JP2004360620A - Air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

To improve deterioration of combustion stability of an internal combustion engine due to enrichment.
A glow plug provided in a combustion chamber of an internal combustion engine and heated by energization, an exhaust purification unit provided in an exhaust system of the internal combustion engine, and an excess air ratio of exhaust flowing into the exhaust purification unit are reduced. Determining means for determining whether or not a condition is satisfied; power controlling means for starting power supply to the glow plug when the condition is satisfied; and An air-fuel ratio control device for an internal combustion engine, comprising: Since fuel-rich combustion is performed in a state where the temperature in the combustion chamber of the internal combustion engine is high, combustion stability is improved.
[Selection] Figure 2

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an air-fuel ratio control device for an internal combustion engine that is mainly operated in a state leaner than a stoichiometric air-fuel ratio.
[0002]
[Prior art]
In a diesel engine, a glow plug is generally provided in the combustion chamber for preheating fuel during cold start or operation in a low-load rotation range, and the glow plug must be heated when the combustion chamber temperature is low. To assist ignition. A method is known in which the glow plug is energized when the excess air ratio is small (that is, when the fuel is rich) to increase the temperature of the combustion chamber and improve combustion stability (see Patent Document 3). If this method is used, the stability of combustion can be improved even when the amount of intake air is reduced for fuel enrichment.
[0003]
[Patent Document 1]
JP-A-9-49485 [0004]
[Problems to be solved by the invention]
However, it takes a certain amount of time to raise the temperature to an appropriate temperature due to the temperature rising characteristics of the glow plug. Therefore, as in a rich spike during regeneration of the NOx trapping catalyst, the excess air In this case, the condition for executing the reduction of the excess air ratio is satisfied, and even if the glow plug is energized when the reduction of the excess air ratio is performed, the temperature of the glow plug rises in time. As a result, there may be a case where the combustion stability is not improved.
[0005]
Accordingly, an object of the present invention is to provide an air-fuel ratio control device capable of improving deterioration of combustion stability of an internal combustion engine due to a decrease in excess air ratio.
[0006]
[Means for Solving the Problems]
One aspect of the present invention is a glow plug provided in a combustion chamber of an internal combustion engine and heated by energization, an exhaust purification unit provided in an exhaust system of the internal combustion engine, and an excess air ratio of exhaust flowing into the exhaust purification unit. Determining means for determining whether or not a condition for reducing the pressure is satisfied; power controlling means for starting power supply to the glow plug when the condition is satisfied; air excess when a predetermined time has elapsed after the start of power supply; An air-fuel ratio control device for an internal combustion engine, comprising: an exhaust control unit that starts decreasing the rate.
[0007]
According to this aspect, when the condition for reducing the excess air ratio of the exhaust gas is satisfied, the glow plug is energized before the reduction of the excess air ratio starts, and the excess air ratio is reduced when a predetermined time has elapsed after the start of the energization. Since the reduction starts, fuel-rich combustion is performed in a state where the temperature in the combustion chamber of the internal combustion engine is high, and the combustion stability is improved.
[0008]
The condition for reducing the excess air ratio of exhaust gas is determined, for example, based on whether or not the estimated integrated value of NOx trapped by the exhaust gas purification device has exceeded a predetermined value. Alternatively, the determination may be made based on a signal from a NOx sensor or a LAF sensor provided downstream of the exhaust gas purification device.
[0009]
The decrease in the excess air ratio may be started based on a parameter related to the temperature of the glow plug, instead of starting when a predetermined time has elapsed after the start of energization of the glow plug. Means for starting the reduction of the excess air ratio include means for controlling the DBW to reduce the amount of intake air, means for increasing the EGR amount to reduce the amount of fresh air to be taken, fuel injection timing and fuel Means are included to control the amount of injection to reduce the amount of gas flowing into the exhaust system. When the determining means determines that the condition for lowering the excess air ratio of the exhaust is no longer satisfied, the lowering of the excess air ratio is terminated, and the energization to the glow plug is stopped accordingly.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
[0011]
FIG. 1 is a schematic configuration diagram of an internal combustion engine (hereinafter, referred to as “engine”) including an air-fuel ratio control device according to an embodiment of the present invention. The engine 1 is an in-line four-cylinder engine having a piston 1a and a cylinder 1b (only one cylinder is shown in FIG. 1), and a combustion chamber 1c is formed between the piston and the cylinder head. The fuel injection valve 6 and the glow plug 18 are provided in the combustion chamber 1c. The fuel injection valve 6 is connected to a fuel supply pump (not shown) and injects fuel under the control of an electronic control unit (hereinafter referred to as “ECU”) 5. The intake air flowing from the intake pipe 2 is compressed in the combustion chamber to have a high temperature and a high pressure, and the high pressure fuel is injected from the fuel injection valve 6 to spontaneously ignite the vaporized fuel to perform combustion. Is discharged.
[0012]
The glow plug 18 is heated by energization to warm the inhaled air. As a result, ignition is promoted, so that combustion is stabilized even at the time of starting or at a low temperature, leading to a reduction in emissions and vibration. The fuel injection valve 6 and the glow plug 18 may be provided inside the combustion chamber 1c, or may be provided inside the sub combustion chamber in a type of engine having a sub combustion chamber. Each cylinder of the engine 1 is also provided with an intake valve 17 for performing intake and exhaust and an exhaust valve 19.
[0013]
An intake throttle valve (DBW: Drive By Wire) 3 for adjusting the flow rate of air flowing in the intake pipe 2 is mounted in the middle of the intake pipe 2 and connected to an actuator (not shown) for controlling the opening degree θTH. I have. The actuator is electrically connected to the ECU 5, and changes the intake throttle valve opening θTH, that is, the intake air amount, according to a signal from the ECU 5. An intake pressure sensor 8 and an intake temperature sensor 9 are attached to the intake pipe 2 downstream of the intake throttle valve 3. The intake pressure sensor 8 and the intake temperature sensor 9 detect a pressure PB and a temperature TA in the intake manifold, respectively, and send signals to the ECU 5. .
[0014]
A water temperature sensor 10 is attached to the main body of the engine 1, detects a cooling water temperature TW of the engine, and sends a signal thereof to the ECU 5. The engine is also provided with a rotation speed sensor 13 which detects the engine rotation speed NE and sends a signal to the ECU 5.
[0015]
A crank angle sensor is mounted on a crankshaft (not shown) of the engine. The crank angle sensor outputs a TDC pulse signal at a predetermined timing near the top dead center position at the start of the intake stroke of the piston in each cylinder as the crankshaft rotates.
[0016]
An exhaust gas recirculation (EGR) passage 12 that connects the exhaust pipe 14 and the intake pipe 2 is provided in the middle of the exhaust pipe 14, and an EGR valve 11 is provided in the middle of the passage. . By adjusting the opening degree of the EGR valve 11, the amount of exhaust gas recirculating from the exhaust pipe 14 into the intake pipe 2 is controlled. The exhaust gas recirculated to the intake pipe 2 via the EGR passage 12 is mixed with fresh air flowing from the upstream of the intake pipe 2, guided to the combustion chamber of each cylinder of the engine 1, and burned. An actuator (not shown) for driving the EGR valve 11 is attached to the EGR valve 11, and is controlled by a signal from the ECU 5.
[0017]
The exhaust gas that has passed through the exhaust pipe 14 flows into the exhaust gas purification device 15. The exhaust purification device 15 includes an electric heater, a NOx trapping catalyst, a diesel particulate filter (DPF), and the like.
[0018]
The NOx trapping catalyst traps NOx with the NOx trapping agent in a lean state in which the air-fuel ratio of the exhaust is thinner than the stoichiometric air-fuel ratio. In a rich state where the air-fuel ratio of the exhaust gas is richer than the stoichiometric air-fuel ratio, the trapped NOx is reduced by HC and CO and discharged as nitrogen gas, and at the same time, HC and CO are oxidized and discharged as steam and carbon dioxide.
[0019]
In a diesel engine, lean operation is performed during normal operation, so the NOx trapping catalyst traps NOx in exhaust gas. When the NOx trapping catalyst is regenerated, the exhaust gas is temporarily made rich (rich spike) by reducing the intake air amount, increasing the fuel injection amount, and delaying the injection timing. Thus, the excess air ratio of exhaust gas can be reduced without lowering the engine output torque. This will be described in detail with reference to FIG. The post-injection also has a role of regenerating the DPF by increasing the temperature of the exhaust gas by burning the fuel.
[0020]
An air-fuel ratio sensor (hereinafter, referred to as a “LAF sensor”) 16 that generates an output in a level that is proportional to the air-fuel ratio of exhaust gas over a wide range is provided upstream of the exhaust gas purification device 15. The output of this sensor is sent to the ECU 5. A temperature sensor for detecting the temperature in the exhaust pipe is also provided on the downstream side (not shown). The outputs of these sensors are sent to the ECU 5.
[0021]
The ECU 5 is formed of a computer, and includes an input interface 5a for processing input signals from various sensors, a ROM for storing programs and data, and a RAM for temporarily storing programs and data required at the time of execution to provide an arithmetic work area. A memory 5c, a CPU 5b for executing various control programs, and an output interface 5d for sending a control signal to each unit. Signals from the sensors are received by the input interface and processed according to a program stored in the ROM.
[0022]
The ECU 5 detects operating conditions such as an engine speed and an accelerator opening, searches a predetermined map, and calculates a required torque. Subsequently, the basic fuel injection amount corresponding to the required torque is calculated, and the timing for further fuel injection is determined.
[0023]
Further, the ECU 5 determines the operating state of the engine 1 based on the input of each sensor. Then, various calculations are executed in accordance with a control program or the like stored in the ROM, and drive signals corresponding to the calculation results are output via the output interface 5d, and the glow plug 18, the intake throttle valve 3, the intake valve 17, and the exhaust It controls the valve 19 and the like.
[0024]
FIG. 2 is a flowchart of an embodiment of control for reducing the excess air ratio for the regeneration of the NOx trapping catalyst. First, an estimated integrated value of NOx trapped by the NOx trapping catalyst is calculated according to the following equation (S30).
[0025]
(Equation 1)
When the air-fuel ratio of the exhaust gas is rich ΣNOx = ΣNOx (previous value) + Qair × Mnx × Ktemp1 (1)
When the air-fuel ratio of the exhaust is lean ΣNOx = ΣNOx (previous value) −Qair × Dnox × Ktemp2 (2)
Here, Qair is the exhaust flow rate (or intake air amount), which is detected by a flow sensor or the like, or calculated from the engine speed and torque. MNox is the NOx concentration in the exhaust gas, and is obtained by searching a predetermined map based on the engine speed and the torque. Ktempl is a NOx trapping temperature coefficient, and represents a ratio of NOx trapped by the NOx catalyst at the exhaust gas temperature. The exhaust temperature is obtained by, for example, a temperature sensor.
[0026]
Dnox is a reduction ratio of NOx trapped by the NOx catalyst, and is obtained by searching a predetermined map based on the engine speed and the torque. Ktemp2 is a NOx reduction temperature coefficient, and represents a ratio of NOx reduced from the catalyst at the exhaust gas temperature.
[0027]
In each of the above equations (1) and (2), the first term is the amount of NOx trapped by the NOx trapping catalyst up to the previous time, and the second term is the amount of NOx newly trapped by the NOx trapping catalyst or NOx trapping. It represents the amount of NOx reduced from the catalyst. As described above, the NOx amount is added or subtracted according to the lean / rich air-fuel ratio of the exhaust gas, and the integrated value of the NOx currently captured by the NOx capturing catalyst is estimated.
[0028]
It is determined whether the NOx integrated value thus obtained has exceeded a predetermined value (S32). This predetermined value is set to a value obtained by subtracting the NOx amount accumulated during energization in consideration of the energization time of the glow plug from the NOx amount to regenerate the NOx trapping catalyst. If not, the calculation of the NOx integrated value is continued. If it exceeds, before the reduction of the NOx trapping catalyst by reducing the excess air ratio, the energization of the glow plug is started (S34).
[0029]
Here, the temperature rise characteristics of the glow plug are shown in FIG. As can be seen from the figure, since the temperature does not rise immediately after the energization of the glow plug is started, the combustion stability by increasing the temperature in the combustion chamber must be maintained for a few seconds (for example, 5 seconds) after the energization. May not lead to improvement.
[0030]
After the energization of the glow plug is continued for a predetermined time (S36), the reduction of the excess air ratio is started (S38). Alternatively, energization may be continued until the temperature of the glow plug reaches a predetermined temperature. The reduction of the excess air ratio is performed by the intake throttle. In order to execute the intake throttle, means for controlling the DBW to reduce the amount of intake air, means for increasing the EGR amount to reduce the amount of fresh air to be taken, and control of the fuel injection timing and the fuel injection amount Means for reducing the amount of gas flowing into the exhaust pipe. Since the NOx trapped by the NOx trapping catalyst is reduced by lowering the excess air ratio, the NOx integrated value calculated in the next step S30 decreases. Subsequently, in S40, it is determined whether the NOx integrated value has fallen below a predetermined value. When the value is below the predetermined value, the reduction of the excess air ratio is terminated, and the energization of the glow plug is terminated (S42).
[0031]
The conditions for executing the reduction of the excess air ratio include estimating the integrated value of NOx trapped by the NOx trapping catalyst as described above, and detecting the signal of the NOx sensor or the LAF sensor provided downstream of the exhaust gas purification device. The determination may be made based on this.
[0032]
As described above, since the current is supplied to the glow plug prior to the decrease in the excess air ratio, the combustion stability can be effectively improved even in a short-time rich operation such as regeneration of a NOx trapping catalyst. Therefore, it is possible to use the enrichment by the intake throttle, which has been the subject of combustion deterioration, as a main means. Accordingly, the post-injection can be minimized, so that the disadvantages peculiar to the post-injection (the generation of oil dilution and the deterioration of fuel efficiency) can be suppressed.
[0033]
As mentioned above, although one Embodiment of this invention was described, this invention is not limited to this. For example, the engine is preferably a diesel engine, but the scope of the present invention is not limited to a diesel engine, but is also applicable to a gasoline engine of a type in which fuel is directly injected into a combustion chamber. The present invention is also applicable to an engine for a marine propulsion device such as an outboard motor having a vertical crankshaft.
[0034]
【The invention's effect】
According to the present invention, after the glow plug is energized, the excess air ratio starts to decrease after a predetermined time has elapsed, so that the excess air ratio of the exhaust gas is reduced in a state where the glow plug is heated and combustion easily occurs. The combustion stability is improved.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an internal combustion engine to which an embodiment of the present invention is applied.
FIG. 2 is a flowchart of control for reducing an excess air ratio for catalyst regeneration.
FIG. 3 is a graph showing a temperature rise characteristic of a glow plug.
[Explanation of symbols]
1 internal combustion engine (engine)
2 intake pipe 3 intake throttle valve 5 electronic control unit (ECU)
6 fuel injection valve 11 EGR passage 12 EGR valve 15 exhaust purification device 16 LAF sensor 17 intake valve 18 glow plug 19 exhaust valve

Claims (1)

A glow plug provided in a combustion chamber of the internal combustion engine and heated by energization;
Exhaust purification means provided in an exhaust system of the internal combustion engine,
Determining means for determining whether a condition for reducing the excess air ratio of the exhaust gas flowing into the exhaust gas purifying means has been satisfied,
An energization control unit that starts energization of the glow plug when the condition is satisfied;
Exhaust control means for starting the reduction of the excess air ratio when a predetermined time has elapsed after the start of energization,
An air-fuel ratio control device for an internal combustion engine having:

Images