JP2010230610A - Temperature measurement sensor for internal combustion engine, and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the thermal response and reliability of an exhaust temperature sensor. <P>SOLUTION: For improving the thermal response and reliability of the exhaust temperature sensor, cement filled into a gap between a thermistor and a sack-shaped tube is made of a high-heat conduction object made of nitride. Especially, a filler filled into the gap between the thermistor of a temperature detection section and the sack-shaped tube is devised, the thermal response is improved, and a reliable filler is designed. Specifically, as the cement as the filler, a filler produced by blending thermally conductive materials such as silicon nitride (Si<SB>3</SB>N<SB>4</SB>), aluminum nitride (AlN), boron nitride (BN), and sialon is used. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  It is suitable as a temperature sensor for measuring the temperature of each part gas fluid in an internal combustion engine. In particular, the present invention relates to a temperature sensor used for measuring a temperature of a gas fluid from about 100 ° C. to 1000 ° C.

  Techniques related to the present invention are as follows.

JP 2000-266609 A JP 2008-26012 A

  As a measure to prevent global warming, reducing the amount of fossil fuel used in automobiles to reduce carbon dioxide emissions is a proposition of the automobile industry, and the development of diesel engines and fuel-efficient gasoline engines I'm in a hurry. As a countermeasure, diesel engines and gasoline engines tend to cope by improving the accuracy of combustion control. As information indispensable for improving the accuracy of the combustion control, the temperature of the combustion gas passing through each part of the internal combustion engine is important. However, since the temperature of the combustion gas itself is a high temperature range of 400 ° C. to 800 ° C. and the combustion gas itself is a corrosive gas fluid such as SOx, NOx, COx, a temperature sensor is used as a countermeasure against high temperature oxidation and corrosion. Due to the structure completely covered with corrosion-resistant stainless steel, there was a drawback of poor thermal response.

  To increase the accuracy of combustion control in internal combustion engines, it is important to detect the temperature of the gas flowing through each part in real time and to provide detailed combustion control by feeding back the combustion state. If the thermal response of the signal is slow, the control error increases and the intended control cannot be performed.

  The present invention is a gas temperature sensor for an internal combustion engine, such as automobile exhaust gas, EGR gas, combustion gas, exhaust gas before and after DPF, etc., and a temperature sensor with high thermal responsiveness while guaranteeing high temperature oxidation and corrosion resistance. It can be invented.

  The above object can be achieved by the invention described in the claims.

  For example, in the case of a thermistor temperature sensor that uses a thermistor for temperature measurement in the market as a temperature measurement sensor for each part of an exhaust system of an internal combustion engine, the entire thermistor element is used to protect the thermistor element from corrosive gas. It is a simple structure in which the electrode signal from the thermistor is output to the outside with a simple structure in which it is covered with a stainless steel bag tube to be covered and a heat insulating structure is provided in the middle. Here, the gap between the thermistor of the temperature detection unit and the bag is filled with cement made of silica, alumina, etc., so that the thermal response is improved, but in the present invention In addition, the filler which fills the gap between the thermistor of the temperature detection unit and the bag is devised to improve the thermal response and to devise a highly reliable filler.

Specifically, a filler in which a material having high thermal conductivity such as silicon nitrite (Si ₃ N ₄ ), aluminum nitride (AlN), boron nitride (BN), and sialon is blended with the cement as the filler is used. Is achieved.

In addition, as a structure for filling the gap between the thermistor of the temperature detection unit and the bag, the gap between the thermistor of the temperature detection unit and the bag is once filled with powdered silicon nitrite (Si ₃ N ₄ ), aluminum nitride ( This is achieved by filling with a material having high thermal conductivity such as AlN), boron nitride (BN), sialon, etc., and then blowing and sealing the powdery filler with cement containing a glass member.

  ADVANTAGE OF THE INVENTION According to this invention, a temperature sensor with quick thermal responsiveness can be provided as a gas temperature sensor of internal combustion engines, such as exhaust gas for motor vehicles, EGR gas, combustion gas, and exhaust gas before and after DPF.

Diesel engine system. Gas temperature sensor mounting part. General exhaust temperature sensor structure. FIG. 4 is a cross-sectional structure diagram of FIG. 3. The cross-sectional structure of the exhaust temperature sensor of the present invention. The mechanism for improving the thermal response according to the present invention. 4 is another embodiment of the exhaust temperature sensor of the present invention.

  Hereinafter, specific examples will be described.

  Before describing the features of the present invention, an internal combustion engine for an automobile will be described. Here, a diesel engine will be described briefly. FIG. 1 shows a general diesel engine 1. The system is a system in which intake air 2 is combusted when air whose flow rate is adjusted by a throttle valve 3 installed upstream of the intake manifold is sent into the cylinder 4 and compressed inside the cylinder 4. The combustion gas 5 branches through the exhaust pipe 6. One is sent to the turbocharger 7 and output is added by the supercharger. The combustion gas 5 discharged from the turbocharger 7 passes through a purification device 8 (DPF) provided with a catalyst as exhaust gas, and is discharged to the outside as clean air. On the other hand, the non-burning gas in the combustion gas 5 is re-refluxed to the cylinder 4 again, thereby reducing the NOx and SOX components contained in the unburned components. There is a bypass pipe that is provided in a part of the exhaust pipe 6 and flows the combustion gas 5, and the flow rate of the combustion gas 5 is controlled by the EGR valve 10 through the bypass pipe 9. Since the temperature of the combustion gas 5 as the exhaust gas is as high as 400 ° C. or higher, the gas temperature is lowered to 200 ° C. or lower through the EGR cooler 11. The system is sent to the downstream side of the throttle valve 3 through the EGR recirculation pipe and burned again in the cylinder 4, which greatly contributes to the purification of exhaust gas.

  The key components used in the diesel engine 1 are an air flow meter 12, an intercooler 13, a throttle valve 3, an EGR valve 10, an EGR cooler 11, a turbocharger 7, a DPF 8, and the like. In the diesel system, EGR is gasoline. Since the flow rate is larger than that of the engine and the recirculation is intentionally performed by EGR, the reliability of each part is important.

  In particular, since diesel engine 1 uses light oil as a fuel, the ignition point of the fuel is high, and the combustion gas 5 tends to generate not only completely burned gas but also unburned gas. In the state where NOx, SOx, and COx are mixed in the unburned gas, the components change every moment according to changes in the operating state and the environmental state. Further, the unburned gas and the exhaust gas are corrosive gas because NOx, SOx, and COx are mixed, and special metals and inorganic members tend to be used because general members are not used.

  The temperature of exhaust gas and unburned gas, which are combustion gases, varies depending on operating conditions and environmental conditions, but is said to be 400 ° C to 900 ° C for exhaust gas and 600 ° C or higher for unburned gas. Therefore, special metals and inorganic members are used.

  In recent years, regulations on exhaust gas have been strengthened, so each car manufacturer is considering improvements to exhaust clean exhaust gas from which NOx and SOx have been removed from the exhaust gas. As a method that can be most easily realized, the concept of the system of the current diesel engine 1 is to realize a system that can perform combustion control with higher accuracy as it is. An example of the high-precision combustion control system is the system configuration shown in FIG.

  In FIG. 2, there is no change in the combustion system itself of the diesel engine. However, there is a change point in that the gas temperature sensor 17 is provided in each part of the system. The gas temperature sensor 17 is an existing product, and is an exhaust gas temperature sensor 17 that is attached to an exhaust pipe mainly for exhaust gas temperature measurement and measures the temperature of the exhaust gas. The main function was a temperature monitor.

  In the high-precision control system, as described above, the gas temperature sensor 17 is provided in each part of the system, so that the combustion state of each part can be monitored.

  However, current exhaust temperature sensors are difficult to handle. The reason for this will be described later.

  In the diesel system, the DFF gas temperature sensor 17 is provided at the front and rear 14 of the DPF 8 in addition to the exhaust pipe, in addition to the exhaust pipe. By using the gas temperature sensors 17 before and after the DPF 8, it is possible to ask the catalyst activation state of the DPF 8, and it can be a control sensor for the DPF 8 catalyst.

  Similarly, a gas temperature sensor 17 may be provided on the front and rear 15 of the EGR cooler 11 to control the active state of the EGR cooler. A gas temperature sensor 17 that measures the gas temperature itself may be attached to the front and rear 16 of the EGR valve 10.

  In other words, by providing the gas temperature sensor 17 at each part into which the gas fluid of the diesel engine 1 flows, the state of the exhaust gas purification system and the cooling device can be a secondary signal that can further confirm the combustion state. Thus, by monitoring the gas temperature of each part, it can be a system capable of performing more accurate combustion control.

  However, the gas temperature sensor 17 for the internal combustion engine currently listed has many restrictions due to the environmental conditions as described above, corrosive gases such as NOx and SOx, and high-temperature environments exceeding 400 ° C. It is a difficult sensor to handle.

  3 and 4 show the structure of a gas temperature sensor 17 for measuring a general exhaust temperature currently listed.

  In recent years, it is likely that the gas temperature sensor 17 generally uses a thermistor element 18 as a temperature detection element. As the thermistor, a thermistor element obtained by kneading a metal such as iron, chromium, nickel or cobalt with an organic binder and firing it is used. Since the signal line 19 coming out of the thermistor element 18 has a measurement target gas temperature of 400 ° C. or higher, the signal line 19 is made of a heat-resistant and corrosion-resistant material such as platinum, platinum alloy containing platinum, or stainless steel. Is the lead. The signal line 19 is extended as it is, and the signal line 19 is extended through a hole formed in the sheath tube 20 made of an inorganic material to prevent contact and cope with vibration resistance. Further, the signal line 19 is extended to the outside through a grommet 21 made of heat-resistant rubber. The signal line 19 is welded and crimped with a normal copper wire in the vicinity of the grommet 21 and transmits a signal to the ECU.

  The grommet 21 and the sheath tube 20 are fixed by being installed in a flange tube 23 made of a heat-resistant and corrosion-resistant member that covers the outer periphery of the grommet 21 and a mounting screw, and a fixing screw cut. The thermistor element 18 of the gas temperature sensor 17 is structured to cover the thermistor element 18 with a cylindrical bag tube 24 covering the thermistor element 18 and weld the contact portion with the flange tube 23. In the present invention, the thermistor element 18 is described as a representative example of the temperature measuring element of the temperature sensor, but the same applies to thermocouples, and it refers to all elements that generate signals that can measure temperature. Not too long.

  Although the temperature sensor using the thermistor element has a simple structure and can be manufactured at a low price, there is room for improvement in performance and reliability. An improvement item in performance is thermal responsiveness. The improvement item in reliability is the reliability of the filler that fills the gap between the thermistor of the temperature detection element and the bag, and the reliability of itself.

  Hereinafter, the present invention will be described with the problems and the improvement points clearly specified.

  First, performance improvement items will be described. As described above, in order to clear the new exhaust gas regulations, it is necessary to measure the gas fluid temperature of each part of the exhaust, but the temperature sensors currently distributed in the market have the disadvantage of slow thermal response. is there. In order to optimize the combustion using the temperature signal, it is indispensable that the response characteristic is at least 10 seconds or less. However, the current commercial product takes about 14 to 20 seconds, and therefore engine control is required. In this case, the gas temperature sensor 17 is difficult to handle. As an extreme idea, if the structure without the bag tube 24, that is, the thermistor element 18 is exposed to the combustion gas 5, the thermal response naturally becomes faster. However, when exposed to the combustion gas 5 (exhaust gas), the thermistor element 18 is corroded. Therefore, a bag tube 24 serving as a protective tube for preventing direct contact with the combustion gas 5 is required.

  This is because a temperature measuring element such as the thermistor element 18 is not in direct contact with the gas fluid, but through the bag tube 24 and further through the cement 25 located between the bag tube 24 and the thermistor element 18. Therefore, this is a mechanism for slowing the thermal response when the gas temperature changes.

  An improvement item in reliability is a temperature sensor structure that can withstand thermal stress. The exhaust gas temperature is said to be 200 to 400 ° C. in a steady state, but in the case of a sudden accelerator opening, the exhaust gas is up to 800 ° C. when a sudden load is applied to the engine. It will be in a state of rising rapidly in the moment. When the thermistor element 18 is exposed to this environment, there is a high possibility that it does not have a resistance sufficient to withstand thermal stress against a sudden change in the temperature of the thermistor element 18.

  The present invention has invented a structure capable of providing a temperature sensor capable of solving the above-mentioned problems.

  Details of the present invention will be described with reference to FIGS. 3, 4, 5 and 6.

  The structure of the gas temperature sensor 17 of the present invention will be introduced. In the present invention, there is no change in the appearance and internal structure of the temperature sensor described above. The point of the present invention is that the cement 25 that fills the gap 26 between the bag tube 24 and the thermistor element 18 is devised. The purpose of the cement 25 filling the gap 26 between the bag tube 24 and the thermistor element 18 of the gas temperature sensor 17 currently distributed in the market is for mechanical fixation so that the thermistor element 18 does not become a pendulum due to vibration. is there. Therefore, for the purpose of sealing only the thermistor element 18 and the stainless steel tube that becomes the bag tube 24, the bag tube 26 is filled with cement 25 prepared by dissolving a mixture of inorganic powders such as alumina and silica with an organic binder. It has a bamboo structure.

  In the present invention, the cement 25 is devised to improve the reliability while improving the thermal response by improving the cement 25 originally intended to prevent the pendulum in vibration.

  FIG. 5 is a structure representing the present invention. The cement 25 of a general gas temperature sensor 17 is made by adding glass to an inorganic powder such as alumina or silica and making a paste with an organic binder, and filling the bag tube with a dispenser or the like. The gap 26 of the tube 24 is filled.

  The main components differ depending on the temperature sensor manufacturer, but when alumina is the main, the thermal conductivity of alumina is 25 (W / m · k) and the thermal conductivity of glass is 2-5 (W / m · k). Therefore, it cannot be said that the heat conductivity is good. That is, the factor that deteriorates the thermal response in general products is that the thermal conductivity of the cement 25 is small. In particular, glass is about 1/10 of an inorganic substance and can be said to be a thermal insulator. This glass is an important substance that causes alumina and silica to be dispersed and held in this state, and to develop an adhesive action between the thermistor element 18 and the bag tube 24, and cannot be easily removed. Although it is indispensable to mix a glass component, this glass component causes a slow thermal response.

In the present invention, an inorganic material having a high thermal conductivity is selected for the cement 25 and blended with glass. As the cement 25, powder, bulk, or crystal formed from a member having high thermal conductivity such as silicon nitrite (Si ₃ N ₄ ), aluminum nitride (AlN), boron nitride (BN), sialon, or the like is used. Most of the high thermal conductivity inorganic materials described above are nitrides 27. By blending the glass 28 with these high thermal conductivity inorganic members, the cement 29 can cover the low thermal conductivity of the glass 28. Is completed, the cement 29 can immediately conduct the heat from the bag tube to the thermistor element 18, and the structure of a high-speed thermal response temperature sensor is obtained.

  FIG. 6 is an image of an effective embodiment for improving the thermal response. Stainless steel is often used for the bag tube 24 covering the thermistor, but stainless steel is a member having a thermal conductivity of 15 (W / m · k), which is not so good. According to the present invention, the cement 25 filled in the stainless steel bag tube 24 is estimated to be 5-10 (W / m · k) as a general product, and the cement 25 has a lower thermal conductivity than the stainless steel bag tube 24. It is estimated. Therefore, if the temperature is taken into account as a signal, the heat received by the bag tube reaches the thermistor while being attenuated, resulting in a slow thermal response. Therefore, by increasing the thermal conductivity of the cement 29 more than the thermal conductivity of the bag tube, thermal diffusion is accelerated and the sensor has a quick thermal response.

  In the present invention, in order to improve the thermal response, the cement 25 filled in the bag tube 24 is characterized by using a highly heat conductive inorganic member as the cement 29. However, these are inorganic materials having high heat conductivity. The problem with the members is that, when exposed to high temperatures for a long time, the nitrides, which are the main components of cement, are oxidized to normal alumina and boron oxide, and the thermal conductivity deteriorates. is there. In this case, as the thermal response is transformed from nitridation to oxidation, the engine response is deteriorated.

  Another embodiment of the present invention is shown in FIG. In the present invention, the cement 29 filled in the bag tube 24 is roughly made of an inorganic member, particularly nitride 27 in powder or bulk form. Glass 28 is added thereto, the paste kneaded with an organic binder is filled into the bag tube 24, and once heated to a temperature at which the glass 28 is fired, it is vitrified. Once cooled, the bag tube 24 is further filled with an inorganic filler 30 and baked to cover the gap 26 between the thermistor element 18 and the bag tube 24 so that the cement 29 does not come into contact with oxygen, thereby preventing oxidation. By functioning as a film, it can be a highly reliable temperature sensor in which the physical constant such as the thermal conductivity of the cement 29 covering the gap 26 between the thermistor element 18 and the bag tube 24 does not change even after long-term use.

  In the present embodiment, a structure is proposed in which the cement 25 or the thermistor element 18 is not destroyed by the thermal stress even by the thermal stress of the cement 25 covering the gap 26 between the thermistor element 18 and the bag tube 24. Generally, the thermal expansion coefficient of the thermistor element 18 is 5-10 (ppm / ° C.), and the thermal expansion coefficient of the thermistor element 18 to be the bag tube 24 is considerably different from 16-18 (ppm / ° C.). Therefore, if the thermal expansion coefficient of the cement 29 in contact with both is not taken into consideration, the thermistor element 18 may be destroyed in some cases.

  In the present invention, considering that the thermistor element 18 is not destroyed, the thermal expansion coefficient of the cement 29 to be filled coincides with that of the thermistor element 18 or the thermal expansion coefficient α1 of the thermistor element 18 is used. When the expansion coefficient α2 is defined, the difference δα between the two thermal expansion coefficients is obtained. In the present invention, the coefficient of thermal expansion αs of the cement 29 is δα ≦ αs ≦ α1.

  According to this, the thermistor element 18 is combined with the thermistor element 18 or has an expansion coefficient smaller than that of the bag tube, so that the thermistor element 18 performs the same expansion and contraction behavior together with the cement 29 due to thermal expansion. The thermistor element 18 does not break down due to thermal stress, and the temperature sensor is highly reliable.

  According to the present invention, it is expected that the temperature of each part gas fluid of the internal combustion engine can be supplied with a temperature sensor that has a fast thermal response and can guarantee long-term reliability that also serves as corrosion resistance.

1 Diesel Engine 2 Intake Air 3 Throttle Valve 4 Cylinder 5 Combustion Gas (EGR Gas)
6 Exhaust pipe 7 Turbocharger 8 DPF
9 Bypass pipe 10 EGR valve 11 EGR cooler 12 Air flow meter 13 Intercooler 14 DPF front and rear 15 EGR cooler front and rear 16 EGR valve front and rear 17 Gas temperature sensor 18 Thermistor element 19 Signal line 20 Sheath pipe 21 Grommet 22 Flange 23 Flange pipe 24 Bag pipe 25 Cement 26 Crevice 27 Nitride 28 Glass 29 Cement 30 Filler

Claims (5)

A thermistor element;
A lead wire joined to the electrode of the thermistor element;
A metal surrounding member surrounding the thermistor element and the lead wire,
In the temperature sensor for an internal combustion engine in which a part of the gap of the surrounding member is filled with cement,
A temperature sensor for an internal combustion engine, wherein the cement is mixed with an inorganic nitride. In claim 1,
A temperature sensor for an internal combustion engine, wherein the cement contains silicon nitride, aluminum nitride, boron nitride, and sialon. In claim 1,
A temperature sensor for an internal combustion engine, wherein the cement has a thermal conductivity that is at least greater than that of the metal surrounding member. In claim 1,
The thermal expansion coefficient of the cement is the same as that of the thermistor element, or the thermal expansion coefficient α1 of the thermistor element and the thermal expansion coefficient α2 of the surrounding member are defined as the difference δα between the two. In this case, the internal combustion engine temperature sensor is characterized in that the thermal expansion coefficient αs of the cement is δα ≦ αs ≦ α1. A thermistor element;
A lead wire joined to the electrode of the thermistor element;
A metal surrounding member surrounding the thermistor element and the lead wire,
In the manufacturing method of a temperature sensor for an internal combustion engine in which a part of the gap of the surrounding member is filled with cement,
After the gap between the thermistor and the surrounding member is filled with inorganic nitride, it is further filled with inorganic cement,
A method for producing a temperature sensor for an internal combustion engine, characterized in that an inorganic nitride and a multilayer filling that does not directly contact air are filled.

Images