JPH01201117A - Hot-wire type air flowmeter - Google Patents

Abstract

PURPOSE:To increase the output response of the air flowmeter by arranging a heat generating resistance body for air flow rate measurement in a by-pass passage slantingly to an air flow. CONSTITUTION:The heat generating resistance body 5 is provided slantingly to the air flow in the by-pass passage 3, so the length of the resistance body 5 is increased without varying the diameter of the passage 3. A support body is formed circularly, the heat generating resistance body 5 and a resistance body 6 for temperature compensation are arranged above and blow it in parallel at 45 deg. to the air flow, and then the length of the resistance body is longest and increased by about 1.4 time. Variation of the temperature distribution of the heat generating resistance body to the air flow rate is reduced by increasing the length l of the heat generating resistance body, the delay of the output response of the resistance body 5 due to the temperature distribution variation is reduced, and consequently the output response of the air flowmeter is increased to improve the performance.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a hot wire air flowmeter.

[Conventional technology]

2. Description of the Related Art Conventionally, in the field of internal combustion engines, for example, hot wire air flowmeters have been used as a means for measuring the amount of intake air. There are various types of hot wire air flowmeters of this type. Among them, for example, JP-A-59-19062
As disclosed in Publication No. 4, etc., a bypass passage is provided in a part of the main passage of the intake system, and a heating resistor (hot wire) for measuring air flow rate and a temperature-sensitive resistor for temperature compensation are arranged in this bypass passage. In the above system, the heat generating resistor is provided in the bypass having a small passage diameter, so compared to a system in which the heat generating resistor is provided in the intake passage itself, the resistor and thus the hot wire airflow meter can be made smaller. Further, by devising the bypass passage structure, it is possible to prevent dust from adhering to the resistor.

[Problem to be solved by the invention]

This type of hot wire air flow meter maintains a predetermined temperature in the heating resistor even if the degree of heat transfer of the heating resistor to the airflow, and hence the resistance value, changes due to changes in the intake air flow (bypass air amount). The purpose is to flow an output current and measure the amount of air based on the output state of this current. Therefore, speeding up the output response of the heating resistor in response to changes in the amount of air determines the performance of the hot wire air flowmeter.Especially in engine control, etc., speeding up the output response of the heating resistor in response to changes in the amount of intake air There is a strong demand for improved responsiveness.

By the way, this type of heating resistor has the following characteristics. This will be explained based on FIGS. 5 and 6.

FIG. 5 shows a heating resistor 5 (the heating resistor is a heat-resistant insulating cylinder made of alumina or the like wrapped around a hot wire such as platinum wire).

Alternatively, the surface temperature distribution of the platinum film deposited and the air flow rate (
It expresses the relationship with the flux). As shown in the figure, the higher the flow rate of air passing through the heating resistor, the greater the change in temperature distribution on the surface of the heating resistor.

In addition, Figure 6 shows the air flow meter (
It shows the output characteristics of the heating resistor 5), where the solid line shows the state of change in air flow rate and the dotted line shows the output signal of the air flow meter. Therefore, depending on the air flow rate, the heating resistor 5
When the surface temperature distribution changes, the response of the air flow meter output signal (hereinafter referred to as H/W signal) when the air flow rate changes is delayed as shown by the dotted line in FIG. Part A of the delay in the H/W signal is determined by the heat capacity of the heating resistor and the circuit constant, and the delay in part B is the time required for the temperature distribution to move from the solid line to the broken line in FIG.

Therefore, the delay in section B becomes smaller if the change in temperature distribution shown in FIG. 5 is smaller. Here, the change in temperature distribution is represented by a gradient temperature region Qc in FIG. Qc is calculated as equation (1).

2\, where d is the diameter of the heating resistor probe (H/W probe), λ is the thermal conductivity of the H/W probe, and h is the heat transfer function between the H/W probe and the air flow.

Furthermore, since the above-mentioned Qc is smaller than the length Q of the H/W probe, the change in temperature distribution is small, and the delay in FIG. 5 is small.

Therefore, if we express this in the formula, becomes.

Considering the above, in order to improve the output response of a hot wire air flow meter, it is desirable to make the length Q of the heating resistor as long as possible. Since the body is disposed perpendicular to the air flow in the bypass passage, its length is limited by the diameter of the bypass passage, the position of the support pin, etc.

The present invention has been made in view of the above points, and its purpose is to increase the total length of the heat generating resistor without enlarging the bypass passage, thereby improving output response and performance. The purpose of the present invention is to provide a hot wire air flow meter.

[Means to solve the problem]

The above purpose is to provide an air flow N disposed inside the bypass passage in this type of bypass passage type hot wire air flow meter.
This is achieved by arranging the heating resistor for measurement at an angle with respect to the air flow in the bypass passage.

[Effect]

As described above, by changing the arrangement of the heat generating resistor from the conventional arrangement perpendicular to the airflow to the oblique arrangement, the length of the heat generating resistor can be increased without changing the diameter of the bypass passage. As shown in equation (2) above, by increasing the length Q of the heating resistor, it is possible to reduce the change in temperature distribution with respect to the air flow rate. The delay in the output response characteristic can be reduced, and as a result, the output response of the air flow meter can be improved.

〔Example〕

An embodiment of the present invention will be described based on FIGS. 1 and 2.

FIG. 1 is a longitudinal sectional view showing an embodiment of the present invention, and FIG. 2 is a partial sectional view of a bypass passage viewed from direction A in FIG.

In FIG. 1, a body 1 constitutes a part of an intake system of an internal combustion engine, and inside the body 1, a main intake passage 2 and a bypass passage 3 are formed.

Reference numeral 4 denotes a support body for supporting the heat generating resistor 5 and the temperature sensitive resistor 6 for temperature compensation, and pins 7a, 7b and 8a, 8b for supporting the resistors are attached to the support body 4. The support body 4 in this embodiment has a perfectly circular cylindrical shape, and is fitted into the wall of the body 1 at a position where the bypass passage 3 is located. Also,
As shown in FIG. 2, pins 7a and 7b form a pair, and pin 8
a.

It is paired with 8b. 7a, 7 of each pair of pins
b, 8a and 8b each face the inside of the bypass passage 3 in a height-shifted arrangement structure, and the heating resistor 5 is supported in an oblique arrangement with respect to the air flow via pins 7a and 7b, and The temperature compensating resistor 6 is also supported by the pins 8a and 8b in an oblique arrangement with respect to the air flow.

The heat generating resistor 5 is made of, for example, a heat-resistant insulating tube made of alumina wrapped around a platinum wire or a platinum film deposited thereon. The heating resistor 5 is combined with the temperature compensating resistor 6 and other resistance elements to form a bridge, and is connected to the drive circuit 9.

The drive circuit 9 supplies a current to keep the heat generating resistor 6 at a predetermined heat generation temperature, and when the intake air flow rate changes, the amount of heat transfer, and therefore the resistance value and output current value change accordingly. By extracting this change in output current as a signal (output voltage), the intake air flow rate can be measured. The temperature compensation resistor 6 detects the intake air temperature and compensates for a mass error in the intake air flow rate due to a change in the air temperature.

However, in this embodiment, the heating resistor 5 is connected to the bypass passage 3.
Since it is set to be placed diagonally with respect to the airflow,
The length of the heating resistor 5 can be made longer than that of a conventional heating resistor without changing the diameter of the bypass passage. Specifically, when the support body 4 is made into a perfect circular shape and the heating resistor 5 and the temperature compensation resistor 6 are arranged vertically and parallel to each other on the surface of the support body, it is possible to The length of the resistor can be made the longest when the resistors 5 and 6 are arranged diagonally at 45 degrees with respect to the air flow. In the case of this 45° diagonal arrangement, the conventional resistor arrangement method as shown in Fig. 7 (Fig. 7 shows that the heating resistor 5 and the temperature compensation resistor 6 are placed in the bypass passage 3 at right angles to the airflow) These resistors 5 and 6 are placed on the surface of the support 4 using pins 7a.

7b, 8a, 8b), the length of the resistors 5 and 6 can be increased by about 1.4 times without changing the bypass diameter.

Therefore, according to this embodiment, by increasing the length Q of the heating resistor, the change in the temperature distribution of the heating resistor with respect to the air flow rate can be reduced, as already mentioned in the "effects" section of the invention. Furthermore, the delay in the output response characteristics of the heating resistor 5 due to changes in temperature distribution can be reduced, and as a result, the output response of the air flowmeter can be improved.

The dotted line in FIG. 4 indicates the output response of the air flow meter by changing the arrangement angle θ of the heating resistor 5 of this example with respect to the air flow and changing the length of the heating resistor 5 that can be taken at that time. The solid line represents the sensitivity characteristic of the heating resistor at that time, and the characteristic value is expressed based on the conventional example (current state) of FIG. 7 as 100%. However, the fourth
As shown in the characteristic diagram in the figure, the output responsiveness is
The length of the resistor is proportional to its characteristic value, and the output response reaches its peak value at an angle θ (approximately 45 degrees) at which the length of the resistor can reach its maximum flame. As shown in the shaded area in Fig. 4, when the angle θ is in the range from just before 45° to 45°, the output response of the heating resistor is significantly improved, and the sensitivity characteristics of the resistor are not affected. Therefore, it is most preferable to set the resistor arrangement angle within this shaded area.

Furthermore, according to this embodiment, the length of the resistor can be increased without increasing the diameter of the bypass passage 3, so the performance of the air flow meter can be improved without increasing the size of the entire device.

In the above embodiment, the heating resistor 5 and the temperature compensating resistor 6 are arranged diagonally in parallel, but the resistors 5 and 6 are crossed on the surface of the support 4 as shown in FIG. Even in the diagonal arrangement state, the same effect as described above on the actual flow side can be achieved.

Further, although the support body 4 is made into a perfect circle, it may be made into an ellipse or other various shapes instead.

〔Effect of the invention〕

As described above, according to the present invention, the total length of the heating resistor can be increased without enlarging the bypass passage, and as a result, the output response and performance of the hot wire air flow meter can be improved.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing a first embodiment of the present invention, FIG. 2 is a partial sectional view of FIG. 1 viewed from direction A, and FIG. 3 is a partial sectional view showing a second embodiment of the present invention. Figure 4 is a diagram showing the output response characteristics and sensitivity characteristics with respect to the arrangement angle and length of the heat generating resistor in the first embodiment, Figure 5 is a surface temperature distribution characteristic diagram of the heat generating resistor, and Figure 6 is the heat generation characteristic. FIG. 7 is a partial cross-sectional view showing a conventional example of a hot wire air flowmeter. 1...Body, 2...Intake system main passage, 3...Bypass passage Figure 1 4. Illustration rate 5 figures

Claims (1)

[Claims] 1. A bypass passage is provided in a part of the main passage of the intake system, and a heating resistor for measuring air flow rate and a temperature-sensitive resistor for temperature compensation are arranged inside this bypass passage. What is claimed is: 1. A hot wire air flow meter, characterized in that the heating resistor is arranged obliquely with respect to the air flow in the bypass passage. 2. The hot wire air flow meter according to claim 1, wherein the heating resistor is arranged at an angle of about 45 degrees with respect to the air flow in the bypass passage.