JPH08313319A - Thermal air flow meter - Google Patents

Abstract

(57) [Abstract] [Purpose] In a thermal type air flow meter that measures the intake air amount of an internal combustion engine such as an automobile, avoid measurement error when a partial backflow of the intake air amount is involved, and improve the measurement accuracy of the air flow rate. (EN) Provided is a thermal type air flowmeter which enables backflow detection for improvement and has a high speed. [Structure] At least two heating resistors made of a temperature-dependent resistance film are formed adjacent to each other on an upstream side and a downstream side on a substantially flat plate-shaped substrate arranged in an intake passage, and the two adjacent heat generations are performed. The resistance value per unit area is reduced as the resistors are close to each other. [Effect] It becomes possible to measure the air flow rate in the normal air flow 7 (forward flow) and in the opposite direction (backflow) at high speed, and to detect the flow rate of the intake air flow in both directions with high accuracy and at high speed. Type air flow meter can be provided.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art Conventionally, as an air flow meter provided in an electronically controlled fuel injection device for an internal combustion engine of an automobile or the like, which measures the intake air amount, a hot wire type has become mainstream because it can directly detect the mass air amount. Ori, SAE paper 80046
The one described in 8,830615 has been put to practical use. Further, as an air flow meter that uses a membrane resistor to achieve a high-speed response, the one described in JP-A-60-236029 has been devised.

[0003]

FIG. 9 is a schematic view of JP-A-60-23.
It is a top view of the conventional thermal type air flow meter which aimed at the high-speed response described in 6029 publication. The flow rate of the air flow 7 is increased by increasing the resistance value per unit area of the upstream portion of the film type resistance pattern 31 formed on the substrate 30 to be larger than the resistance value per unit area of the downstream side. are doing.

However, in the above-mentioned prior art, the accuracy is lowered in the case of a pulsating flow with a large backflow, where the pulsation amplitude of the intake air amount is large, such as when the engine with four or less cylinders has a low rotational speed and a heavy load. When the intake valve called backflow at the time of pulsation overlaps, the blowback phenomenon of air returning from the exhaust valve side to the intake valve side with positive pressure as the piston rises is measured with a conventional thermal air flow meter. The signal outputs a positive signal corresponding to the absolute value of the flow velocity regardless of the flow direction of forward flow and reverse flow. Therefore, when the backflow occurs, the signal is as if it were a forward flow, and a signal larger than the true average air flow rate is output. There is a problem that the measurement error at this time reaches 30 to 100%. The above-mentioned prior art does not consider such a problem at the time of backflow.

An object of the present invention is to provide a thermal air flow meter capable of detecting the flow rate of the intake air flow in both directions with high accuracy and high speed.

[0006]

The above object is to provide at least two heat-generating resistors made of a temperature-dependent resistance film on a substantially flat plate-shaped substrate arranged in the intake passage so as to be adjacent to each other on the upstream side and the downstream side. This is achieved by forming the two adjacent heating resistors so that the resistance value per unit area becomes smaller as the two adjacent heating resistors become closer to each other.

[0007]

Operation: At least two heating resistors made of a temperature-dependent resistance film are formed adjacent to each other on the upstream side and the downstream side on a substantially flat substrate arranged in the intake passage. Since the resistance value per unit area becomes smaller as the resistors get closer to each other, when the air flow 7 is normal (forward flow), the forward flow air flow rate is increased by the upstream heat generating resistor having a higher heat dissipation effect. Direction opposite to air flow 7 (backflow)
At times, the backflow air flow rate can be measured at high speed by the downstream heating resistor, and it is possible to provide a thermal air flowmeter capable of detecting the flow rate of the intake air flow in both directions with high accuracy and at high speed.

[0008]

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 5 is a plan view of an embodiment of the thermal air flow meter of the present invention. Reference numeral 1 denotes a heating resistor arranged on the substrate 4 on the upstream side of the air flow 7, 2 is a heating resistor arranged on the downstream side, 3 is a temperature compensation resistor, and 5 is a support for supporting the substrate 4, Reference numeral 10 is a slit, and 6a, 6b, 6c, 6d, 6e and 6f are terminal electrodes for connection with an external circuit. Further, enlarged views of the patterns of the heating resistors 1 and 2 are shown in FIGS. 1, 2 and 3, and enlarged views of the pattern of the temperature compensating resistor 3 are shown in FIG. Here, FIG. 1 shows the resistance pattern of the first embodiment in which the width of the resistance pattern becomes narrower toward both ends of the substrate 4, and the resistance patterns are close to each other and are densely arranged. FIG. 2 shows a resistance pattern of the second embodiment, in which the pattern width is constant and the pattern pitch is arranged smaller toward both ends of the substrate 4. FIG. 3 shows a resistance pattern of the third embodiment, which is arranged such that the pattern pitch is constant and the pattern width of the resistance pattern becomes narrower toward both ends of the substrate 4. In any of the embodiments, the resistance value per unit area is configured to increase as the both ends of the substrate 4 are approached. Further, as can be seen from FIG. 4, the temperature compensating resistor 3 is composed of two temperature compensating resistors 3a and 3b, and the resistance pattern has a resistance value per unit area increasing toward the tip of the substrate 4. In addition, the patterns of the two temperature compensating resistors 3a and 3b are arranged in pairs to be drawn out to have substantially the same shape.

The substrate 4 is made of ceramics such as alumina and has an extremely thin thickness of 0.05 mm to 0.15 mm in order to enhance the response speed. The heating resistors 1 and 2 and the temperature compensating resistor 3 (3a, 3b) are made of a platinum thin film and are made to have a thickness of 0.1 micron to 2 by a method such as sputtering or vapor deposition.
After being collectively deposited on the substrate 4 with a film thickness of micron, it is formed into the shape shown in FIGS. 1, 2, 3 and 4 by a method such as photoetching. Terminal electrodes 6a, 6b, 6c, 6
The lead electrodes for connecting the electrodes d, 6e, 6f and the resistors 1, 2, 3 to the electrode terminals are made of a platinum-silver alloy or the like thicker than the platinum thin film of the resistors 1, 2, 3 in order to lower the electric resistance. A thick film is formed on the platinum thin film by a method such as printing. Also,
Although not shown in the figure, a protective film made of alumina, silicon dioxide, glass or the like is formed on the resistors 1, 2, and 3 to protect the elements. The slit 10 is provided for thermal insulation between the heating resistors 1 and 2 and the temperature compensating resistor 3 (3a, 3b), and is formed by a method such as laser processing. The substrate 4 on which the resistor and the electrode terminal are formed is supported by the support 5 for mechanically supporting the substrate 4 and for connecting the external circuit and the electrode terminal by a wire bond or the like for electrical connection. It

FIG. 6 is a sectional view of an embodiment of the present invention provided in an intake passage to an internal combustion engine. Reference numeral 8 is a body of the main passage of the intake air, 27 is a body of the auxiliary passage, and 9 is an external circuit for the resistor 1,
2, 3 and the support 5 are electrically connected.

FIG. 7 shows an external circuit 9 and resistors 1, 2, 3
It is an electric circuit diagram of (3a, 3b). The operation method of the embodiment of the present invention will be described below. Hot wire drive circuit 11,
Reference numeral 12 is an independent circuit, which is connected to the power supply 17 and outputs separately according to the air flow rate. Heat ray drive circuit 1
1 is a heating resistor 1, a temperature compensation resistor 3a, resistors 18 and 1
The Wheatstone bridge circuit of 9 is configured to adjust the current flowing through the heating resistor 1 by the differential amplifier 20 and the transistor 21 so that the potential difference at the bridge midpoint becomes zero. With this configuration, the resistance value of the heating resistor 1 is controlled to be constant regardless of the air flow rate, 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 1 is the potential at point A in the figure. The same applies to the heating resistor 2 of the heat wire drive circuit 12, and the signal corresponding to the air flow velocity by the heating resistor 2 is the potential at point B in the figure. The heating resistors 1 and 2 are provided in an intake passage of an internal combustion engine of an automobile or the like as shown in FIG. 6, and for example, the heating resistor 1 is provided on the intake upstream side and the heating resistor 2 is provided on the intake downstream side. . The temperature of the heating resistors 1 and 2 is the same as in a normal constant temperature type thermal anemometer so that the difference from the air temperature becomes a constant value regardless of the air velocity.
It is electrically heated by 1 and 12. First, when air flows in the forward direction from the intake upstream side to the downstream side, the heating resistor 1 is cooled more by the air flow than the heating resistor 2. Therefore, the current supplied from the heat wire drive circuit 11 is the heating resistor 1. Is greater than 2. On the other hand, when air flows in the opposite direction from the intake downstream side to the upstream side, cooling by the air flow is greater in the heating resistor 2 than in the previous case, and the current supplied from the heat wire drive circuit 12 is the heating resistor 2. Is greater than 1. Therefore, the direction of the air flow can be detected by the difference in the magnitude of the current supplied to the heating resistors 1 and 2. The equalizer circuits 13 and 14 are
The frequency response of each of the heating resistors 1 and 2 according to the air flow rate is electrically improved, and the direction of the air flow is detected by the voltage comparator 15 based on the difference between the outputs of the equalizer circuits 13 and 14. At the same time, the switch circuit 16 switches the outputs of the equalizer circuits 13 and 14 to output as a flow rate signal with a small backflow error.

Next, the operation will be described in more detail with reference to FIG. Here, all the heat ray signals are converted into the air flow rate and displayed. Generally, the air flow rate has a large pulsation amplitude of the intake air amount when the engine speed of four cylinders or less is low and the load is heavy, and as shown in FIG. 8 (1), a sine wave with a negative air flow rate called backflow. The waveform is close to. This has a pulsation frequency of about 33 Hz when the engine speed is 1000 rpm, for example. Such a phenomenon varies depending on the shape of the combustion chamber of the engine, the shape of the intake and exhaust pipes, the shape of the air cleaner, and the like. When an ideal hot-wire probe with fast response is used for the pulsating flow accompanied by the backflow, a positive signal corresponding to the absolute value of the flow velocity is obtained irrespective of the direction of the forward flow and the backflow as shown in FIG. 8 (2). Is output. In an actual heat ray probe, since a response delay as shown in FIG. 8 (3) occurs, a heat ray signal that does not become zero is output when switching between forward flow and reverse flow. Further, the output A of the heating resistor 1 arranged on the intake upstream side is large during forward flow and small during reverse flow.
On the contrary, the output B of the heating resistor 2 arranged downstream of the intake air is
Large during backflow and small during forward flow. As a result of comparing these two signals by the voltage comparator 15, a high potential level (Hi) indicating forward flow and a low potential level (Low) indicating reverse flow as shown in FIG. 8 (4) are repeated. The hot-wire signal, which has been subjected to backflow correction by performing forward / reverse switching using the direction signal by the switch circuit 16, has a composite waveform with backflow as shown in FIG. However, since the phase shifts with respect to the true air flow rate, and there is a jump in the waveform when the air flow rate is near zero,
If the average air flow rates are compared, an error will occur if they are simply combined using the direction signal. Furthermore, the equalizer circuit 1
By adopting Nos. 3 and 14, the response delay can be electrically recovered and the signal becomes as shown in FIG. 8 (6). The two forward and reverse heat ray signal outputs A2 and B2 that have recovered the response delay are adjusted by the equalizer circuits 13 and 14 so that the phase and the amplitude are close to the true air flow rate, and the true heat flow signal outputs as shown in FIG. A backflow-corrected heat ray signal close to the air flow rate itself can be obtained, and the error in the average air flow rate can be made extremely small.

In the above embodiment, an example in which an equalizer circuit is used to correct the response delay has been shown. However, the air flow can be changed by using the resistance patterns shown in FIGS. 1, 2, 3 and 4. Since the resistance value per unit area becomes high at both ends of the hitting substrate 4 and the air flow rate measurement can be speeded up, even if the equalizer circuit is not necessarily used, it is possible to obtain a highly accurate true value as shown in FIG. 8 (7). A signal close to the air flow rate of is obtained.

In the embodiment shown in FIG. 5, the temperature compensating resistors 3 (3a, 3b) with respect to the heat generating resistors 1 and 2 have a step structure in which they are retracted in the vertical direction of the air flow 7 and slits are provided. Therefore, even when the backflow occurs, the influence of the airflow heated by the heating resistors 1 and 2 does not affect the temperature compensating resistor 3 (3a, 3b), and the airflow rate can be measured with high accuracy. Further, since the heating resistors 1 and 2 and the temperature compensating resistor 3 (3a, 3b) are formed on the substrate 4 in the same process and with the same material and the same film thickness, the heating resistors 1, 2, and Since the temperature coefficients of the electric resistances of the temperature compensating resistors 3 (3a, 3b) are the same, variations in the temperature characteristics of the air flow rate measurement can be reduced.

Further, in this embodiment, the temperature compensating resistor 3 is used.
(3a, 3b) is arranged on the upstream side of the heating resistors 1 and 2, but the temperature compensating resistor 3 (3a, 3b) forms a step with respect to the heating resistors 1 and 2. Even if it is arranged on the downstream side, the effect of the present invention does not change. Further, although an example of the resistance pattern of the temperature compensating resistor 3 is shown in FIG. 4, even if it is configured in the same manner as the example of the heating resistor shown in FIGS. 2 and 3, it is close to the tip of the substrate 4. Accordingly, the resistance value per unit area of the resistance pattern can be increased and the effect of the present invention can be realized.

[0016]

According to the present invention, at least two heating resistors made of a temperature-dependent resistance film are formed adjacent to each other on the upstream side and the downstream side on a substantially flat plate-shaped substrate arranged in the intake passage. Since the resistance value per unit area becomes smaller as the two adjacent heating resistors come close to each other, the upstream side heat generation having a higher heat dissipation effect during the normal air flow 7 (forward flow) The forward flow air flow rate can be measured at high speed by the resistor, and the backward flow air flow rate can be measured at high speed by the downstream heating resistor when the flow direction is opposite to the air flow 7 (reverse flow). It is possible to provide a thermal air flow meter that can be detected by.

[Brief description of drawings]

FIG. 1 is a resistance pattern diagram of a heating resistor element portion according to a first embodiment of the present invention.

FIG. 2 is a resistance pattern diagram of a heating resistor element portion according to a second embodiment of the present invention.

FIG. 3 is a resistance pattern diagram of a heating resistor element portion according to a third embodiment of the present invention.

FIG. 4 is a resistance pattern diagram of a temperature compensation resistor element portion.

FIG. 5 is a plan view of a thermal type air flow meter according to an embodiment of the present invention.

FIG. 6 is a cross-sectional view of a flow rate detection unit of the thermal type air flow meter according to the embodiment of the present invention.

FIG. 7 is a circuit diagram of an embodiment of the present invention.

FIG. 8 is an operation explanatory diagram of the embodiment of the present invention.

FIG. 9 is a plan view of an element portion of a conventional thermal air flow meter.

[Explanation of symbols]

1, 1a, 1b, 1c, 2, 2a, 2b, 2c, 31 ...
Heating resistors, 3, 3a, 3b ... Temperature compensating resistors, 4,
30 ... Substrate, 5 ... Support, 6a, 6b, 6c, 6d, 6
e, 6f ... Terminal electrode, 8, 27 ... Body, 11, 12 ...
Heat ray drive circuit, 13, 14 ... Equalizer circuit, 15, 2
0, 24 ... Differential amplifier, 17 ... Power supply, 18, 19, 2
2, 23 ... Resistors, 21, 25 ... Transistors.

Front page continuation (72) Inventor Izumi Watanabe 2477, Kashima Yatsu, Hitachi, Hitachinaka, Ibaraki Prefecture 3477 Hitachi Automotive Engineers Ring Co., Ltd. (72) Inventor, Tadashi Isono 2477 Kashima, Yatsu, Hitachinaka, Hitachinaka, Ibaraki 3 Hitachi Automotive Engineering Co., Ltd. (72) Inventor Toshihiko Nakato 2477 Kashima Yatsu Kaita, Hitachinaka City, Ibaraki Prefecture 3 Hitachi Automotive Engineering Co., Ltd.

Claims (9)

[Claims] 1. A thermal air flow meter in which at least two heating resistors made of a temperature-dependent resistance film are formed adjacent to each other on an upstream side and a downstream side on a substantially flat substrate arranged in an intake passage. A thermal air flowmeter, wherein the resistance value per unit area decreases as the two adjacent heating resistors approach each other. 2. The thermal air flow meter according to claim 1, wherein the resistance pattern densities of the heating resistors become sparser as they come closer to each other. 3. The thermal type air flow meter according to claim 1, wherein the line widths of the resistance patterns of the heat generating resistors increase as they approach each other. 4. The thermal type air flow meter according to claim 1, wherein the film thicknesses of the heating resistors become thicker as they approach each other. 5. A substantially flat substrate is provided with at least two temperature compensating resistors made of a temperature-dependent resistance film, and one end of the substrate on the side on which the lead-out electrode is formed, which is far from the resistors, is supported by a supporting member. In the thermal air flow meter, the resistor is installed in the fluid to be measured, and the flow rate of the fluid to be measured is detected by detecting the temperature of the fluid to be measured and the amount of heat released when the heating resistor is heated. The resistance patterns of the two temperature compensating resistors are routed as a pair, and the respective portions of the two resistance patterns have substantially the same shape and occupy substantially the same position on the substrate. A thermal air flow meter characterized by. 6. The thermal air flow meter according to claim 5, wherein the two temperature compensating resistors are configured so that the resistance value per unit area increases as the distance from the supporting member increases. 7. The thermal air flow meter according to claim 5, wherein the resistance pattern density of the temperature compensating resistor becomes denser as the distance from the supporting member increases. 8. The thermal air flow meter according to claim 5, wherein the line width of the resistance pattern of the temperature compensating resistor becomes smaller as the distance from the supporting member increases. 9. The thermal air flow meter according to claim 5, wherein the film thickness of the temperature compensating resistor becomes thinner as the distance from the supporting member increases.