This application is based upon and claims benefit of priority of Japanese Patent Application No. 2007-243720 filed on Sep. 20, 2007, the content of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a temperature sensor for detecting temperature in a combustion chamber of an internal combustion engine.
2. Description of Related Art
In a system for controlling operation of an internal combustion engine, an electronic control unit (ECU) controls engine operation to optimum conditions based on signals fed from various sensors. A misfire in a combustion chamber is detected, as one of such signals, by a pressure sensor for detecting pressure in the combustion chamber. An example of the misfire detection based on the pressure in the combustion chamber is disclosed in JP-A-2005-326336.
The pressure sensor disclosed therein is composed of a housing mounted on a cylinder of an internal combustion engine, an elongated pipe extending from the housing, a diaphragm connected to the elongated pipe for directly receiving pressure in a combustion chamber, and a pressure-sensitive element mounted on a rear surface of the diaphragm. The rear surface means a surface which is opposite to a front surface of the diaphragm exposed to the combustion chamber. As shown in
However, a following problem is involved in the pressure sensor disclosed in JP-A-2005-326336. Temperature in the combustion chamber becomes very high when the mixture is fired and exploded, for example, 2000-3000° C. The pressure-sensitive element used in the pressure sensor has a relatively low durability at a high temperature. Accordingly, an accuracy of the detected pressure tends to become low. For protecting the pressure-sensitive element from a high temperature, it is required to provide a temperature-resistive structure for the pressure-sensitive element. This makes the pressure sensor complex and expensive.
The present invention has been made in view of the above-mentioned problem, and an object of the present invention is to provide a temperature sensor for an internal combustion engine for efficiently detecting a misfire in a combustion chamber.
The temperature sensor according to the present invention includes a housing mounted on a cylinder head or a cylinder block of an internal combustion engine. An elongated cylindrical probe portion is connected to the housing so that the probe portion extends into a combustion chamber of the engine. A diaphragm is disposed on a tip of the probe portion so that the diaphragm is exposed to the combustion chamber. A sensor element for measuring temperature in the combustion chamber is mounted on a rear surface, which is opposite to a front surface exposed to the combustion chamber, of the diaphragm. A conductor member for electrically connecting the sensor element to an outside circuit is led out through an inner space of the probe portion and a connector portion coupled to the housing.
The combustion chamber temperature becomes maximum after 5-10 degrees after a top dead center when an air-fuel mixture is successfully ignited, while it does not reach the maximum level when a misfire occurs. By measuring the combustion chamber temperature at a certain degree (e.g., 5-10 degrees) after the top dead center and comparing the detected temperature with a reference temperature, whether a misfire occurred or not is easily detected.
The sensor element may be mounted on a rear surface of a front surface of the diaphragm, or it may be embedded in the diaphragm. The probe portion having the diaphragm and the sensor element may be integrally formed in a spar plug to thereby save a space for the temperature sensor. The sensor element may be composed of a thin film thermistor or a thermocouple coated with a heat-resistive material.
According to the present invention, the misfire in the combustion chamber is surely detected by measuring the combustion chamber temperature with a temperature sensor having a high heat-resistivity without using a pressure sensor having a low heat-resistivity. Other objects and features of the present invention will become more readily apparent from a better understanding of the preferred embodiments described below with reference to the following drawings.
A first embodiment of the present invention will be described with reference to
Now, the temperature sensor 10 will be described with reference to
The probe portion 12 has a screw 12a that is screwed into a female-crew formed in the mounting hole 8 to thereby mount the temperature sensor 10 on the cylinder block 2. A diaphragm 15 is connected to the tip of the probe portion 12 by welding or the like so that it is exposed to the combustion chamber 1 when the temperature sensor 10 is mounted on the engine. The diaphragm 15 is made of a metallic material such as SUS (stainless steel) into a cup shape having an upper opening, as shown in
As shown in
The temperature sensor 10 described above is installed in the cylinder block 2 by fastening the screw 12a to the female screw formed in the mounting hole 8, so that the tip of the probe portion 12 is exposed to the combustion chamber 1. Signals outputted from the sensor element 16 and processed in the signal-processing circuit 17 are fed to the ECU 9 through the terminal 14 disposed in the connector portion 13. The temperature sensor 10 is installed to each cylinder of the multi-cylinder engine.
Advantages attained in the temperature sensor described above will be summarized. Temperature in the combustion chamber is detected by the sensor element 16 attached to the rear surface of the metallic diaphragm 15 with a high response. The temperature in the combustion chamber reaches to a high level, e.g., 2000-3000° C. Since the sensor element 16 for detecting the temperature has a sufficiently high heat-resistivity compared with the pressure sensor element used in the conventional pressure sensor, the sensor element 16 is not much affected by the high temperature, and combustion chamber temperature is accurately detected.
Since the sensor element 16 is attached to the rear surface of the diaphragm 15, the sensor element 16 is not directly exposed to the mixture at a high temperature in the combustion chamber. Since the inner space of the probe portion 12 is closed with the diaphragm 15, the mixture at a high temperature and high pressure does not enter into the inner space of the probe portion 12. Only the conductor element 19 and the sensor element 16 are disposed in the inner space which becomes at a high temperature, while the signal-processing circuit 17 including the IC-chip 18 which has a relatively low heat-resistivity is disposed inside the housing 11 which is kept at a relatively low temperature. Therefore, the components of the temperature sensor are well protected from the high temperature without providing a complex heat-insulating structure.
The ECU 9 controls operation of the engine based on signals fed from various sensors including the temperature sensor 10. The ECU determines whether a misfire occurred or not in the combustion chamber 1 based on the signal from the temperature sensor 10. As shown in
In the present invention, in place of directly measuring the combustion chamber pressure P, the temperature in the combustion chamber is detected by the temperature sensor 10. The combustion chamber pressure P is indirectly detected based on the temperature in the combustion chamber. A relation between the pressure P and the temperature T is expressed in the formula: PV=nRT, where V is a volume of the combustion chamber at a given crankshaft angle α. This means that PV/T is constant. Since the combustion chamber volume V is a known value at a given crankshaft angle, the combustion chamber pressure P can be calculated from the detected temperature T in the combustion chamber. Accordingly, the misfire can be easily determined based on the combustion chamber temperature T. Since the temperature sensor 10 is mounted on each cylinder of the engine, the misfire occurred in each cylinder is accurately detected by the ECU 9.
Thus, according to the present invention, whether the misfire occurred or not is determined based on the temperature detected by the temperature sensor 10 which uses the sensor element 16 having a high heat-resistivity. Therefore, the misfire is surely detected without providing a complex structure for insulating heat.
A second embodiment of the present invention is shown in
A third embodiment of the present invention is shown in
A fourth embodiment of the present invention is shown in
The present invention is not limited to the embodiments described above, but it may be variously modified. For example, the sensor element 16, 37 may be composed of other elements than the thin film thermistor. For example, the sensor element may be composed of a thermocouple made of fine iridium coated with heat-resistive ceramics. Similar advantages are attained in this sensor element, too. Though the temperature sensor is mounted on each cylinder of the engine in the foregoing embodiment, one or more temperature sensors may be selectively installed in a cylinder or cylinders. The conductor member formed on flexible substrate, which is used in the foregoing embodiments, may be replaced with lead wires or other conductors.
While the present invention has been shown and described with reference to the foregoing preferred embodiments, it will be apparent to those skilled in the art that changes in form and detail may be made therein without departing from the scope of the invention as defined in the appended claims.
Number | Date | Country | Kind |
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2007-243720 | Sep 2007 | JP | national |