JPH07318448A - Cylinder internal pressure detecting device - Google Patents

Abstract

PURPOSE:To accurately detect cylinder internal pressure at all strokes by adding a receiving heat reducing means to a diaphragm so as to reduce a quantity of heat received by the diaphragm. CONSTITUTION:A spark plug A having a cylinder internal pressure detecting device is provided with a main body metal fitting 1 which has a spot facing hole 11, an insulator arranging hole 12 or the like and is installed on an engine head of an internal combustion engine, a pressure receiving member 2, a heat shielding plate 3, a pressing-down screw 41, a piezoelectric sensor 42 and a central electrode 6 to be installed in a shaft hole 51. This member 2 has a diaphragm 21 and a pressure receiving rod 22 to be installed in the spot facing hole 11. When the diaphragm 21 receives combustion pressure caused by combustion, the diaphragm 21 is backward pushed, and a thin part 222 of the rod 22 is contractively deformed. When contractive deformation of the rod 22 by this combustion pressure is detected, the combustion pressure can be detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cylinder pressure detecting device for detecting combustion pressure in a combustion chamber of an engine.

[0002]

2. Description of the Related Art As shown in FIG. 9, a cylinder internal pressure detecting device C includes a metal shell 90 screwed to an engine head 901.
2, an ignition assembly 903, and a pressure sensor 904. Then, the engine head 9 of the metal shell 902
A gas volume 906 that opens to the combustion chamber 905 is formed at the tip on the 01 side, and the gas volume 906 and the pressure sensor 904 are connected by a pressure guiding passage 907, and the combustion pressure of the combustion chamber 905 passes through the pressure guiding passage 907. Pressure sensor 9
It is transmitted to 04.

Further, in order to prevent the influence of heat from combustion gas, a water jacket 908 and cooling water ports 909, 91 are provided.
0 is provided around the pressure sensor 904 for cooling (Prior Art 1; Japanese Utility Model Laid-Open No. 59-16088).

In the cylinder internal pressure detecting device C of the prior art 1, the pressure guiding passage 907 is indispensable in order to enable the mounting to the screw portion 911 which is restricted in space.
There is a problem that a measurement error occurs due to the resonance due to the pressure guiding passage 907.

Further, there is the following prior art 2 which is an improvement of this prior art 1. Cylinder pressure detector D
As shown in FIG. 10, a counterbore 920 and a through hole 921.
And a metal shell 924 disposed in the screw portion 923 of the engine head 922, a diaphragm 925 that receives combustion pressure, a screw portion 926, and a spring portion 927 that contracts and deforms due to combustion pressure. Of the pressure receiving member 9 through the through hole 921.
28 and is screwed into the threaded portion 926 of the pressure receiving member 928 so that the pressure receiving member 928 is inserted into the counterbore 92 of the metal shell 924.
A screw 929 that is pressed and fixed to the 0 bottom surface, and a piezoelectric element 931 that is interposed between the head 930 of the screw 929 and the metal shell 924 in a compressed state are provided. This cylinder pressure detector D
Has the advantage that the pressure guiding passage 907 is unnecessary and the piezoelectric element 931 is not directly exposed to the combustion gas (Prior Art 2; Japanese Patent Laid-Open No. 1-312439).

[0006]

DISCLOSURE OF THE INVENTION The inventors of the present application have found that the cylinder internal pressure detection device D of the prior art 2 tends to detect a higher-than-actual pressure curve in the exhaust stroke after combustion {Fig. 5 (a), see the broken line in FIG. 6 (a)}.

As a result of investigating the cause, it was found that the diaphragm 925 which receives the combustion pressure is thermally deformed by the high temperature combustion gas.

That is, in the explosion stroke, the diaphragm receives heat from the combustion gas together with the combustion pressure, and thermally expands in the rearward direction under pressure. Next, in the exhaust stroke, the diaphragm is cooled, but since the portion of the heat received is smaller than the area of the diaphragm, cooling is delayed and heat contraction is delayed. Therefore, the pressure higher than the actual pressure is detected in the exhaust stroke.

An object of the present invention is to provide a cylinder internal pressure detecting device capable of accurately detecting the cylinder internal pressure in all strokes.

[0010]

[Means for Solving the Problems] In order to solve the above problems,
The present invention has the following configurations. (1) A metal shell having a counterbore hole communicating with a combustion chamber, which is mounted on an engine head of an internal combustion engine, a plate-like diaphragm fitted in the combustion chamber side opening of the counterbore hole, and connected to the diaphragm And a pressure receiving rod disposed in the counterbore, and the diaphragm is received by a cylinder pressure detecting device that detects the combustion pressure of the combustion chamber based on contraction deformation of the pressure receiving rod due to combustion pressure. Heat receiving reduction means for reducing the amount of heat is added to the diaphragm.

(2) The in-cylinder pressure detection device has the structure of (1) above, and detects the combustion pressure by piezoelectrically converting the displacement, deformation, or contraction deformation of the pressure receiving rod due to the combustion pressure by the piezoelectric element.

(3) The cylinder internal pressure detection device has the structure of (1) or (2) above, and as the heat receiving reduction means, a heat insulating material coated on the side surface of the combustion chamber of the diaphragm,
Alternatively, at least one of the heat shield plates fixed to the front surface of the diaphragm by the pillar protruding in the center of the diaphragm is adopted.

(4) The spark plug with a cylinder internal pressure detecting device is provided with an insulator mounting hole in the metal shell of the cylinder internal pressure detecting device of any one of the above (1) to (3). An insulator with a shaft hole is fitted in and the center electrode is inserted into the shaft hole.

[0014]

[Operation and effect of the invention]

[Claim 1] When the diaphragm receives the combustion pressure associated with the combustion, the diaphragm is pushed rearward, and the pressure receiving rod body arranged in the counterbore hole contracts and deforms. Then, the combustion pressure can be detected by detecting the contracting deformation of the pressure receiving rod due to the combustion pressure.

When the diaphragm is directly exposed to the high-temperature combustion gas, the amount of thermal deformation of the diaphragm is large, and the cooling of the diaphragm that has been thermally expanded is delayed in the exhaust stroke after combustion, so that a combustion pressure higher than the actual pressure is detected. .

However, since the heat receiving reduction means for reducing the amount of heat received by the diaphragm is added to the diaphragm,
The amount of heat received by the diaphragm decreases, the amount of thermal deformation of the diaphragm due to high-temperature combustion gas decreases, and in the exhaust stroke after combustion, the pressure receiving rod contracts and deforms according to the combustion pressure, and the combustion pressure is approximately equal to the actual combustion pressure. Can be detected. Therefore, the cylinder pressure can be accurately detected in all strokes.

[Claim 2] When the diaphragm receives the combustion pressure associated with combustion, the diaphragm is pushed rearward, and the pressure receiving rod is displaced or deformed (including contraction deformation). This is piezoelectrically converted by a piezoelectric element, and the combustion pressure is detected from the obtained electric output. Further, since the piezoelectric element often has pyroelectricity, the conduction of heat received by the diaphragm can be reduced by the heat reception reducing means, so that pyroelectricity can be suppressed. The combustion pressure can be easily detected by incorporating the piezoelectric element in the detection device and connecting the measuring instrument and the piezoelectric element at a distant position with a wire.

[Claim 3] The cylinder internal pressure detecting device is a heat insulating material for reducing the amount of heat received by the diaphragm from the high-temperature combustion gas. The heat insulating material is coated on the side surface of the combustion chamber of the diaphragm or protrudes into the center of the diaphragm. At least one of the heat shield plates fixed to the front surface of the diaphragm by the pillar is adopted.

Therefore, the amount of heat received by the diaphragm is reduced by the heat insulating material and the heat shield plate, the thermal deformation amount of the diaphragm due to the high temperature combustion gas is reduced, and the diaphragm is contracted and deformed according to the combustion pressure in the exhaust stroke after combustion. , The combustion pressure corresponding to the actual combustion pressure can be detected. Therefore, the cylinder pressure can be accurately detected in all strokes. In addition, in the case of heat insulating material, the front surface of the diaphragm is coated thoroughly,
In the case of a heat shield plate, it is preferable that the outer diameter is substantially the same as that of the diaphragm.

[Claim 4] An insulator mounting hole is provided in the metal shell of the cylinder internal pressure detecting device having the structure of claims 1, 2 and 3, and the insulator mounting hole has an axial hole. And the center electrode is inserted into the shaft hole to form a spark plug with a cylinder pressure detector.

Therefore, it is possible to install the spark plug with the cylinder internal pressure detecting device in the cylinder of the engine by utilizing the hole for installing the ordinary spark plug in the cylinder, and the hole for detecting the cylinder internal pressure. Need not be drilled in the engine head.

In order to improve the efficiency of the engine, it is necessary to make the intake / exhaust valve large (a recent trend). By adopting this configuration and integrating the spark plug and the cylinder internal pressure detection device, it is not necessary to separately secure a space for forming a hole for detecting the cylinder internal pressure, and the intake and exhaust valve The installation space can be maximized.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a first embodiment of the present invention will be described with reference to FIGS.
It will be described based on. The spark plug A with a cylinder internal pressure detecting device has a counterbore hole 11, an insulator arranging hole 12, and the like, and is a metal shell 1 mounted on an engine head of an internal combustion engine.
The pressure receiving member 2, the heat shield plate 3, the cap screw 41, the piezoelectric sensor 42, the insulator 5 with the shaft hole 51 fitted in the insulator mounting hole 12, and the shaft hole 51. Center electrode 6 for

The metal shell 1 (made of low carbon steel) has a tip surface 11
A head 110 having an outer electrode 112 welded thereto and a screw portion 113 screwed into a plug mounting hole of a cylinder head.
And a body 120 for crimping and fixing the insulator 5 in the insulator disposing hole 12. The metal shell 1 includes an insulator mounting hole 12, a gas volume 13, a counterbore hole 11, and a communication hole 1.
4 and a large diameter hole 15 are formed.

The insulator disposing hole 12 is formed so that the hole center axis is parallel to the center axis of the metal shell 1 and is eccentric so as to penetrate from the metal shell tip to the metal shell rear end. The gas volume 13 is formed in a columnar shape at the front part of the head 110, leaving the head edge, and opens into the combustion chamber.

In the counterbore 11, the combustion chamber side opening 114 communicates with the gas volume 13, and from the combustion chamber side opening 114,
The metal shell 1 is formed with an equal diameter in an oblique direction away from the central axis of the metal shell 1 up to a substantially rear position of the head.

The communication hole 14 is formed in the front portion of the body with a diameter smaller than that of the counterbore 11. The front surface communicates with the counterbore 11, and the rear surface communicates with the front surface of the large diameter hole 15. Large hole 1
5 is formed on the thick-walled body portion 120, and the front surface is the communication hole 1
4 communicates with the rear surface, and the rear surface penetrates the body rear surface.

The pressure receiving member 2 (made of stainless steel) includes a diaphragm 21 and a pressure receiving rod 22 inserted into the counterbore 11.
Have and. Then, when the diaphragm 21 receives the combustion pressure due to the combustion, the diaphragm 21 is pushed backward,
The thin portion 222 of the pressure receiving rod 22 contracts and deforms. The diaphragm 21 is a disk having a thickness of about 0.15 mm and a diameter of 4 mm, and after the pressure receiving rod 22 is inserted into the counterbore hole 11 from the combustion chamber side opening 114, the outer periphery is laser-cut to form a metal shell of the combustion chamber side opening 114. 1 is seam welded 210 (see FIGS. 2 and 3).

The pressure-receiving rod 22 has a tubular shape, and has a collar-shaped portion 221 that is held against the inner bottom surface of the counterbore 11, a thin portion 222 that contracts and deforms in the axial direction due to combustion pressure, and a screw 22 on the inner circumference.
The thick portion 223 in which 3a is formed, and the diaphragm 21.
Has a small diameter portion 224 formed integrally therewith.

The heat shield plate 3 (made of stainless steel) is a disc having a thickness of about 0.15 mm to 0.2 mm and a diameter of 4 mm, and has a small diameter convex portion formed at the tip of the small diameter portion 224 on the front side of the diaphragm 21. The central small hole 31 is fitted into the portion 224a and laser-welded (see FIGS. 2 and 3).

The cap screw 41 has a male screw portion 411 screwed into the screw 223a, and the communication hole 14 with the Teflon tube 1.
A rod-shaped portion 413 having a cylindrical portion 412 covered with 40 (which makes the movement of the pressing screw 41 smooth) is inserted, and a head portion 414 that holds the piezoelectric sensor 42. The pressing screw 41 is fitted with the piezoelectric sensor 42 after the pressure receiving rod 22 is inserted and after the welding is completed, and the counterbore hole 11 is provided from the large diameter hole 15 side.
It is screwed in and screwed with a predetermined torque.

It should be noted that the combustion pressure associated with the combustion is measured by the diaphragm 21.
When it is received, the diaphragm 21 is pushed backward, and mainly the thin portion 222 of the pressure receiving rod 22 contracts and deforms, and the cap screw 4
The tightening force of 1 is reduced.

The piezoelectric sensor 42, which converts a change in the tightening force of the presser screw 41 into a change in the electric output value, includes a packing 42.
1- Piezoelectric element 422- Electrode plate 423- Piezoelectric element 424-
Packing 425 (these all have a through hole in the center)
In this order, each member is laminated (shown in FIG. 4).

Then, the insulating tube 4 is attached to the electrode plate 423.
The lead wire 427 covered with 26 is connected, and the other end of the lead wire 427 is connected to the center pin 154 of the output extraction connector 153 fitted in the rear opening 152 of the large diameter hole 15.

The insulator 5, which is made of ceramics mainly composed of alumina, has its seat surface locked to the step of the metal shell 1 through a packing (not shown), and the rear end of the body 120 is inward. It is installed in the insulator installation hole 12 by caulking.
The insulator mounting hole 12 is formed in a position displaced outward from the axis parallel to the axis.

The center electrode 6 (made of Ni alloy) is inserted into the shaft hole 51 so that its tip portion slightly projects from the tip surface of the insulator 5, and spark discharge is performed with the outer electrode 112.

Next, advantages of the spark plug A with a cylinder internal pressure detecting device according to this embodiment will be described. [A] With the spark plug A with a cylinder pressure detector,
The cylinder internal pressure is detected based on the magnitude of the electric output of the piezoelectric sensor 42. When the diaphragm 21 receives the combustion pressure due to combustion, the diaphragm 21 is pushed backward, and the pressure receiving rod 22 arranged in the counterbore hole 11 is detected. Contracts and deforms, the tightening force of the holding screw 41 weakens, and the electric output of the piezoelectric sensor 42 changes.

In the type in which the diaphragm 21 faces the combustion chamber, the diaphragm 21 is directly exposed to the high-temperature combustion gas, so that the diaphragm 21 has a large thermal deformation amount, and the thermal contraction of the diaphragm 21 is delayed in the exhaust stroke after combustion. As shown by the broken lines in FIG. 5A and FIG. 6A, the piezoelectric sensor 42 tends to output an electric quantity corresponding to a higher pressure than it actually is.

However, since the heat shield plate 3 is disposed on the front surface of the diaphragm 21, the amount of heat received by the diaphragm 21 in the exhaust stroke after combustion is reduced, and the amount of thermal deformation of the diaphragm 21 due to the high temperature combustion gas is reduced. Less. Therefore, in the exhaust stroke after combustion, etc., the pressure receiving rod 22 contracts and deforms in accordance with the actual cylinder internal pressure, and the cap screw 4
1 clamps the piezoelectric sensor 42 and the piezoelectric sensor 42 delivers an electrical output.

Therefore, as shown by the broken line in FIG.
A high pressure curve is detected in the exhaust stroke after combustion.
The cylinder pressure can be accurately detected during all strokes.
This enables highly accurate detection of combustion parameters such as IMEP.
it can. The noise N₁, N ₂(Intake / exhaust valve seating noise
(B) is a waveform due to resonance of the heat shield plate 3.

[A] Since the diaphragm 21 is a thin disk, it is sensitively displaced rearward due to a slight change in the cylinder internal pressure, and the outer circumference is seam welded 210 to the metal shell 1 of the combustion chamber side opening 114. For this reason, the cylinder internal pressure can be detected with high sensitivity, and since the combustion gas does not enter the counterbore 11 or the like, the influence (combustion state etc.) due to the installation of the spark plug A with the cylinder internal pressure detection device is small.

[C] In the spark plug A with a cylinder internal pressure detection device, the insulator 5 and the center electrode 6 are inserted into the metal shell 1 to serve as both functions of the spark plug and the cylinder internal pressure sensor. Therefore, the spark plug A with the cylinder internal pressure detection device can be installed in the cylinder of the engine by utilizing the hole for installing the ordinary spark plug in the cylinder, and the hole for detecting the cylinder internal pressure can be provided in the engine. There is no need to pierce the head, and the effect (combustion state etc.) of mounting the spark plug A with a cylinder internal pressure detection device is small, and it does not take time and effort.

Next, a second embodiment of the present invention will be described with reference to FIG. 7 (see also FIG. 1). The spark plug with a cylinder internal pressure detector differs from the spark plug A with a cylinder internal pressure detector in the following points.

Similar to the first embodiment, the diaphragm 21 is a disk having a thickness of about 0.15 mm and a diameter of 4 mm. After the pressure receiving rod 22 is inserted into the counterbore 11 from the combustion chamber side opening 114, the outer circumference is changed. The laser opens the combustion chamber side opening 114.
The metal shell 1 is seam welded 210 (see FIG. 7).

The pressure-receiving rod 22 has a tubular shape, and is provided with a collar-shaped portion 221 and a thin-walled portion 22 that are held against the bottom surface of the counterbore 11.
2. It has a thick portion 223 on the inner circumference of which a screw 223a is formed.

Reference numeral 7 denotes a heat insulating layer such as RTV rubber, Teflon, oxide coating (for example, alumina sprayed), which is coated on the surface of the diaphragm 21, and is responsive to combustion pressure and heat shielding property. 0.5mm-1mm
To be filmed to the thickness of. As a result, the diaphragm 21
The amount of heat received by the diaphragm is reduced, and thermal deformation of the diaphragm 21 can be prevented.

The spark plug with a cylinder internal pressure detecting device of this embodiment has the advantages according to the above [a] to [c].

The detected pressure curve of the spark plug with a cylinder internal pressure detecting device of the present embodiment shows the pressure in the exhaust stroke after combustion as shown by the wavy lines in FIGS. 5 (c) and 6 (c). The curve is not detected too high, the cylinder pressure can be accurately detected in all strokes, and seating noise of the intake and exhaust valves does not occur.

Next, a third embodiment of the present invention will be described with reference to FIG. The cylinder internal pressure detecting device B has the same configuration as the spark plug with a cylinder internal pressure detecting device of the first embodiment except that the insulator disposing hole 12 is not provided and the spark plug is not assembled. The cylinder internal pressure detection device B of this embodiment has the advantages according to the above [a].

[Brief description of drawings]

FIG. 1 is a sectional view of a spark plug with a cylinder internal pressure detecting device according to a first embodiment of the present invention.

FIG. 2 is a sectional view of a main part of the spark plug.

FIG. 3 is a perspective view of a main part of the spark plug.

FIG. 4 is a sectional view of a main part of the spark plug.

FIG. 5 is a graph comparing the relationship between the crank angle and the in-cylinder pressure of the spark plug with the in-cylinder pressure detecting device according to the related art and the present invention.

FIG. 6 is a graph comparing the P-V diagrams of the spark plug with the cylinder internal pressure detection device according to the related art and the present invention (second embodiment).

FIG. 7 is a cross-sectional view of essential parts of a spark plug with a cylinder internal pressure detecting device according to a second embodiment of the present invention.

FIG. 8 is a cross-sectional view of essential parts of a cylinder internal pressure detection device according to a third embodiment of the present invention.

FIG. 9 is a cross-sectional view of a cylinder internal pressure detection device according to Related Art 1.

FIG. 10 is a cross-sectional view of another cylinder internal pressure detection device according to Related Art 2.

[Explanation of symbols]

 A spark plug with cylinder internal pressure detection device B cylinder internal pressure detection device 1 metal shell 2 pressure receiving member 3 heat shield plate (heat reception reduction means) 5 insulator 6 center electrode 7 heat insulation layer (heat reception reduction means, heat insulation material) 11 counterbore hole 12 insulation Body disposing hole 14 Communication hole 21 Diaphragm 22 Pressure receiving rod 42 Piezoelectric sensor (piezoelectric element) 51 Shaft hole 114 Combustion chamber side opening

Claims (4)

[Claims] 1. A metal shell having a counterbore communicating with a combustion chamber, which is mounted on an engine head of an internal combustion engine, a plate-like diaphragm fitted in a combustion chamber side opening of the counterbore, and the diaphragm. A pressure receiving rod that is connected to the counterbore hole and that detects the combustion pressure of the combustion chamber based on contraction deformation of the pressure receiving rod due to combustion pressure. A cylinder internal pressure detection device characterized in that heat receiving reduction means for reducing the amount of heat received by the cylinder is added to the diaphragm. 2. Displacement or deformation of the pressure receiving rod due to combustion pressure,
Alternatively, the cylinder internal pressure detection device according to claim 1, wherein the contraction deformation is piezoelectrically converted by a piezoelectric element to detect combustion pressure. 3. As the heat reception reducing means, at least one of a heat insulating material coated on the side surface of the combustion chamber of the diaphragm or a heat shield plate fixed to the front surface of the diaphragm by a pillar protruding in the center of the diaphragm. The adopted cylinder internal pressure detection device according to claim 1 or 2. 4. An insulator installation hole is provided in the metal shell of the cylinder internal pressure detection device according to claim 1, and an insulation having an axial hole is provided in the insulation installation hole. A spark plug with a cylinder pressure detector that fits the body and inserts the center electrode into the shaft hole.