JPS61169721A - Mass air flow rate measuring apparatus - Google Patents

Abstract

PURPOSE:To obtain a correct measuring signal corresponding to a mass flow rate eliminating changes in the air flow velocity at a vortex generation mechanism part, by variably controlling the bypass air path area with a weir mechanism to make up for the area of a main air path corresponding to changes in the representative dimensions with the movement of a mobile vortex creating body. CONSTITUTION:The representative dimensions (d) of a vortex generation mechanism 18 are variably controlled according to the pressure state of measuring air flow with the movement of a mobile vortex creasing body 17. A guide hole 25 is formed on a partition 13 corresponding to the piercing part of a connecting rod 21 and a weir 26 is so set to be inserted into the guide hole 25. The weir 26 is mounted integral on the connecting rod 21 and when the mobile vortex creating body 17 is driven with a bellows 23, it is driven together with the vortex creator 17 to control the area of a bypass air path 15 variably.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention measures the intake air flow rate of, for example, an internal combustion engine, and improves the Karman vortex type flowmeter to measure the intake air mass flow rate. The present invention relates to a mass air flow rate measuring device.

[Background Art] A Karman vortex type flow rate measurement means generates a vortex due to turbulence in the airflow using a columnar vortex generator, that is, a vortex generator set in the airflow. It is constructed by taking advantage of the fact that the frequency of occurrence is proportional to the flow velocity of the air. That is, the frequency of the Karman vortex generated on the downstream side of the vortex forming body is detected by, for example, a hot wire type vortex detection sensor,
The flow velocity of the air is measured using this detection frequency.

This kind of Karman vortex type flow measuring device has a small resistance that obstructs the flow of air, so even if it is installed in the intake pipe of an internal combustion engine, it will not affect the flow of intake air. It can be used effectively without giving up.

In such a Karman vortex type flow rate measuring device, the frequency of the generated vortex is proportional to the flow velocity of the air, and therefore the Karman vortex frequency corresponds to the volumetric flow rate of the air.

However, the air flow rate signal required for controlling a 1f internal combustion engine is of quality III related to the combustion operation of fuel, and the output of such a Karman vortex flowmeter cannot be used as is.

In consideration of these points, a Karman vortex type air flow rate measuring device has been proposed that can directly measure and output the mass flow rate of an air flow. For example, in Japanese Patent Application No. 59-112301 filed by the present applicant, the representative dimensions of the surface of the vortex-forming body facing the air flow are changed in accordance with air conditions such as air pressure, and the state of air density is changed. is reflected on the measured output, so that a Karman vortex frequency is generated corresponding to the mass air flow rate. in particular,
A movable vortex-forming body is set together with a fixed vortex-forming body for the duct where intake air is set to be supplied, and the movable vortex-forming body is driven by a bellows, so that the representative dimensions of the vortex-forming body can be variably controlled. . In this case, the inside of the bellows is filled with gas at a predetermined pressure, and the bellows is set within the air pressure environment in the duct, and the bellows is displaced in response to the air pressure in the duct. The movable vortex forming body is driven so that its representative dimensions can be changed in accordance with the air density state.

However, in a mass air flow measuring device constructed in this way, when the movable vortex-forming body constituting the vortex-generating mechanism is driven in accordance with the air pressure in the duct, the representative area changes. As a result, the air passage area of the duct also changes. Therefore, in response to this change in passage area,
The flow velocity of the air also changes, and the relationship between the mass flow rate of the air passing through the duct and the Karman vortex frequency essentially breaks down. Fluctuations in measurement output corresponding to changes in air flow velocity due to changes in passage area are:
It would be sufficient to correct the correction according to the amount of movement of the movable vortex-forming body, but in order to perform this electronically, a more complicated movement amount detection mechanism and arithmetic circuit are required. , which complicates the configuration of this measuring device.

[Problems to be solved by the invention] This invention has been made in view of the above points, and a Karman vortex generation mechanism is constructed by a combination of a fixed vortex-forming body and a movable vortex-forming body, and it corresponds to the mass flow rate. In the case where the vortex frequency is set based on the vortex frequency, even if the representative area of the vortex generation mechanism changes due to the movement of the movable vortex forming body, and the area of the air flow passage changes, the vortex generation It is an object of the present invention to provide a mass air flow measuring device that prevents the air flow velocity of a mechanical part from being changed and that allows an accurate measurement signal corresponding to the mass flow rate to be obtained.

[Means for Solving the Problems] That is, in the mass air flow measuring device according to the present invention, the main air passage in which the vortex generating mechanism consisting of the fixed vortex forming body and the movable vortex forming body is set is Bypass air passages are formed in parallel, and a weir mechanism is set for variably controlling the area of the bypass air passages. This weir mechanism is simultaneously driven by the movement control mechanism of the movable vortex-forming body, and when the representative dimensions of the vortex-generating mechanism change due to the movement of the movable vortex-forming body and the area of the main air passage changes, the bypass air passage The area is variably controlled to compensate for changes in the area of the main air passage, thereby preventing changes in the air flow velocity in the vortex generating mechanism.

[Operation] In the mass air flow measuring device configured as described above, the movable vortex forming body is driven according to the pressure state of the amount of air flowing in the duct, and faces the air flow of the Karman vortex generating mechanism. The representative dimensions are variably controlled to generate a Karman vortex frequency corresponding to the mass air flow rate flowing within the duct. When the representative dimensions of such a temperature generating mechanism are variably controlled, the area of the bypass air passage is also variably controlled according to the amount of change in the above representative dimension, and the area of the main air passage where the vortex generating mechanism exists The passage area control is performed so as to compensate for the variation in the bypass air passage. In other words, the total value of the area of the main air passage where the vortex generation mechanism exists and the area of the bypass air passage is controlled so that it always remains constant, and therefore the representative dimensions of the vortex generation mechanism change and the area of the main air passage Even if the area of the air passage changes, the flow velocity of the air flowing inside the duct is assumed to be constant, and the state of the Karman vortex frequency is always set and controlled to correspond to the mass flow rate. It is something that

[Example〕 Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

Fig. 1 shows its configuration. Although the duct 11 is not particularly shown in the figure, it is connected to the intake pipe of the internal combustion engine, and intake air flowing into the intake pipe is supplied and passed therethrough. ing. A honeycomb rectifying grid 12 is provided at the entrance of the duct 11 so that the airflow flowing through the duct 11 is rectified. The interior of this duct 11 is divided by a partition plate 13 into a main air passage 14 and a bypass air passage 15 through which measurement operations are performed.

For the main air passage 14 of the duct 11, the duct 1
A fixed vortex-forming body 16 is set which extends in a columnar manner across 1. This fixed vortex forming body 16 has a groove formed along its longitudinal direction, and a columnar movable vortex forming body 11 is fitted and set in this groove portion, and this movable vortex forming body 11 is installed in the duct. It is in a state where it can move freely in the direction across the airflow of 11. The fixed vortex forming body 16 and the movable vortex forming body 11 constitute a Karman vortex generating mechanism 18 in which the representative dimension d facing the airflow is variably controlled by the movement of the movable vortex forming body 17. It is something. That is, the Karman vortex street 19 is generated on the downstream side of the vortex generating mechanism 18 by the airflow flowing through the main air passage 14 of the duct 11 . The generation state of this vortex row 19 is detected by a vortex detection sensor 20, for example, a hot wire type, which is attached to the downstream side surface of the fixed vortex forming body 16.

The movable vortex-forming body 17 is driven by a connecting rod 21, which passes through the partition plate 13 and the duct 11, is taken out, and is formed on the outside of the duct 11. It is coupled to a bellows 23 within the air chamber 22. Here, the air v22 is communicated with the inside of the duct 11 through the opening 24, and the inside of this air chamber 22 is set to the same state as the air pressure inside the duct 11. Further, gas is sealed inside the bellows 23, so that the bellows 23 is sealed with gas.
3 is controlled to expand and contract and is displaced in response to the pressure state of the air flow flowing through the duct 11, and this displacement state is transmitted to the movable vortex forming body 11 via the connecting rod 21. That is, by moving the vortex forming body 11, the representative dimension d of the vortex generating mechanism 18 is variably controlled in accordance with the pressure state of the measured air flow.

A guide hole 25 is formed in the partition plate 13 in correspondence with the penetrating portion of the connecting rod 21, and a weir 26 is set to be inserted into the guide hole 25. This weir 26 is integrally attached to the connecting rod 21, and when the movable vortex-forming body 17 is driven by the bellows 23, it is driven integrally with this vortex-forming body 11,
The area of the bypass air passage 15 is variably controlled.

That is, when the movable vortex forming body 17 is driven in a direction that reduces the representative dimension d, that is, when it is moved downward in the figure, the weir 26 enters into the bypass air passage 15 by the same amount as the amount of movement. will be moved to Therefore, although the area of the main air passage 14 increases due to the movement of the movable vortex forming body 17, the area of the bypass air passage 15 is reduced by an area equal to the increased area by the weir 26. . That is, the total area of the duct 11 through which air passes is always set to a constant state even if the movable vortex-forming body 17 is controlled to move.

The frequency f of the Karman vortex street generated by the Karman vortex generating mechanism 18 is expressed as a function of the flow velocity V of the air flow and the representative dimension d of the vortex forming body, as shown in the following equation.

f-st (V/d) (St is the Strouhal number) If there is no structure corresponding to the weir 26 as in the above embodiment, the movable vortex-forming body 17 moves and the representative dimension is d
When V changes, the area of the duct 11 changes due to this change in the representative dimension, and the air flow velocity V of the duct 11 changes at the same time.

Therefore, a state is created in which the rate of change of the Karman vortex frequency with respect to the quality flow rate decreases.

The relationship between the Karman vortex frequency f and the representative dimension d of the vortex generating mechanism 18 is expected to be as shown by the solid line in FIG. When the air velocity changes and the air flow velocity changes, the relationship between the Karman vortex frequency f and the representative dimension d becomes as shown by the broken line in FIG. Therefore, the representative dimension control range of the movable vortex forming body 17 in a state corresponding to the air density for converting the volumetric flow rate into a quality improving device is subject to limitations.

However, if configured as shown in the above embodiment, even if the representative dimension d of the vortex generating mechanism 18 changes and the area of the main air passage 14 changes, the bypass air passage 10 can compensate for this change.
5 changes, and the total flow path area remains constant. Therefore, even if the representative dimension d changes, the air flow velocity around the vortex generating mechanism 18 is always kept constant, and therefore the relationship between the representative dimension d and the generated Karman vortex frequency f is This is the state shown by the solid line in the figure.

Here, regarding the size of the weir 26, the minimum movable vortex forming body 1
requires a width equal to the variable amount by 7. However, if the size of the weir 26 is set too large, the entire measuring device will become undesirably large. Therefore, it is preferable to set the weir 26 to be slightly larger than the variable amount of the vortex forming body 17.

[Effects of the Invention] As described above, in the mass air flow II measuring device according to the present invention, the mass flow rate of the air flow flowing through the duct can be measured and detected by observing the Karman vortex frequency. In addition, even if it is assumed that the representative dimensions of the vortex generating mechanism are variably controlled during this measurement operation and the air flow velocity changes, the actual air flow velocity in the vortex generating mechanism may vary depending on the change in the representative dimensions. Therefore, the mass flow rate is always measured with high accuracy.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram illustrating a quality air flow rate measuring device according to an embodiment of the present invention, and FIG. 2 is a diagram illustrating the relationship between representative dimensions of the vortex generating mechanism and generated vortex frequency in the above-mentioned measuring device. This is a diagram. DESCRIPTION OF SYMBOLS 11... Duct, 13... Partition plate, 14... Main air passage, 15... Bypass air passage, 16... Fixed swirl body, 17... Movable swirl body, 18...・Vortex generation mechanism, 19... Karman vortex street, 23... Bellows, 2
6...Weir. Applicant's representative Patent attorney Takehiko Suzue (Figure 1 d) - Procedural amendment (method) 16 Indication of case Patent application No. 1984-008445 2 Name of invention Mass air lit measuring device 36 Person making amendment Relationship to the case Patent applicant (426) Nippondenso Co., Ltd. 4, Agent 17 Mori Building 7, 1-26-5 Toranomon, Minato-ku, Tokyo;
Contents of the amendment (1) In the third line of page 1 of the specification attached to the application, the phrase "mass air flow rate measuring device" is corrected to "mass air flow rate measuring device."

Claims (1)

[Claims] A duct in which a flow of measurement air is set; a fixed vortex-forming body set in the duct so as to extend in the direction of the diameter of the duct; and a combination set in the fixed vortex-forming body. a movable vortex-forming body set to be movable in a direction perpendicular to the direction of the air flow, and a main airflow passage of a vortex-generating mechanism portion consisting of the fixed and movable vortex-forming bodies in the duct in parallel with each other. Means for forming a bypass air passage and the movable vortex-forming body are driven in accordance with the pressure state of the air flow flowing in the duct, and representative dimensions of the vortex-generating mechanism are set in combination with a fixed vortex-forming body. and a weir mechanism that is driven together with the means for driving the movable vortex-forming body and variably controls the area of the bypass air passage, and is adapted to respond to changes in representative dimensions due to movement of the movable vortex-forming body. A mass air flow measuring device characterized in that the area of the bypass air passage is variably controlled by the weir mechanism so as to compensate for the area of the main air passage.