JP2014022048A - Combustion sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spark plug incorporating a pressure sensor which can be attached without requiring any special extra work of a combustion chamber.SOLUTION: A spark plug including a cylindrical insulator, and a conductive socket being screwed into the external wall of an internal combustion engine while housing the insulator partially from one end side thereof and fixed in place, is further provided with a piezoelectric element having a hollow cylindrical shape and being held, in the axial direction, between the end face at an enlarged diameter part of the insulator fitted to the hollow cylinder and a flange provided in the socket.

Description

  The present invention relates to a combustion sensor for detecting a combustion pressure in a combustion chamber in an internal combustion engine such as an engine, and more particularly, a plug-type combustion sensor to which a sensor for detecting pressure fluctuations in the combustion chamber is added and fixed to a cylinder head of the engine. About.

  In recent years, for example, an improvement in fuel consumption in an engine has been demanded. At that time, a combustion sensor for detecting a combustion pressure is used for evaluation of fuel consumption improvement performance. Here, when a known pressure sensor is to be directly attached to the engine, it is necessary to add a port for attachment, the pressure sensor generates a temperature drift due to a heat value, and a large fluctuation in pressure or heat For this reason, due to the fact that problems are likely to occur in durability, a method of incorporating a pressure sensor into a spark plug directly connected to the engine cylinder has been studied.

  As a specific configuration based on this technique, for example, Non-Patent Document 1 discloses a configuration in which a piezoelectric element is fixed to a hook-shaped member and the pressure change is measured by fixing the hook-shaped member to a spark plug. Is disclosed. Patent Document 1 discloses a configuration in which an element for pressure measurement is embedded in the spark plug in parallel with the ignition configuration and directly contacts the combustion chamber. Patent Document 2 discloses a configuration in which a ring-shaped piezoelectric element is formed and the piezoelectric element is sandwiched and fixed between an outer wall of an engine cylinder and a spark plug. Patent Document 3 discloses a configuration in which a diaphragm-type pressure detection element is arranged inside a spark plug, and thereby the combustion pressure is measured. In Patent Document 4, an annular groove is disposed between an insulator disposed around the center electrode of a spark plug and a so-called washer disposed around the insulator, and the piezoelectric element in the annular groove is provided. A configuration to be arranged is disclosed.

JP 2001-093646 A Japanese Patent Laid-Open No. 05-203526 Japanese Patent Laid-Open No. 03-216983 Japanese Patent Laid-Open No. 04-034327

Japanese Utility Model Publication No. 63-183528

  In the case of the configuration disclosed in Non-Patent Document 1 described above, it is necessary to add a male thread portion to the engine cylinder, which is problematic in terms of versatility. In the case of the configuration disclosed in Patent Document 1, the spark plug itself has a large diameter, which still cannot solve the problem in terms of versatility. In addition, when using a so-called washer type pressure sensor disclosed in Patent Document 2, there is a risk that the pressure sensor may be damaged due to a tightening condition or inclination when teaching. In the case of the configuration shown in Patent Document 3, there is a high possibility that adhesion of carbon or the like generated during combustion occurs on the diaphragm serving as the pressure receiving portion, and the sensitivity decreases with time. Furthermore, in the case of the configuration shown in Patent Document 4, the piezoelectric element itself is exposed to a high temperature, so that there is a problem that the demand for durability becomes very severe.

  The present invention has been made in view of the above situation, and can be attached to the combustion chamber without requiring any additional work, and has excellent durability and suppresses the influence of temperature drift and the like. An object is to provide a plug-type combustion sensor.

  In order to solve the above-described problems, a spark plug according to the present invention includes a cylindrical insulator portion through which an electrode material penetrates in the axial direction, and an internal combustion chamber in which the insulator portion is partially accommodated in the axial direction from one end side. A spark plug having a conductive socket screwed and fixed to the outer wall of the engine, and having a hollow cylindrical shape having piezoelectric characteristics in the axial direction. The piezoelectric element is further characterized in that it is sandwiched in the axial direction between the end face in the axial direction of the enlarged diameter portion and the flange provided in the socket.

  In the spark plug described above, the piezoelectric element is preferably made of a single crystal having a preferential orientation in the axial direction. Furthermore, in this case, the piezoelectric element has a first electrode formed on one end surface and the outer peripheral surface in the axial direction, and a second electrode formed on the other end surface and the inner peripheral surface in the axial direction, It is preferable to generate a potential between the first electrode and the second electrode when pressure is applied to the insulator. More preferably, the piezoelectric element is disposed between the surface of the flange portion toward one end of the socket and the receiving surface of the lever portion toward the other end portion. Furthermore, it is more preferable to have a collar member that comes into contact with the end face of the piezoelectric element between at least one of the piezoelectric element and the collar and between the piezoelectric element and the receiving surface.

  According to the plug-type combustion sensor of the present invention, temperature drift, etc. is excellent in versatility so that it can be attached to the combustion chamber without requiring any additional work, and maintains high durability. It becomes possible to measure the combustion pressure while suppressing the influence of the above.

It is a figure which shows typically the structure of the axial cross section of the ignition plug which concerns on 1st embodiment of this invention. 2A and 2B are diagrams showing the structure of the piezoelectric element 21 used in the embodiment shown in FIG. 1, in which FIG. 2A shows an axial cross-sectional structure, and FIG. FIG. 2 (c) is a diagram schematically showing the state seen from the direction of arrow B in FIG. 2 (a). FIG. 2 is an explanatory diagram schematically showing a configuration for obtaining a voltage value corresponding to a combustion pressure from a piezoelectric element 21 in the spark plug shown in FIG. 1. FIGS. 4A and 4B are diagrams showing a structure of an ignition plug according to a second embodiment of the present invention, in which FIG. 4A is an axial sectional structure, and FIG. Each state is shown. It is a figure which shows typically the structure of the axial cross section of the ignition plug in 3rd embodiment of this invention.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 schematically shows a cross-sectional structure of a plug type combustion sensor according to an embodiment of the present invention when the plug type combustion sensor is cut in the axial direction. In the spark plug 100 according to the present embodiment, a terminal 11, an insulator portion 13, a socket 15, and an electrode portion 17, which are basic configurations, are arranged from one end portion toward the other end portion in the axial direction. The insulator part 13 has a shaft hole 13a penetrating the center, and a center electrode 19 for electrically connecting the terminal 11 and the electrode part 17 is disposed in the shaft hole 13a. That is, it has a cylindrical shape through which the insulator 13 and the center electrode 19 made of an electrode material penetrate in the axial direction of the spark plug 100.

  The socket 15 also has an insulator hole 15a penetrating in the axial direction, and the insulator portion 13 is fitted into the insulator hole 15a on the side opposite to the terminal 11 in the axial direction and fixed. The socket 15 has a male screw part 15c on the outer periphery from the other end, and is fixed to the engine by screwing the male screw part 15c into an engine cylinder (not shown). That is, the socket 15 partially accommodates the lever portion 13 from one end side in the axial direction of the spark plug 100 and is screwed and fixed to the engine cylinder which is the outer wall of the internal combustion engine.

  In this embodiment, the piezoelectric element 21 that functions as a pressure sensor is sandwiched between the socket 15 and the insulator 13. Specifically, a receiving surface 13b directed to one end in the axial direction is disposed in a region disposed in the lever hole 15a in the lever portion 13, and one end side of the lever hole 15a of the socket 15 is disposed. A flange portion 15d projecting inward is disposed in the opening, and the piezoelectric element 21 is sandwiched and fixed between the receiving surface 13b and the flange portion 15d. In the present embodiment, a collar member 23 is disposed between the flange portion 15d and the piezoelectric element 21 in order to suitably abut one end surface of the piezoelectric element 21 described later with respect to the receiving surface 13b. It is possible to urge the piezoelectric element 21 in the direction of the receiving surface 13b in a range wider than the protruding area of 15d.

  Here, the piezoelectric element 21 used in this embodiment will be described. 2A is a diagram showing a cross section in the axial direction of the piezoelectric element 21, and FIG. 2B is a diagram showing a structure when the piezoelectric element 21 is viewed from the direction of arrow A in FIG. 2A. FIG. 2 (c) is a diagram showing a structure when the piezoelectric element 21 is viewed from the direction of arrow B in FIG. 2 (a). The piezoelectric element 21 includes a CNGS single crystal 31, a first electrode 33, and a second electrode 35. The CNGS single crystal 31 has a hollow ring (cylindrical) shape having a thickness, and has a preferred orientation in the thickness direction. The first electrode 33 is formed so as to cover one end surface of the ring shape and the outer peripheral surface. The second electrode 35 is formed so as to cover the other end surface of the ring shape and the inner peripheral surface.

  FIG. 3 schematically shows the principle of combustion pressure measurement when the piezoelectric element 21 is used. One end of the hollow piezoelectric element 21 is fixed and disposed so that the combustion pressure is applied in the thickness direction, that is, the axial direction from the other end. In other words, it is preferable to match the priority direction with this so that the piezoelectric characteristics are preferably presented in the axial direction. When a pressure resulting from the combustion pressure is applied in the axial direction of the piezoelectric element 21, a potential is generated between the first electrode 33 and the second electrode 35. By measuring this potential, it is possible to know the pressure applied to the piezoelectric element 21. The piezoelectric element 21 has a hollow cylindrical shape having piezoelectric characteristics in the axial direction as described herein, and the insulator portion 13 is fitted into the hollow cylinder.

  In addition, when measuring an additional pressure with the piezoelectric element 21, when applying a pressure to the tension | pulling side, it is necessary to give a pressurization with respect to the piezoelectric element 21 beforehand, and the restriction | limiting on a material may arise. For this reason, the pressure receiving direction is preferably the compression side. In the spark plug 100, it is preferable to measure the combustion pressure applied to the insulator part 13 via the electrode part 17, so that the piezoelectric element 21 is fixed to a socket 15 fixed to an engine cylinder (not shown). It is preferable. However, the present invention is not limited to this form, and in the third embodiment described later, the piezoelectric element 21 is provided with a receiving surface 13b provided at the enlarged diameter portion of the lever portion 13 and a flange portion 15d provided at the socket 15. A suitable output voltage value can be obtained. Accordingly, the piezoelectric element 21 can be arranged at various positions in the axial direction of the spark plug 100 according to the required characteristics as long as the conditions are satisfied.

  According to the present invention, by disposing the piezoelectric element 21 having the above-described configuration on the spark plug 100, it is possible to use an element made of a piezoelectric material having a high high temperature resistivity, and detecting pressure directly from the combustion chamber. Is possible. Further, by adopting a configuration in which the piezoelectric element 21 for pressure detection is directly mounted in the spark plug 100, it is not necessary to arrange an additional configuration for sensor attachment in the engine cylinder, and high versatility is obtained. In addition, since the configuration is simple, it is not necessary to increase the diameter of the spark plug 100, and it is possible to detect and control the combustion state by arranging the spark plug 100 for each cylinder in the engine. Accordingly, direct combustion control of each cylinder can be performed. In addition, since the spark plug 100 has a simple shape of the element itself, it is possible to provide an inexpensive sensor having high rigidity.

  Further, according to the present invention, since the degree of freedom of mounting the piezoelectric element is high, a configuration for protecting the sensor is not required for the case where a diaphragm or the like is used, and therefore the reliability can be easily improved. In addition, the application range of the piezoelectric element is wide, and it is easy to obtain a sensor that can be used even in an environment of 500 ° C. or more, a cooling circuit is not required, and no special mechanism is required. Furthermore, since the structure is simple, noise countermeasures are easy, and a shield and a structure for temperature calibration that can accurately detect a weak charge even in a high voltage environment can be easily obtained. Furthermore, the pressure applied to the plug is directly detected, providing excellent responsiveness, and the angle phase and pressure fluctuations during engine operation can be detected in real time, so abnormal combustion and weak torque fluctuations can be detected. Efficient combustion can be realized. Furthermore, it is possible to contribute to the construction of an ideal combustion system.

  Next, a second embodiment of the present invention will be described. In addition, about the thing similar to the component degree in embodiment shown in FIG. 1, this shall be shown using the same reference number, and detailed description is abbreviate | omitted. FIG. 4A is a schematic diagram showing the spark plug 200 according to the present embodiment in the same manner as FIG. 1, and FIG. 4B shows the spark plug 200 shown in FIG. It shows a state of being disassembled. In the present embodiment, the piezoelectric element 21 is sandwiched in the axial direction by the collar member 23 and the second collar member 25, and these are fixed to the socket 15 by the cap 27. The cap 27 is fixed to the socket 15 with screws. According to this embodiment, the piezoelectric element 21 is sandwiched and fixed by the pair of collar members, whereby the positional relationship and posture between the insulator portion 13 and the piezoelectric element 21 in the axial direction can be kept constant.

  According to the present embodiment, the cap 27 is integrated with the socket 15, and the piezoelectric element 21 is sandwiched between the receiving surface 13 b of the flange portion of the lever portion 13 and the cap 27. When the combustion pressure in the engine rises, the insulator 13 transmits the pressure in the right direction in the figure, which is the axial direction. In this case, the socket 15 is not subjected to pressure because it is fixed to an engine cylinder (not shown). Due to this difference, pressure is applied to the piezoelectric element 21, and a suitable output voltage can be generated. As for the above-described collar member, as in the first embodiment or the third embodiment described later, at least one of between the piezoelectric element 21 and the flange 15d and between the piezoelectric element 21 and the receiving surface 13b. In such a case, the piezoelectric element 21 may be brought into contact with the end face. Use for both is suitable for suitably controlling the posture of the piezoelectric element 21 with respect to the pressure application direction, but it is preferable to appropriately adjust the number of the collar portions in order to obtain pressure fluctuation more directly.

  Next, a third embodiment of the present invention will be described. In addition, about the thing similar to the component degree in embodiment shown in FIG. 1, this shall be shown using the same reference number, and detailed description is abbreviate | omitted. FIG. 5 is a schematic view showing a spark plug 300 according to the present embodiment in the same manner as FIG. In the present embodiment, the piezoelectric element 21 is disposed closer to the ground side electrode side of the spark plug 300 than in the first embodiment. The insulator portion 13 basically has a cylindrical shape and has a region whose diameter is increased near the central portion in the axial direction. One end side of the enlarged diameter portion is located at or near the opening when the insulator portion 13 is inserted into the socket 15 during assembly, and the other end contacts the inner wall of the socket 15 at the back of the socket 15. The positional relationship with the socket 15 is defined by contact.

  In this embodiment, an area corresponding to the receiving surface 13b and the flange portion 15d in the first embodiment described above is formed in this contact portion, and the piezoelectric element 21 is fixed to the insulator portion 13 via the collar member 23. doing. According to the present embodiment, it is possible to arrange the piezoelectric element 21 at a position closer to the actual pressure applying portion as compared with the first or second embodiment. Therefore, it is possible to sense the pressure fluctuation due to combustion in more detail, suppress the voltage conversion loss from the charge, and increase the sensitivity as a pressure sensor.

  In the present invention, a material made of a single crystal having a piezoelectric property such as CNGS having a hollow ring shape and having a preferential orientation in the thickness direction is used as the piezoelectric element 21. Compared with a case where a pressure sensor made of a piezoelectric element formed by bonding a known thin plate member is used, for example, a value more than doubled is obtained as an output voltage when a pressure of 7 Mpa is applied. Further, the output variation itself can be suppressed to 1/2 or less by using a hollow ring-shaped one. In the case of a conventional bonded product, the amount of deformation and deflection varies depending on the individual thin plate, but in the case of this embodiment, the manner of bending in the length direction of the cylinder is stable in shape, and variations in output location are caused. It is possible to suppress it.

  As described above, according to the present invention, the combustion pressure of an engine or the like can be measured by lowering the currently used spark plug from the plug type pressure sensor according to the present invention. Also, since it is not different in size from ordinary spark plugs, it can be arranged for each cylinder like the current spark plug, and the combustion pressure of each cylinder can be independently controlled. Become. In addition, according to the present invention, since the deformation of the insulator portion can be directly detected and associated with the pressure value, highly sensitive measurement can be performed. For the same reason, a so-called peak waveform of the pressure change can be suitably obtained, and data necessary for improving the fuel supply amount and the compression ratio can be obtained. Furthermore, it is possible to use a simple structure and a piezoelectric element having a high strength, and it is possible to obtain durability as a sensor.

100, 200, 300: Spark plug, 11: Terminal, 13: Insulator part, 13a: Shaft hole, 13b: Receiving surface, 15: Socket, 15a: Insulator hole, 15b: Ground side electrode, 15c: Male screw part, 15d: collar part, 17: electrode part, 19: center electrode, 21: piezoelectric element, 23: color member, 25: second color part material, 27: cap, 31: CNGS single crystal, 33: first electrode , 35: second electrode

Claims (5)

A cylindrical insulator portion through which an electrode material penetrates in the axial direction; and a conductive socket that is partially accommodated in the axial direction from one end side of the insulator portion and screwed into the outer wall of the internal combustion engine. A spark plug having
It has a hollow cylindrical shape having piezoelectric characteristics in the axial direction, the insulator portion is fitted into the hollow cylinder, and the axial end surface of the enlarged diameter portion of the insulator portion and the flange portion provided in the socket A spark plug further comprising a piezoelectric element sandwiched in the axial direction therebetween.   The spark plug according to claim 1, wherein the piezoelectric element is made of a single crystal having a preferential orientation in the axial direction.   The piezoelectric element includes a first electrode formed on one end surface and an outer peripheral surface in the axial direction, and a second electrode formed on the other end surface and an inner peripheral surface in the axial direction, and the insulator The spark plug according to claim 2, wherein a potential is generated between the first electrode and the second electrode when pressure is applied to the part.   The piezoelectric element is disposed between a surface of the flange portion toward the one end portion of the socket and the receiving surface of the lever portion toward the other end portion. The spark plug according to any one of 3.   5. The collar member according to claim 1, further comprising a collar member that abuts an end face of the piezoelectric element between at least one of the piezoelectric element and the flange and between the piezoelectric element and the receiving surface. A spark plug according to claim 1.

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