JPS59619A - Thermal detector for engine suction air flow rate - Google Patents

Abstract

PURPOSE:To improve the precision of flow rate measurement and to simplify a chamber shape, by providing straightening elements in a cylindrical center chamber formed of an air cleaner element and arranging thermo-sensitive elements in a by-pass air passage provided separately from a main air passage. CONSTITUTION:Air from an intake passes through an inflow part 19, the window hole 18 of an outer circumferential edge, and a gap part 14 and then passes through the air cleaner element 12 uniformly in an inward radial direction to enter the cylindrical center chamer 16, wherein the air is straightened axially by straightening elements in a cylindrical guide cylinder 10 and passed through an air buffer chamber 7, main air passage part 1, and venturi 2. The air buffer chamber 7 is coupled directly with the front end of the air passage part 1, so dust is carried mainly by the main air flow and almost no dust enters the by- pass passage 3 provided aside. Therefore, no dust sticks to neither thermosensitive resistor 4 nor 5 and high-precision measurement is performed. The straightening elements 11 are arranged in the extra space, so the shape of the chamber is simplified.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for measuring intake air flow rate using a thermal flow meter in an electronically controlled fuel injection system for an internal combustion engine, and particularly to a structure as an air cleaner.

Among the intake air flow rate detection methods for electronically controlled fuel injection systems mentioned above, the thermal method applies the phenomenon in which a temperature-sensitive resistor conducts heat in the intake air flow, and has the advantage of being able to measure the mass flow rate of air. If the temperature resistor is made smaller in size, its response becomes faster, reducing power consumption and improving mechanical strength. Measuring air flow with such a thermal flowmeter reads the mass flow rate by detecting the average flow velocity, so in order to obtain high accuracy over the entire flow rate range to be detected, it is necessary to ensure that the flow velocity and density in the passage are uniform. It is necessary for the air flow to proceed axially symmetrically along the axial direction of the passage. However, in the case of the above-mentioned conventional methods, such as the movable vane method and the Karman vortex method, the movement of vanes and other movable bodies due to the full flow rate is used, so there is no need to strictly restrict or correct the flow as described above in the case of the thermal method. I don't even ask for it.

Therefore, air cleaner configurations designed for non-thermal systems are generally not necessarily suitable for localized, static flow rate sensing methods such as thermal systems. Additionally, if a conventional flow rate detection type passage configuration or air cleaner other than the thermal type described above is applied to a thermal type flowmeter, there is the problem that dust can easily adhere to the temperature-sensitive resistor and cause the characteristics to change over time. . Furthermore, in the case of a thermal flowmeter, a major problem is that the curvature of the air passage, the cross-sectional area, the unevenness of the inner wall surface, uneven dirt due to dust on the air cleaner element, etc. tend to cause changes in characteristics over time.

The present invention aims to solve the conventional problems listed above regarding an intake air flow rate detection device using a thermal flowmeter, and has fc features as described in the claims section above. It is something.

FIG. 1 is a longitudinal sectional front view showing an embodiment of the apparatus of the present invention having the above characteristics. In the figure, 1 is the main air passage, 2
is a venturi, 3 is a bypass air passage that bypasses the main air passage section 1 and opens to the inner wall surface of the narrowest part of the venturi 2, and 4 and 5 are temperature-sensitive resistors of a thermal flow meter installed in the bypass passage 3. 6 is a drive circuit module for both the resistors 4 and 5; 7 is a flat cylindrical air buffer chamber installed concentrically on the upstream side of the main air passage section 1; 8 is a peripheral edge of the air buffer chamber 7; 9 is an air cleaner structure support plate attached to the upstream side of the air buffer chamber 7; 10 is a cylindrical support plate 5 that is concentric with the main air passage 1 and the air buffer chamber 7; A guide tube formed through the
11 is an air flow rectifying element such as a honeycomb core or mesh installed in the guide tube 10; 12 is an air cleaner element fixed on the support plate 9 surrounding the guide tube 10 concentrically at appropriate intervals; Reference numeral 13 denotes an outer wall that concentrically surrounds the outer periphery of the air cleaner element 12 via the spacer 14 and is supported by the support plate 9. Reference numeral 15 denotes an upstream block of the cylindrical central chamber 16 surrounded by the air cleaner element 12. A plate 17 is an upstream blocking plate 1 of the spacer 14.
8 is the same! 1IAl! l? Window hole provided in plate 17, 1
Reference numeral 9 designates an external air inflow port formed between the shielding plates 15, 17 and the cover plate 20, and 21 designates an external air intake port.

In the case of a bypass type air flow meter as in this embodiment, the air buffer chamber 7 is provided to take in the bypass flow sucked from the bypass port 8 into static pressure by creating a venturi negative pressure. It is something. In contrast, in the embodiment shown in FIG. 2, instead of providing the air buffer chamber 7 as described above, the upstream side of the main air passage section 1 is directly connected to the downstream side of the guide tube 10 and surrounded by an air cleaner element 12. The case is shown in which it is installed in the central chamber 16.

As is clear from the embodiments described above, in the device of the present invention, the air flowing into the inflow part 19 from the intake port 21 passes through the outer peripheral edge through hole 18 into the spacer part 1 surrounded by the cylindrical outer wall 13.
4, the air passes through the air cleaner element 12 uniformly in an inward radial direction, enters the cylindrical central chamber 16, and is further rectified in the axial direction by the rectifying element 11 in the cylindrical guide tube 10. It passes through the main air passage section 1 and the venturi 2. That is, the air passing through the air cleaning structure always flows in an axially symmetrical and uniform distribution, so there is no possibility of dirt, and as a result, changes in characteristics over time due to drifting can be reduced.

Further, by arranging the guide tube 10 and the rectifying element 11 such as a honeycomb coil or mesh inside the central chamber 16, a rectifying effect on the air flow and a buffering effect against the drift can be obtained.

Further, as described above, since the air buffer chamber 7 is directly connected to the front end of the main air passage section 1, the dust is mainly carried by the flow toward the main air passage section 1 due to inertia, and hardly flows into the bypass air passage 3. Therefore, the adhesion of dust to the temperature-sensitive resistor 4.5 is reduced accordingly, and this, together with the effect of preventing uneven distribution of dirt due to the axial symmetry of the air flow path mentioned above, reduces changes in characteristics over time due to uneven flow. , the desired high precision required for electronic control of the engine can be obtained.

In addition to the above-mentioned effect of improving performance accuracy, the present invention also provides the following structural advantages.

That is, the rectifying element 11 is replaced by the air cleaner element 1.
2, the cylindrical central chamber 16 formed by the cylindrical central chamber 16 is interposed in the extra space, which saves space. That is, by providing the bypass passage 8 by utilizing the space farthest from the main air flow, the chamber shape can be simplified to make the bypass passage 3 a static pressure intake type that has a large inertia and is difficult for dust to pass through. It is.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional front view showing one embodiment of the device of the present invention, and FIG.
The figure is a longitudinal sectional front view showing another embodiment.

Claims (1)

[Scope of Claims] 1. In the air intake path to the engine, a rectifying guide tube installed in a concentric cylindrical shape on the upstream side of the main air passage venturi section entrance, and a concentric cylindrical rectifying guide tube installed at intervals between the rectifying guide tubes. In the respective axial center directions of an air cleaner element that surrounds the air cleaner element, an outer wall that surrounds the outer periphery of the air cleaner element in a concentric cylindrical shape through a gap, and an external air inlet that has a communication part with the gap. An engine intake air flow rate thermal type detection device, characterized in that the engine intake air flow rate thermal detection device is formed to substantially coincide with the direction of the center of movement of the intake air flow in the venturi portion of the main air passage. 2. A patent characterized in that a heat-sensitive element of a thermal flowmeter is installed in a bypass air passage formed between the main air passage venturi entrance and a buffer chamber provided between the rectification guide cylinder. An engine intake air flow rate thermal detection device according to claim 1.