JPH0245785Y2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a device for detecting the resonance point of a hot wire used in a hot wire flowmeter for detecting the intake air amount of an internal combustion engine.

<Prior art> The hot wire used in a hot wire flow meter vibrates due to collision with the fluid. When the vibration frequency caused by the collision with the fluid matches the resonance frequency of the hot wire, the hot wire vibrates greatly and the flow rate increases. It is necessary to remove the resonant frequency of the hot wire from the oscillation range under actual use conditions, as there is a risk that the detection accuracy will decrease or the amplitude of the hot wire will become extremely large and the hot wire will eventually be cut. There is.

For this reason, in recent years, a holder holding a hot wire stretched therein has been forced to vibrate with a mechanical vibrator while changing the vibration frequency sequentially, and the amplitude of the hot wire has been observed with a microscope to confirm the resonance point. however,
When using a mechanical vibrator to forcibly vibrate a hot wire in this way, it is necessary to sequentially change the vibration frequency as described above, so it takes time to detect the resonance point, and it is difficult to detect the resonance point using a microscope, etc. Since it is necessary to visually detect the point of maximum amplitude, there are problems such as low detection accuracy.

<Problems to be solved by the invention> The present invention was made in view of the above-mentioned circumstances, and aims to quickly and accurately measure the resonance point (frequency) of a hot ray without relying on visual inspection or other primary factors. The purpose is to provide a measuring device that can detect

<Means for Solving the Problems> In order to achieve the above object, the present invention provides an air nozzle that blows air toward a hot wire held in tension on a holder, and forms a magnetic field that crosses the hot wire. In addition, a means is provided for frequency-analyzing the induced electromotive force generated in the hot wire due to the vibration generated by the collision with the air ejected from the air nozzle.

<Function> Based on the frequency analysis results, the resonance point of the hot wire can be measured and detected.

<Examples> Examples of the present invention will be described below in detail based on the drawings.

A base 1 of the resonance point measuring device is equipped with clamps 4, 4 as holder holding means for removably positioning and fixing a holder 3 holding a hot wire 2 made of Pt wire or the like stretched inside. Moreover, the base 1
A rod 6 that is raised and lowered by an air cylinder 5 is provided below the rod 6, and permanent magnets 7, 7 are fixed to the upper end of the rod 6 as a magnetic field forming means for forming a magnetic field that crosses the hot wire 2. ing. As shown in FIG. 2, the permanent magnets 7, 7 are adhesively fixed to two substantially orthogonal adjacent surfaces formed on the outer circumferential surface of the rod 6 with an adhesive or the like, and are in contact with the rod 6, for example. The magnetic field formed by these magnets 7 crosses the hot wire 2 by making the part the north pole and the part facing the hot wire 2 the south pole, but the opposite polarity It may be.

On the other hand, by installing air nozzles 9, 9 above the board 1 via the bracket 8, the hot wire 2 of the holder 3 mounted on the board 1 via the clamps 4, 4 as described above is directed. Then, air is ejected from the air nozzles 9, 9, and the hot wire 2 is vibrated by collision with the air.

FIG. 3 shows an example of the air supply circuit to the air cylinder 5 and the air nozzles 9, 9.
Air at a predetermined pressure is supplied from an air tank (not shown) through the moisture separating means 10 and the regulating valve 11 to the foot switch lever 12.
A control valve 13 whose switching is controlled by
A pipe 14 branched from one port of the air cylinder 5, which is supplied to the air cylinder 5 through the air cylinder 5 and is normally open to the atmosphere, and the air nozzles 9, 9
By connecting these through the regulating valve 15, the foot switch lever 12 is operated to raise the permanent magnets 7, 7, and the spool of the control valve 13 is moved downward in the figure, thereby extending the air cylinder 5. Air is ejected from the air nozzles 9 only when they are in operation.

When measuring the resonance point of the hot wire 2 using the resonance point measuring device as described above, the holder 3 holding the hot wire 2 in tension is positioned and fixed on the base 1 with clamps 4, 4, and the hot wire 2 is A pair of terminals with both ends fixed are connected to a spectrum analyzer 16 as frequency analysis means. Incidentally, since the foot switch lever 12 is initially set as shown in FIG. 3, the spool of the control valve 13 is held in the position shown in the same figure, and the air cylinder 5 is held short-circuited. Therefore, in this state, the permanent magnets 7, 7 are located sufficiently below the heating wire 2, as shown in FIG.

When the hot wire 2 is installed as described above,
The foot switch lever 12 is operated to move the spool of the control valve 13 downward in the figure. Then, air is supplied to the lower chamber of the air cylinder 5, so that the air cylinder 5 is extended and the rod 6 is raised. At the same time, piping 14
Since air is also supplied to the air nozzles 9, 9 via the air nozzles 9, the hot wire 2 begins to vibrate due to collision with the air ejected from the air nozzles 9, 9.

Then, when the air cylinder 5 is extended and the rod 6 is raised as described above, this rod 6
The magnetic field formed by the permanent magnets 7, 7 attached to the magnets also rises. Therefore, the magnetic field generated by the permanent magnets 7 always crosses the hot wire 2 during the expansion process of the air cylinder 5.

Furthermore, when the magnetic field and the hot wire 2 move relative to each other, an induced electromotive force is generated in the hot wire 2 along with this movement, and this induced electromotive force changes in accordance with the speed of the relative movement.

Therefore, when a magnetic field passes through the hot wire 2 which is vibrating due to collision with the air as described above, the hot wire 2
The induced electromotive force changes depending on the vibration frequency. Then, this induced electromotive force is frequency-analyzed by the spectrum analyzer 16, and this analysis result (fourth
The resonance frequency (natural frequency) of the hot wire can be determined from the peak of the data obtained by printing out or displaying the data on a monitor (see figure).

In the above embodiment, the magnetic field forming means is the permanent magnet 7,
7, the permanent magnets 7, 7 are gradually raised while vibrating the hot wire 2, and finally the hot wire 2 is made to cross the magnetic field, thereby increasing the ease of mounting of the holder 3 on which the hot wire 2 is stretched. However, the position of the magnetic field may be fixed. Furthermore, it is desirable to set the flow rate of the air ejected from the air nozzles 9, 9 to a value that approximates the actual flow rate of the fluid, but if the hot wire 2 is randomly excited by collision with the air, There is no need to match the flow rate with the actual value.

<Effects of the invention> As explained above, according to the invention, air collides with a hot wire placed in a magnetic field to vibrate the hot wire, and this vibration is extracted as an induced electromotive force generated in the hot wire. Since the frequency analysis of the induced electromotive force is performed to detect the resonance point (natural frequency) of the hot wire, the detection accuracy of the resonance point can be increased compared to the conventional method of visually checking the maximum amplitude. At the same time, the detection time can be significantly shortened.

[Brief explanation of drawings]

Fig. 1 is a partially cutaway front view showing an embodiment of the present invention, Fig. 2 is a plan view enlarging the main parts, Fig. 3 is an air piping diagram, and Fig. 4 shows the resonance point of the hot wire. FIG. 2... Hot wire, 3... Holder, 4... Clamp (holder holding means), 5... Air cylinder, 7...
Permanent magnet (magnetic field forming means), 9...Air nozzle,
16...Spectrum analyzer (frequency analysis means).

Claims (1)

[Scope of utility model registration request] means for holding a holder of a hot wire flowmeter; an air nozzle for jetting air toward a hot wire stretched and held on the holder; a magnetic field forming means for forming a magnetic field that crosses the hot wire; A hot wire resonance point measuring device for a hot wire flowmeter, comprising means for frequency analyzing induced electromotive force and means for displaying the output of the means.