JPH0634475A - Combustion pressure sensor - Google Patents

Abstract

PURPOSE:To prevent the discoloration of the pressure receiving surface of a combustion pressure sensor which is installed in the combustion chamber of an internal combustion engine, with the pressure receiving surface being exposed, due to the adhesion of carbon, etc., generated in the combustion chamber so as to maintain the sensitivity of the sensor for a long period. CONSTITUTION:The pressure receiving surface 13a of a diaphragm 13 is blackened in advance by a heat resistive coloring method. A heat insulator 14 is provided perpendicularly to the surface 13a at the central part of the surface of the diaphragm 13 opposite to the surface 13a. The diaphragm 13 is fitted to a housing 11 so that the insulator 14 can press a compressive force detecting section 16 in the perpendicular direction with a prescribed compressive force through a semi-sphere 14. A combustion pressure sensor 10 is set in the combustion chamber of an internal combustion engine, with the surface 13a being exposed. Since the surface 13a is blackened, the combustion heat absorptivity of the surface 13a does not change even when carbon, etc., adheres to the surface 13a.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combustion pressure sensor, and more particularly to a combustion pressure sensor arranged in a combustion chamber of an internal combustion engine so that a pressure receiving surface is exposed.

[0002]

2. Description of the Related Art Conventionally, a combustion pressure generated in a combustion chamber of an internal combustion engine is monitored, and ignition timing control of the internal combustion engine is performed. Therefore, the combustion pressure in the combustion chamber is converted into a predetermined electric signal and output. Combustion pressure sensors are known.

Such a sensor is required to accurately detect pressure fluctuations in the combustion chamber. For this reason, the applicant of the present invention, in order to ensure a highly accurate combustion pressure detection accuracy,
A combustion pressure sensor is proposed in which the pressure receiving surface of the sensor is directly exposed in the combustion chamber for use (Japanese Patent Application No. 25385/1990).
9).

In the above-mentioned conventional combustion pressure sensor, a diaphragm manufactured by cutting or the like is used on its pressure receiving surface. The pressure receiving surface (diaphragm) is connected to the compression force detecting portion of the combustion pressure sensor via the heat insulator. Therefore, when the displacement of the pressure receiving surface fluctuates with the pressure fluctuation in the combustion chamber, the compressive force applied to the compressive force detector fluctuates.

As described above, in this combustion pressure sensor, the pressure medium in the combustion chamber is directly guided to the pressure receiving surface. Therefore, the pressure fluctuation in the combustion chamber is accurately propagated to the compression force detection unit, and the combustion pressure is detected with high precision.

[0006]

However, since the above-mentioned conventional combustion pressure sensor is arranged so that the pressure receiving surface is exposed in the combustion chamber, a deposit such as carbon adheres to the pressure receiving surface during use. Therefore, the surface of the pressure receiving surface manufactured by cutting or the like changes from metallic color to black as it is used.

When the surface of the pressure receiving surface is blackened by carbon in this way, the absorption rate of light generated in the combustion chamber changes, and the absorption rate of combustion heat on the pressure receiving surface changes. Therefore, the temperature of the pressure receiving surface in the steady state of the internal combustion engine differs between the new pressure receiving surface and the pressure receiving surface after the passage of time. When the temperature is different, the relationship between the combustion pressure applied to the pressure receiving surface and the displacement, that is, the spring constant changes, and the compression force transmitted to the compression force detection unit changes.

Therefore, in the above-mentioned conventional combustion pressure sensor, due to the requirement for high detection accuracy, the sensitivity of the sensor changes as it is used, even though very strict sensitivity adjustment is performed at the initial stage. Had a point.

The present invention has been made in view of the above points, and prevents the pressure receiving surface from being discolored due to the deposition of deposits of carbon or the like generated in the combustion chamber, so that the sensor sensitivity can be maintained for a long period of time. It is intended to provide a sensor.

[0010]

The above-mentioned problems are transmitted to a compression force detecting section for converting the pressure in the combustion chamber into a compression force and converting the compression force into a predetermined electric signal in the combustion chamber of the internal combustion engine. In the combustion pressure sensor arranged so that the pressure receiving surface of the diaphragm is exposed, the pressure receiving surface is solved by a combustion pressure sensor which is previously blackened by a heat resistant coloring method.

[0011]

According to the above construction, since the pressure receiving surface of the combustion pressure sensor is previously blackened by the heat resistant coloring method, it is not discolored by the heat of combustion and is used as it is in the combustion chamber. There is no discoloration due to carbon generated in. Therefore, the absorption rate of combustion heat on the pressure receiving surface does not change, and the spring constant of the pressure receiving surface does not change with time.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 2 is a block diagram of an example in which a combustion pressure sensor according to the present invention is installed in an internal combustion engine. In the figure, reference numeral 1 represents an internal combustion engine body including the combustion pressure sensor of this embodiment. In the combustion chamber 2 of the internal combustion engine body 1, a piston 3 that reciprocates vertically inside is arranged. The piston 3 is connected to a crankshaft (not shown) via a connecting rod 4, and the reciprocating motion of the piston 3 is converted into rotational motion by this crankshaft.

In the space inside the combustion chamber 2 above the piston 3 at the time of top dead center, an intake pipe 7 and an exhaust gas 8 whose conduction is controlled by an intake valve 5 and an exhaust valve 6 communicate with each other, and an ignition plug. 9 and the combustion pressure sensor 10 having the pressure receiving surface of the present embodiment configuration are arranged. The combustion pressure sensor 10 is connected to an electronic control unit (not shown) via a wire harness, and supplies the electronic control unit with an electric signal corresponding to the combustion pressure in the combustion chamber 2. The electronic control unit controls the ignition timing and the like by the ignition plug 9 so that the combustion is efficiently performed in the combustion chamber 2 based on the electric signal.

The pressure in the combustion chamber 2 of the four-cycle internal combustion engine shown in the figure changes in a four-cycle cycle. That is,
In the intake stroke, the piston 3 with the intake valve 5 opened
Moves from a position near the top dead center to a position near the bottom dead center and tries to suck the fuel gas, the pressure in the combustion chamber 2 becomes a negative pressure. Next, in the compression process, the piston 3 moves from the vicinity of the bottom dead center to the vicinity of the top dead center with the intake valve 5 closed, and the fuel gas sucked into the combustion chamber is compressed. Becomes

Next, in the explosion process, when the spark plug 9 emits a spark, the compressed fuel gas ignites and explodes, and the piston is pushed down toward the bottom dead center. The pressure in the combustion chamber 2 has a maximum during this process. Finally, in the exhaust process, when the piston 3 moves from the vicinity of the bottom dead center toward the top dead center with the exhaust valve 6 open, the exhaust gas in the combustion chamber 2 is compressed by the ventilation resistance between the exhausts 8. It is exhausted while being done. Therefore, the pressure in the combustion chamber 2 in this step becomes a positive pressure.

The combustion pressure sensor 10 is arranged so that the pressure receiving surface is exposed in the combustion chamber, and is exposed to the combustion pressure repeated every four steps described above. That is, it is necessary to accurately detect a wide range of pressure from a negative pressure in the intake process to a positive pressure in the explosion process, and durability against combustion heat is required.

FIG. 1 shows an enlarged view of an embodiment of a combustion pressure sensor according to the present invention. The configuration of the combustion pressure sensor 10 will be described below with reference to FIG.

In the figure, reference numeral 11 indicates a housing of the combustion pressure sensor 10. The housing 11 accommodates various components described below inside, and a threaded portion 12 is provided around the small diameter portion. The combustion pressure sensor 10 is attached to the internal combustion engine body 1 with the screw portion 12.

A diaphragm 13, which is an essential part of this embodiment, is arranged at the tip of the screw portion 12 with the pressure receiving surface 13a as the outside. The pressure receiving surface 13a is circular, and the pressure receiving surface 1
When the pressure applied to 3a changes, the central portion of the diaphragm 13 is displaced in the direction perpendicular to the pressure receiving surface 13a.

A heat insulator 14 is arranged on the surface of the diaphragm 13 opposite to the pressure receiving surface 13a. The other end of the heat insulator 14 presses the compression force detection unit 16 via the hemisphere 15. That is, the compression force detection unit 16 of the combustion pressure sensor 10 used in this embodiment is in a pre-pressurized state. Therefore, the combustion pressure sensor 10 can detect the negative pressure in the combustion chamber 2.

However, this pre-pressurization is applied to the diaphragm 1.
3, it varies depending on the dimensional accuracy of the heat insulator 14, the hemisphere 15, and the like. Therefore, the combustion pressure sensor 10 used in the present embodiment needs to be adjusted using a hydraulic bench or the like so that a predetermined electric signal is output for a predetermined pressure in the assembled state.

The compressive force detector 16 is a semiconductor element that converts the compressive force into a predetermined electric signal and is damaged when the combustion heat in the combustion chamber 2 is directly applied due to heat resistance.

Therefore, the combustion pressure sensor of this embodiment has a structure in which the heat insulator 14 is sandwiched between the diaphragm 13 and the compression force detecting portion 16. That is, the heat insulator 14 has a function of propagating the compressive force supplied via the diaphragm 13 to the compressive force detection unit 16 and a function of thermally disconnecting the diaphragm 13 and the compressive force detection unit 16. ing. Therefore, a semiconductor compression force detection circuit can be used for the compression force detection unit 16 of the combustion pressure sensor of this embodiment without concern about heat resistance.

The hemisphere 15 interposed between the heat insulator 14 and the compression force detecting portion 16 is provided in the compression force detecting portion 16 even if the heat insulator 14 and the compression force detecting portion 16 are not vertically pressed for some reason. It acts to apply a force in the vertical direction.

The compression force detector 16 is connected to the output circuit 18 by a lead 17. An amplifier circuit and a filter circuit are incorporated in the output circuit 18, and the electric signal supplied from the compression force detection unit 16 is converted into a desired electric signal.

The output terminal 19 of the output circuit 18 is connected to the connector terminal 20, and to the connector terminal 20, a wire harness with a connector (not shown) is connected. Therefore, the desired electric signal output from the output circuit 18 is supplied to the electronic control unit via the wire harness.

FIG. 3 is an enlarged view of the diaphragm 13 having the pressure receiving surface having the structure according to the present invention. The configuration of the pressure receiving surface of the diaphragm, which is the main part of this embodiment, will be described below. In the figure, the same parts as those in FIG. 2 are designated by the same reference numerals and the description thereof will be omitted.

Diaphragm 1 of the combustion pressure sensor of this embodiment
3 is made of stainless steel. As mentioned above,
If the pressure receiving surface 13a is formed of a surface of stainless steel having a metallic luster, the pressure receiving surface 13a becomes black with the passage of time due to adhesion of carbon or the like. On the other hand, in the combustion chamber 2 of the internal combustion engine, when the fuel is combusted in the explosion process, combustion light is generated along with the combustion.

Therefore, the absorptance of combustion light is different and the temperature of the diaphragm 13 is different between the case where the pressure receiving surface 13a is exposed of stainless steel and the case where carbon or the like adheres to the pressure receiving surface 13a and is made black. It will be. When the temperature of the diaphragm 13 is different, the elasticity is different, and the spring constants are different, and even if the same combustion pressure is applied to the pressure receiving surface 13a, the compressive force transmitted to the compressive force detecting unit 16 is different.

That is, when the pressure receiving surface 13a is made of bare stainless steel, the sensor sensitivity of the combustion pressure sensor 10 changes with time as the spring constant of the diaphragm 13 changes. For this reason, a desired electric signal may not be obtained from the combustion pressure sensor 10 with the passage of time even though the pressure is adjusted strictly using a hydraulic bench or the like when the product is new.

The pressure receiving surface 13a of the combustion pressure sensor 10 of the present embodiment has been blackened in advance by a heat resistant coloring method in order to prevent fluctuations in sensor sensitivity due to blackening of the pressure receiving surface. In other words, the pressure receiving surface 13a has been black since it was new, and even if carbon or the like adheres to the pressure receiving surface 13a when it is used in the combustion chamber, a large difference does not occur in the absorption rate of combustion light. Therefore, the temperature of the diaphragm 13 when the internal combustion engine 1 is operating is
Since the temperature is almost the same both when the product is new and after a lapse of time, and the spring constants thereof are almost the same, the sensor sensitivity as adjusted when the product is new is maintained.

As described above, according to the combustion pressure sensor having the pressure receiving surface of the present embodiment, the sensor sensitivity is unlikely to change with time. Furthermore, since it is not affected by the generation state of carbon and the like which is influenced by the running conditions and the like, it is possible to maintain a highly accurate sensor sensitivity for a long period of time regardless of individual differences in the usage environment and the like.

As the heat-resistant coloring method for the pressure-receiving surface of the constitution of this embodiment, an acidic black oxidation method of immersing stainless steel in an aqueous sulfuric acid solution to blacken it, or a mixture of caustic soda, sodium phosphate, sodium sulfate, etc. It is possible to use an alkaline black coloring method for blackening the liquid.

The heat-resistant coloring method for the pressure-receiving surface is not limited to these methods. For example, other known methods for surface hardening treatment of stainless steel, such as carburizing or nitriding treatment of the surface of stainless steel, or It can also be realized by applying heat-resistant coating or the like using a silicone resin coating to the pressure receiving surface of the diaphragm.

[0035]

As described above, according to the present invention, it is possible to prevent the pressure receiving surface from being discolored by carbon or the like generated in the combustion chamber. Therefore, there is no change in the combustion heat absorption rate on the pressure receiving surface, and no change occurs in the diaphragm temperature during steady operation. Therefore, the diaphragm always converts the pressure received by the pressure receiving surface into a compressive force with a constant spring constant.

Therefore, in the combustion pressure sensor having the pressure receiving surface of the conventional structure, when the carbon or the like adheres to the pressure receiving surface, the sensor sensitivity is changed. On the contrary, the combustion pressure sensor having the pressure receiving surface having the structure of the present invention is It has the feature that the sensor sensitivity can be kept almost constant over a long period of time.

[Brief description of drawings]

FIG. 1 is a sectional view showing the configuration of an embodiment of a combustion pressure sensor according to the present invention.

FIG. 2 is a configuration diagram showing an example of a state in which an embodiment of a combustion pressure sensor according to the present invention is attached to an internal combustion engine.

FIG. 3 is a configuration diagram of an example of a diaphragm that is a main part of a combustion pressure sensor according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Internal combustion engine body 2 Combustion chamber 10 Combustion pressure sensor 13 Diaphragm 13a Pressure receiving surface 14 Heat insulator 16 Compressive force detector

Claims (1)

[Claims] 1. A pressure receiving surface of a diaphragm is exposed in a combustion chamber of an internal combustion engine so as to convert a pressure in the combustion chamber into a compression force and transmit the compression force to a compression force detection unit for converting the compression force into a predetermined electric signal. In the disposed combustion pressure sensor, the pressure receiving surface is previously blackened by a heat resistant coloring method.