JPS614926A - Thermal type detecting device of air flow - Google Patents

Abstract

PURPOSE:To burn off the material adhered to temp. sensing element without issuing a special command by setting the burn off time width with the detecting condition of the completion of the signal for starting electrification transmitting to a temp. sensing element and by flowing a burn-off heating current to the temp. sensing element in the time width thereof. CONSTITUTION:The output of the bridge circuit consisting of a temp. sensing element 12, supplementary tamp. sensing element 13 and resistances 14, 15 is fed to a flip flop circuit 19 via a comparator 18 as a resetting command, the electrification starting signal synchronizing with the engine revolution of a signal input terminal 20 is fed as a setting command to the circuit 19 and the output singal Q' at the resetting time of the circuit 19 is taken out as a detecting output signal from the output terminal 23 via an invertor 22. On the other hand the electrification starting signal transmitted from the terminal 20 is fed to a retrigger monostable multivibrator 27 set up by the time width sufficiently longer than the generation period thereof, and the outpu Q' thereof is fed to the monostable multivibrator 28 and the signal with the prescribed time width is outputted by the circuit 19, and the burn off heating current is generated.

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention relates to a heat sensor that measures and detects the intake air amount, etc., which is used as one of the engine operating state detection signals, for example, when an engine is electronically controlled. This invention relates to a type of air flow rate detection device.

[Background of the Invention] For example, when controlling an automobile engine electronically,
The operating state of the engine is constantly monitored and signals corresponding to the operating state are detected. Based on this detection signal, for example, the amount of injected fuel to be supplied to the engine is calculated and set, so that the engine can be controlled most efficiently. As such operating state monitoring means, there are engine rotation speed detection means, engine temperature detection means, exhaust temperature detection means, throttle opening detection means, etc.; Related to this is means for detecting the amount of intake air.

As a means for detecting the amount of intake air, for example, a thermal air flow rate detection device is known. In this detection device, a temperature sensing element having a temperature resistance characteristic is placed in the intake pipe, and the temperature sensing element is heated by a heating current.
The temperature increase state of the temperature sensing element, which is set to a heat dissipation state by the air flow, is then monitored and measured. In other words, the temperature of the temperature sensing element increases slowly in proportion to the air flow rate, and by measuring the temperature rise rate, the air flow rate flowing into the intake pipe can be calculated. .

However, if the humidity sensing element is used in an air stream for a long period of time as described above, impurities in the air will adhere to the temperature sensing element, causing the temperature transfer of the temperature sensing element. The characteristics become worse. Therefore, when this impurity adheres to the temperature sensing element, the concentration change state of the temperature sensing element does not correspond accurately to the air flow rate, resulting in a large error in measuring the air flow rate.

As a means to solve this problem, for example, as shown in Japanese Patent Application Laid-Open No. 54-76182, it is possible to remove deposits from the thermosensor by increasing the heat generation temperature of the thermosensor (e.g., to 800°C). It is considered that burn-off can be carried out by incineration. For example, when this air flow rate detection device is used in combination with 1. an engine electronic control system, the above-mentioned burn-off is executed based on instructions from a computer that constitutes this control system. It is.

However, this configuration requires a special program for the engine control system and a burn-off device for burn-off, making the configuration complicated.

[Object of the Invention] The present invention has been made in view of the above-mentioned points. For example, when used in a control system for an automobile engine, it is possible to detect the air flow rate after the engine operation control state has ended. An object of the present invention is to provide a thermal air flow rate detection device that enables incineration control of deposits on a temperature sensing element to be executed in a state where no operation is required and without generating a special control system odor control command. It is.

[Summary of the Invention] That is, in the thermal air flow rate detection device according to the present invention, disappearance of the energization start signal for controlling the supply of heating current to the temperature sensing element is detected by the energization start signal monitoring means. At the same time, a burn-off time width is set in the detection state of extinction of the energization start signal, and a heating current for burn-off is controlled to be supplied to the temperature sensing element according to the set burn-off time width.

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

Figure 1 shows the circuit configuration of an air flow rate detection device that supplies a measurement signal of the amount of intake air flowing into the intake pipe as one of the engine operating state detection signals to an electronic control unit of an automobile engine, for example. It is something.

That is, in this detection device, a temperature sensing element 12 constituted by a heating wire having temperature resistance characteristics, such as a platinum wire, is arranged in an intake pipe 11 that supplies air to the engine. The intake pipe 1
The airflow flowing through the temperature sensing element 12 directly contacts the temperature sensing element 12.
The heat dissipation is controlled by the air flow.

Further, an auxiliary temperature sensing element 13 configured similarly to the temperature sensing element 12 is also arranged in the intake pipe 11, and this auxiliary temperature sensing element 13 measures the temperature of the air flowing through the intake pipe 11. configured to detect. The temperature sensing element 12 and the auxiliary temperature sensing element 13 are connected to the fixed resistance element 1.
4 and 15 to form a bridge circuit, and transistor 16 is connected to this bridge circuit.
Electrical m17 is connected via .

The output terminal portion of the bridge circuit including the temperature sensing element 12 is connected to the comparator 18, and the temperature of the temperature sensing element 12 is specified with respect to the air temperature measured by the auxiliary temperature sensing element 13. The output signal of the comparator 18 is set to rise when the temperature rises to the temperature state. The output signal from the comparator 18 is supplied to the flip-flop circuit 19 as a reset command.

Further, a pulse-like energization start signal is supplied to this detection device from a control unit part of the engine (not shown in the figure) in a state synchronized with the rotational state of the engine, for example, and the signal input terminal 20 The energization start signal supplied to the flip-flop circuit 19 is supplied as a set command to the flip-flop circuit 19 via the OR circuit 21.

That is, the flip-flop circuit 19 is set-controlled by the energization start signal, and reset-controlled by the output signal from the comparator 18. The output signal of the flip-flop circuit 19 upon resetting, that is, the Q output, is taken out from the output terminal 23 via the inverter 22 as a detection output signal.

Further, the d output of the flip-flop circuit 19 is supplied to the base of the transistor 24. The 1-transistor 24 controls the base potential of the transistors 1-16, and when the flip-flop circuit 19 is in the reset state, the transistor 24 is set to the on state and the base of the transistor 16 is grounded. ,
This transistor 16 is turned on when the flip-flop circuit 19 is set, and is set to supply heating current to the bridge circuit including the temperature sensing element 12. That is, the heating current is supplied to the temperature sensing element 12 when the flip-flop circuit 19 is set.

In this case, since the flip-flop circuit 19 is set-controlled by the energization start signal and reset-controlled by the output signal from the comparator 18, the time width of the heating current is determined by the temperature rise rate of the temperature sensing element 12, that is, the intake air. The state corresponds to the air flow rate within the pipe 11. Therefore, the output signal from the output terminal 23 corresponding to the setting and resetting of the flip-flop circuit 19 is a pulse-like signal whose time width corresponds to the detected air flow opening.

Here, the voltage of the heating current supplied to the bridge circuit via the transistor 16 is monitored by the differential amplifier 25 via the resistor R1; Reference power supply 26 via R2
Supply and set the reference voltage signal from. The output signal of the differential amplifier 25 causes the transistor 16 to
The base of the heating current is controlled to set the voltage value of the heating current as a reference.

The energization start signal supplied to the input terminal 20 is further supplied to the first glue 1 to the riggable mono multivib break 27. This mono multivibrator 27 is
It is set within a time range specified from the rise of the input signal, for example, 10 seconds, which is sufficiently longer than the generation cycle of the energization start signal, and the d output in the reset state is the second monomulti The bird supplies the vibrator 28 as a signal. This second mono multivibrator 28 is controlled after the first seven-degree multivibrator 27 is reversed to the reset state, and is controlled to have a time width required for burn-off, for example, 3 seconds. generates an output signal. The Q output signal of the second mono-multivibrator 28 is supplied to the OR circuit 21 and used as a set command signal for the flip-flop circuit 19.
The transistor 29 is turned on. This transistor 2
Reference numeral 9 connects the reference voltage terminal of the differential amplifier 25 to ground via a resistor R3, and during the burn-off period in which the mono multivibrator 28 is in the set state, a heating current is supplied to the bridge circuit including the temperature sensing element 12. The voltage state of is set to a lower state than that during the air flow rate detection operation, and the temperature of the temperature sensing element 12 is set to a temperature in a range suitable for burn-off and in which the temperature sensing element 12 does not burn out (for example, 800 ° C.). Do it like this.

That is, in the air flow rate detection device configured as described above, in the operating state of the engine, (A
The energization start signal shown in > is generated, for example, in a state where the engine rotations are synchronized.

Then, the flip-flop circuit 19 is set and controlled in response to this signal, and its d output becomes as shown in (B) of the figure. Since the Q output of this flip-flop circuit 19 controls the transistor 29 and turns on the transistor 1G, a heating current is supplied to the temperature sensing element 12, and this heating current Correspondingly, the degree of intensity of the temperature sensing element 12 increases as shown in (C) of the figure.

When the temperature of the temperature sensing element 12 rises and its rejection value drops by one level from the potential set by the auxiliary temperature sensing element 13, the output signal from the comparator 18 changes as shown in the figure.
As shown in D), the flip-flop circuit 19
will be set. That is, the air flow port measurement and detection operation as described above is executed, and the time width in which the flip-flop circuit 19 is in the set state is made to correspond to the air flow rate in the intake pipe 11. Become.

When the engine is in a state in which the engine is controlled to stop when such an air flow rate detection operation is performed, the energization start signal disappears from the time of stop, as shown in (A> in Fig. 3). During the period when the energization start signal exists, the input signal to the first mono-multivibrator 27 is shorter than the time constant set in this mono-multivibrator 27, so the input signal is in this state. The mono-multivibrator 27 is always kept in the set state. However, when the energization start signal disappears as described above, the last energization start signal disappears.

; When the time width T1 (10 seconds) set in the first monomer multivibrator 27 has elapsed, the monomer 1 multivibrator 27 is reset. That is, the set state of the first mono-multivibrator 27 is as shown in (B,) in FIG.
The mono multi-byte/lator 27 comes to monitor the presence of the energization start signal.

When this first mono-multivibrator 27 is reversed to the reset state, its output rises and the second mono-multivibrator 2B is triggered.

Then, as shown in (C) of the same figure, the output signal from this second mono-multivibrator 28 has a time width T23 seconds).
It will now occur in Then, while the output from this second mono-multivibrator 28 exists, the flip-flop circuit 19 is set to the set state, and the @temperature element 12
The heating current is set to be supplied to.

Here, the flip-flop circuit 19 is configured to give priority to the set, and as long as the set command signal is present, the flip-flop circuit 19 is maintained in the set state and set to A, regardless of the output signal from the comparator 18. . - That is, during the period T2 in which the second mono-multivibrator 28 is in the set state, a heating current is continuously supplied to the temperature sensing element 12, and burn-off is performed. During this burn-off period, the transistor 29 is controlled to be turned on, and the supply voltage to the temperature sensing element 12 is switched to a low state.
The occurrence of burnout accidents has been effectively prevented.

(D> in FIG. 3 shows the state of the signal obtained from the output terminal 23, and (E) in the same figure shows the state of the heating current supplied to the bridge circuit including the temperature sensing element 12. In this case, in the burn-off state, the voltage state is set to be lower than that at the time of measurement.

In addition, in the description of the above embodiment, the means for setting the supply of heating current to the temperature sensing element 12 when performing burn-off is not limited to the example described above, and for example, the means for setting the midpoint potential of the bridge circuit during burn-off for a certain period of time. It can be implemented in the same manner by controlling the feed and back pack. In addition, in the embodiment shown here, power is constantly supplied to the device from the on-board battery, which means that power is constantly supplied to the device from the on-board battery, that is, regardless of whether the system power switch (ignition key switch) is on or off. The power supply is fixed at the supply stage. However, when the ignition key switch is off, the power to the engine control unit is also off, and no energization start signal is present. Therefore, no current flows to the temperature element 12, and the current consumption of this device is sufficiently negligible.

[Effects of the Invention] As described above, in the thermal air flow rate detection device according to the present invention, in the end state of the detection operation in which the energization start signal disappears, the energization start signal monitoring means detects the energization start signal. In a state where the extinction is detected, the burn-off mode is automatically set, and the burn-off for incinerating and removing the deposits on the humidity sensing element is executed. Furthermore, this burn-off control is executed without using, for example, an engine control unit, and can be effectively applied to automobile engine control systems and the like.

[Brief explanation of drawings]

FIG. 1 is a circuit configuration diagram illustrating a thermal air flow rate detection device according to an embodiment of the present invention, FIG. 2 is a signal waveform diagram illustrating the detection operation of the device, and FIG. 3 also illustrates a burn-off state. FIG. 11... Intake pipe, 12... Temperature sensing element, 13... Auxiliary temperature sensing element, 16... Transistor (heating current control)
, 17...power supply, 18...comparator, 19...
- Flip-flop circuit 27...first mono multivibrator (monitoring energization start signal), 28...second mono multivibrator (burn-off time setting).

Claims (1)

[Claims] a temperature sensing element set in the air flow and having temperature resistance characteristics;
means for setting and supplying a heating current to the temperature sensing element in response to an energization start signal generated at a specified period; and a state in which the temperature of the temperature sensing element rises to a specified temperature state with respect to air temperature. means for detecting the heating current, means for cutting off the heating current by detecting a temperature rise state of the temperature sensing element, means for monitoring the generation state of the energization start signal and detecting the end state of the signal, A thermal type characterized by comprising means for setting a burn-off time width specified by a signal end detection state, and means for setting a burn-off heating current to be supplied to the temperature sensing element in the time width set by the means. Air flow detection device.