JP2008089507A - Sensor mounting structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem that detection may be adversely affected by air column resonance which occurs between a detection part of a sensor and an opening end of a sensor mounting hole formed in a sensor mounting member in the case that the sensor is required to be mounted to the sensor mounting member in a state in which a detection part at a tip of the sensor is located more inside than the opening end of the sensor mounting hole. <P>SOLUTION: In a sensor mounting structure in which a tube internal pressure sensor 10 is mounted to the sensor mounting hole 12 of a cylinder head 11 in such a way that the detection part 10a at the tip of the tube internal pressure sensor 10 may be located more inside than the opening end of the sensor mounting hole 12 formed in the cylinder head 11, a restricting part 14 in a smaller-diameter ring shape than the inner diameter of the sensor mounting hole 12 is arranged between the detection part 10a of the sensor 10 and the opening end of the sensor mounting hole 12 to shift a natural frequency due to air column resonance which occurs between the detection part 10a of the sensor 10 and the opening end of the sensor mounting hole 12 to a higher one so as to prevent adverse effects to detection by the sensor 10. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a sensor mounting structure for detecting pressure at an extremely high cycle.

  Detecting the pressure in the combustion chamber of the internal combustion engine is extremely effective in setting the amount of fuel supplied to the combustion chamber, its timing, or the timing of ignition timing. As such a pressure detection device, an in-cylinder pressure sensor as disclosed in Patent Document 1 is known. This in-cylinder pressure sensor is formed in the cylinder head such that a pressure introduction passage facing the combustion chamber surface is formed in the cylinder head, and the pressure receiving portion is located in the pressure introduction passage.

Japanese Utility Model Publication No. 6-22945 JP-A-1-285632

  In the in-cylinder pressure sensor disclosed in Patent Document 1, natural vibration due to air column resonance in the pressure introduction passage is generated. Therefore, if this matches or approximates the detection frequency of the in-cylinder pressure sensor, it is large. It was found that detection noise was generated. Although the influence of such noise can be eliminated by electrical filter processing, detection delay occurs due to the processing, and it becomes difficult to smoothly perform combustion control of the internal combustion engine in real time. .

  Patent Document 2 discloses a technology in which a resonance suppression protrusion is formed on a connector plug of a knocking sensor so that resonance of the connector plug does not appear as noise in a detection signal by a piezoelectric element. However, since this method does not change the natural vibration due to air column resonance, it is not a fundamental solution to reduce detection noise caused by air column resonance.

  An object of the present invention is to provide a sensor mounting structure that can reduce the adverse effects of detection noise when detecting pressure at an extremely high cycle.

  In the sensor mounting structure of the present invention, the sensor is mounted in the sensor mounting hole of the sensor mounting member so that the detection portion at the tip of the sensor is positioned inside the opening end of the sensor mounting hole formed in the sensor mounting member. The sensor mounting structure is characterized in that an aperture portion having an annular shape smaller in diameter than the inner diameter of the sensor mounting hole is arranged between the detection portion of the sensor and the opening end of the sensor mounting hole. is there.

  In the present invention, the throttle part having an annular shape smaller than the inner diameter of the sensor mounting hole is arranged between the sensor detection part and the opening end of the sensor mounting hole, and the natural frequency due to air column resonance is reduced by the throttle part. It will shift to a higher position than the case where it is not arranged.

  In the sensor mounting structure according to the present invention, it is preferable that the distance between the sensor detection unit and the diaphragm unit is v / 6f, where v is the speed of sound and f is the detection frequency of the sensor.

  According to the sensor mounting structure of the present invention, since the throttle part having an annular shape smaller than the inner diameter of the sensor mounting hole is arranged between the sensor detection part and the opening end of the sensor mounting hole, the natural frequency due to air column resonance is obtained. Can be shifted higher with respect to the detection frequency of the sensor. As a result, detection with a high period can be performed in a state in which noise is reduced.

  When the speed of sound is v, the detection frequency of the sensor is f, and the distance between the detection part and the diaphragm part of the sensor is set to v / 6f, the effect of the present invention can be obtained more reliably.

  An embodiment in which the sensor mounting structure according to the present invention is applied to an in-cylinder pressure sensor for detecting the pressure in a combustion chamber in an internal combustion engine will be described in detail with reference to FIGS. However, it goes without saying that the present invention is not limited to such an embodiment but can be applied to any other technique belonging to the spirit of the present invention.

  FIG. 1 schematically shows the structure of the cylinder head portion in the present embodiment, and FIG. The in-cylinder pressure sensor 10 according to the present embodiment uses a piezoelectric element (electrostrictive element) to transmit an electrical output corresponding to the amount of strain of the detection unit 10a to a signal processing unit (not shown). It is fixed to the cylinder head 11 using fastening means that does not. For this reason, a sensor mounting hole 12 for attaching the in-cylinder pressure sensor 10 is formed in the cylinder head 11. The sensor mounting hole 12 in the present embodiment is a so-called stepped hole having a large diameter portion 12a and a small diameter portion 12b, and the large diameter portion 12a accommodates the detection portion 10a of the in-cylinder pressure sensor 10 in a non-contact state. The small diameter portion 12b communicates the large diameter portion 12a and the combustion chamber 13.

  It is not essential that the sensor mounting hole 12 has the small-diameter portion 12b, and it is naturally possible to omit the small-diameter portion 12b and open the large-diameter portion 12a to the combustion chamber 13 as it is. What is necessary is just to be a structure which can propagate the pressure in 13 to the detection part 10a of the cylinder pressure sensor 10. FIG. Further, the structure of the in-cylinder pressure sensor 10 itself having the detection portion 10a facing the combustion chamber 13 through the small diameter portion 12b is well known in the art and is not directly related to the present invention. A description of the specific configuration is omitted.

  The distance from the opening end of the small diameter portion 12b on the combustion chamber 13 side to the detection portion 10a of the in-cylinder pressure sensor 10 (hereinafter referred to as the length of the small diameter portion 12b for convenience) L, that is, the small diameter portion 12b. The air gap causes Hertzholm's air column resonance, and when its natural frequency is λ, it is expressed as λ = 4L. On the other hand, when the detection frequency of the pressure in the combustion chamber 13 by the in-cylinder pressure sensor 10 is f and the speed of sound is represented by v, the small-diameter portion 12b of the small-diameter portion 12b with respect to the detection signal by the in-cylinder pressure sensor 10 when λ = v / f. Noise due to air column resonance is maximized. Specifically, when f = 8 kHz and v = 331 m / s, the detection noise becomes maximum when the length L of the small diameter portion 12b is about 0.010 m. Therefore, when using the in-cylinder pressure sensor 10 of f = 8 kHz, it can be said that it is preferable to set the length L of the small diameter portion 12b as short as possible to about 0.010 m.

In the present embodiment, an annular throttle portion 14 is formed on the inner peripheral wall of the small diameter portion 12b, thereby increasing the natural frequency λ of the small diameter portion 12b. The distance S between the throttle unit 14 and the detection unit 10a of the in-cylinder pressure sensor 10 is preferably set so that it does not coincide with λ / 2 ⁿ as much as possible when n is an integer of 1 or more. Further, the inner diameter of the throttle portion 14 prevents the throttle portion 14 from being blocked by deposits so that the detection portion 10a of the in-cylinder pressure sensor 10 does not adversely affect the pressure change from the combustion chamber 13. It is preferable to set at least 2 · or more, and if it is 2 · or more, about 1/2 of the inner diameter of the small diameter portion 12b will be appropriate. In this case, the aperture 14 may be not only a circular opening but also a rectangular opening.

  In this way, by increasing the natural frequency λ of the small diameter portion 12b, the detection noise for the in-cylinder pressure sensor 10 can be reduced. For example, when the length L of the small-diameter portion 12b has to be set to about 0.010 m described above, the above-described throttle portion formation distance S is set to λ / 6, for example. This is about 0.007 m, which is about 1/3 from the opening end of the small diameter portion 12b on the combustion chamber 13 side.

  The cross-sectional shape of the narrowed portion 14 may be a trapezoid other than a regular triangle having an apex angle of 60 degrees and a base of 2 mm as in the present embodiment. Alternatively, it is also effective to form the narrowed portion 14 by press-fitting an annular member made by pressing or the like into the small diameter portion 12b. When the cross-sectional shape of the narrowed portion 14 is trapezoidal, for example, the upper base (inner peripheral surface) is set to 1 mm, the lower base is set to 2 mm, and the height, that is, the protruding amount from the inner peripheral surface of the small diameter portion 12b can be set to 1.5 mm. it can.

  Needless to say, these dimensional shapes are merely examples, and can be changed as appropriate according to the inner diameter of the small diameter portion 12b.

  An example of a measurement result obtained by the above-described in-cylinder pressure sensor 10 according to the present embodiment is indicated by a solid line in FIG. This shows the pressure change in the combustion chamber 13 from the compression stroke to the expansion stroke with reference to the bottom dead center of the internal combustion engine, and the conventional case where the throttle portion 14 is not formed is shown by a two-dot chain line. . As can be seen from FIG. 3, it can be recognized that there is an influence of noise caused by air column resonance when the throttle portion 14 is not formed. Although the influence of such noise can be eliminated by electrical filter processing, detection delay occurs due to the processing, and it becomes difficult to smoothly perform combustion control of the internal combustion engine in real time. .

  In the above-described embodiment, the in-cylinder pressure sensor 10 has been described, but the present invention is also applied to other sensor mounting structures and mounting methods, such as a fuel pressure sensor for detecting the pressure of fuel supplied to the combustion chamber 13 of the internal combustion engine. It goes without saying that it is possible. In addition, the present invention should be construed only from the matters described in the claims, and in the embodiment described above, all the changes and modifications included in the concept of the present invention are other than those described. Is possible. That is, all matters in the above-described embodiment are not intended to limit the present invention, and include any configuration not directly related to the present invention. To get.

It is sectional drawing which represents typically the structure of the cylinder head part of one Embodiment which applied this invention to the cylinder pressure sensor of an internal combustion engine. FIG. 2 is a sectional view in which a mounting portion of the in-cylinder pressure sensor shown in FIG. 1 is extracted and enlarged. It is a graph showing an example of the detection data by the in-cylinder pressure sensor shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 In-cylinder pressure sensor 10a Detection part 11 Cylinder head 12 Sensor mounting hole 12a Large diameter part 12b Small diameter part 13 Combustion chamber 14 Throttle part L Length of small diameter part S Distance between detection part and throttle part of in-cylinder pressure sensor

Claims (2)

A sensor mounting structure in which the sensor is mounted in a sensor mounting hole of the sensor mounting member such that a detection portion at the tip of the sensor is positioned inside an opening end of a sensor mounting hole formed in the sensor mounting member,
A sensor mounting structure characterized in that an aperture portion having an annular shape smaller in diameter than the inner diameter of the sensor mounting hole is disposed between the detection portion of the sensor and the open end of the sensor mounting hole.   2. The sensor mounting structure according to claim 1, wherein an interval between the detection unit of the sensor and the diaphragm unit is v / 6f, where v is a sound velocity and f is a detection frequency of the sensor.

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