JP2626628B2 - Heating resistance type air flow meter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot-wire air flow meter, and more particularly to a hot-wire air flow meter for detecting an intake air amount of an internal combustion engine.

[0002]

2. Description of the Related Art A movable vane type, a Karman vortex type, a swirl type, a hot wire type, etc. have been conventionally used as an air flow meter provided in an electronic control fuel injection device of an internal fuel engine such as an automobile for measuring an intake air amount. In particular, the hot-wire type is considered to be the mainstream of air flow meters for measuring the amount of intake air since it can directly detect the mass air flow rate directly involved in combustion. 58−
The one disclosed in, for example, 135916 has been put to practical use.

[0003]

However, according to these conventional hot wire air flow meters which have been put into practical use, a high-accuracy air flow rate signal is output at light load such as when the engine is cruising. When the number of cylinders is small, especially at low engine speeds and heavy loads of engines with four or less cylinders, the suction air flow becomes a pulsating flow with a large pulsating amplitude and a partial backflow.
There is a problem that the accuracy is rapidly reduced.

An object of the present invention is to provide an air flow meter capable of measuring an average air flow rate of a pulsating air flow accompanied by a backflow with high accuracy.

[0005]

SUMMARY OF THE INVENTION The above object is achieved by using the first heating resistor provided on the upstream side of the air flow, and a second heating resistor provided on the downstream side of the air flow, the in the heating resistor type air flow meter for measuring the flow rate of air flowing in the air passage, one common for the temperature compensation resistor and provided corresponding to the first heating resistor and the second heating resistor ,
Means for supplying a constant current to the temperature compensation resistor .

[0006]

The constant temperature control of the first heating resistor for measuring the flow rate in the forward direction and the second heating resistor for measuring the flow rate in the reverse direction is performed by one common temperature compensation resistor. As a result, the measurement accuracy can be prevented from lowering.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the hot wire type air flow meter according to the present invention will be described below with reference to the drawings. 1 to 6 show one embodiment of the present invention. Hot wire probe 10 used in this embodiment
Is similar to the conventional example shown in FIG. 15 as shown in FIG.
On the surface of a cylindrical or cylindrical bobbin 1 made of an insulating material having good heat conductivity such as ceramic, film-shaped heating resistors 2 and 3 are formed by a thin-film or thick-film technique. Of the resistors 2 and 3, the heating resistor 2 is provided on the intake upstream side A, and the heating resistor 3 is provided on the intake downstream side B, and the surface thereof is covered with a coating material 4. These heating resistors 2 and 3 are made of platinum, tungsten, or the like, and are formed symmetrically on the circumferential surface of the bobbin 1 by half a circumference.
3 is made of glass, ceramic or the like for preventing oxidation and corrosion.

As shown in FIGS. 2 to 4, lead wires 5 connected to the heating resistors 2 and 3 are attached near both ends of the hot wire probe 10 thus configured. As shown in FIG. 5, these four lead wires 5 are fixed to a holder 6 made of an electrically insulating material having V heat insulation.
8 is fixed. Furthermore, this hot wire probe 1
FIG. 6 shows the holder 6 to which the temperature probe 11 and the temperature probe 11 are fixed.
As shown in (1), it is inserted into the narrowest part of the venturi 9a formed in the intake cylinder 9, and is integrated with the heat ray drive circuit 12 outside the intake cylinder 9. Venturi 9
A throttle valve 13 is provided in the intake cylinder 9 downstream of “a”.

The operation of the embodiment constructed as described above will be described below. Using the hot wire probe 10 according to the present embodiment, the temperature of the heating resistors 2 and 3 is set to a constant value irrespective of the air flow velocity, similarly to a normal constant temperature hot wire flow meter. Electric heating is performed by the hot wire drive circuit 12. First, when air flows in the direction of arrow A in FIG. 1, the heating resistor 2 is more cooled by the airflow than 3, so the supply current from the hot wire drive circuit 12 is smaller than that of the heating resistor 2. Is greater than 3. On the other hand, when air flows in the direction of arrow B in FIG. 1, cooling by the air flow is larger in the heating resistor 3, as opposed to before, and the heating wire driving circuit 1
The current supplied from the heating resistor 3 is larger than that of the heating resistor 3. Therefore, the direction of the air flow can be detected based on the difference between the supply currents to the heating resistors 2 and 3.

FIG. 7 shows a first reference example of the hot-wire drive circuit 12. As shown in FIG. Heating resistor 2, temperature probe 11a, resistor 14,
15 form a Wheatstone bridge, and the differential amplifier 1 is set so that the potential difference at the midpoint of the bridge becomes zero.
The current flowing through the heating resistor 2 is adjusted by the transistor 6 and the transistor 17. With this configuration, the resistance value of the heating resistor 2 is controlled to be constant regardless of the air flow velocity, that is, the temperature is controlled to be a constant value. At this time, the signal corresponding to the air flow velocity by the heating resistor 2 is the potential at point C in the figure. Further, similarly to the heating resistor 2, the heating resistor 3 forms a Wheatstone bridge with the temperature probe 11b and the resistors 18 and 19, and the differential amplifier 20 and the transistor are arranged so that the potential difference at the bridge midpoint becomes zero. 21 is configured to adjust the current flowing through the heating resistor 3. Therefore, the signal corresponding to the air flow velocity by the heating resistor 3 is the potential at point D in the figure. Further, when the difference between the potentials at the points C and D is obtained by the differential amplifier 22, the output of the differential amplifier 22 is a signal from the hot wire air flow meter using the hot wire probe 10 shown in FIG.

When the resistors 15 and 19 are adjusted so that the output signal of the differential amplifier 22 when the air flow rate is zero becomes zero, the relationship between the air flow rate and the signal becomes as shown in FIG. That is, in the hot wire probe shown in FIG. 1, when the air flow is a forward flow indicated by an arrow A, the signal corresponds to the (+) potential corresponding to the air flow, and when the air flow is a reverse flow indicated by an arrow B, the signal corresponds to the air flow. (-) Potential. Therefore, in order to obtain the average air flow rate of the pulsating flow accompanied by the backflow, signals during one cycle of the pulsating flow are sequentially taken into a computer, converted into a flow rate according to the characteristic curve shown in FIG.
An average air flow rate can be obtained by adding and averaging the cycles. At the time of the backflow, the signal has the potential of (-), so that an accurate average flow rate can be obtained by subtracting after converting into the air flow rate.

FIG. 9 is a circuit diagram showing a second reference example of the hot-wire drive circuit 12. As shown in FIG. In the first circuit embodiment shown in FIG. 7, since a signal having a (-) sign potential is also output as a signal, it is necessary to operate the differential amplifier 22 with the (+) and (-) power supplies. On the other hand, the power source of the battery of the bicycle is usually a single power source of only (+). Therefore, as shown in FIG.
The heating resistors 1 and 2 output the higher one of the potentials of the signals C and D of the hot-wire air current meter as a signal, and output a signal E for determining which is larger. That is, when the potentials C and D are input to the converter 23 and the potential C is higher than the potential D, that is, when the air flow is a forward flow in FIG. C is output as an output signal. Conversely, when the potential D is higher than the potential C, that is, in the case of a reverse flow in FIG.
Becomes low level, the electronic switch 24 is turned off and the electronic switch 25 is turned on, and the potential D is output as an output signal. 26 is a NOT element.

[0013] According to the second reference example, as described above, heat rays flow air flow in hot wire probe 10 shown in FIG. 1 in the case of forward flow, the potential E goes high, and be composed of the heating resistor 2 The signal of the hot wire air flow meter constituted by the heating resistor 3 is output. Then, a characteristic curve indicating the relationship between the air flow rate and the signal as shown in FIG. 10 is input as a table in the computer for the hot wire flow meter constituted by the heating resistors 2 and 3, respectively. The flow rate is measured by converting a signal input to the computer into an air flow rate.

FIG. 11 is a circuit diagram showing a third embodiment of the hot-wire drive circuit 12. In the above-described first and second circuit embodiments, the hot wire flowmeters composed of the heating resistors 2 and 3 have the temperature probes 11a and 11b and the temperature probes 11a and 11b respectively.
Although three temperature probes are required, the third circuit embodiment shown in FIG. 11 has a configuration in which the temperature probes are shared by two hot-wire flow meters, and one temperature probe is used. This hot-wire drive circuit is a case where the one disclosed in Japanese Patent Application No. 56-2088 is used for a hot-wire probe 10 provided with two heating resistors as shown in FIG. It is modified to be individual. A value obtained by sample-holding and amplifying a voltage change caused by a change in the resistance value of the heating resistors 2 and 3 corresponding to a change in the air flow rate is compared with a temperature probe terminal voltage, and the difference is integrated, and the difference is integrated. The voltage is compared with the output voltage from the sawtooth wave generator, and the duty ratio is changed so that the difference between the temperature of the hot wire and the ambient temperature detected by the temperature compensation resistor is kept constant. The ratio is used as the air flow signal. That is, in FIG. 11, the heating resistors 2 and 3 are connected to the other ends of the constant current sources 31A and 31B whose one ends are grounded via the switches 32A and 32B, respectively. The constant current sources 31A and 31B provide a constant current I _H
Is supplied to the heating resistors 2 and 3 via the switches 32A and 32B. The constant current source 35 is connected for supplying a constant current I _H to a temperature probe 11 of which one end is provided on the same line as the heating resistor 2 and 3 are grounded.

The heating resistors 2 and 3 have switches 36A and 3
The resistors 37A and 37B are connected via 6B, and the other ends of the resistors 37A and 37B are connected to the negative input terminals of the integration circuits 38A and 38B. The integration circuits 38A, 3
8B is for integrating the difference between the terminal voltage of the heating resistors 2 and 3 and the terminal voltage of the temperature compensation resistor, and the output thereof is configured to be input to the negative input terminals of the comparison circuits 40A and 40B. The switches 36A and 36B and the resistors 37A and 3
Capacitors 42A and 42B are connected to the connection point with 7B via buffers 45A and 45B, and the other ends of the capacitors 42A and 42B are grounded.

Saw wave generators 43A and 43B are connected to the positive input terminals of the comparison circuits 40A and 40B, respectively.
A and 40B are configured to be input to the positive input terminals. This comparison circuit compares the output voltages output from the integration circuits 38A and 38B with the sawtooth wave generators 43A and 43A.
The output voltage is compared with the output voltage from B, and a pulse signal is output at the intersection of both output voltages.

When the switches 32A and 32B are turned on in the hot-wire drive circuit thus configured, a pulse-like constant current is applied to the heating resistors 1 and 2. This switch 32
A and 32B and the switches 36A and 36B operate in conjunction with each other, so that when the switches 32A and 32B are ON, the switches 36A and 36B are also ON and the buffer 4
A voltage resulting from a voltage drop due to the resistance of the heating resistors 2 and 3 is sampled and held in the capacitors 42A and 42B via 5A and 45B. A voltage is obtained by comparing and integrating the sample value with the terminal voltage of the temperature probe 11 for a constant current of IK. The duty ratio is determined by comparing this voltage with the sawtooth voltage output from the integrating circuits 38A and 38B and the sawtooth generators 43A and 43B. At this time, the switches 32A, 32B, 36A, 36
B is turned ON and OFF.

In this hot wire drive circuit, the air flow rate is increased, and the heating resistors 2 and 3 are cooled. As a result, the resistance is reduced and the voltage drop of the heating resistors 2 and 3 is reduced by the temperature probe 1.
Below 1's. At this time, the integration circuits 38A and 38B
The output voltage results drops below stable point so far, the output pulse width of the comparator 40A, 40B increases, which increases the flow time of the I _H. Thus, the amount of heat supplied to the heating column increases, the temperature of the hot wire is prevented from lowering, and the temperature is maintained at a constant temperature.

The ratio T ₁ of the pulse width T _{1 at} this time to the period T of the sawtooth wave of the sawtooth wave generators 43A and 43B.
/ T is the time ratio, and this time ratio is a signal corresponding to the air flow rate. Therefore, as in the case shown in FIG. 9, of the signals of the hot-wire anemometer constituted by the heating resistor 2 and the hot-wire anemometer constituted by the heating resistor 3, the one with the larger heat radiation, that is, the duty ratio T ₁ / T is the same. Output the larger one as the output signal,
Further, a signal F for determining which is larger is output. Specifically, as shown in FIG. 1, when the potential of the output signal of the integrating circuit 38A is lower than the potential of the output signal of the integrating circuit 38B, that is, in the case of the forward flow in FIG.
5 becomes low level, and the electronic switch 48 is turned off.
Then, the electronic switch 47 is turned on via the NOT element 46, and the output signal is the signal of the hot-wire anemometer constituted by the heating resistor 2, that is, the output of the comparator 40A, and the signal F at that time is high level. Becomes Conversely, when the output potential of the integrating circuit 38A is higher than the output potential of the integrating circuit 38B, that is, in the case of the reverse flow in FIG. 1, the output of the comparator 45 is at a high level, the electronic switch 48 is turned on, and the electronic switch 47 is turned off. As the output signal, the signal of the hot wire anemometer constituted by the heating resistor 3, that is, the output of the comparator 40B is output, and the signal F at that time becomes low.

As described above, according to the present embodiment, even in the pulsating intake state accompanied by the backflow which occurs at the low rotation full load of the internal combustion engine, the backflow component is precisely corrected to actually inhale into the engine. The detected air flow rate can be accurately detected. At the same time, an accurate intake air flow rate can be detected in other general operation regions.

Further, by employing the principle of a constant temperature difference type hot-wire anemometer as the hot-wire drive circuit, the mass air flow rate can be measured with high accuracy even when the air temperature changes. The venturi 9 a formed in the intake cylinder 9 has an effect of rectifying the airflow passing through the hot wire probe 10.

In the above embodiment, the case where both ends of the hot wire probe 10 are directly supported by the leads 5 has been described. As shown in FIG. 12, four lead wires are provided in parallel with the axial direction of the hot wire probe 10. 5 and the lead wire 5
May be attached to the lead wire 5 at a right angle to the lead wire 5 and the lead wire 5a may be fixed to the holder 6.

FIG. 13 shows a case where the hot-wire probe 10 and the temperature probe 11 are mounted on the intake cylinder 90 disclosed in Japanese Patent Application No. 57-17511. As in the embodiment shown in FIG. And the temperature probe 11 is the holder 6
And is inserted into the bypass passage 13 formed in the intake cylinder 90 integrally with the hot-wire drive circuit 12. At this time, the airflow in the bypass passage 13 merges with the airflow in the main flow passage at the bypass passage outlet 13a.

FIGS. 14 and 15 are a plan view and a sectional view, respectively, showing another embodiment of the structure of the present invention. Intake cylinder 9
A hot-wire drive circuit 12 is fixed to the outer peripheral surface of the inner cylinder 50, and an inner cylinder 50 is fixed in the intake cylinder 9 via the block 6.
In the inner cylinder 50, plate-like heat generating resistors 2, 3 in which a foil of nickel, platinum or the like is coated with a heat-resistant resin such as polyimide are used.
Are provided side by side on the upstream and downstream sides of the intake air, respectively. These heat generating resistors 2, 3 are fixedly held by a mount 51, and are fixed to the inner cylinder 50 via the mount 51. In the case where air flows in the direction of the arrow in the figure, the amount of heat radiation of the heating resistor 2 becomes larger than the amount of heat radiation of the heating resistor 3. Direction can be detected. In order to rectify the air flow on the surfaces of the heating resistors 2 and 3, the inner cylinder 50 has a structure in which the flow path area decreases in the direction of the arrow in the figure.

FIGS. 16 and 17 show another embodiment of the structure of the hot-wire probe according to the present invention. Heating resistors 2, 3 are formed on the surfaces of two cylindrical columns 1, respectively, and these heating resistors 2, 3 are joined by a coating material 4. The heating resistor 2 strongly detects the airflow in the direction of the arrow in the figure and the heating resistor 3 strongly detects the airflow in the opposite direction, as in the above-described embodiment.

[0026]

As described above, according to the present invention, heating resistors are provided on the upstream side and the downstream side of the intake of the hot wire type air flow meter, respectively, and the difference in the amount of heat dissipated by these heating resistors is electrically determined. And the flow direction of the intake air and the air flow rate are detected, so that the average air flow rate of the pulsating air flow accompanied by the backflow can be measured with high accuracy.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a hot wire probe used in an embodiment of the air flow meter of the present invention.

FIG. 2 is a side view of the hot wire probe of FIG.

FIG. 3 is a front view of the hot wire probe of FIG. 1;

FIG. 4 is a plan view of the hot wire probe of FIG. 1;

FIG. 5 is a perspective view showing a support structure of the hot-wire probe.

FIG. 6 is a sectional view showing the structure of the air flow meter of the present invention.

FIG. 7 is a diagram showing a reference example of the present invention.

FIG. 8 is a diagram showing a relationship between an air flow rate and a signal.

FIG. 9 is a diagram showing another reference example of the present invention.

FIG. 10 is a diagram showing a relationship between an air flow rate and a signal.

FIG. 11 is a diagram showing another embodiment of the present invention.

FIG. 12 is a perspective view showing another embodiment of the support structure of the hot-wire probe used in the present invention.

FIG. 13 is a sectional view showing another embodiment of the structure of the air flow meter of the present invention.

FIG. 14 is a plan view of FIG. 13;

FIG. 15 is a sectional view showing another embodiment of the structure of the air flow meter of the present invention.

FIG. 16 is a plan view showing another embodiment of the hot-wire probe of the present invention.

FIG. 17 is a plan view of FIG. 16;

FIG. 18 is a graph showing the relationship between the air flow rate and time when the intake air flow is a pulsating flow with a backflow.

FIG. 19 is a graph showing a relationship between a hot-wire signal and time in the case of FIG. 18;

Claims (1)

(57) [Claims] And 1. A first heating resistor provided on the upstream side of the air flow, and a second heating resistor provided on the downstream side of the air flow, the air flow rate flowing through the air passage with In the heating resistance type air flow meter to be measured , one common temperature compensation resistor provided corresponding to the first heating resistor and the second heating resistor, and the temperature compensation resistor are fixed. And a means for supplying an electric current .