JPH0584852U - Air-fuel ratio detector for internal combustion engine - Google Patents

Abstract

(57) [Summary] [Objective] When an oxygen sensor with a heater is arranged downstream of a catalytic converter, it is prevented that moisture in the exhaust pipe comes into contact with a sensor element that has become hot and cracks due to a thermal shock. [Structure] The heater of the oxygen sensor is energized at the same time as the engine is started, and energization is continued until the element temperature reaches 330 ° C (S1, S2). When the temperature reaches 330 ° C., the exhaust pipe temperature is judged (S3).
The energization is ON / OFF controlled so that the temperature is within the range of 00 ° C to 330 ° C (S4, S5). If the temperature of the exhaust pipe is 100 ° C. or higher, water becomes water vapor, so that there is no fear of cracking and the heater is continuously energized.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to an air-fuel ratio detecting device used for an air-fuel ratio feedback control system of an internal combustion engine, and more particularly to an air-fuel ratio detecting device having an oxygen sensor with a heater arranged downstream of a catalytic converter in an exhaust system.

[0002]

[Prior Art]

 For example, in an air-fuel ratio feedback control system for an internal combustion engine, an oxygen sensor is arranged upstream of the catalyst converter in the exhaust system to detect the air-fuel ratio, that is, the residual oxygen concentration in the exhaust. This oxygen sensor uses a tube-shaped ceramic element such as zirconia with a sealed tip, as the sensor element, so that the atmosphere is in contact with the inner surface and the exhaust gas is in contact with the outer surface. Has become. A metal protector having a cylindrical shape with a bottom is provided so as to cover the tip of the sensor element supported by the holder, and protects the brittle ceramic sensor element. The protector is provided with, for example, a slit-shaped communication hole for allowing exhaust gas to flow therethrough. In addition, this type of oxygen sensor is not activated until the sensor element reaches a high temperature of about 350 ° C., for example, and an appropriate output cannot be obtained. Therefore, in order to accelerate the activation, a tubular sensor is required. A so-called heater-equipped oxygen sensor in which a heater such as a ceramic heater is arranged in the center of the element is often used. The heater is energized at the same time when the engine is started, and is deenergized when the sensor is sufficiently activated.

[0003]

[Problems to be solved by the device]

 By the way, in recent years, in order to improve the control accuracy of an air-fuel ratio feedback control system for an internal combustion engine, some systems have been proposed in which an oxygen sensor is provided not only on the upstream side of the catalytic converter but also on the downstream side of the catalytic converter.

However, on the downstream side of the catalytic converter of the exhaust pipe, when the exhaust system is not sufficiently warmed, the water condensed in the catalytic converter may be scattered along with the exhaust gas, or depending on the piping layout, it may be at the bottom of the exhaust pipe. Condensed water may accumulate. Therefore, if an oxygen sensor with a heater is placed downstream of the catalytic converter, water droplets that have penetrated through the communication hole of the protector come into contact with the sensor element that has become hot due to the heater and rapidly cool the sensor element. There was a risk that the thermal shock would cause the sensor element to crack.

[0005]

[Means for Solving the Problems]

 Therefore, the present invention proposes an exhaust pipe temperature detecting means for detecting an exhaust pipe temperature in the vicinity of an oxygen sensor in an air-fuel ratio detecting device in which an oxygen sensor with a heater is arranged downstream of a catalytic converter in an exhaust system of an internal combustion engine. An element temperature detecting means for detecting the element temperature of the oxygen sensor, and a heater control means for controlling heater energization so that the element temperature does not exceed a predetermined temperature until the exhaust pipe temperature reaches about 100 ° C. or more. It is characterized by

[0006]

[Action]

 Cracking of the sensor element occurs only when the exhaust pipe temperature is low, water remains in the liquid state, and the element temperature is higher than a certain temperature. If the temperature of the exhaust pipe is high and the water content is steam, no cracks will occur. Further, when the element temperature is low, even if water drops come into contact with each other, cracking does not occur.

Therefore, in this invention, the exhaust pipe temperature and the sensor element temperature are detected, and the heater energization is controlled based on the relationship between them. When the temperature of the exhaust pipe is a low temperature of about 100 ° C. or less, water in a liquid state exists, so that the element temperature is controlled so as not to exceed a predetermined temperature. This predetermined temperature is set in a range in which the sensor element does not break even if it comes into contact with water droplets.

[0008]

【Example】

 FIG. 1 shows an embodiment of an air-fuel ratio detecting device according to the present invention, in which an exhaust pipe 2 extending from an internal combustion engine 1 is provided with a catalytic converter 3 and a downstream side of the catalytic converter 3. An oxygen sensor 4 with a heater is arranged. Further, a temperature sensor 5 for detecting the temperature of the exhaust pipe 2 is provided near the oxygen sensor 4.

The oxygen sensor 4 is configured, for example, as shown in FIG. 2, and the sensor element 6 is made of ceramics such as zirconia and has a tube shape with a closed tip. . The sensor element 6 is fitted and held in the central part of a holder 7 made of metal, and the base end is pressed down by an intermediate insulating material 8 made of ceramics. A contact plate 9 for extracting an output signal is held between the base end of the sensor element 6 and the intermediate insulating material 8, and the output terminal 10 is electrically connected to the contact plate 9. A base end side insulating material 11 is further connected to the base end of the intermediate insulating material 8, and the disc spring 12 is pressed against the holder 7 as a unit. A ceramics heater 13 is provided at the center of the sensor element 6, and a heater terminal 14 is connected to the base end of the ceramics heater 13. Further, 15 is a cylindrical inner cap welded to the holder 7 so as to cover the outer peripheries of the insulating materials 8 and 11, 16 is an outer cap further welded to the base end of the inner cap 15, and 17 is an outer cap. It is a synthetic resin seal cap fixed in the inside 16. A protector 18 having a slit-shaped communication hole (not shown) is provided at the tip of the holder 7 so as to cover the sensor element 6 protruding from the holder 7.

The output signal of the oxygen sensor 4 is input to the control unit 19 together with the output signal of the temperature sensor 5. The energization of the heater 13 of the oxygen sensor 4 is controlled by the control unit 19 described above. In this embodiment, the temperature of the sensor element 6 is detected by the voltage level of the voltage signal output by the oxygen sensor 4.

FIG. 3 is a flow chart showing the contents of the energization control of the heater 13. The heater 13 is turned on (step 1) at the same time when the engine is started, and the sensor element 6 is turned on at step 2. Repeatedly determine whether the temperature is 330 ° C or higher. Here, electricity is continuously supplied to the heater 13 until the element temperature reaches 330 ° C. If the element temperature has reached 330 ° C., it is determined in step 3 whether the exhaust pipe temperature is 100 ° C. or lower. If the exhaust pipe temperature is 100 ° C. or higher, the energization to the heater 13 is continued, but if it is 100 ° C. or lower, the process proceeds to step 4 and the energization to the heater 13 is stopped. Then, in step 5, it is determined whether or not the element temperature is 300 ° C. or lower, and the heater 13 is kept in the OFF state until the temperature drops to 300 ° C. or lower. When the temperature falls below 300 ° C., the process returns to step 1 and the heater 13 is energized again.

Therefore, according to this embodiment, as shown in FIG. 4, after the cold start, until the exhaust pipe temperature reaches 100 ° C., the heater is turned off when the element temperature reaches 330 ° C., 300 When the temperature drops to ℃, the heater is turned on and the current is repeatedly and continuously energized, and the element temperature is suppressed within the range of 300 to 330 ℃. When the temperature of the exhaust pipe rises to 100 ° C. or higher, the heater 13 is continuously energized and reaches a sufficient activation temperature immediately.

Therefore, even if water droplets are generated in the exhaust pipe 2 and come into contact with the sensor element 6, the element temperature is kept within a safe range, and therefore the sensor element 6 is not cracked. It never happens. Also, if the exhaust pipe temperature is 100 ° C. or higher, water becomes water vapor, so that there is no problem even if the element temperature rises. The broken line in FIG. 4 indicates the increase in the element temperature in the conventional configuration in which the energization control of the heater 13 is not performed, and the element temperature becomes very high while the temperature of the exhaust pipe is low. It is easy to cause element cracking.

Next, FIGS. 5 and 6 show different embodiments of the present invention. In this embodiment, the exhaust pipe 2'where the oxygen sensor 4 is arranged has a two-layer structure composed of an inner cylinder 2A and an outer cylinder 2B as shown in detail in FIG. A spiral exhaust pipe heater 21 is interposed between 2A and the outer cylinder 2B. The exhaust pipe heater 21 is also controlled by the control unit 19 and is energized until the exhaust pipe temperature detected by the temperature sensor 5 reaches 100 ° C. The heater 13 of the oxygen sensor 4 is controlled in the same manner as in the above-described embodiment.

Therefore, according to this embodiment, the temperature of the exhaust pipe can be raised to 100 ° C. in a very short time, and the element cracking due to the contact of moisture can be prevented more reliably. Further, since the period for suppressing the element temperature of the oxygen sensor 4 becomes short, the activation temperature can be reached quickly, and the air-fuel ratio feedback control can be started early.

In each of the above embodiments, the energization control of the heater 13 is performed ON and OFF, but the heating amount may be controlled by variable control of the applied voltage or the like.

[0017]

[Effect of the device]

 As is clear from the above description, according to the air-fuel ratio detection device for an internal combustion engine of the present invention, the element temperature of the oxygen sensor becomes excessive when the exhaust pipe temperature is low and water droplets may be generated. Since the heater energization is controlled so that it does not rise, cracks do not occur even if water droplets come into contact with the elements of the exhaust sensor located downstream of the catalytic converter.

[Brief description of drawings]

FIG. 1 is a structural explanatory view showing an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing an oxygen sensor.

FIG. 3 is a flowchart showing heater control of this embodiment.

FIG. 4 is a characteristic diagram showing changes in element temperature and exhaust pipe temperature after a cold start.

FIG. 5 is a plan view of a main part of an exhaust pipe showing a different embodiment of the present invention.

FIG. 6 is an enlarged sectional view of an exhaust pipe in this embodiment.

[Explanation of symbols]

 2 ... Exhaust pipe 3 ... Catalytic converter 4 ... Oxygen sensor 5 ... Temperature sensor 19 ... Control unit

Claims (1)

[Scope of utility model registration request] 1. An air-fuel ratio detecting device in which an oxygen sensor with a heater is arranged downstream of a catalytic converter in an exhaust system of an internal combustion engine, and an exhaust pipe temperature detecting means for detecting an exhaust pipe temperature near the oxygen sensor, and an oxygen sensor. Element temperature detecting means for detecting the element temperature and heater control means for controlling heater energization so that the element temperature does not exceed a predetermined temperature until the exhaust pipe temperature reaches approximately 100 ° C. or more. An air-fuel ratio detector for an internal combustion engine.