JP4872793B2 - Control device for internal combustion engine - Google Patents

Description

  The present invention relates to a control device for an internal combustion engine.

  Conventionally, in an internal combustion engine, sensors such as an air-fuel ratio sensor and an oxygen sensor are arranged in an exhaust passage. Such a sensor has a sensor element and a heater that activates the sensor element.

  On the other hand, when the internal combustion engine is started, exhaust gas is condensed in the exhaust passage after the previous engine stop and water remains in the exhaust passage, or the exhaust gas discharged from the engine after the start is the inner wall of the low temperature exhaust passage. Condensed water may be generated when touched.

  If the condensed water is applied to the sensor when the sensor is heated by the heater, the sensor element may be cracked. Patent Document 1 discloses a heater control device for a sensor in which measures against such problems are taken.

JP 2001-73827 A

  The device disclosed in Patent Document 1 prevents the sensor from being damaged by energizing the heater when the coolant temperature at the start of the internal combustion engine reaches a predetermined temperature.

  By the way, it is conventionally known that the boiling point of water varies with the variation of atmospheric pressure. For example, at a pressure lower than the standard atmospheric pressure, the boiling point of water has a value lower than 100 ° C. The same applies to the condensed water generated in the exhaust passage, and when it is lower than the standard atmospheric pressure, the condensed water evaporates earlier than the case of the standard atmospheric pressure.

  Therefore, in an environment where the atmospheric pressure is lower than the standard atmospheric pressure, the condensed water has already evaporated even when the heater energization is set earlier than in the standard atmospheric pressure environment. In this case, the sensor element does not break. However, the apparatus disclosed in Patent Document 1 has not been considered from such a viewpoint.

  Accordingly, an object of the present invention is to provide a control device for an internal combustion engine that can activate a gas sensor at an early stage in consideration of fluctuations in atmospheric pressure.

The above object is provided in the exhaust passage, and includes a gas sensor including a sensor element and a heating unit that activates the sensor element, and a heating control unit that controls the operation of the heating unit. The control of the internal combustion engine can be achieved by controlling the operation of the heating means according to the atmospheric pressure.
With this configuration, since the operation of the heating unit is controlled in consideration of the atmospheric pressure, the sensor element of the gas sensor can be activated in consideration of fluctuations in the boiling point of moisture that varies depending on the atmospheric pressure. Therefore, in an environment where the atmospheric pressure is lower than the standard atmospheric pressure, the heating means can be operated earlier than in an environment based on the standard atmospheric pressure. Thereby, control according to the detection result by a gas sensor can be performed at an early stage.

  The said structure WHEREIN: The said heating control means can employ | adopt the structure which starts the action | operation of the said heating means early, so that atmospheric pressure is low.

In the above configuration, air-fuel ratio feedback control means for performing feedback control so that the air-fuel ratio of the engine approaches the target air-fuel ratio based on the output from the exhaust gas sensor is provided, and the air-fuel ratio feedback control means is fed back according to atmospheric pressure. A configuration that executes control can be adopted.
With this configuration, in an environment where the atmospheric pressure is lower than the standard atmospheric pressure, feedback control can be performed earlier than in an environment based on the standard atmospheric pressure, and deterioration of emissions, drivability, and the like can be prevented.

  The said structure WHEREIN: The said air-fuel ratio feedback control means can employ | adopt the structure which performs the said feedback control early, so that atmospheric pressure is low.

  ADVANTAGE OF THE INVENTION According to this invention, the control apparatus of the internal combustion engine which can activate a gas sensor early considering the fluctuation | variation of atmospheric pressure can be provided.

  Embodiments according to the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic diagram showing a configuration of an engine system according to the present embodiment. A multi-cylinder in-cylinder injecting gasoline engine (hereinafter abbreviated as “engine”) 2 mounted on an automobile and its electronic control unit ( Hereinafter, the schematic configuration of the ECU 4 is referred to as “ECU”. In FIG. 1, the configuration of one cylinder is mainly shown.
Here, the output of the engine 2 is finally transmitted as a driving force to the wheels via a transmission (not shown). The engine 2 is provided with a fuel injection valve 12 that directly injects fuel into the combustion chamber 10 and an ignition plug 14 that ignites the injected fuel.

  The intake port 16 connected to the combustion chamber 10 is opened and closed by driving an intake valve (not shown). A surge tank 22 is provided in the middle of the intake passage 20 connected to the intake port 16, and a throttle valve 26 whose opening degree is adjusted by a throttle motor 24 is provided upstream of the surge tank 22.

  The intake air amount is adjusted by the opening of the throttle valve 26 (throttle opening TA). The throttle opening degree TA is detected by a throttle opening degree sensor 28, and the intake pressure PM in the surge tank 22 is detected by an intake pressure sensor 30 provided in the surge tank 22 and read into the ECU 4. An air flow meter 21 is disposed in the intake passage 20 to output the intake air amount to the ECU 4.

  The exhaust port 32 connected to the combustion chamber 10 is opened and closed by driving an exhaust valve (not shown). The exhaust passage 36 connected to the exhaust port 32 performs oxidation of unburned components (HC, CO) and reduction of nitrogen oxide (NOx) in the exhaust gas, and has a three-way catalyst having oxygen storage and release functions. A start catalyst 38 is provided. Further, a NOx occlusion reduction catalyst 40 is provided in the exhaust passage 36 downstream of a start catalyst (hereinafter simply referred to as “catalyst”) 38.

  In the exhaust passage 36, an air-fuel ratio sensor 64 is disposed upstream of the catalyst 38, and an oxygen sensor 66 is disposed between the catalyst 38 and the NOx storage reduction catalyst 40. As the air-fuel ratio sensor 64, a linear air-fuel ratio sensor that outputs a voltage signal corresponding to the air-fuel ratio of the exhaust gas flowing into the catalyst 38 is used. The oxygen sensor 66 is a sensor that detects whether the air-fuel ratio is richer or leaner than the stoichiometric air-fuel ratio based on the residual oxygen concentration in the exhaust gas.

  The ECU 4 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like, and controls the operation of the entire engine.

  In addition to the throttle opening sensor 28 and the intake pressure sensor 30, the ECU 4 inputs a signal from an accelerator opening sensor 56 that detects the amount of depression of the accelerator pedal 44 (accelerator opening ACCP). Further, the ECU 4 receives signals from an engine speed sensor 58, an air-fuel ratio sensor 64, and an oxygen sensor 66 that detect the engine speed NE from the rotation of the crankshaft 54, respectively. Further, a water temperature sensor 41 for detecting the engine coolant temperature is provided, and the detected engine coolant temperature is output to the ECU 4.

  The ECU 4 appropriately controls the fuel injection timing, the fuel injection amount, and the throttle opening TA of the engine 2 based on the detection contents from the various sensors described above. As a result, the combustion mode is switched between stratified combustion and homogeneous combustion.

  In order to increase the oxidation / reduction ability of the catalyst 38, the ECU 4 sets the fuel injection amount to the output of the air-fuel ratio sensor 64 or the output thereof so that the air-fuel ratio of the exhaust gas flowing into the catalyst 38 becomes the stoichiometric air-fuel ratio. Air-fuel ratio feedback control is performed based on the output of the oxygen sensor 66.

  In the air-fuel ratio feedback control, when the air-fuel ratio is richer than the stoichiometric air-fuel ratio, the fuel injection amount is reduced, and when it is lean, the fuel injection amount is increased, so that the air-fuel ratio becomes the stoichiometric air-fuel ratio. It is maintained within a predetermined range near the fuel ratio. The above-described catalyst 38 exhibits high purification performance when the air-fuel ratio is in the vicinity of the stoichiometric air-fuel ratio.

Next, the configuration of the air-fuel ratio sensor 64 will be briefly described. FIG. 2 is a schematic diagram of the air-fuel ratio sensor 64.
As shown in FIG. 2, the air-fuel ratio sensor 64 includes therein a sensor element 65a made of a material such as zirconia and a heater 65b for heating the sensor element 65a.

  One terminal of the sensor element 65a is connected to a constant voltage source (not shown), and the other terminal is connected to the ECU 4 and grounded. At the temperature at which the sensor element 65a is activated (about 650 ° C.), the current flowing through the sensor element 65a changes according to the oxygen concentration in the exhaust passage 36.

  On the other hand, the operation of the heater 65b is controlled by the ECU 4. By operating the heater 65b by the ECU 4, the sensor element 65a can be heated and raised to the activation temperature at an early stage. The oxygen sensor 66 has substantially the same configuration and includes a sensor element and a heater.

  The ECU 4 starts the operation of the heater 65b after a predetermined period has elapsed after the engine is started. Specifically, after the condensed water generated in the exhaust passage 36 is vaporized, the heater 65b is operated to activate the sensor element 65a. This is because if the heater 65b is operated before the condensed water is vaporized, the air-fuel ratio sensor 64 may be damaged.

Next, the relationship between the disappearance time of the condensed water generated in the exhaust passage 36 and the atmospheric pressure will be described.
FIG. 3 is a graph showing the relationship between the disappearance time of condensed water and atmospheric pressure. The vertical axis indicates the time until the condensed water generated in the exhaust passage 36 disappears, and the horizontal axis indicates the atmospheric pressure. FIG. 3 assumes a case where the temperature of the exhaust gas is constant at 100 ° C. or higher.

As shown in FIG. 3, the condensed water generated in the exhaust passage 36 has a shorter time until it disappears as the atmospheric pressure is lower. This is because the boiling point of water becomes lower as the atmospheric pressure is lower, so the time until the condensed water evaporates becomes shorter.
Therefore, for example, the time until the condensed water generated in the exhaust passage 36 disappears under a standard atmospheric pressure such as a flat ground and under an atmospheric pressure lower than the standard atmospheric pressure such as a high altitude.

Next, energization control processing of the air-fuel ratio sensor executed by the ECU 4 will be described.
FIG. 4 is a flowchart showing an example of the energization control process of the air-fuel ratio sensor executed by the ECU 4.

  The ECU 4 first determines whether or not the water temperature of the engine cooling water is equal to or lower than a predetermined value based on the output from the water temperature sensor 41 (step S1). This is because it can be determined from the engine coolant temperature whether the engine has just started. Specifically, it is determined whether the engine coolant temperature is 0 ° C. or lower.

  If it is less than the predetermined value, the ECU 4 calculates the current atmospheric pressure (step S2). Specifically, the ECU 4 determines the current intake air weight and the standard atmospheric pressure based on the intake air weight map corresponding to the engine speed NE and the throttle opening TA under the standard atmospheric pressure. The current atmospheric pressure is calculated by comparing the intake air weight. The intake air weight in the current state can be calculated from the engine speed NE and the intake air amount. The intake air weight can be calculated from the intake air amount detected from the air flow meter 21 and the engine speed NE.

  Next, the ECU 4 sets the time from when the engine is started until the heater 65b is energized according to the current atmospheric pressure (step S3). Specifically, based on the map shown in FIG. 5, the time until the energization of the heater 65b is started is set. In FIG. 5, the vertical axis indicates the time until energization of the heater 65 b is started, and the horizontal axis indicates the calculated current atmospheric pressure. The lower the atmospheric pressure, the shorter the time until the heater 65b is energized. That is, the lower the atmospheric pressure, the earlier the operation of the heater 65b is started.

  When the energization start time for the heater 65b is set, the ECU 4 determines whether the energization start time has elapsed (step S4). If it has elapsed, the heater 65b is energized (step S5), and if it has not elapsed, energization to the heater 65b is prohibited (step S6).

  As described above, since the operation of the heating unit is controlled in consideration of the atmospheric pressure, the sensor element 65a of the air-fuel ratio sensor 64 can be activated in consideration of the fluctuation of the boiling point of moisture that varies depending on the atmospheric pressure. As a result, the ECU 4 can execute the control according to the detection result by the air-fuel ratio sensor 64 at an early stage.

  Next, the ECU 4 executes the air-fuel ratio feedback control early as the air-fuel ratio sensor 64 can be activated early. FIG. 6 is a flowchart showing an example of the air-fuel ratio feedback control process executed by the ECU 4.

First, the ECU 4 determines whether or not the water temperature of the engine cooling water is equal to or lower than a predetermined value (step S11), and if it is equal to or lower than the predetermined value, calculates the current atmospheric pressure (step S12).
Next, the ECU 4 sets the time from the engine start to the start of the air-fuel ratio feedback control according to the atmospheric pressure (step S13). Specifically, the time until air-fuel ratio feedback control is started is set based on the map shown in FIG. FIG. 7 shows the time until the start of air-fuel ratio feedback control on the vertical axis and the calculated current atmospheric pressure on the horizontal axis. The lower the atmospheric pressure, the shorter the time until the air-fuel ratio feedback control is started. That is, the air-fuel ratio feedback control is executed earlier as the atmospheric pressure is lower.

  Next, when the time until the start of the air-fuel ratio feedback control is set, the ECU 4 determines whether or not the air-fuel ratio feedback control start time has elapsed (step S14). Control is started (step S15), and if it has not elapsed, air-fuel ratio feedback control is prohibited (step S16).

  Thus, in an environment where the atmospheric pressure is lower than the standard atmospheric pressure, the air-fuel ratio sensor 64 is activated at an early stage as described above, so that the air-fuel ratio feedback control can also be executed at an early stage. It can prevent deterioration and drivability.

  Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to the specific embodiments, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims. It can be changed.

  The energization control process may be executed not only for the air-fuel ratio sensor 64 but also for the oxygen sensor 66 as in the case of the air-fuel ratio sensor 64. Accordingly, the ECU 4 may execute sub feedback control based on the output of the oxygen sensor 66.

  When the energization control to the heater 65b is duty control, the duty ratio may be changed depending on the time when condensed water disappears.

  In addition, when the elapsed time from the cold start of the engine is integrated by the intake air amount and the energization start time to the heater 65b is controlled, the integrated intake air amount is set according to the atmospheric pressure. It may be corrected. That is, it is possible to start energization of the heater 65b at an early stage by correcting the intake air amount that is actually integrated to be larger as the atmospheric pressure is lower.

  An atmospheric pressure sensor that detects the atmospheric pressure may be provided, and the ECU 4 may execute the above-described processing according to the output of the atmospheric pressure sensor.

It is the schematic diagram which showed the structure of the engine system which concerns on a present Example. It is a schematic diagram of an air fuel ratio sensor. It is the graph which showed the relationship between the extinction time of condensed water, and atmospheric pressure. It is the flowchart which showed an example of the electricity supply control process of the air fuel ratio sensor which ECU performs. It is a map for setting the energization start time to a heater. It is the flowchart which showed an example of the air fuel ratio feedback control process which ECU performs. It is a map for setting the start time of air-fuel ratio feedback control.

Explanation of symbols

2 Engine 4 ECU (heating control means, air-fuel ratio feedback control means)
DESCRIPTION OF SYMBOLS 10 Combustion chamber 12 Fuel injection valve 14 Spark plug 16 Intake port 20 Intake passage 22 Surge tank 24 Throttle motor 26 Throttle valve 28 Throttle opening sensor 30 Intake pressure sensor 32 Exhaust port 36 Exhaust passage 38 Catalyst 40 NOx storage reduction catalyst 41 Water temperature sensor 44 Accelerator pedal 54 Crankshaft 56 Accelerator opening sensor 58 Engine speed sensor 64 Air-fuel ratio sensor 65a Sensor element 65b Heater (heating means)
66 Oxygen sensor

Claims (1)

A gas sensor installed in the exhaust passage and including a sensor element and heating means for activating the sensor element;
Heating control means for controlling the operation of the heating means;
Air-fuel ratio feedback control means for performing feedback control so that the air-fuel ratio of the engine approaches the target air-fuel ratio based on the output from the exhaust gas sensor,
The heating control means sets an energization start time which is a period from the time when the heating means is not operated to the time when the heating means is started , according to only the atmospheric pressure, and the lower the atmospheric pressure, Set the energization start time to a short time,
The air-fuel ratio feedback control means, in accordance with only the atmospheric pressure, setting the feedback control start time is a period until when initiating execution of the feedback control from when the feedback control is not executed, the atmospheric pressure The control apparatus for an internal combustion engine, characterized in that the feedback control start time is set to be shorter as the value is lower.

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