JPS6130718A - Hot-wire type flow meter - Google Patents

Abstract

PURPOSE:To reduce power consumption and to prevent the lowering in detection accuracy, by detecting an air flow amount from the supply time of a current to a hot-wire resistor in usual and selecting a burning-off means at a necessary time to burn off the adhered substance of the hot-wire resistor. CONSTITUTION:A hot-wire resistor 11, the power transistor 30 of a switching means, the oscillator 20 of a detection start and finish signal generation means, a comparator 16, FF18 for constituting a current supply time control means and transistors 23, 26, 31 are provided. The switching means is turned ON by transistors 46, 51 for selectively changing over the burning-off means of a differential amplifier 41 and the current supply time control means by a control apparatus to supply a large current for burning off an adhered substance to the hot-wire resistor 11. By this method, power consumption is reduced and the adhered substance is accurately burnt off and the lowering in detection accuracy can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a hot wire flowmeter for detecting the intake air flow rate in, for example, an internal combustion engine for an automobile, and particularly to one equipped with a device for burning off hot wire resistance deposits.

<Prior art> An example of such a conventional hot wire flowmeter is the one shown in FIG. 3 (see Utility Model Application No. 166161/1983).
.

That is, a hot wire resistance 1 and resistances 2, 3a, 3b, and 4 (2 is an output resistance, and 3a is a temperature compensation resistance for suppressing fluctuations in intake air amount detection characteristics due to changes in intake air temperature) are arranged in the intake passage. , 3b is a first reference resistor which is placed in the same atmosphere as the 29th reference resistor 4 in order to ensure the potential between it and the second reference resistor 4), forming a bridge circuit.

Then, the current supplied to the bridge circuit is controlled by controlling the power transistor RO with the output of the differential amplifier 5, which changes depending on the unbalanced voltage of the bridge circuit, that is, the potential difference between points a and b, The intake air flow rate is detected based on the voltage change of the output resistor 2.

Here, the output voltage of the output resistor 2 is A/D converted, and a control device (not shown) such as a microcomputer reads it and processes it to detect the intake air flow rate.

<Problems to be Solved by the Invention> However, in such a conventional hot-wire flowmeter, the intake air flow rate is always measured based on changes in the output voltage of the output resistor 2.

When pulsation occurs in the intake air flow, it is sensitive to the pulsation (as the output voltage of output resistor 2 changes accordingly, the control force for controlling the fuel injection amount, etc. based on intake air flow rate detection; hunting occurs and becomes unstable) As a result, the engine output fluctuates, resulting in a decrease in drivability.For this reason, an attempt has been made to average the detected value of the intake air flow rate multiple times to eliminate the influence of pulsation.

In this case, it was difficult to sample a large number of detected values due to calculation speed, and a sufficient effect could not be achieved.

Furthermore, since the intake air flow rate is detected based on the output voltage value of the output resistor 2, it is necessary to input the output voltage through an A/D converter to a control device usually constituted by a microcomputer. Furthermore, since the power transistor 6 is operated in the active region by the output voltage of the differential amplifier 5,
The power transistor 60 generated a lot of heat and consumed a lot of power.

The present invention was made in view of these conventional problems, and it detects the intake air flow rate without being affected by the pulsation of the intake air flow, and reduces power consumption by controlling the switching of the power transistor. It is an object of the present invention to provide a hot wire type flowmeter that can be used with a hot wire, and further to make it possible to burn off deposits on the hot wire resistance.

Means for Solving the Problems> Therefore, the present invention provides a switching means for controlling ON/OFF of energization to a hot wire resistor disposed in an intake passage, and a signal for starting intake flow rate detection at a predetermined period. detection end signal generating means for detecting the resistance value of the hot wire resistance and outputting a signal for terminating intake flow rate detection when the detected value reaches a predetermined value; When a signal for starting intake flow rate detection is inputted from the signal generating means, the switching means is turned ON to start energizing the hot wire resistor, while a signal for terminating intake flow rate detection is input from the detection end signal generating means. energization time control means for turning on the switching means to stop energization to the hot wire resistor when the switching means is turned on, and switching means for selectively turning on the switching means for a predetermined period of time.

While the intake air flow rate is detected from the time when electricity is applied to the resistor, the burn-off means is selected to burn off the deposits on the hot wire resistor when necessary.

<Example> An example of the present invention will be described below based on FIG. 1.

In the figure, a hot wire resistor 11 disposed in the intake passage and a first reference resistor 12 are connected in series, and a temperature compensation resistor 13 is connected to this series circuit to suppress fluctuations in intake air amount detection characteristics due to changes in intake air temperature. A reference voltage setting circuit consisting of a third reference resistor 15 connected in series with the resistor 13 and placed in the same atmosphere as the second reference resistor 14 is connected in parallel to ensure a potential between the second reference resistor 14 and the second reference resistor 14. It is connected.

The potential between the second reference resistor 14 and the third reference resistor 15 is
゛ Applied to the non-inverting side terminal of the comparator 16,
A potential between the hot wire resistor 11 and the first reference resistor 12 is applied to the inverting side terminal of the comparator 16 . The output terminal of the comparator 16 is connected via a first inverter 17 to the clear terminal of a D-type 7 flip-flop 18, and the clock terminal of the flip-flop 18 is connected via a second inverter 19 to a detection start signal generating means. The output terminal of the oscillator 20 is connected to the output terminal of the oscillator 20. The oscillator 20 outputs a pulse signal of a predetermined width at regular intervals. Also.

A constant voltage is applied to the D terminal and the power supply terminal of the flip-flop 18, and the silk terminal of the flip-flop 18 is connected to the base terminal of the first transistor 230 whose emitter is grounded via the third inverter 21 and the current limiting resistor 22. It is connected.

A load resistor 24 is connected to the collector terminal of the first transistor 23.
A constant voltage is applied through the transistor, and its collector terminal is connected to the base terminal of a second transistor 260 whose collector is grounded via a current limiting resistor 25. The emitter terminal of the second transistor 26 is connected to a pair of voltage dividing resistors 27a,
27b to the output terminal of the first constant voltage generation circuit 28, and this generation circuit 28 outputs a constant voltage of, for example, 8. The output terminal of the first constant voltage generation circuit 28 is used for current limiting. It is connected to the collector terminal of a power transistor 30 as a switching means via a resistor 29, and the emitter terminal of the power transistor 30 is connected to the input terminal of the bridge circuit. The base terminal of the power transistor 30 is connected to the collector terminal of the third transistor 31, and the emitter terminal of the third transistor 31 is connected to the emitter terminal of the power transistor 30. The base terminal of the third transistor 310 is connected between the voltage dividing resistors 27a and 27b.

Further, the collector terminal of the power transistor 30 and the base terminal of the third transistor 310 are connected by a voltage smoothing capacitor 32.

A current limiting resistor 33a is connected to each input terminal of the comparator 16.
, 33b are connected. A voltage is applied between the voltage dividing resistors 35a and 35b through the inverting side terminal diode 34 and the current limiting resistor 33b of the comparator 16060, and when the power transistor 30 is turned off, the output of the comparator 16 is It is forcibly held at the "L" level. Further, a second constant voltage generation circuit 36 is provided that supplies a constant voltage (Vcc) of, for example, 5V to each part.

The output terminal of the bridge circuit is connected to the input terminal of a control device composed of a microcomputer (not shown). The control device stores in advance the intake air flow rate corresponding to the change in the energization time to the bridge circuit, that is, the ON time of the power transistor 30, and searches the detected intake air flow rate from the actual energization time to the bridge circuit. It has become.

Here, the first to third transistors 23, 26 and 31 and the power transistor 30 are set to be ON/OFF controlled between a saturation region and a cutoff region. Also,
Flip-flop 18 and first to third transistors 23
, 26.31 constitute an energization time control means.

Note that 37.38 is the load resistance.

Next, a circuit for burning off the deposits on the hot wire resistor will be explained.

A voltage dividing resistor 3 is connected to the pace terminal of the third transistor 31.
9 to the emitter terminal of a fourth transistor 40 whose collector is grounded. An output terminal of a differential amplifier 41 for burnout is connected to the base terminal of the fourth transistor 400.

The non-inverting side terminal of the amplifier 41 is connected so that the potential between a voltage dividing fixed resistor 42 and a voltage dividing variable resistor 43 connected to the emitter terminal of the power transistor 30 can be input. Further, a constant voltage is applied to the non-inverting side terminal of the comparator 16 via a load resistor 44 and a diode 45.

Next, a selective switching circuit such as the energization time control means and the burnout circuit will be explained.

The anode terminal of the diode 45 has a fifth terminal with a grounded emitter.
The collector terminal of transistor 46 is connected. Further, the inverting side terminal of the amplifier 410 is connected to the inverting side terminal of the comparator 16 via a current limiting resistor 4T. The output terminal and the inverting side terminal of the amplifier 41 are connected through a feedback resistor 48.

The output terminal of a control device (not shown) is connected to the base terminal of the fifth transistor 460 via current limiting resistors 48 and 49. A current limiting resistor 50 is connected to the base terminal side of the fifth transistor 46. The base terminal of a sixth transistor 51 whose emitter is grounded is connected thereto, and the collector terminal of the sixth transistor 51 is connected to the base terminal of the first transistor 230.

When the control device performs intake air flow rate detection control, the fifth
While outputting an "L" signal to the transistor 46 and the sixth transistor 51, when burning out deposits such as dust that adhere to the isothermal wire resistor 11 immediately after the engine stops, the transistors 46 and 51 are given a burning operation time (approximately 1 second). It is designed to output an "H" signal having a pulse width set to .

Note that 52 and 53 are load resistances, 54 is a smoothing capacitor, and 55a and 55b are surge absorption diodes.

Next, the operation of this device will be explained with reference to the signal waveform diagram of each part shown in FIG.

During intake air flow rate detection control, the fifth and sixth
A "L" signal is input to transistors 46 and 51, and these transistors 46 and 51 are turned off. therefore,
Since a constant voltage is applied to the non-inverting side terminal of the amplifier 41, the output of the comparator 16 becomes "H", the fourth transistor 40 is turned off', and the operation of burning off the deposits is not performed.

Then, the pulse signal of a predetermined width output from the oscillator 20 is inverted by the second inverter 19, and the "L" shown in FIG.
When the "signal" is input to the clock terminal of the flip-flop 18, the "L" signal is continuously output from the Q terminal of the flip-flop 1B. This output signal is transmitted to the third inverter 2.
1 and input to the base terminal of the first transistor 230. This causes the first transistor 23 to become
Since the voltage becomes N, its collector voltage decreases as shown in FIG. 2f, and the second transistor 26 also turns on.

Therefore, the potential between the voltage-dividing resistors 27a and 27b decreases, and the third transistor 31 is turned on.

The power transistor 30 is turned on and a constant voltage is applied to the bridge circuit. Immediately before this constant voltage is applied, the hot wire resistor 11 is cooled by the intake air flow and its resistance value decreases, so immediately after the voltage is applied, the potential between the hot wire resistor 11 and the first reference voltage 12 is 2 reference resistance 14 and 3rd
Since the potential is higher than that between the reference resistor 15 and the reference resistor 15, the output of the comparator 16 is held at the "L" state.

As the hot wire resistor 11 is energized, the temperature of the hot wire resistor 11 rises and its resistance value also increases. Due to this increase, the potential between the hot wire resistor 11 and the first reference resistor 12 gradually decreases, and when that potential becomes lower than the potential of the non-inverting terminal, the output of the comparator 16 becomes "H" as shown in FIG.
This "H" signal is inverted by the first inverter 17, and the "L" signal is input to the clear terminal of the flip-flop 1B as shown in FIG. 2C.

As a result, the output of the Q terminal of the 7-lip flop 18 becomes H'' as shown in FIG.
The "L" signal is input to the first transistor 23 through the transistor 23, and the first transistor 23 is turned off.Therefore, since the collector voltage of the first transistor 23 becomes "H", the second transistor 23 is turned off.
The transistor 26 is turned off and the third transistor 3
1 is turned off, and the power transistor 30 is turned off.

Therefore, the constant voltage supply to the bridge circuit is stopped, and the control device energizes the bridge circuit for a period T (see Figure 2 a).
Correspondingly, the intake air flow rate is searched and read out from a map of intake air flow characteristics previously determined through experiments or the like. By the way, since the degree of cooling of the hot wire resistance 11 differs depending on the flow rate change of the intake air flowing through the intake passage, the hot wire resistance 1
In other words, the energization time T until the resistance value of 1 becomes constant, that is, the potentials of the non-inverting side terminal and the inverting side terminal of the comparator 16 become approximately the same, changes in accordance with the change in the intake air flow rate.
The intake air flow rate can be detected from the energization time T.

In this way, the intake air flow rate is detected from the energization time T every time a pulse from one oscillator 20 is output, that is, the oscillation period is used as the sampling period.

In this detection method, one energization time T corresponds to the total amount of intake air that has flowed from the end of energization (thermal equilibrium point) to the end of current energization, and this interval When the intake air flows steadily with pulsation, it is maintained at a value close to the oscillation period, although it varies somewhat, so when the current is applied, it corresponds well to the average value of the intake air flow rate with the oscillation period as a unit time.

Therefore, the intake air flow rate is detected smoothly while avoiding the influence of pulsation, and the fuel injection amount control based on this detection is also stable, resulting in stable engine operability. In particular, since the oscillation period of the oscillator 20 can be set to a large value, the averaging process can be performed over a substantially longer sampling period compared to the averaging process using a microcomputer or the like, and the effect on the pulsation is more excellent.

Furthermore, since the control device detects the intake air flow rate from the time when the bridge circuit is energized, the conventionally used A/D converter becomes unnecessary.

Furthermore, first to third transistors 23 and 26.

31 and the power transistor 30 are turned on and off in the saturation region and cutoff region, so the amount of heat generated in each transistor is small (power consumption can be reduced).

Further, when an "H" signal is input from the control device to the fifth and sixth transistors 46.51 immediately after the engine is stopped, the fifth and sixth transistors 46.51 are turned on and the first transistor 230 paces. The terminal is forcibly grounded, the first transistor 23 is turned off, and the second transistor 26 is also turned off.

On the other hand, when the fifth transistor 46 is turned on, the anode side potential of the diode 45 decreases, and a voltage divided by the fixed resistor 42 and the variable resistor 43 is applied to the non-inverting side terminal of the amplifier 41. At this time, since the "H" signal is input to the inverting side terminal via the feedback resistor 47, the output of the amplifier 41 becomes "L". This turns on the fourth transistor 40, lowers the base voltage of the third transistor 310, and turns on the third transistor 31. therefore,
Since the power transistor 30 is turned on and a predetermined current is passed through the hot wire resistor 11, the hot wire resistor 11 is heated and its deposits are burned off.

At this time, the hot wire resistor 11 is heated by energization and its resistance value increases, so that the potential divided by the hot wire resistor 11 and the first reference resistor 12 is divided by the rotating resistor 42 and the variable resistor 43. When the partial pressure becomes equal to or lower than the partial pressure value, the output of the amplifier 41 is controlled by the partial pressure value, and the burnout temperature (about 1000° C.) of the hot wire resistor 11 is kept substantially constant. Thereafter, when the output of the control device becomes "L" and the inputs of the fifth and sixth transistors 46.51 are turned off, the output of the amplifier 41 becomes "H" and the pace voltage of the third transistor 310 becomes "H". Then, the third transistor 31 is turned off, so the power transistor 30 is turned off, and the hot wire resistance 1
1 is stopped, and the burnout operation is completed.

In this way, since the operation for burning off deposits is performed by switching between the intake airflow detection control and the control, it is possible to set the energization time to the hot wire resistance during burning off regardless of the intake air detection control, thereby reducing the burning of deposits. Able to cut accurately.

Here, the temperature for burning off the deposits, that is, the control of the amount of current applied to the hot wire resistor 11 is set by adjusting the resistance value of the variable resistor 43.

Note that the output period of the pulse signal of the oscillator 20 may be changed depending on operating conditions such as the engine rotation speed.

<Effects of the Invention> As explained in Section 5 above, the present invention detects the intake air flow rate from the time of energization of the hot wire resistor cooled by the intake air flow, so that even if pulsations occur in the intake air pressure, the intake air flow rate is detected. The intake air flow rate can be detected by averaging the pulsations. Furthermore, since the intake air flow rate is detected from the time during which current is applied to the hot wire resistor, the conventional A/D converter is not required.

Furthermore, since the switching means is configured to be turned on and off by a signal from the energization time control means, when a power transistor is used as the switching means, the power transistor is turned on and off in the saturation region and the cutoff region.
control, and the power consumption of power transistors can be reduced.

Furthermore, since the switching means selects and operates the burnout means to apply a large current for burnout to the hot wire resistor, it is possible to burn off the deposits on the hot wire resistor, thereby increasing the accuracy of intake air flow rate detection. can prevent a decline in

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing one embodiment of the present invention, and Fig. 2 is a circuit diagram showing an embodiment of the present invention.
FIG. 3 is a circuit diagram showing a conventional example. 11... Hot wire resistance 16... Comparator 17...
・Flip-flop 20...Oscillator 23...
・First transistor 26... Second transistor
30... Power transistor 31... Third transistor 40... Fourth transistor 41.
... Differential amplifier 46 ... Fifth transistor 5
1...6th transistor

Claims (1)

[Claims] A hot wire resistor disposed in an intake passage of an internal combustion engine, a switching means for controlling ON/OFF of energization to the hot wire resistor, and a detection start signal generating means for outputting a signal for starting intake flow rate detection at a predetermined period. detection end signal generating means for detecting the resistance value of the hot wire resistance and outputting a signal for terminating intake flow rate detection when the detected value reaches a predetermined value; When a signal is input, the switching means is turned on to start energizing the hot wire resistor, and when a signal for ending intake flow rate detection is input from the detection end signal generating means, the switching means is turned off. energization time control means for turning on the switching means for a predetermined period of time to stop energizing the hot wire resistor; A hot wire flowmeter comprising: switching means for selectively switching between the energization time control means and the energization time control means.