JPH07103077A - Exhaust reflux controller for internal combustion engine - Google Patents

Abstract

PURPOSE:To avoid that moisture in an intake system increases to make a large quantity of moisture freeze to a fuel injection valve by forcedly stopping the reflux of exhaust until a fixed time elapses from a start-up time in the case where engine temperature at the start-up time is lower than a fixed temperature in carrying out the reflux of exhaust. CONSTITUTION:In an internal combustion engine 1, both an exhaust and an intake manifold 2, 3 are made to communicate mutually through an exhaust reflux passage 4, which is arrangedly provided with a control valve 5. A negative pressure introducing passage 7 to make the pressure chamber of the control valve 5 communicate with the intake manifold 3 on the downstream side of a throttle valve 6 is opened and closed by a solenoid 9 arrangedly provided in the passage 7 to open and close the control valve 5. In this case, the solenoid 9 is controlled on engine temperature, for instance a detection signal issued from a water temperature sensor 11, by a control unit 8. Namely, the exhaust reflux passage 4 is forcedly kept in a blocked up state for a fixed time corresponding to the engine temperature detected at the time of starting the engine from the start-up time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas recirculation control device for an internal combustion engine, which recirculates a part of engine exhaust gas to an intake system.

[0002]

2. Description of the Related Art Conventionally, in an internal combustion engine for automobiles,
As a device for reducing NOx in engine exhaust, an exhaust gas recirculation device (EGR) is known that lowers the maximum combustion temperature by recirculating a part of engine exhaust to an intake manifold to reduce NOx production. There is.

[0003]

By the way, since a relatively large amount of water is present in the engine exhaust, if the exhaust gas recirculation is executed, the amount of water in the engine intake system will be increased. The amount of water in the intake system includes not only the amount due to the exhaust gas recirculation, but also the amount due to the water in the oil being carried by the blow-by gas, but the amount of water carried in the exhaust gas recirculation is larger than this. Have characteristics.

Here, when a large amount of water is carried to the intake system by exhaust gas recirculation, icing occurs in the metal portion around the injection hole of the fuel injection valve due to the following process, fluctuations in injection characteristics, start failure, etc. There was a fear of inviting. That is, during engine operation in a state where the outside air temperature is low (0 ° C. or less), the vicinity of the injection hole of the fuel injection valve is cooled by the latent heat of vaporization of the fuel, so that the water content in the intake air adheres to the vicinity of the cooled injection hole. And it freezes like frost. If the engine is stopped in this state,
As the atmospheric temperature of the intake system rises, the temperature of the fuel injection valve rises, the frost-like ice melts into water droplets, and dew condensation occurs due to the difference between the temperature of the fuel injection valve and the atmospheric temperature. The amount of water adhering to the fuel injection valve increases. In this way, when a large amount of water droplets are attached and the temperature of the fuel injection valve is lowered due to the influence of the outside air temperature, the attached water droplets are frozen. If the above-mentioned frost formation occurs in the injection hole portion of the injection valve, the fuel injection at the time of restart may be adversely affected, and in the worst case, a start failure may occur.

Such a problem is caused by the temperature environment and the amount of water in the intake system, and in particular, the amount of water in the intake system is greatly affected by exhaust gas recirculation as described above and increases. is there. The present invention has been made in view of the above problems, and it is possible to increase the amount of water in the intake system by exhaust gas recirculation under the environmental condition (temperature condition) in which icing occurs near the injection hole of the fuel injection valve. It is an object of the present invention to avoid the occurrence of freezing and prevent the occurrence of freezing.

[0006]

Therefore, an exhaust gas recirculation control system for an internal combustion engine according to the present invention is constructed as shown in FIG. In FIG. 1, the exhaust gas recirculation control means opens and closes an exhaust gas recirculation passage for recirculating a part of the engine exhaust gas to the intake system according to engine operating conditions.

Further, the exhaust gas recirculation stop means at the time of starting has priority over the exhaust gas recirculation control means for a predetermined period corresponding to the engine temperature at the engine start detected by the engine temperature detecting means from the engine start, and the exhaust gas recirculation passage is prioritized. Forcibly held in the closed state.

[0008]

With this structure, the exhaust gas recirculation is forcibly stopped for a period corresponding to the engine temperature at the time of starting after the engine is started. Therefore, it is possible to forcibly stop the exhaust gas recirculation when the temperature condition for ice formation in the injection valve is satisfied at the time of cold engine start, and to avoid a large increase in the amount of water in the intake system. Even if the temperature condition for the formation of ice is satisfied, the amount of water in the intake system can be suppressed to be low, so that the formation of ice in the vicinity of the injection hole of the fuel injection valve can be avoided.

[0009]

EXAMPLES Examples of the present invention will be described below. In FIG. 2 showing the system configuration of one embodiment, an exhaust gas recirculation passage 4 that connects the exhaust manifold 2 and the intake manifold 3 of the engine 1 is provided.
The GR control valve 5 opens and closes.

The EGR control valve 5 is a diaphragm type valve which is opened by applying a suction negative pressure of the engine against the biasing force of the coil spring in the valve closing direction. 6 is provided with a negative pressure introducing passage 7 that communicates with the intake manifold 3 on the downstream side, and the valve is opened by introducing the negative suction pressure of the engine 1 into the pressure chamber through the negative pressure introducing passage 7.

An EGR control solenoid 9 which is on / off controlled by a control unit 8 is interposed in the negative pressure introduction passage 7. The opening / closing control of the EGR control solenoid 9 controls the EGR control valve 5 to operate. Opening / closing, that is, exhaust gas recirculation can be controlled on / off. In addition, 10 is the diaphragm operated by the exhaust pressure and the manifold negative pressure,
A diaphragm-type BPT valve that determines a negative pressure for controlling the R control valve 5, and includes the EGR control valve 5, the EGR control solenoid 9, and the BP.
The T valve 10 and the control unit 8 constitute exhaust gas recirculation control means in this embodiment.

In addition to the cooling water temperature signal Tw output from the water temperature sensor 11 (engine temperature detecting means), the control unit 8 receives detection signals such as the engine speed Ne and the engine intake air amount Q from each sensor. At the same time, an ON / OFF signal of an ignition switch (not shown) is input, and the EGR control solenoid 9 is ON / OFF controlled in order to effectively reduce NOx in the exhaust gas based on the engine operating conditions determined from these signals.

An electromagnetic fuel injection valve 12 is provided at each branch of the intake manifold 3, and the control unit 8 sends an injection pulse to the injection valve 12 on the basis of each detection signal described above. The pulse width of the signal is calculated, and the injection pulse signal is output at the timing synchronized with the engine rotation. Here, the exhaust gas recirculation control by the control unit 8 will be described in detail with reference to the flowchart of FIG.

In this embodiment, the function of the exhaust gas recirculation stopping means at the time of starting is provided by software in the control unit 8 as shown in the flow chart of FIG. In the flowchart of FIG. 3, first, in step 1 (denoted as S1 in the figure. The same applies hereinafter), various parameters indicating engine operating conditions such as the cooling water temperature Tw, the engine intake air amount Q, and the engine speed Ne are input. .

In the next step 2, for example, by referring to an exhaust gas recirculation region which is preset according to the engine load and the engine speed, it is determined whether or not the current operating condition corresponds to the exhaust gas recirculation execution region. Determine whether. Here, when it is determined that the operating condition is such that the exhaust gas recirculation is scheduled to be executed, the routine proceeds to step 3, where the cooling water temperature detected by the water temperature sensor 11 when the engine is started (the engine temperature at the time of starting) )
Is determined to be below a preset predetermined temperature.

When it is determined that the cooling water temperature Tw at the time of starting is lower than the predetermined temperature, step 4 is further executed.
Then, it is determined whether or not the elapsed time since the engine is started exceeds a preset predetermined time (fixed value). When it is determined in step 4 that the elapsed time after the engine has started does not exceed the predetermined time, even though it is determined in step 2 that the exhaust gas recirculation is in the execution region,
Proceed to step 5, and EGR control solenoid 9
Is controlled to be turned off, so that the stopped state of the exhaust gas recirculation is forcibly held.

On the other hand, in step 3, the temperature T of the cooling water at the time of starting is increased.
When it is determined that w is equal to or higher than the predetermined temperature, or when it is determined in step 4 that the elapsed time from the start exceeds the predetermined time, the process proceeds to step 6 and the exhaust gas recirculation is executed according to the determination in step 2. The EGR control solenoid 9 is turned on. That is, even if the operating condition is such that the exhaust gas recirculation is originally performed, when the cooling water temperature Tw at the time of starting is below a predetermined value, the exhaust gas recirculating time is maintained until a predetermined time elapses from the start (a predetermined period). Is forcibly stopped from executing.

As a result, since the elapsed time from startup is short even when the engine is cold started, the temperature condition is such that the water in the intake air is frozen in the form of frost near the injection hole of the injection valve. Even so, since the exhaust gas recirculation that would bring a large amount of water to the intake system is forcibly stopped, the amount of water in the intake air can be maintained at a low level, and thus, the icing in the injection hole portion can be prevented. Can be suppressed.

If the amount of icing on the injection valve during engine operation can be suppressed as described above, it is possible that the water once melted during engine stoppage will freeze on the injection holes and adversely affect the injection characteristics at restart. This can be avoided in advance, so that restartability in a low temperature environment can be secured. By the way, in the embodiment shown in the flowchart of FIG. 3, the exhaust gas recirculation is forcibly stopped at the time of cold start and even when the elapsed time from the start is within the predetermined time set in advance. However, in order to suppress the NOx emission amount to a low level, it is desired that exhaust gas recirculation can be executed as soon as possible.

Therefore, as shown in the flow chart of FIG. 4, it is preferable to variably set the time for forcibly stopping the exhaust gas recirculation according to the water temperature at the time of starting. In the flowchart of FIG. 4, first, in step 11, various parameters indicating engine operating conditions are input, and in next step 12,
It is determined whether or not the current operating conditions correspond to the exhaust gas recirculation execution region.

When it is determined in step 12 that the exhaust gas recirculation is in the execution region, the process proceeds to step 13,
Cooling water temperature Tw detected by the water temperature sensor 11 when the engine is started
Time Ts for forcibly stopping exhaust gas recirculation from startup based on
Variably set. Here, the lower the cooling water temperature Tw (engine temperature) at the time of starting, the longer the temperature condition in which the water in the intake air freezes with respect to the injection valve.
The lower the starting water temperature, the longer the forced stop time Ts is set.

When the stop time Ts is set in step 13,
In the next step 14, it is judged whether or not the elapsed time from the actual start exceeds the stop time set in the step 13. Until the stop time set in step 13 is exceeded, the process proceeds to step 15 to turn off the EGR control solenoid 9 to keep the exhaust gas recirculation stopped state even under the exhaust gas recirculation execution condition. .

On the other hand, when the elapsed time from the start exceeds the stop time set in accordance with the water temperature at the start in step 14, the process proceeds to step 16, and the EGR control solenoid 9 is turned on according to the execution region determination in step 12. Then, the exhaust gas recirculation is executed. In the embodiment shown in the flow chart of FIG. 4, the time during which exhaust gas recirculation is forcibly stopped is variably set according to the water temperature at the start, so that it is possible to avoid unnecessary compulsory stop of exhaust gas recirculation, and to prevent icing on the injection valve. While avoiding NOx and effectively recirculating exhaust gas to NOx
The amount of emissions can be suppressed.

[0024]

As described above, according to the present invention, the exhaust gas recirculation is forcibly stopped under the temperature condition where the water content of the intake system increases due to the exhaust gas recirculation and the water content of the injection valve freezes. Therefore, there is an effect that the freezing can be prevented in advance and good injection characteristics of the injection valve can be maintained.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of the present invention.

FIG. 2 is a system schematic diagram showing an embodiment of the present invention.

FIG. 3 is a flowchart showing exhaust gas recirculation control according to the first embodiment.

FIG. 4 is a flowchart showing exhaust gas recirculation control according to the second embodiment.

[Explanation of symbols]

 1 Internal Combustion Engine 2 Exhaust Manifold 3 Intake Manifold 4 Exhaust Gas Recirculation Passage 5 EGR Control Valve 6 Throttle Valve 7 Negative Pressure Introduction Passage 8 Control Unit 9 EGR Control Solenoid 10 BPT Valve 11 Water Temperature Sensor 12 Fuel Injection Valve

Claims (1)

[Claims] 1. An exhaust gas recirculation control device for an internal combustion engine, comprising: an exhaust gas recirculation control means for opening and closing an exhaust gas recirculation passage for recirculating a part of the engine exhaust gas to an intake system in accordance with engine operating conditions. Temperature detection means and forcibly holding the exhaust gas recirculation passage in a closed state prior to the exhaust gas recirculation control means for a predetermined period according to the engine temperature detected by the engine temperature detection means when the engine is started from the engine start time. An exhaust gas recirculation control device for an internal combustion engine, comprising: an exhaust gas recirculation stop means for starting.