JP3053483B2 - 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 an air flow meter having a bypass passage which bypasses a main passage, and is particularly suitable for detecting the amount of intake air of an internal combustion engine. It is suitable for a thermal air flow meter using a body.

[0002]

2. Description of the Related Art Conventionally, as a thermal air flow meter, for example, as disclosed in JP-A-54-134223,
2. Description of the Related Art A flowmeter using a characteristic in which a heat release amount changes according to an intake air amount of an internal combustion engine is known. In this device, a heating resistor is provided in an air passage through which intake air flows, and the amount of intake air is detected from an electric signal corresponding to the air flow rate determined by the relationship between the air flow rate and the heat transfer amount of the heating element.

As another conventional air flow meter for an internal combustion engine, as shown in Japanese Utility Model Laid-Open Publication No. 54-143904, a throttle portion is formed in a bypass passage provided in an intake passage of an internal combustion engine. Which is provided with a heating resistor for measuring the flow rate. There is no detailed description of what shape the throttle section has or what action and effect the throttle section has.

[0004]

However, according to such a conventional thermal air flow meter, the flow rate of a part of the passage cross section is measured by a change in the amount of heat transferred by a small heating resistor, and the overall flow rate is measured. Since the measurement is performed, there is a problem that the measurement is easily affected by the flow from the air cleaner. Specifically, if dirt adheres to the element of the air cleaner and the flow velocity distribution upstream of the air flow meter changes, a measurement error occurs in the air flow meter, or the increase in the ventilation resistance due to the contamination of the element causes the passage portion to increase. If it varies depending on the flow rate, the flow rate fluctuation increases, and the output fluctuation of the air flow meter easily increases.

In general, when an air flow meter is mounted immediately downstream of an air cleaner, the direction of the intake air flow may be bent immediately upstream of the air flow meter. Also causes an error. Furthermore, in order to properly measure the air flow rate over the entire operating range of the internal combustion engine, for example, from a low load range to a high load range, the air flow rate at that time must be accurately determined regardless of the flow rate fluctuation. It is necessary to generate a sensor output signal corresponding to

SUMMARY OF THE INVENTION An object of the present invention is to provide an air flow meter capable of performing accurate flow measurement even when the amount of intake air of an internal combustion engine varies greatly.

[0007]

According to the present invention, there is provided an air flow meter according to the present invention, wherein a housing defining a main passage through which air passes, and an inlet portion for taking in air from the main passage, a shaft. An upstream bypass passage having a uniform passage diameter in the direction, and an outlet formed downstream of the upstream bypass passage, having a passage diameter smaller than the upstream bypass passage diameter, and discharging air to the main passage. A downstream bypass passage communicating with the section, and a flow rate measurement sensor provided in the downstream bypass passage.

[0008]

According to the air flow meter of the present invention, a part of the air which has flowed into the main passage flows into the upstream bypass passage from the inlet, and is returned to the main passage again from the outlet through the downstream bypass passage. Then, a flow rate measurement sensor is provided in the downstream side bypass passage, and measures the flow rate. At this time,
According to the present invention, the passage diameter of the downstream bypass passage is smaller than that of the upstream bypass passage, so that the flow velocity fluctuation in the downstream bypass passage is greatly reduced. For this reason, the flow rate measurement sensor provided in the downstream side bypass passage enables accurate flow rate measurement which is hardly affected by the flow velocity fluctuation of the main passage.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a first embodiment in which the present invention is applied to a thermal flow meter provided in an intake air passage of an internal combustion engine. Air is introduced in the direction of arrow A shown in FIG. The downstream side of the thermal flow meter 100 is connected to a combustion chamber of an internal combustion engine via a throttle valve (not shown).

The thermal flow meter 100 comprises a cylindrical housing 1 forming a main passage 2 and a central member 4 arranged at the center of the main passage 2 of the housing 1. The housing 1 is formed of, for example, a resin material by injection molding or the like. The downstream side of the main passage 2 is formed so that the passage diameter increases. The center member 4 is formed of, for example, a resin material by injection molding or the like, and is held at a center position of the housing 1 by a rib 18.

The upstream portion 5 of the central member 4 has a hollow inside 6 and a cylindrical bypass passage 7 that bypasses the main passage 2 by an inner peripheral surface.
The bypass passage 7 includes an upstream bypass passage 7a and a downstream bypass passage 7b. The upstream bypass passage 7a and the downstream bypass passage 7b are formed so that their diameters are substantially uniform in the axial direction. Upstream bypass passage diameter d ₁
It is formed to have a larger diameter than the downstream-side bypass passage diameter d _2. Accordingly, the area of the bypass passage on the downstream side of the step portion 19 formed between the upstream side bypass passage 7a and the downstream side bypass passage 7b is smaller than the area of the bypass passage on the upstream side of the step portion 19. And the main passage 2 of the housing 1
The passage formed by the rear end portion 9 of the portion 5 on the upstream side of the central member 4 forms a downstream passage narrowing portion C. The flow passage area of the downstream flow passage narrowing portion C is larger than the flow passage area of the upstream flow passage narrowing portion B.

The downstream portion 10 of the central member 4 is formed such that the inside 11 is hollow like the upstream portion 5 and the outer diameter gradually decreases toward the downstream side. The downstream portion 10 holds a flow rate measuring resistor 12 and a temperature compensating resistor 13 disposed in the downstream bypass passage 7b.
3 is electrically connected to a control circuit 14 for electrically controlling the control circuit 3.
The flow rate measuring resistor 12 is heated by the control circuit 14 to a certain temperature difference with respect to the intake air temperature, and detects the flow rate of air flowing in the downstream side bypass passage 7b.

The upstream part 5 and the downstream part 10
A radial passage 15 that is perpendicular to the bypass passage 7 is formed in the entire circumferential direction. Further, between the inner peripheral surface of the rear end 9 of the upstream portion 5 and the outer peripheral surface of the downstream portion 10, an annular outlet passage 16 which is perpendicular to the radial passage 15 is formed. ing. The outlet portion 17 of the outlet passage 16 is opened in a slit shape so as to be parallel to the main passage 2 over substantially the entire periphery except for the rib 18.

Next, the operation of the above embodiment will be described. In FIG. 1, air introduced from the atmosphere is introduced into a main passage 2 in a thermal flow meter 100 through an air cleaner (not shown) as indicated by an arrow A. At this time, since the flow passage area is reduced by the downstream flow passage narrowing portion C, the flow velocity of the air flowing through the main passage 2 at this portion increases, and thereby a negative pressure is generated at the outlet portion 17. Therefore, a flow of air is generated in the bypass passage 7 due to a pressure difference between the inlet portion 8 and the outlet portion 17 of the bypass passage 7.

When the flow velocity fluctuation (turbulence) of the air on the upstream side of the thermal flow meter 100 occurs, when the turbulence is introduced into the inlet portion 8, a part of the flow of the turbulent air is changed to an upstream bypass passage. It is rectified at 7a. Further, the flow velocity fluctuation (turbulence) of the air is reduced by the contraction at the step portion 19. Therefore, even if the air flow from the upstream of the thermal flow meter 100 is turbulent or unbalanced, accurate flow measurement can be performed without being affected by these. Even when the fluctuation of the intake air amount is large, since the configuration is such that an accurate electric output signal corresponding to the intake air amount is generated, there is an advantage that post-processing such as correcting the electric signal becomes unnecessary.

Next, the bypass passage 7 of the thermal flow meter 100
FIG. 2 shows an experimental result in comparison with a comparative example as to how the flow velocity fluctuation of the air flowing through each part is changed. Thermal flow meter of the comparative examples herein, as shown in FIG. 7 has a straight uniform passage diameter d ₃ from the starting 37a to the end 37b of the bypass passage 37, even the step portions 19 shown in the embodiment It is nothing. In the experiment, the flow velocity fluctuation (turbulence) of the air is obtained by measuring the degree of reduction in the flow velocity fluctuation (turbulence) of the air in the bypass passage 7 using a high response hot wire anemometer.

According to the embodiment of the present invention, as shown by the solid line in FIG. 2, it can be seen that the flow velocity fluctuation is greatly reduced downstream of the step portion 19. On the other hand, according to the comparative example, as shown by a dotted line in FIG. Next, using the ratio d ₁ / d ₂ of the upstream side bypass passage diameter d ₁ and the downstream side bypass passage diameter d ₂ of the step portion 19 in the above embodiment as a parameter, this thermal flow meter is mounted on the downstream side of the air cleaner. FIG. 3 shows an experimental result of measuring the sensor output fluctuation in the case of performing the above.

As shown in FIG. 3, when the ratio d ₁ / d ₂ of the upstream bypass passage diameter d ₁ to the downstream bypass passage diameter d ₂ exceeds 1.2, the sensor output fluctuation is greatly reduced. Turned out to be. It has also been found that even if the ratio d ₁ / d ₂ is sufficiently increased, the sensor output fluctuation is not reduced so much. Further, FIG. 4 shows the result of an experiment on how the sensor output fluctuation changes when the flow velocity of the intake air flowing in the thermal flow meter 100 changes.

It will be understood that in the embodiment of the present invention, even when the flow rate is low, the sensor output fluctuation is sufficiently reduced. Thus, according to the above-described embodiment, it has been found that the sensor output fluctuation is relatively small in the entire range from the low flow rate range to the high flow rate range, so that there is an effect that the air flow rate can be accurately measured. On the other hand, in the comparative example, it is understood that the sensor output fluctuation is relatively large when the flow rate is relatively low. In particular, even in a situation in which the operating condition fluctuates remarkably, such as an internal combustion engine mounted on an automobile, there is an effect that an accurate air flow rate measurement can be performed in a wide flow speed range from a low speed to a high speed.

FIG. 5 shows a thermal flow meter according to a second embodiment of the present invention. The second embodiment is an example in which a conical slope 20 is formed between the upstream bypass passage 7a and the downstream bypass passage 7b instead of the step portion 19 according to the first embodiment. In this example, as compared with the comparative example shown in FIG. 7 in which the diameters of the bypass passages are uniform, the flow velocity fluctuation of the air in the downstream bypass passage 7b on the downstream side of the inclined surface 20 is greatly reduced. Therefore, the flow rate measuring resistor 12 and the temperature compensating resistor 13 provided in the downstream side bypass passage 7b can accurately measure the air flow passing through the main passage 2 even if there is a change in the temperature of the intake air or a change in the flow speed. This has the effect of being replaced by a signal.

FIG. 6 shows a thermal flow meter according to a third embodiment of the present invention. The third embodiment is an example in which a smooth bell-mouth-shaped curved surface 30 is formed between the upstream bypass passage 7a and the downstream bypass passage 7b instead of the step portion 19 according to the first embodiment. In this example, as compared with the comparative example shown in FIG. 7 in which the diameters of the bypass passages are uniform, the flow velocity fluctuation of the air in the downstream bypass passage downstream of the curved surface 30 is significantly reduced. Therefore, the flow rate measuring resistor 12 and the temperature compensating resistor 13 provided in the downstream side bypass passage 7b can accurately measure the air flow passing through the main passage 2 even if there is a change in the temperature of the intake air or a change in the flow speed. Can be replaced by a signal.

[0022]

As described above, according to the air flow meter of the present invention, the air flow measurement sensor provided in the bypass passage bypassing the main passage can accurately measure the air flow even if the flow velocity of the air fluctuates upstream. There is an effect that can be performed.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a first embodiment of the present invention.

FIG. 2 is a characteristic diagram showing a flow velocity variation in each part of a bypass passage according to the first embodiment of the present invention.

FIG. 3 is a characteristic diagram showing sensor output fluctuation when the diameter of the upstream bypass passage and the diameter of the downstream bypass passage of the step portion are changed in the first embodiment of the present invention.

FIG. 4 is a characteristic diagram showing a relationship between an air flow rate and a sensor output fluctuation in a first embodiment of the present invention and a conventional comparative example.

FIG. 5 is a sectional view showing a second embodiment of the present invention.

FIG. 6 is a sectional view showing a third embodiment of the present invention.

FIG. 7 is a sectional view showing a comparative example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Housing 2 Main passage 7a Upstream bypass passage 7b Downstream bypass passage 8 Inlet 12 Flow rate measuring resistor (flow rate measuring sensor) 13 Temperature compensation resistor (flow rate measuring sensor) 17 Outlet section 19 Stepped section 100 Thermal flow meter (Air flow meter)

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Rei Nagasaka 1-1-1, Showa-cho, Kariya-shi, Aichi Japan Inside Denso Co., Ltd. (72) Inventor Noboru 1-1-1, Showa-cho, Kariya-shi, Aichi Japan Nihon Denso Co., Ltd. (56) References JP-A-58-6414 (JP, A) JP-A-56-126527 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01F 1/68 F02D 35 / 00

Claims (3)

(57) [Claims] 1. A housing forming a main passage through which air passes, an upstream bypass passage communicating with an inlet portion for taking in air from the main passage, and having an axially uniform passage diameter; and an upstream bypass passage. A downstream bypass passage formed at a downstream side of the pump, having a passage diameter smaller than the upstream bypass passage diameter, and communicating with an outlet for discharging air to the main passage; and a flow rate provided in the downstream bypass passage. An air flow meter comprising a measurement sensor. 2. The air flow meter according to claim 1, wherein a step portion is formed between the upstream bypass passage and the downstream bypass passage. 3. A ratio d ₁ / d _{2 of} an upstream bypass passage diameter d ₁ of the upstream bypass passage to a downstream bypass passage diameter d ₂ of the downstream bypass passage is 1.2 or more. The air flow meter according to claim 1, wherein