JPH01280218A - Hot wire type air flowmeter - Google Patents

Abstract

PURPOSE:To improve the accuracy of detection by providing a by-pass passage adjacently to a main passage and using part of the contraction part of the main passage as the downstream annular blowout part of the by-pass passage. CONSTITUTION:The by-pass passage 3 is provided adjacently to the main passage 2 to smooth a flow of air at the branch part between the main passage 2 and by-pass passage 3. Further, the downstream annular blowout part 9 of the by-pass passage 3 is used in common as the contraction part 7 of the main passage 2 to simplify the passage shape, and the length of the downstream blowout part 9 can be increased, so errors in case of air pulsation are reducible.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a hot wire air flow meter, and more particularly to a hot wire air flow meter for detecting the intake air amount of an internal combustion engine.

[Conventional technology]

Conventional bypass-type hot wire air flowmeters have a bypass passage outside the main passage, which has the disadvantage that the air is turbulent at the branching point and signal noise becomes large. On the other hand, in JP-A No. 61-65053, there is an example in which a flow rate measuring tube is provided in a direction substantially perpendicular to the main passage, and an air intake port and an air outlet are provided in the flow rate measuring tube to provide a bypass passage.

[Problem to be solved by the invention]

The above conventional technology takes into consideration the shape of the flow rate measurement tube in order to solve the problem that the measured value is smaller than the true average air flow rate due to the response delay of the heating resistor when measuring the pulsating air flow rate. This has the disadvantage that the process becomes complicated and the processability and assemblability are poor. Furthermore, there is a restriction on the total length of the bypass, and there is a limit to the reduction of the error.

An object of the present invention is to provide a highly accurate hot wire air flow meter with improved productivity.

[Means to solve the problem]

The above object is achieved by providing a bypass passage within the main passage so as to be adjacent to the main passage, and by making a part of the throttle part of the main passage also serve as a downstream annular blowing part of the bypass passage.

[Effect]

Since the bypass passage is provided within the main passage so as to be adjacent to the main passage, air flows smoothly at the branch portion between the main passage and the bypass passage. Furthermore, by using the downstream annular blowout part of the bypass passage as the throttle part of the main passage, the shape of the passage can be easily changed and the length of the downstream blowout part can be made approximately three times longer than before, reducing errors caused by air pulsation. can.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2. A detection unit 4 for detecting the intake air flow rate is installed in a bypass passage 3 inscribed in the main passage 2 of the body 1, and is composed of a heating resistor 4a and a temperature compensation resistor 4b. Furthermore, the heating resistor 4a and the temperature compensating resistor 4b are connected and fixed to a support pin 5 and connected to a drive circuit section 6.

The heat generating resistor 4a is maintained at a constant temperature by the drive circuit 6, and when the intake air flow rate changes, the amount of heat transfer changes accordingly, and the current of the heat generating resistor 4a also changes according to the principle of constant temperature difference type. Therefore, it is possible to obtain an output voltage corresponding to the intake air flow rate.

On the other hand, the temperature compensation resistor 4b detects the intake air temperature,
Care has been taken to compensate for errors caused by changes in air temperature.

Here, a pipe 3a is provided at the entrance of the bypass passage 3 in order to further reduce turbulence in the intake air.

Further, a lid 8 is adhesively fixed to the constricted portion 7 of the body 1 constituting the main passage 2 to constitute a downstream annular blow-off portion 9. Therefore, for example, when the body 1 is made of plastic, integral molding is easy, and processability and assemblability are greatly improved.

Furthermore, since the outlet direction of the downstream annular blow-off section can be provided in the same direction as the air flow, there is less turbulence in the air at the outlet section, and signal noise can be reduced as shown in FIG.

In addition, since the inlet and outlet parts of the body 1 are on the same central axis,
Easy to install in the car.

〔Effect of the invention〕

According to the present invention, it is possible to provide a highly accurate hot wire air flow meter with improved productivity.

[Brief explanation of the drawing]

FIG. 1 is a top view showing one embodiment of the present invention, FIG. 2 is a cross-sectional structural view thereof, and FIG. 3 is a diagram showing the signal S/N ratio. 2... Main passage, 3... Bypass passage, 4a... Heat generating resistor, 4b... Temperature compensation resistor, 6... Drive circuit, 7... Throttle section, 9... Downstream Annular blowout part. Is Figure 1 Figure 2

Claims (1)

[Claims] 1. Consisting of a main passage and a bypass passage, a heating resistor and a temperature compensation resistor provided in the bypass passage, and a heating current of the heating resistor as a signal corresponding to the air flow rate. A hot wire air flowmeter comprising a drive circuit for taking out the air, characterized in that the centers of the inner and outer diameters of the main passage are the same, and a part of the throttle part of the main passage also serves as a downstream annular blowout part of the bypass passage. Hot wire air flow meter. 2. The hot wire air flow meter according to item 1, wherein the main passage and the bypass passage are integrally formed of a plastic material. 3. The hot-wire air flow meter according to item 2, wherein the downstream annular blow-off section is comprised of a body and a lid that constitute a main passage.