WO2013161412A1

WO2013161412A1 - Heating control device and heating control method for exhaust sensor

Info

Publication number: WO2013161412A1
Application number: PCT/JP2013/056842
Authority: WO
Inventors: 梓小林; 民一木村; 良輔佐々木
Original assignee: 日産自動車株式会社
Priority date: 2012-04-25
Filing date: 2013-03-12
Publication date: 2013-10-31

Abstract

In the present invention, an air-fuel ratio sensor (5) and an oxygen sensor (6) have electric heaters (5a and 6a) for heating their respective sensor elements, and are arranged in the exhaust passage (2) of an internal combustion engine (1). When the internal combustion engine (1) is started the fuel temperature of the fuel tank (16), which correlates with the outside air temperature, is detected by a fuel temperature sensor (11), and a heating control prohibition time (an energization prohibition period) is set in accordance with the detected fuel temperature. During the interval from starting of the internal combustion engine (1) until the heating control prohibition time has elapsed, energization of the electric heaters (5a, 6a) is prohibited, and heating of the electric heaters (5a, 6a) begins after the heating control prohibition time has elapsed. Thus, it is possible to prevent breaking of the exhaust sensor elements even in an environment in which the outside air temperature is low, such as a cold climate.

Description

Exhaust sensor heating control device and heating control method

The present invention relates to a heating control device and a heating control method for a sensor element of an exhaust sensor such as an air-fuel ratio sensor or an oxygen sensor provided in an exhaust passage of an internal combustion engine.

The exhaust gas contains moisture generated by the combustion of fuel. For this reason, when moisture in the exhaust gas is condensed and attached (watered) to the high-temperature sensor element of the exhaust sensor disposed in the exhaust passage, the sensor element may be cracked due to rapid cooling of the surface element temperature.

Therefore, in Patent Document 1, based on the cooling water temperature of the internal combustion engine so that energization of the heater is started after the exhaust gas temperature becomes sufficiently high and condensed water does not exist in the exhaust passage. By setting a heater energization prohibition period for prohibiting energization of the heater and starting the energization of the heater after the heater energization prohibition period has elapsed after the start of the internal combustion engine, the sensor element of the exhaust sensor The element is prevented from being cracked by water.

Here, the condensed water in the exhaust gas is more likely to be generated as the outside air temperature becomes lower. Therefore, when the outside air temperature is low, it is effective to lengthen the heater energization prohibition period and delay the energization start timing of the heater in order to prevent element cracking due to the wetness of the sensor element.

However, in Patent Document 1 described above, the heater energization prohibition period is not set in consideration of the outside air temperature. For example, after the warmed-up internal combustion engine is stopped in an environment where the outside air temperature is low such as a cold district. When the internal combustion engine is started before the cold state is reached, there is a possibility that condensed water in which the moisture in the exhaust gas has condensed is present in the exhaust passage when the sensor element is heated. Then, there is a possibility that element cracking occurs.

JP 2010-77848 A

Therefore, the present invention sets an energization prohibition period according to the outside air temperature estimated at the time of starting the internal combustion engine, and until the above energization prohibition period elapses from the start of the internal combustion engine, electric heating for heating the sensor element of the exhaust sensor. Energizing the heater is prohibited, and energization of the electric heater is started after the energization prohibition period has elapsed.

According to the present invention, the energization prohibition period is set according to the outside air temperature, and heating of the sensor element of the exhaust sensor by the electric heater is prohibited during a period in which condensed water exists in the exhaust passage due to condensation or the like. Therefore, even in an environment where the outside air temperature is low, such as a cold district, the sensor element is not wetted while the sensor element is heated by the electric heater, and the element breakage of the sensor element can be prevented.

BRIEF DESCRIPTION OF THE DRAWINGS Explanatory drawing which showed typically the system configuration | structure of the internal combustion engine 1 to which this invention is applied. Explanatory drawing which showed typically the installation condition of various temperature sensors. The heating control prohibition time calculation table used when calculating the heating control prohibition time from the starting fuel temperature. The flowchart which shows the calculation procedure of heating control prohibition time.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is an explanatory diagram schematically showing a system configuration of an in-vehicle internal combustion engine 1 to which the present invention is applied.

A manifold catalyst 3 and an underfloor catalyst 4 for purifying exhaust gas are disposed in an exhaust passage 2 of the internal combustion engine (engine) 1. The manifold catalyst 3 is provided at a position that is relatively close to the combustion chamber, for example, immediately downstream of the collection portion of the exhaust manifold. The underfloor catalyst 4 is provided at a position such as under the floor that is relatively far from the combustion chamber on the downstream side of the manifold catalyst 3.

The exhaust passage 2 is provided with an exhaust sensor that detects an air-fuel ratio or a specific component concentration in the exhaust gas. In this embodiment, as an exhaust sensor, the air-fuel ratio sensor 5 having a substantially linear output characteristic corresponding to the air-fuel ratio, and the output voltage change ON / OFF (rich, lean) in a narrow range near the theoretical air-fuel ratio. Thus, an oxygen sensor 6 that detects only the rich and lean air-fuel ratio is provided in the exhaust passage 2.

The air-fuel ratio sensor 5 is arranged upstream of the manifold catalyst 3 and detects the air-fuel ratio in the exhaust gas flowing into the manifold catalyst 3. The oxygen sensor 6 is disposed on the upstream side of the underfloor catalyst 4 and detects the rich / lean of the air-fuel ratio of the exhaust gas flowing into the underfloor catalyst 4. Note that reference numeral 7 in FIG. 1 denotes an intake passage of the internal combustion engine 1.

Here, the air-fuel ratio sensor 5 and the oxygen sensor 6 can detect the air-fuel ratio and determine whether the air-fuel ratio is rich or lean when the sensor element rises to a predetermined activation temperature. Electric heaters 5a and 6a to be activated are provided. The air-fuel ratio sensor 5 and the oxygen sensor 6 can activate and maintain the activation of the sensor elements by energizing the electric heaters 5a and 6a. Energization control (heating control) of the electric heaters 5 a and 6 a is performed by an ECM (engine control module) 10.

The ECM 10 incorporates a microcomputer and performs various controls of the internal combustion engine 1. The ECM 10 is an outside air temperature estimating means for detecting the temperature of the fuel in addition to the detection signals detected by the air-fuel ratio sensor 5 and the oxygen sensor 6. Signals from various sensors such as the fuel temperature sensor 11 are input.

Here, the exhaust gas contains moisture generated by the combustion of fuel, and there is a possibility that condensation occurs in the exhaust passage 2 when the outside air temperature is low and the wall temperature of the exhaust passage 2 is low. . Further, the condensed water generated in the exhaust gas increases as the outside air temperature is lower.

When moisture in the exhaust gas is condensed and adheres to the high-temperature sensor elements of the air-fuel ratio sensor 5 and the oxygen sensor 6 disposed in the exhaust passage 2, the sensor element is damaged due to rapid cooling of the surface element temperature (element Cracking). Therefore, in the state where the wall temperature of the exhaust passage 2 is low immediately after the internal combustion engine 1 is started, it is not preferable to energize the electric heaters 5a and 6a to heat the sensor elements of the air-fuel ratio sensor 5 and the oxygen sensor 6. Therefore, it is necessary to delay the heating of the air-fuel ratio sensor 5 and the sensor element of the oxygen sensor 6 by the electric heaters 5a and 6a until the dew condensation is not generated in the exhaust passage 2.

If the wall temperature of the exhaust passage 2 around the air-fuel ratio sensor 5 and the oxygen sensor 6 is sufficiently high, the moisture in the exhaust gas is vaporized at least around the air-fuel ratio sensor 5 and the oxygen sensor 6, It is considered that the sensor elements of the air-fuel ratio sensor 5 and the oxygen sensor 6 do not get wet.

That is, what we want to know directly is the wall temperature of the exhaust passage 2 around the mounting position of the air-fuel ratio sensor 5 and the oxygen sensor 6, but this is proportional to the outside air temperature. Although the outside air temperature can be directly measured by an outside air temperature sensor used for air conditioner control or the like, the outside air temperature sensor is often provided at the upper part of the dashboard of the vehicle. Due to the heat received, the outside air temperature may not be accurately measured.

Also, since the outside air temperature sensor for controlling the air conditioner is mounted only in the car equipped with the auto air conditioner, the outside air temperature cannot be detected directly in the car equipped with the manual air conditioner or the car not equipped with the air conditioner.

FIG. 2 is an explanatory diagram schematically showing the installation status of various temperature sensors mounted on a car equipped with an auto air conditioner.

In FIG. 2, 12 is a cooling water temperature sensor that detects the cooling water temperature, 13 is an outside air temperature sensor that detects the outside air temperature, 14 is an oil temperature sensor that detects the engine oil temperature, and 15 is the intake air temperature in the intake passage 7. This is an intake air temperature sensor to be detected. Reference numeral 16 denotes a fuel tank in which the above-described fuel temperature sensor 11 is disposed. Among the temperatures detected by these various temperature sensors, the coolant temperature, the engine oil temperature, and the intake air temperature rise due to the heat generated by the internal combustion engine 1, and thus the correlation with the outside air temperature is lost. Further, as described above, the outside air temperature sensor 13 may not be able to accurately measure the outside air temperature.

On the other hand, since the fuel temperature in the fuel tank 16 receives little heat from the internal combustion engine 1 and a sufficient amount of liquid is often secured, there is a difference from the outside air temperature regardless of the operating state of the internal combustion engine 1. Least. That is, for example, even when the warmed-up internal combustion engine 1 is stopped and started before the cool air state is entered, the outside air temperature can be accurately estimated from the fuel temperature.

Therefore, in this embodiment, the start timing of the heating control of the sensor element by the electric heaters 5a and 6a of the air-fuel ratio sensor 5 and the oxygen sensor 6 after the internal combustion engine 1 is started according to the outside air temperature when the internal combustion engine 1 is started. When changing, the outside air temperature is estimated from the fuel temperature in the fuel tank 16 correlated with the outside air temperature.

More specifically, the lower the fuel temperature at the time of starting the internal combustion engine 1, that is, the lower the outside air temperature at the time of starting the internal combustion engine 1, the time from when the internal combustion engine 1 is started until the electric heaters 5a and 6a are energized. The heating control prohibition time is set to be long. In other words, the lower the outside air temperature at the start of the internal combustion engine 1, the longer the heating control prohibition time as the energization prohibition period is set, and the energization start timing for the electric heaters 5a and 6a is delayed.

The heating control inhibition time is calculated from the fuel temperature at the start using, for example, a heating control inhibition time calculation table as shown in FIG. This heating control inhibition time calculation table is stored in the ECM 10 in advance. That is, the ECM 10 in which the heating control prohibition time calculation table is stored corresponds to the energization prohibition period setting unit.

In this embodiment, the heating control prohibition time is set to the maximum value when the fuel temperature is equal to or lower than the predetermined temperature T1, and the heating control prohibition time is set to the minimum value when the fuel temperature is equal to or higher than the predetermined temperature T2. Is set to the shortest time for which heating control is prohibited. When the fuel temperature is higher than the predetermined temperature T1 and lower than the predetermined temperature T2, the heating control prohibition time is set to be shorter as the fuel temperature is higher. That is, as a whole, the heating control prohibition time is set to be shorter as the fuel temperature approaches normal temperature.

Thus, after the internal combustion engine 1 is started, the wall temperature of the exhaust passage 2 is low, condensed water is generated in the exhaust passage 2, and the sensor elements of the air-fuel ratio sensor 5 and the oxygen sensor 6 are easily wet. Energization of the heaters 5a and 6a is prohibited.

That is, since the heating control prohibition time is set in accordance with the outside air temperature, the internal combustion engine 1 is stopped before the engine is cooled down after the warmed-up internal combustion engine 1 is stopped in an environment where the outside air temperature is low such as a cold district. Even in the case of restarting, it is possible to prevent the sensor element from being wetted by condensed water during heating of the air-fuel ratio sensor 5 and the sensor element of the oxygen sensor 6 by the electric heaters 5a and 6a. Therefore, it is possible to prevent the sensor elements of the air-fuel ratio sensor 5 and the oxygen sensor 6 from being cracked due to a sudden temperature change caused by water.

Then, by estimating the outside air temperature from the fuel temperature, even in a vehicle without the outside air temperature sensor 13 for air conditioner control, the outside air temperature can be reduced without providing a wall temperature of the exhaust passage 2 or a sensor for measuring the outside air temperature. Since the estimation can be performed with high accuracy, it is advantageous in terms of cost.

FIG. 4 is a flowchart showing a procedure for calculating the heating control inhibition time. Note that the calculation of the heating control inhibition time is performed in the ECM 10.

In S1, it is determined whether or not the fuel temperature sensor 11 has failed. If not, the process proceeds to S2, and if it has failed, the process proceeds to S4. The failure of the fuel temperature sensor 11 is determined as a failure, for example, when the signal voltage output from the fuel temperature sensor 11 to the ECM 10 is too low or too high.

In S2, it is determined whether or not fuel has been refueled while the internal combustion engine 1 is stopped. If not, the process proceeds to S3, and if refueling, the process proceeds to S4. For example, the fuel amount at the start of the internal combustion engine 1 detected by the fuel sensor for detecting the fuel amount in the fuel tank 16 is increased by a predetermined amount or more than the fuel amount detected by the fuel sensor when the internal combustion engine 1 was stopped last time. If it is, it is determined that the fuel was supplied while the internal combustion engine 1 was stopped.

In S3, a heating control prohibition time determined according to the fuel temperature at the start of the internal combustion engine 1 is applied.

On the other hand, if the fuel temperature sensor 11 is out of order or is being refueled during stoppage, estimation of the outside air temperature using the fuel temperature in the fuel tank 16 is prohibited in S4, and in S5 Regardless of the outside air temperature, the heating control prohibition maximum time, which is the maximum time that can be set, is applied.

That is, when the fuel temperature sensor 11 is out of order, the fuel temperature cannot be accurately measured, and the outside air temperature cannot be estimated with high accuracy. Therefore, in order to protect the air-fuel ratio sensor 5 and the oxygen sensor 6, Apply the maximum heating control prohibition time that is sometimes applied. Further, when fuel is supplied, the fuel temperature in the fuel tank 16 may change greatly, and the fuel temperature may greatly deviate from the outside air temperature, so that the air-fuel ratio sensor 5 and the oxygen sensor 6 are protected. Therefore, the maximum heating control prohibition time applied at extremely low temperatures is applied.

In calculating the heating control prohibition time, the same heating control prohibition time calculation table may be used for the air-fuel ratio sensor 5 and the oxygen sensor 6, or individual heating for the air-fuel ratio sensor 5 and the oxygen sensor 6 may be used. A control prohibition time calculation table may be used. That is, even when the fuel temperature is the same, the heating control inhibition time of the air-fuel ratio sensor 5 and the heating control inhibition time of the oxygen sensor 6 may be set as different values.

Since the heat capacity from the internal combustion engine 1 to the sensor mounting position increases as the mounting position of the air-fuel ratio sensor 5 or the oxygen sensor 6 becomes farther from the internal combustion engine 1, the heating prohibition time is individually set for the air-fuel ratio sensor 5 and the oxygen sensor 6. Is set to a longer heating prohibition time in proportion to the length of the exhaust passage from the internal combustion engine 1 to the sensor mounting position. In addition, it is preferable to set the heating prohibition time relatively long even when there is a portion where the condensed water tends to accumulate due to the shape of the exhaust passage 2 on the upstream side of the sensor mounting position.

In the above-described embodiment, the heating control of the electric heaters 5a and 6a is prohibited until the elapsed time from the start of the internal combustion engine 1 reaches the heating control prohibition time, but the accumulation from the start of the internal combustion engine 1 is prohibited. Heating control of the electric heaters 5a and 6a is prohibited until the engine speed and the cumulative intake air amount become the heating control prohibition cumulative engine speed and the heating control prohibition cumulative intake air amount calculated according to the outside air temperature. Also good.

Claims

An exhaust sensor having an electric heater for heating the sensor element and disposed in the exhaust passage of the internal combustion engine;
An outside air temperature estimating means for estimating the outside air temperature,
An energization prohibition period setting means for setting an energization prohibition period according to the outside air temperature estimated by the outside air temperature estimating means at the start of the internal combustion engine,
An exhaust sensor heating control apparatus that prohibits energization of the electric heater from the start of the internal combustion engine until the energization prohibition period elapses, and starts energization of the electric heater after the energization prohibition period elapses.
2. The exhaust sensor heating control device according to claim 1, wherein the outside air temperature detecting means estimates the outside air temperature using a detection value of a fuel temperature sensor that detects a fuel temperature in the fuel tank.
3. The exhaust sensor heating control device according to claim 2, wherein the energization prohibition period setting means sets the energization prohibition period longer as the fuel temperature at the start of the internal combustion engine detected by the fuel temperature sensor is lower.
When fuel is supplied to the fuel tank between the previous internal combustion engine stop and the current internal combustion engine start, the energization prohibition period setting means supplies the energization to the electric heater for a predetermined period. The exhaust sensor heating control device according to claim 3, wherein the control is prohibited.
The exhaust sensor heating control device according to claim 3 or 4, wherein, when the fuel sensor is out of order, the energization prohibition period setting means prohibits energization of the electric heater for a predetermined period set in advance.
The exhaust sensor heating control device according to claim 4 or 5, wherein the predetermined period is a longest period of the energization prohibition period set in accordance with a fuel temperature.
An exhaust sensor having an electric heater for heating the sensor element and disposed in the exhaust passage of the internal combustion engine;
Set the energization prohibition period according to the outside air temperature calculated from the fuel temperature in the fuel tank when starting the internal combustion engine,
An exhaust sensor heating control method for prohibiting energization of the electric heater from the start of the internal combustion engine until the energization prohibition period elapses, and starting energization of the electric heater after the energization prohibition period elapses.