JPS61164115A - Karman's vortex street type air flow rate measuring instrument - Google Patents

Abstract

PURPOSE:To accurately measure an air flow rate in an air flow speed range from low to high, by forming the surface section of a vortex-making body to be set in a duct facing the air flow to have a semiconductor cross section. CONSTITUTION:A pillar-like vortex-making body 13 is fitted and set in a duct 11 in a condition where the body 13 traverses the diameter section of the duct 11. An air flow colliding with the front vortex-making body 131 of the vortex- making body 13 is split into two parts and led to both sides of the vortex- making body 131 and produces a Karman's vortex streets 15 behind the rear vortex-making body 132. The vortex streets 15 are detected by means of a vortex detector 16 fitted to the rear surface of the vortex-making body 132. When the front face of the front vortex-making body 131 is constituted to have a semicircular cross section, a uniform air break-away angle is obtained from a low air flow speed condition to a high air flow speed condition. Namely, the Karman's vortex streets are stably controlled in a wide flow speed range of the air to be measured from low to high and a wide measuring range can be set.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention can effectively measure the total intake air flow rate, etc. particularly for an internal combustion engine, and can effectively execute electronic control of the engine. This invention relates to a Karman vortex type air flow rate measuring device.

[Background technology] A Karman vortex type air flow measuring device is constructed by setting a columnar vortex generator in the air flow, and the Karman vortex generated on the downstream side of this vortex generator is The frequency is proportional to the speed of the air flow.

That is, by measuring the frequency of the Karman vortex generated in the wake of the vortex generator, a measurement signal corresponding to the air flow rate is detected.

This type of Karman vortex air flow measuring device not only has a simple structure, but also has low resistance that would obstruct air flow, so it is effective as an intake air flow measuring device for internal combustion engines, for example. It can be used in many ways.

In such a Karma vortex type air flow measuring device,
The shape of the vortex-forming body that generates the Karman vortex is, for example, a structure having a surface with which airflow collides, and the colliding airflow is separated and flowed to both sides of the vortex-forming body.

However, with the shapes of Karman vortex generators known so far, the range in which the frequency f of the generated Karman vortex and the air flow IQ are proportional is 10 to several tens of times. However, when trying to use such an air flow measuring device as an intake air amount measuring device for an internal combustion engine for an automobile, as the engine becomes smaller and has higher output (turbo etc.), A measurement range of 100 to several 100 times larger is required.

[Problems to be Solved by the Invention] This invention has been made in view of the above points, and has a simple configuration in which a vortex-forming body is installed in the duct where the measurement air flow is set, and the Karman vortex frequency and It is an object of the present invention to provide a Karman vortex type air flow measuring device that allows a measurement range in which the air flow rate is proportional to the air flow rate to be sufficiently permissible, for example, when measuring the intake air amount for an automobile engine.

[Means for Solving the Problems] That is, in the Karman vortex type air flow rate measuring device according to the present invention, the vortex forming body set in the duct faces the air flow to be measured flowing into the duct. The surface portion is formed to have a semicircular cross section.

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

FIG. 1 shows its configuration, and although ducts 1 to 11 are not shown in detail, they are connected to, for example, the intake pipe of an engine. The intake air supplied to the engine is in a state where it is flowing. This airflow is then rectified by the rectification mechanism 12 and taken into the duct 11.

A columnar vortex forming body 13 is installed and set inside the duct 11 so as to cross the diameter of the duct 11. In this case, the vortex forming body 13 is constituted by a front vortex forming body 131 located on the upstream side with respect to the air flow, and a rear vortex forming body 132 located on the downstream side thereof, and this rear vortex forming body 132 A rectifying tail 133 is formed behind the rectifying tail 133 . A slit 14 is formed between the front vortex forming body 131 and the rear vortex forming body 132.

This slit 14 is used to apply negative pressure to the air flow separated by the front swirl body 131 on both sides of the swirl body 131, and to apply negative pressure to the air flow. is behind the rear vortex forming body 132,
This allows for smooth guidance.

That is, the airflow colliding with the front vortex forming body 131 is divided into both sides by this vortex forming body 131 and guided, and a Karman vortex street 15 is created behind the rear vortex forming body 132. It is something that will occur. The Karman vortex array 15 is detected by a vortex detector 16 mounted on the rear surface of the rear recorder 132. The vortex detector 16 is configured by, for example, a heater whose supply of heating current is controlled, and utilizes the property that the heat dissipation characteristics of this heater are influenced by the air flow acting on this heater. It is. For example, if the heating current supplied to this heater is configured to be controlled so that the temperature state of this heater is constant, the heating current will be controlled at a cycle corresponding to the Kalman frequency. It is something that becomes. Therefore, the Karman vortex frequency is measured and detected from the period of change of this heating current, and this measurement signal is sent to, for example, the engine control unit l as one of the engine operating state detection signals. It will be supplied as.

In such a Karman vortex type flow rate measurement device, it is difficult to maintain excellent linearity in the relationship between Karman vortex frequency and changes in air flow velocity from low to high air flow velocity. . The reason for this loss of linearity is that on the air flow collision surface of the front vortex forming body 131, the separation angle of the air streamlines is different between when the air flow is at low speed and when it is at high speed. Specifically, under conditions of low air flow velocity,
This is because when the separation angle is small and the air flow velocity is high, the flow of air that hits the vortex forming body 131 thickens (spreads) outward and the separation angle becomes large.

Therefore, when the air flow rate is high, the frequency per unit flow rate (f/Q>) decreases compared to when the air flow rate is low.

In the Karman vortex type air flow control device shown in the above embodiment, taking the above points into consideration, the air flowing in the duct 11 collides and separates the air flow. The front surface of the front vortex-forming body 131 that performs the action is configured to have a semicircular cross section, so that a uniform air separation angle can be obtained from a low air velocity state to a high air velocity state.

Further, in this vortex forming body 13, a slit 14 is formed between the front vortex forming body 131 and the rear vortex forming body 132, and the separated air flowing on both sides of this slit 14 Negative pressure corresponding to the speed of the flow is applied to the air flow flowing on both sides of the vortex forming body 13. In other words, a negative pressure corresponding to the flow velocity acts on the separated air flow,
The separation angle by a front vortex-forming body is corrected in accordance with the air flow velocity, so that an air flow corresponding to a uniform measured air flow velocity is set regardless of the air flow velocity.

That is, the Karman vortex street is stably generated and controlled over a wide range of measurement air flow velocities from low to high speeds, and a wide measurement range can be set.

Here, the cross-sectional shape of the vortex forming body 13, particularly the front vortex forming body 131, is formed as shown in (A) to (D) in FIG. 2, and the relationship between the Strouhal number and the Reynolds number determined by this shape is determined. were determined through experiments, and the results are shown in Figure 3. In other words, the one shown in Figure 2 (A>) has a semicircular cross section, and the one shown in Figure 2 (B) has a shape in which a 1 mm thick plate is attached to this columnar body with a semicircular cross section. The experimental results for such a vortex-forming body shape are shown in A and B in Figure 3, respectively.In addition, the results shown in (C) and (D> in Figure 2 are , the cross-sectional shape of the vortex-forming body 131 is formed into an arc shape of a large circle and further into a flat plate state, and the experimental results for such a vortex-forming body shape are shown in FIG.
and D.

In other words, the most effective results are obtained when the cross-sectional shape of the front vortex-forming body is semicircular, and the range in which the Karman vortex frequency is proportional to the air flow condition is 100 times or more. It has been confirmed through experiments that the linearity can be maintained at ±2%. [Effects of the Invention] As described above, the Karman vortex type air flow measuring device according to the present invention In this case, the relationship between the air flow velocity and the Karman vortex frequency is set to a linear characteristic over a wide range of air flow speeds flowing in the duct, and from low to high air flow speeds. It is possible to accurately measure and detect speed information up to the state of the vehicle. Therefore, for example, it can be used effectively in combination with an electronic engine control unit, etc., as a measuring device for the intake air flow rate of an internal combustion engine, and it can also be used effectively as a measuring device, etc. for detecting the operating state of an internal combustion engine. It is.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram illustrating a Karman vortex type air flow measuring device according to an embodiment of the present invention, and (A) to (D) in FIG.
FIG. 3 is a diagram showing an example of the shape of the vortex forming body used in the above-mentioned measuring device, and FIG. 3 is a diagram showing the operating characteristics corresponding to the above-mentioned vortex forming body shape. DESCRIPTION OF SYMBOLS 11... Duct, 13... Vortex forming body, 131... Front vortex forming body, 132... Rear vortex forming body, 15... Karman vortex street.

Claims (1)

[Claims] A vortex-forming body that generates a vortex corresponding to the air flow velocity on the downstream side is set in a duct in which the air flow to be measured is set so as to intersect with the air flow, and the vortex-forming body is A Karman vortex type air flow measuring device characterized in that the surface facing the air flow is formed to have a semicircular cross section.