JPH0522845B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention provides a detection signal that measures and detects the amount of intake air for an internal combustion engine, and that can be effectively used for the electronic control system of this engine. This invention relates to a thermal air flow rate detection device that generates.

[Background Art of the Invention] When an internal combustion engine such as an engine is electronically controlled, the operating state of the engine is constantly monitored, a signal corresponding to the operating state is detected, and based on this signal, for example, the fuel injection amount is adjusted. This is to control the settings. As one means for detecting the operating state of such an engine, there is a detection device that detects the flow rate of air taken in from an intake pipe. As this air flow rate detection device, for example, a thermal type air flow rate sensor is known. This system monitors and measures the temperature change state of the temperature sensing element corresponding to the temperature sensor.

Here, in such a thermal air flow rate detection device, for example, the temperature sensing element is constituted by a resistance element having temperature resistance characteristics, and this temperature sensing element is
The single resistor element forms a bridge circuit together with a plurality of other fixed resistor elements, and is configured to supply a heating current periodically set in a pulsed manner to the bridge circuit. Then, the output signal from the bridge circuit is detected by a differential amplifier, etc., and the temperature rise state of the temperature sensing element from the rise of the heating current is monitored until the temperature of the temperature sensing element reaches a certain specified temperature. The heating current is made to fall in the elevated state.

Specifically, for example, a flip-flop circuit is set by a periodically generated signal, and when the temperature sensing element rises to a specified temperature state, the flip-flop circuit is reset and controlled, and the flip-flop circuit is set and controlled. The heating current to the temperature sensing element is controlled intermittently based on the signal generated in response to the reset.

That is, the heating current width is set and controlled by utilizing the property that the temperature rise time of the temperature sensing element to the specified temperature state corresponds to the integrated value of the air flow rate in one cycle. Therefore, the control width of the heating current is directly used as a detection signal for the air flow rate.

However, in a device configured in this manner, a large current for heating is controlled to be supplied intermittently in a pulsed manner to the bridge circuit including the temperature sensing element. Here, the equilibrium state of the bridge circuit is monitored by a comparator, but due to the distributed capacitance and inductance on the wiring, the current value generated at the output part of the bridge circuit varies depending on the flow. It will start to vibrate at the beginning.
In other words, the input signal from the bridge circuit to the comparator becomes unstable when the heating current rises, and there is a risk that it will be difficult to accurately capture the temperature change state of the temperature sensing element. This creates a condition that affects the reliability of the air flow rate detection device.

[Object of the Invention] The present invention has been made in view of the above points, and is capable of constantly performing highly reliable air flow rate measurement operations, and is also effective as an intake air amount detection means for electronic control of internal combustion engines, for example. The present invention aims to provide an air flow rate detection device that can be used for various purposes.

[Summary of the Invention] That is, the air flow rate detection device according to the present invention supplies a heating current that is controlled intermittently in a pulsed manner to a bridge circuit including a temperature sensing element, and monitors the equilibrium state of the bridge circuit. In addition to generating a detection signal output corresponding to the air flow rate,
When the heating current rises, the detection state of the detection signal corresponding to the temperature increase change of the temperature sensing element is inhibited within a specified short time range.

[Embodiment of the Invention] An embodiment of the invention will be described below with reference to the drawings. FIG. 1 shows its configuration. A temperature sensing element 12 is fixedly set inside an intake pipe 11 of an engine (not shown in the figure), and an auxiliary temperature sensing element 13 is also fixedly set inside this intake pipe 11. ing. The temperature sensing element 12 is heated and controlled by an electric current, and is made of, for example, platinum wire, which has a temperature characteristic in which the resistance value changes depending on the temperature, and the auxiliary temperature sensing element Similarly to the temperature sensing element 12, the temperature sensing element 13 is also made of platinum wire or the like having temperature resistance characteristics. In this case, the auxiliary temperature sensing element 1
3 is not affected by the heat generated by the temperature sensing element 12,
Temperature characteristics are set by the air flow flowing inside the intake pipe 11, and the air intake pipe 11 is set to act as an air temperature measuring element. And these two temperature sensing elements 1
2 and 13 and fixed resistors 14 and 15 constitute a bridge circuit.
Each connection point is connected to an input terminal portion of the comparator 16, and is configured to detect a temperature change state of the temperature sensing element 12.

That is, when a heating current is supplied to the temperature sensing element 12 and its temperature rises to a specified temperature difference or more with respect to the air temperature detected by the auxiliary temperature sensing element 13, the output signal from the comparator 16 is The output signal from the comparator 16 is sent to the flip-flop circuit 17.
will be reset controlled. This flip-flop circuit 17 is set-controlled by a heating synchronization signal, and this heating synchronization signal is generated in response to a specified rotation angle of the engine, for example, during normal air flow measurement operation. It is something. That is, the flip-flop circuit 17 is set at a specified rotational angle state of the engine, and is reset when the temperature of the temperature sensing element 12 rises to a specified temperature state with respect to the air temperature. A pulse-like signal is generated in response to the control state.

The pulse-controlled output signal from the flip-flop circuit 17 is taken out as a pulse-width-controlled signal via the buffer amplifier 18, and this output signal controls the base electrode of the transistor 19, which controls the temperature sensing element. The power supply to the bridge circuit including 12 is controlled intermittently in a pulsed manner. In this case, the reference voltage setting circuit 20
The voltage of the heating signal to the bridge circuit is monitored by the differential amplifier 21 supplied with the reference voltage setting from the differential amplifier 21, and the base potential of the transistor 19 is controlled by the output signal of the differential amplifier 21. By setting the voltage of the pulsed heating current signal as a reference, heat generation of the temperature sensing element 12 is accurately controlled in accordance with the width of the heating current.

That is, in the air flow rate detection device configured as described above, when a heating synchronization signal is generated corresponding to a specific rotation angle of the engine, the flip-flop circuit 17 is set by this signal, and the transistor 19 is set. A base signal is supplied to the temperature sensing element 12, and the heating current to the temperature sensing element 12 starts to rise. Therefore, the temperature of the temperature sensing element 12 increases with time from the rise of this heating current. In this case, the temperature increase state of the temperature sensing element 12 and the temperature at the start of heating are related to the heat dissipation effect of the air flow acting on the temperature sensing element 12, and the larger the air flow rate, the lower the temperature at the start of heating. The rate of temperature rise will slow down. When the temperature of the temperature sensing element 12 rises in this way, its resistance value rises and the potential at the connection point with the resistor 14 falls, and when the temperature sensing element 12 rises to a certain temperature state, the output signal of the comparator 16 rises and resets the flip-flop circuit 17. That is, the transistor 19 is connected to the intake pipe 1.
The heating current is controlled intermittently in a state corresponding to the flow rate of air flowing through the temperature sensing element 12, and a heating current with a pulse width corresponding to the air flow rate is controlled to be supplied to the temperature sensing element 12. Furthermore, the interval between the set and reset of the flip-flop circuit 17 corresponds to the air flow rate of the intake pipe 11, as described above, and the output signal from the buffer amplifier 18 corresponding to this set and reset state is directly related to the air flow rate. This is output as a detection measurement signal. In this case, the detected air flow rate is expressed digitally as the pulse width of a pulsed output signal, so it can be effectively used for an engine control unit composed of a microcomputer, etc. This is what happens.

Now, considering this circuit further, when a heating synchronization signal that sets the flip-flop circuit 17 is generated as shown at A in FIG. Then, by the above-described operation, the temperature sensing element 1 as shown in B in the figure is
The generation of a pulsed heating current for 2 is now controlled. In this case, the distributed capacitance and inductance on the wiring cause the temperature sensing element 12 and the resistor 14 to
At the beginning of the current flow, the current value oscillates as shown in C in the figure. This temperature sensing element 12
Since the potential at the point where the connection point between the auxiliary thermosensitive element 13 and the resistor 14 becomes the input signal to the comparator 16 is proportional to the potential shown in the above diagram C, the potential at the connection point between the auxiliary thermosensitive element 13 and the resistor 15 is The input potential to the comparator 16 with reference to D is also
It becomes violent as shown in the figure. Further, due to the difference in impedance, the rise time constants of the potentials at both input points of the comparator 16 are also different.

Depending on the operating conditions, the range of change V1 of the waveform shown in Figure D is only a few mV, and when the peak value of the waveform's rampage exceeds V1 and the margin range V2 becomes zero, the comparator 16 changes at this moment. It is determined that the temperature of the temperature sensing element 12 has reached the set temperature, and the supply of heating current to the bridge circuit is cut off, resulting in a malfunction state.

In order to solve this problem, the flip-flop circuit 17 in the device shown in the above embodiment is configured as a level trigger type, and when a signal is present to the set terminal, the flip-flop circuit 17 is connected to the reset terminal. It is maintained in the set state regardless of the signal to the terminal. Then, the time width T1, which is the effective polarity of the heating synchronization signal shown enlarged in FIG. 3A, is set to be larger than the width of the current rampage. That is,
During this time width T1, the flip-flop circuit 17 is held in the set state regardless of the output state of the comparator 16, and the flip-flop circuit 17 is maintained in the set state during the period T2 during which the output of the comparator 16 is guaranteed.
This is the state that is recognized in 7. In other words, the output of the comparator 16 is masked for a certain period of time by the width T1 of the heating synchronization signal, so that the air flow rate detection operation can be executed stably.

In this way, it is sufficient to set a heating synchronization signal with a predetermined pulse width, but this pulse width T
1 directly becomes the lower limit value of the pulse width of the output signal. Therefore, it is desirable that the pulse width of this synchronization signal be as short as possible. but,
Depending on the actual usage environment (installation status, presence of noise, etc.), it may be difficult to use short pulse signals. Further, the burden placed on the heating signal generation circuit is also large.

FIG. 4 shows a different embodiment that is equipped with a heating synchronization signal generation circuit configured with these points in mind, and is configured to drive and control an edge-trigger type monostable multivibrator 22 using a synchronization signal. , the flip-flop circuit 1 is activated by the output signal of the multivibrator 22 whose pulse width is set.
7 is configured to perform set control.

That is, if a synchronization signal is generated as shown in A in FIG. The set level of the flip-flop circuit 17 is set during the mask time T1.

FIG. 6 shows yet another example of the heating synchronization signal generation circuit, in which a switch circuit 23 is provided between the comparator 16 and the flip-flop circuit 17. In this case, the flip-flop circuit 17 is configured as an edge trigger type. be done. Here, the switch circuit 23 may be constituted by a digital switch circuit which is a combination of so-called analog switches and logic circuits. That is, in this example, the output signal of the comparator 16 is not transmitted to the flip-flop circuit 17 for a certain period of time by the output signal of the multivibrator 22, and the masking effect during T1 is performed in the same way as above. There is.

In addition, when the flip-flop circuit 17 is configured as an edge trigger type with a preset terminal, the output signal of the multivibrator 22 set as described above is transferred to the flip-flop circuit 1.
The signal may be supplied to seven preset terminals.

[Effects of the Invention] As described above, according to the present invention, regardless of the mounting state of such an air flow rate detection device,
A state is set that effectively eliminates causes of malfunction due to vibration components generated in response to signals, and a highly reliable air flow rate detection operation is executed, for example, in a sensor mechanism for electronic control of an engine. It will be used effectively as a.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram illustrating an air flow rate detection device according to an embodiment of the present invention, FIG. 2 is a signal waveform diagram illustrating the operating state of the device, and FIG. 3 is a part of the above signal. 4 is a configuration diagram explaining another embodiment of the invention, FIG. 5 is a signal waveform diagram explaining the above embodiment, and FIG. 6 is a diagram explaining still another embodiment of the invention. FIG. 11... Intake pipe, 12... Temperature sensing element, 13...
Auxiliary temperature sensing element, 16... Comparator, 17...
Flip-flop circuit, 19...transistor,
22...Multi-vibrator.

Claims (1)

[Claims] 1. A temperature sensing element having a temperature resistance characteristic that is set for the air flow passage and heated and controlled by a heating current, and a heating current generation control means for the temperature sensing element whose rise is controlled by a set periodic signal. and means for detecting an increase in the temperature of the temperature sensing element heated and controlled by the heating current generated by this means to a specified temperature, and a means for detecting an increase in temperature of the temperature sensing element to a specified temperature by this means. means for controlling the heating current to fall in a rise detection state; and a detection signal corresponding to a temperature rise change of the temperature sensing element within a short time range specified from the rise state of a periodic signal that controls the rise of the heating current. What is claimed is: 1. A thermal air flow rate detection device characterized by comprising means for preventing the detection state of.