JP2005127818A - Gas flow measuring device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve accuracy of flow analysis by enabling measurement of a gas flow distribution in a cylinder by a laser Doppler current meter. <P>SOLUTION: The wavelength of a laser beam generated from a wavelength changing type laser 1 is switched at high speed to λ1, λ2, λ3, and the laser beams having each wavelength λ1, λ2, λ3 are condensed by the same condensing lens 8. Since the condensing position of the condensing lens 8, namely, the measuring position is different according to the difference of a refractive index caused by the difference of the wavelength of the laser beam, confused light generated on each measuring position is detected respectively, to thereby detect a gas flow velocity on each measuring position individually and approximately simultaneously. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a gas flow measurement device for an internal combustion engine, and more particularly to a device for measuring gas flow in a cylinder using a laser Doppler velocimeter.

Conventionally, a laser Doppler velocimeter is used to detect air movement in a cylinder of an internal combustion engine, and an intake port shape, a gas flow control valve, a piston crown shape, and the like are evaluated and selected based on the detection result. (See Patent Documents 1 and 2).
The laser Doppler velocimeter collects two laser beams in the cylinder, thereby generating interference fringes with an interval L in the cylinder, and tracer particles that follow the gas flow in the cylinder pass through the interference fringes. By doing so, the confusion light which generates the burst signal of frequency f is generated.

Then, from the burst signal, the gas flow rate is expressed as follows: Gas flow rate = L × f
Is what you want.
Japanese Patent Laid-Open No. 11-083885 JP 2003-056385 A

By the way, most of the gas flow in the cylinder is swirled vertically, and the flow direction is reversed up and down across the center of the swirl.
For this reason, when the gas flow rate is measured at a specific point, it is determined whether the center of the vortex has changed across the measurement position or the direction of the flow rate has actually been reversed when the reversal of the flow direction is detected. Therefore, there is a problem that the analysis accuracy of the gas flow in the cylinder is lowered.

  The present invention has been made in view of the above problems, and provides a gas flow measuring device that can distinguish and detect a change in the vortex center and a reversal of the flow velocity direction, and thus can analyze the gas flow in the cylinder with high accuracy. The purpose is to do.

  Therefore, in the present invention, two laser beams are condensed at the measurement position in the cylinder, and the confusion light generated when the particles pass through the interference fringes generated at the measurement position is detected, and the gas in the cylinder is detected. A gas flow measuring device for an internal combustion engine for measuring a flow, wherein a gas flow distribution in the cylinder is detected by measuring the gas flow substantially simultaneously based on the scattered light at each of a plurality of measurement positions in the cylinder. The configuration.

According to this configuration, the laser beam is condensed at a plurality of positions in the cylinder, and the gas flow is detected substantially simultaneously at the plurality of positions based on the confusion light at each position.
As a result, the gas flow distribution in the cylinder can be obtained and the vortex center can be estimated, and this is due to the vibration of the vortex center when the reversal of the flow velocity direction is detected at the measurement position. Whether or not the flow velocity direction is actually reversed can be determined, and the evaluation and selection of the intake port shape, gas flow control valve, piston crown shape, etc. can be performed with high accuracy.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a diagram showing a laser Doppler velocimeter constituting a gas flow measuring device for measuring gas flow in a cylinder of an internal combustion engine in the embodiment.
In FIG. 1, a wavelength variation laser 1 is a laser device in which the wavelength of a generated laser beam is changed by voltage or current control.

The laser beam generated by the wavelength-variable laser 1 is incident on the spectral prism 2 and is emitted from the spectral prism 2 through an optical path that differs depending on the wavelength due to a difference in refractive index due to a difference in wavelength of the laser beam.
On the emission side of the spectroscopic prism 2, mirrors 4a, 4b, 4b, 4c, 4c, 4c, 4c, 4c, 4c, 4c, 4c, 4c, 4c, 4c, 4c 4c is arranged.

The wavelengths λ1, λ2, and λ3 satisfy λ1>λ2> λ3.
The laser beam having the wavelength λ1 is reflected by the mirror 4a and enters the beam separation device 3a, and is separated into two laser beams by the beam separation device 3a.
The two laser beams having the wavelength λ1 emitted from the beam separation device 3a are reflected by the half mirrors 5a and 5b, and proceed in a direction parallel to the axis of the condenser lens 8.

The two laser beams having the wavelength λ1 travel along an optical path that is parallel to the central axis of the condenser lens 8 and that is equidistant from the central axis.
The two laser beams are refracted by the condensing lens 8 and intersect at a focal length determined by the wavelength.
Similarly, the laser beam having the wavelength λ2 is reflected by the mirror 4b and is incident on the beam separation device 3b. After being separated into two laser beams by the beam separation device 3b, the laser beam is reflected by the half mirrors 6a and 6b. The

Thereafter, the laser beam with the wavelength λ2 is transmitted through the half mirrors 5a and 5b, and enters the condenser lens 8 through the same optical path as the laser beam with the wavelength λ1.
The laser beam with the wavelength λ2 is focused at a focal position different from the laser beam with the wavelength λ1 due to a difference in refractive index due to a difference in wavelength.
Further, the laser beam having the wavelength λ3 is reflected by the mirror 4c and incident on the beam separation device 3c. After being separated into two laser beams by the beam separation device 3c, the laser beam is reflected by the half mirrors 7a and 7b. .

Thereafter, the laser beam having the wavelength λ3 passes through the half mirrors 6a, 6b, 5a, and 5b, and enters the condenser lens 8 through the same optical path as the laser beam having the wavelength λ1.
The laser beam with the wavelength λ3 is condensed at a focal position different from the laser beams with the wavelengths λ1 and λ2 due to a difference in refractive index due to a difference in wavelength.
As described above, the laser beams having the wavelengths λ1, λ2, and λ3 are condensed by the same condenser lens 8, so that the two laser beams are crossed at different focal positions depending on the refractive index depending on the wavelength. .

Here, the condensing lens 8 is installed in the cylinder head of the internal combustion engine, and the positions where the laser beams of wavelengths λ1, λ2, and λ3 are condensed are linearly arranged in the cylinder.
When the two laser beams cross, as shown in FIG. 2, an interference fringe with an interval L is generated at the crossing position, and tracer particles that follow the gas flow in the cylinder pass through the interference fringe. A confusion light that generates a burst signal of frequency f is generated, and a gas flow velocity is calculated from the burst signal.
Gas flow rate = L x f
As required.

The detection of the scattered light is performed as shown in FIG.
The confusion light is converted into parallel light by entering the condenser lens 8, and enters the spectroscopic lens 10 disposed on the upper side of the condenser lens 8.
The spectroscopic lens 10 is provided on a triangular prism portion 10a having a lower plane on which the parallel light is incident at a right angle and an upper plane obliquely intersecting the lower plane, and on the upper plane of the triangular prism portion 10a. And a convex lens portion 10b.

Then, the confusion light incident on the spectroscopic lens 10 is condensed at different positions in the circumferential direction due to the difference in refractive index depending on the wavelength.
Here, sensors 11a, 11b, and 11c for detecting the confusion light are arranged at positions where the confusion light by the laser beams having the wavelengths λ1, λ2, and λ3 is collected, and the sensors 11a, 11b, and 11c are different for each of the wavelengths λ1, λ2, and λ3. The scattered light generated at the position is detected by each sensor 11a, 11b, 11c.

The gas flow velocities are individually detected from the scattered light detected by the sensors 11a, 11b, and 11c, and these gas flow velocities are measured by three laser beams with the wavelengths λ1, λ2, and λ3. It becomes the gas flow velocity at each position.
Accordingly, the gas flow distribution in the cylinder is obtained as the gas flow velocity at each of the three measurement positions.

The wavelength-variable laser 1 is controlled so that the wavelength of the generated laser beam changes periodically at high speed in the order of λ 1 → λ 2 → λ 3 → λ 2 → λ 1 → λ 2. The gas flow rate at the measurement position is required.
However, when switching the wavelength to three types of λ1, λ2, and λ3, a laser beam having an intermediate wavelength between these wavelengths λ1, λ2, and λ3 is generated, which causes a measurement error.

  Therefore, in this embodiment, the wavelength-variable laser is turned on only at the timing of the required wavelengths λ1, λ2, and λ3, or a laser beam such as a chopper or filter is passed on the optical path of the wavelength-variable laser 1. A shielding device 12 capable of switching and controlling the shielding at a high speed is provided so that the laser beam is allowed to pass only at the required wavelengths λ1, λ2, and λ3 (see FIG. 4).

If the laser beam having a wavelength unnecessary for gas flow measurement is removed as described above, the confusion light at different measurement positions corresponding to the discrete laser beams having the wavelengths λ1, λ2, and λ3 can be obtained. It can be detected with high accuracy.
Thereby, the gas flow velocity measurement at the three measurement positions can be performed at high speed and accuracy in time series, and the gas flow velocity at three different locations in the cylinder can be detected almost simultaneously.

As shown in FIG. 5, the three measurement positions due to the differences in the wavelengths λ1, λ2, and λ3 of the laser beam are arranged in three cylinders in the vertical direction along the central axis in the cylinder. The position with respect to the head is set, and the wavelengths λ1, λ2, and λ3 are selected so that the gas flow is measured at the required measurement position with reference to the position of the condenser lens 8.
Most of the gas flow in the cylinder swirls vertically, and this vortex varies from cycle to cycle, but when the piston moves up, the shape of the vortex is fixed to some extent according to the shape of the combustion chamber. However, the vortex center vibrates due to precession.

Here, as described above, when the gas flow is measured substantially simultaneously at a plurality of different measurement positions on the central axis in the cylinder and the gas flow distribution is obtained, the gas flow direction and flow velocity at each measurement position are obtained. The vortex center can be estimated, and even if the vortex center vibrates, the direction of the vortex flow is not erroneously judged.
Furthermore, if the distance from the measurement position to the wall surface is obtained in advance, the gas flow velocity in the vicinity of the wall surface, that is, the maximum flow velocity can be estimated, and furthermore, the vortex energy can be estimated.

The gas flow rate increases as the piston rises. However, when the gas approaches the top dead center, the flow is converted into turbulence, so the flow rate does not increase.
In general, the flow starts to be converted into turbulence from around BTDC 60 deg, and the flow is suppressed from around BTDC 30 deg.
Therefore, by comparing the flow rates at a specific crank angle (for example, ignition timing), it is possible to determine the turbulence speed, which is an important parameter of the burnup of the internal combustion engine, and to determine whether the engine performance is good or bad.

In addition, since the disturbance is preferably stored as much as possible, if the breakdown of the disturbance is after BTDC 30 deg, it can be evaluated that the disturbance remains so much that combustion efficiency and combustion stability are high.
As described above, the intake port shape, gas flow control valve, piston crown shape, etc. are evaluated from the viewpoint of combustion efficiency and combustion stability by diagnosing the maximum flow velocity, vortex energy, turbulence start time, etc.・ Can be selected.

In the above embodiment, three measurement positions are used, but at least two measurement positions may be used, and four or more measurement points can be set.
In addition, laser beams having different wavelengths can be generated by different lasers, but if a wavelength variation laser is used as in the embodiment, it is not necessary to provide a plurality of expensive lasers, and the laser position Adjustment work can be simplified and the frequency of maintenance can be reduced.

Further, the order of changing the wavelength of the laser beam in the wavelength-variable laser 1 is not limited to the pattern shown in FIG. 4. For example, the wavelength is changed in the order of λ1 → λ3 → λ2 → λ1 →. It is also possible.
In addition, it is possible to use the gas flow rate at only two points in response to a measurement request while allowing measurement at three or more measurement positions.

  In addition, a plurality of measurement positions can be arranged in the horizontal direction (direction parallel to the piston crown surface) in the cylinder, or can be arranged obliquely in the cylinder.

The figure which shows the laser beam condensing system in the laser Doppler velocimeter of embodiment. The figure which shows the mode of the interference fringe generation | occurrence | production in embodiment. The figure which shows the detection system of the confusion light in the laser Doppler velocimeter of embodiment. The timing chart which shows the mode of the generation control of the laser beam in embodiment. The figure which shows the measurement position of the laser Doppler velocimeter in embodiment.

Explanation of symbols

    DESCRIPTION OF SYMBOLS 1 ... Wavelength variation type laser, 2 ... Spectral prism, 3a-3c ... Beam separation apparatus, 4a-4c ... Mirror, 5a, 5b, 6a, 6b, 7a, 7b ... Half mirror, 8 ... Condensing lens, 10 ... Spectroscopy Lens, 11a to 11c ... sensor, 12 ... shielding device

Claims (9)

An internal combustion engine for measuring gas flow in a cylinder by condensing two laser beams at a measurement position in the cylinder and detecting the scattered light generated when particles pass through the interference fringes generated at the measurement position The gas flow measuring device of
A gas flow measuring device for an internal combustion engine, wherein gas flow distribution in the cylinder is detected by measuring gas flow substantially simultaneously based on the scattered light at each of a plurality of measurement positions in the cylinder.   A laser beam having a different wavelength is generated, and the laser beam having a different wavelength is condensed by the same condenser lens, and a plurality of measurement positions are set according to a difference in a condensing position due to a difference in the wavelength of the laser beam. The gas flow measuring device for an internal combustion engine according to claim 1.   3. A gas flow measuring device for an internal combustion engine according to claim 2, wherein the wavelength of the laser beam generated by the wavelength-variable laser is periodically varied at high speed to generate laser beams of different wavelengths in time series. .   The wavelength of the laser beam generated by the wavelength-variable laser is varied at a high speed, and a laser beam having a discrete wavelength corresponding to a plurality of required measurement positions is selectively incident on the condenser lens. The gas flow measuring device for an internal combustion engine according to claim 3.   By turning off the wavelength variation laser while the wavelength variation laser generates a laser beam having an unnecessary wavelength, a laser beam having a discrete wavelength corresponding to a plurality of required measurement positions is applied to the condenser lens. 5. The gas flow measuring device for an internal combustion engine according to claim 4, wherein the light is selectively incident.   While the wavelength-variable laser generates a laser beam having an unnecessary wavelength, the laser beam is shielded on the optical path so that the laser beam having a discrete wavelength corresponding to a plurality of required measurement positions is applied to the condenser lens. 5. The gas flow measuring device for an internal combustion engine according to claim 4, wherein the light is selectively incident.   The laser beam generated by the wavelength-variable laser is dispersed by a spectral prism, and a laser beam having a discrete wavelength corresponding to a plurality of required measurement positions is selectively incident on the condenser lens. Item 7. The gas flow measuring device for an internal combustion engine according to any one of Items 3 to 6.   The scattered light is condensed at different positions for each discrete wavelength corresponding to a plurality of required measurement positions by a spectroscopic lens, and the scattered light is detected by a sensor provided for each discrete wavelength. The gas flow measuring device for an internal combustion engine according to any one of claims 3 to 7.   9. The gas flow measuring device for an internal combustion engine according to claim 1, wherein a maximum gas flow velocity near the vortex center and / or near the wall is obtained based on a gas flow distribution in the cylinder.

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