JPH0523364B2 - - Google Patents

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. This 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 fuel injection amount and ignition for the engine are controlled. It calculates timing, etc., and executes fuel injection amount control and ignition timing control based on the calculation results.

There are engine speed detection sensors, engine cooling water temperature detection sensors, throttle opening sensors, etc. as means for monitoring the operating state of the engine. As an example, there is an air flow measuring device that measures and detects the amount of intake air.

As a means for measuring the intake air amount, for example, as shown in Japanese Patent Application Laid-Open No. 104538/1982,
2. Description of the Related Art A thermal air flow measuring device that utilizes the heat radiation effect of airflow is known. That is, a temperature sensing element made of a low antibody having a temperature characteristic whose resistance value changes depending on the temperature is set in the intake pipe,
A heating current is supplied to the temperature sensing element to monitor its temperature change state, and the heating current is feedback-controlled so that the temperature of the temperature sensing element is controlled to a specified temperature state. It is something. Therefore, from the state of this heating current,
This allows the amount of air flowing into the intake pipe to be measured.

However, in the case of a thermosensor configured to heat the temperature sensing element to a constant temperature state using an analog-controlled current, it is difficult to measure the The output is about 2
It only changes by a factor of two, and its measurement sensitivity is extremely low. Therefore, in order to use this air flow rate sensor for engine control, it is 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 the analog output signal from the sensor to a digital signal, and in this case, a high-precision A/D Conversion must be performed. That is, a high-resolution A/D converter and this A/D
Extremely high accuracy is now required as a reference voltage power source for converters.

[Problems to be Solved by the Invention] The present invention has been made in view of the above-mentioned points, and is designed to provide sufficient measurement detection sensitivity for the flow rate of intake air taken into the engine. At the same time, it is an object of the present invention to provide a thermal air flow rate measuring device that allows a detection signal to be obtained in a state that best suits the operating conditions of an engine, and that does not require a circuit system that requires particularly high accuracy. It is.

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

[Means for Solving the Problems] 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 a voltage signal from a voltage power source, heating power with a voltage standard set is set to be supplied at a specified cycle, 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. This measurement signal is then 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. The power source 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 measuring device configured as described above, a measurement output signal with a time width corresponding to the flow rate of intake air flowing into the intake pipe is generated, and this time width is This will 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. For example, it can be effective for executing engine control with high precision.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows its configuration. 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). has been done. 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 are connected together at one end and grounded via fixed resistors 14 and 15, respectively, to form a bridge circuit. A transistor 16 acts as a switching element for the connecting portion between the temperature sensing element 12 and the holding temperature sensing element 13.
Connect power supply +B via.

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 17, 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 17. 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 the comparator 17 is supplied to the flip-flop circuit 18 as a reset command.

The flip-flop circuit 18 is set and controlled by an energization start signal generated from the engine control unit 19, for example. Here, the 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. It becomes like this.

Therefore, the flip-flop circuit 18 is set by the energization start signal and reset by the output signal from the comparator 18, and the pulse-like signals corresponding to the set and reset operations are used as the measurement signal. Driver circuit 2
0 and controls the transistor 21. This transistor 21 is set to control the base circuit of the transistor 16, and when the flip-flop circuit 18 generates a signal in its reset state, the transistor 16 is set to a conductive state. Thus, 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 sensitive 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 pressure in accordance with a reference voltage.

The driver circuit 20 is configured in a push-pull manner by a pair of transistors 20a and 20b, and the power supply for this driver circuit 20 is configured by a power amplifier circuit 24 set correspondingly to the reference voltage power source 22. has been done.

Here, the driver circuit is used to accurately output the pulse width of the pulsed 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 pulsed measurement signal to the interface circuit. On the other hand, by matching the rise time and fall time, a signal with a highly accurate pulse width can be 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 the rising and falling portions of the pulsed measurement signal are controlled by set time constants. It is now possible to integrate according to . 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 rising edge and falling edge of the measurement signal, the output pulse-like signal can be set delayed by time t1 and t2 from the rising edge and falling edge of the measurement signal, respectively. By setting "t1=t2", the pulse width of the measurement signal and the pulse width of the interface output signal can be made to match.

However, if the measurement output signal is taken out through such an interface circuit, the response of the threshold level 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 above times t1 and t2 will also change, and ``t1=
t2'' cannot be set, and the pulse time width of the measurement signal cannot be reproduced with the pulse time width of the output 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 amplifying circuit 24 that supplies power to the driver circuit 20 in consideration of such points. 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 now set as a standard.

Then, a pulsed signal having a set pulse time width corresponding to the setting and resetting of the flip-flop circuit 18 of this driver circuit 20 is supplied to an interface circuit 25 to remove noise components contained in the pulsed signal. In this state, the air flow rate signal 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 flip-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 sent to a comparator 25c at an inverting input terminal. supply And for the non-inverting input terminal of this comparator 25c,
A comparison voltage set by resistors R1, R2 and R3 is set.

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 sensing The temperature increase rate of the element 12 is influenced by the air flow rate.

That is, in response to the energization start signal, the temperature sensing element 1
2, the time required for the temperature sensing element 12 to rise to the temperature state specified for the air temperature measured by the auxiliary temperature sensing element 13 corresponds to the air flow rate. It becomes like this.
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 airflow flowing through the intake pipe 11.

Such a pulse-like signal with a pulse time width corresponding to the measured air flow rate is supplied to the driver circuit 20, and is output from the driver circuit 20 in a waveform-shaping state, for example, in the state shown in FIG. 4A. Output. With this waveform, tw is set to a time width that corresponds 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. 4B.
By setting the threshold levels V _H and V _L to appropriate values for this waveform, the output waveform of the comparator 25c becomes as shown in FIG. 4C. In other words, the time width with time delays of t1 and t2 at the leading and trailing edges of the above waveform, respectively.
The tw′ signal is now output. By setting the threshold levels V _H and V _L so that t1 and t2 are equal,
The Tw of the waveform shown in Figure A above and the waveform shown in Figure C
Tw′ can now be made the same as Tw′.

However, in a normal configuration, the power for the driver circuit is supplied from the power supply circuit 26 in the same way as the comparator 17, flip-flop circuit 18, etc. 4 Driver circuit 2 shown in Figure A
The voltage value vp of the output pulse waveform from 0 cannot be stabilized. If this Vp changes, the above-mentioned delay times t1 and t2 will change. Specifically, as Vp increases, t1 becomes shorter,
It becomes “tw′>tw”. Conversely, when Vp becomes low, "tw'<tw", and the pulse time width of the output pulse-like signal of the driver circuit 20 is not expressed in the pulse time width of the output pulse waveform of the interface circuit 25. be. 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 power supply 22 used to stably install the heating power supplied to the temperature sensing element 12. Since the voltage Vp is applied from the power amplifier circuit 24 by using the voltage Vp, the peak voltage Vp of the pulse waveform shown in A in FIG. 4 is always set as a reference in a stable state. That is, times t1 and t2 are always set in a stable state, and by appropriately selecting the threshold levels V _H and V _L , the output pulse width tw of the driver circuit 20 and the interface circuit can be adjusted. The output pulse width tw′ of 25 is
This allows the settings to be made to match reliably.

In the above embodiment, the power supply with the reference voltage set is supplied only to the driver circuit 20, but of course the output power from the power amplifier circuit 24 is used as the operating power supply for the comparator 17, the flip-flop circuit 18, etc. You may also use it.

[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 interface circuit output signal The pulse time width of is such that it reliably 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, and the engine control is adjusted to the current The process is executed in accordance with the engine operating condition.

[Brief explanation of the drawing]

FIG. 1 is a 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.
The figure also shows the interface circuit, No. 4.
The figure is a signal waveform diagram illustrating the operation of the interface output portion of the measurement waveform of the above embodiment. 12... Temperature sensing element, 13... Auxiliary temperature sensing element, 1
6... 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.

Claims (1)

[Claims] 1 A temperature sensing element having a temperature resistance characteristic set in an air flow to be measured, means for controlling the rise of heating power supplied to the temperature sensing element in accordance with a specified period, and a temperature sensing element having a temperature resistance characteristic set in an air flow to be measured; means for detecting a state in which the temperature of the heating element has increased to a specified temperature state with respect to the temperature of the air, and controlling the heating power to be cut off in this detected state; and a voltage state of the heating power to be set to the specified voltage. a reference voltage power source for setting control; means for generating a pulsed measurement signal having a time width corresponding to the rise and cutoff of the heating power;
A driver circuit that is supplied with this pulsed measurement signal and generates a pulsed measurement output signal with a set time width, and a filter function that removes noise components included in the pulsed output signal output from this driver circuit. 1. A thermal air flow measuring device, comprising: an interface circuit configured to include an interface circuit, wherein a power source for the driver circuit is configured by the reference voltage power source.