperature. Each of the elements is configured to come into contact with the air flow flowing through the intake pipe 21. A fixed resistor 24 is connected to the temperature sensitive element 22, and a series circuit of resistors 25 and 26 is connected to the temperature measuring element 23 to form a bridge circuit. Then, heating power is supplied to the connection point between the temperature sensitive element 22 and the temperature measuring element 23 through the transistor 27.

The connection point a between the temperature sensitive element 22 and the resistor 24 and the connection point b between the resistors 25 and 26 are respectively connected to the comparator 28, and the temperature of the temperature sensitive element 22 is changed by the heating power. Is set so that the output signal from the comparator 28 rises when a temperature difference specified with respect to the air temperature measured by the temperature measuring element 23 rises.

The output signal from the comparator 28 resets the flip-flop circuit 29. This flip-flop circuit 29
Is set and controlled by a start pulse signal Tin generated by the engine control unit 30, and the start pulse signal is periodically generated in a state in which the engine rotates, for example.

When the reset signal of the flip-flop circuit 29 is output from the output terminal, a switch element 31
Control. The switch element 31 has the base circuit of the transistor 27 grounded. The open state of the switch element 31, that is, the flip-flop circuit 29
In this set state, the transistor 27 is turned on, and heating power is set to be supplied to the bridge circuit including the temperature sensitive element 22. The output signal from the set-side output terminal Q of the flip-flop circuit 29 is output via the buffer to the output circuit 32.
Flip-flop circuit from this output circuit 32
The output signal corresponding to the 29 set states is the measurement output signal T
It is supplied to the engine control unit 30 as out.

Here, the voltage of the heating power supplied from the transistor 27 to the temperature sensitive element 22 is compared with the reference voltage set by the reference voltage power supply 33 by the OP amplifier 34.
The output signal of the P amplifier 34 controls the base potential of the transistor 27. That is, the voltage of the heating power supplied to the bridge circuit including the temperature sensitive element 22 is controlled to be a constant voltage based on the reference voltage.

That is, in the air flow rate measuring device configured as described above, the flip-flop circuit is generated by the start pulse signal Tin generated in synchronization with the rotation of the engine.
29 is set, the heating power is controlled to rise, and the temperature sensitive element 22 is heated. And this temperature sensitive element 22
When the temperature rises to a temperature state specified with respect to the air temperature, an output signal is generated from the comparator 28, the flip-flop circuit 29 is reset, and the heating power is cut off and controlled. In this case, the temperature sensing element 22 is set in a state of being brought into contact with the intake air flow, and its heat dissipation effect is set by the air flow.
The rate of temperature rise due to the heating power of 22 becomes inversely proportional to the air flow rate. Therefore, the time width until the heating power rises and the output signal is generated from the comparator 28 corresponds to the intake air flow rate flowing through the intake pipe 21. That is, the pulse time width of the pulse-like signal generated from the Q terminal of the flip-flop circuit 29 corresponding to the setting and resetting thereof represents the measured air flow rate. Then, this pulsed output signal is supplied to the output circuit 32, and the signal representing the time width corresponding to the pulse time width is supplied from the output circuit 32 to the engine control unit 30 as an air flow rate measurement signal. Will be done.

FIG. 2 shows the output circuit 32 in detail. To its input terminal 41, a signal as shown in FIG. 3 (A) which becomes high level in the set state of the flip-flop circuit 29 is provided. Is entered. This signal is a pulse-like signal that rises in synchronization with the start pulse signal and expresses the air flow rate measurement time width T. This input signal is supplied to the AND circuit 42, the NOR circuit 33, and the exclusive OR circuit 44, and further supplied to the inverter 45.

The output signals from the AND circuit 42 and the NOR circuit 43 are
The switch elements 46 and 47 are controlled to be turned on, respectively, and the switch element 46 is connected in parallel with the constant current circuit 48, and the switch element 47 is also connected in parallel with the constant current circuit 49. The constant current circuit 49 is grounded through the switch element 50, and the switch element 50 is controlled to be turned on by the output of the inverter 45.

The constant current circuit 48 is connected to the power source Vcc, supplies a charging current to the capacitor 51, and charges the capacitor 51 with the switch element 50 turned on. Are discharged via the constant current circuit 49.

The terminal voltage of this capacitor 51 is compared with the reference voltage set by the reference power supply 53 in the comparator 52,
The output signal from the comparator 52 is set to a low level when the terminal voltage of the capacitor 51 exceeds the reference voltage. The output signal from this comparator 52 is
It is inverted by the inverter 54 and supplied to the exclusive OR circuit 44, and also supplied to the AND circuit 42 and the NOR circuit 43.

That is, in the initial state in which the signal supplied to the input terminal is in the low level state, the capacitor 51 is in the discharging state and the output of the comparator 52 is in the high level,
The output of the inverter 54 is low level. Therefore,
In this state, no output signal is generated from the AND circuit 42, the switch element 46 is in an open circuit state, the switch 47 is turned on by the output of the NOR circuit 43, and the terminal voltage of the capacitor 51 is the ground potential. Is.

When a pulse signal having a time width T1 shown in FIG. 3 (A) is input in such a state, the output of the AND circuit 42 becomes the third signal.
Although it remains as shown in FIG. 3B, the output of the inverter 45 is inverted and the switch element 50 is opened in response to the rising edge thereof, and the output of the NOR circuit 43 is shown in FIG. 3C. Thus, the falling switch element 47 is opened.

That is, in this state, a charging circuit in which a time constant is set for the capacitor 51 is formed, and the capacitor 51 is charged through the constant current circuit 48, and its terminal voltage is shown in FIG. Rises as shown in. When the terminal voltage of the capacitor 51 exceeds the reference voltage Vth set by the reference power source 53, the output of the comparator 54 is inverted and the output of the inverter 54 becomes as shown in FIG. 3 (E). Therefore, the exclusive OR circuit 44 generates the first pulse signal I shown in (F) of FIG. 3 which rises with the rise of the input signal and rises with the rise of the output of the inverter 54. At the same time, the high level output of the inverter 54 opens the gate of the AND circuit 42 to turn on the switch element 46 to rapidly charge the capacitor 51 to the power supply voltage Vcc. That is, as shown in FIG. 3D, the terminal voltage of the capacitor 51 is rapidly charged to Vcc in a state of exceeding Vth.

Then, when the falling edge of the input signal is next input, the output of the AND circuit 42 becomes low level, the switch element 46 is opened, and the rapid charging circuit for the capacitor 51 is cut off. Further, the switch element 50 is turned on by the output of the inverter 45, and a discharge circuit having the time constant of the capacitor 51 is formed. Therefore, the capacitor 51
3D, the terminal voltage decreases with a time constant, and when the terminal voltage exceeds Vth, the output of the comparator 52 is inverted and the output of the inverter 54 becomes low level. Becomes Then, in this state, the output of the NOR circuit 43 becomes high level, the switch element 47 is closed, and the capacitor 51 is rapidly discharged.

Then, the exclusive OR circuit 44 generates a second pulse signal as indicated by II in FIG. 3 (F). The first pulse signal I and the second pulse signal II are generated. The time interval T1 between and becomes equal to the pulse time width T1 of the input signal. Therefore, the first and second pulse signals are supplied to the engine control unit 30, the pulse interval T1 is measured as the air flow rate measurement data, and is used to calculate the engine control data. .

Further, assuming that an air flow rate measurement signal expressing a small time width T2 is input to the output circuit 32 as shown in FIG. As soon as the capacitor 51 is charged and its terminal voltage reaches Vth, the switch element 46 is turned on,
This capacitor 51 is rapidly charged. Therefore, the first
Even if the input signal falls immediately after the pulse signal is generated, the terminal voltage of the capacitor 51 is still in the Vcc state at this time, and the formation control of the second pulse signal is performed. Will be executed normally.
That is, even if the pulse time width represented by the input pulse-like signal is narrow, the widths of the first and second pulse signals are set to the same t, and the engine control unit
The measurement and detection will be reliably performed at 30.

EFFECTS OF THE INVENTION As described above, in the air flow rate measuring device according to the present invention, since the pulse-shaped measurement signal expressing the measured air amount is generated by the pulse time width, By measuring, the air flow rate signal can be obtained digitally. However, when using a pulsed signal that represents the measured value with such a pulse time width as it is, the rising and falling parts of the pulse signal are integrated and set by the input circuit including the filter function of the control unit. The integrated waveform is read according to the threshold to be input, and the waveform is shaped and input, but there is a possibility that an error may occur in the reading time width due to changes in the signal level and the like. However, as described above, the pulse time width of the measurement signal is expressed by the first and second pair of pulse signals,
Since the measurement data can be read according to the rising timing time width of the pair of pulse signals, the air flow rate measurement data can be read in a very accurate state. Further, in this case, the pulse widths of the first and second pulse signals can be surely set to stable widths. Therefore, the air flow rate measurement output by the pair of pulse signals is obtained. The signal can be reliably measured and read.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram for explaining a thermal air flow rate measuring device according to an embodiment of the present invention, FIG. 2 is a circuit diagram showing an example of an output circuit used in the above embodiment, and FIG. FIG. 4 is a signal waveform diagram for explaining the operating state of the output circuit, FIG. 4 is a circuit diagram showing an example of the output circuit that has been considered so far, and FIG. 5 is a signal waveform diagram for explaining the operating state of the output circuit. The figure is also a signal waveform diagram for explaining the operation when the input signal is special. 21 ... Intake pipe, 22 ... Temperature sensitive element, 23 ... Temperature measuring element, 27 ... Transistor (heating power switching), 28 ... Comparator, 29 ...
Flip-flop circuit, 30 ... Engine control unit, 32
... output circuit, 42 ... AND circuit, 43 ... NOR circuit, 44 ... exclusive OR circuit, 46, 47, 50 ... switch element, 48, 49 ... constant current circuit, 51 ... capacitor, 52 ... comparator.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Yoshihisa Sato 1-1, Showa-cho, Kariya City, Aichi Prefecture Nihon Denso Co., Ltd. (72) Inventor Masumi Kinokawa, 1-1, Showa-cho, Aichi Prefecture Nippon Denso Co., Ltd. (72) Inventor Atsushi Suzuki 1-1, Showa-cho, Kariya city, Aichi prefecture Nihon Denso Co., Ltd.

Claims (1)

[Claims] 1. A temperature-sensitive element comprising a resistance element having a characteristic that its resistance value changes according to a temperature set in an air flow to be measured, and heating power is supplied to the temperature-sensitive element. An air flow rate measurement unit that generates a pulsed output signal that expresses the time width required for the temperature sensing element to rise to a specified temperature state by the pulse width, and corresponds to the rising and falling edges of the pulsed output signal. And an output circuit which forms a first pulse signal and a second pulse signal with respect to the one pulsed output signal and rises when the output circuit is specified by a rising edge of the pulsed signal. A capacitor that starts charging or discharging with a constant, a means for rapidly controlling charging or discharging when the potential of this capacitor reaches a specified potential, A means for controlling discharge or charge of the capacitor with a specified time constant at the falling edge of the stripe-shaped signal, and a means for rapidly controlling discharge or charge of the capacitor with the potential of the capacitor at the specified potential. The output signal includes first and second pulse signals that rise at each of the rising edge and the falling edge of the pulse-shaped signal, and continue until the potential of the capacitor changes to a specified level state. A thermal type air flow rate measuring device characterized in that