JP2012041863A - Method of controlling recirculation of exhaust gas of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of EGR control which can suppress hunting during transition from internal EGR control to external EGR control.SOLUTION: An internal combustion engine includes a variable valve timing mechanism and an EGR mechanism. An EGR control valve is closed when target opening of the EGR control valve is less than a first threshold, and the EGR control valve is opened to attain the target opening when it is the first threshold or larger. The EGR control valve is closed when the opening gets smaller than a second threshold which is smaller than the first threshold after it becomes the first threshold or larger. The first and second thresholds are set so that the larger the difference between valve timing when the EGR control valve opens and valve timing when the EGR control valve closes, the larger the difference between the first and second thresholds. Actual timing to start recirculation of exhaust gas by means of the EGR mechanism is set so that it occurs after the valve timing is changed over to the valve timing for EGR by the EGR mechanism.

Description

  The present invention relates to an internal combustion engine having an exhaust gas recirculation (hereinafter referred to as EGR) mechanism for recirculating exhaust gas to an intake system and a variable valve timing mechanism for controlling at least one valve timing of an intake valve and an exhaust valve. The present invention relates to an exhaust gas recirculation control method.

  Conventionally, in an internal combustion engine provided with this type of EGR mechanism and variable valve timing mechanism, each mechanism is controlled so as to switch the EGR amount in accordance with the valve timing. For example, in Patent Document 1, different EGR amounts are set for the first valve timing and the second valve timing that is later than the first valve timing, and surging due to a sudden increase in pressure in the intake pipe is performed. By avoiding this, the valve timing can be switched smoothly.

  By the way, in this type of internal combustion engine, by changing the valve timing by a variable valve timing mechanism, so-called internal EGR control in which part of the burnt gas to be discharged remains in the cylinder, and so-called external by the EGR mechanism. There is also known one that switches EGR control depending on the operation region of the internal combustion engine. In such a case, the target opening of the EGR valve of the EGR mechanism is set using, for example, a map with the engine speed and the intake pipe internal pressure, and when the target opening becomes a predetermined value or more, the internal opening The EGR control is switched to the external EGR control. The target opening is updated while the valve timing is controlled by the variable valve timing mechanism, but the EGR mechanism controls the EGR valve so as to reach the target opening while the valve timing is controlled. is not.

  When switching from internal EGR control to external EGR control, the valve timing is changed to the target valve timing for external EGR control, and then the EGR valve is driven to reach the target opening at that time. ing. Since the valve timing is delayed to the target valve timing first, the intake air amount increases, and as a result, the intake pipe pressure temporarily decreases as shown in FIG. When the intake pipe internal pressure decreases in this way, the target opening is set based on the reduced intake pipe internal pressure, and thus the target opening falls below the predetermined value.

  When such a state occurs, there is a possibility that a mode hunting state in which the internal EGR control and the external EGR control are switched back and forth will be replaced with the predetermined value, which is a first determination value for opening the EGR valve. A threshold value and a second threshold value for closing are set to give hysteresis to the opening / closing control of the EGR valve.

  By the way, when the required hysteresis amount by the first threshold value and the second threshold value is set to be constant, the fuel efficiency is optimal even when the valve timing is set. And the hysteresis requirement varies. For this reason, for example, if the hysteresis requirement is set in accordance with the low rotation range, mode hunting occurs in the high rotation range. On the other hand, if the reverse setting is set, the transition to the external EGR control smoothly in the low rotation range. It became impossible to do so and became a factor of reducing fuel consumption.

JP 2007-71075 A

  Accordingly, the present invention focuses on the above points and aims to suppress hunting when executing EGR control by the EGR mechanism in an internal combustion engine including a variable valve timing mechanism and an EGR mechanism.

  That is, according to the exhaust gas recirculation control method for an internal combustion engine of the present invention, the internal combustion engine controls a variable valve timing mechanism that controls the valve timing of at least one of the exhaust valve and the intake valve, and the exhaust gas recirculation amount. An exhaust gas recirculation mechanism having a recirculation control valve, and when the target opening of the recirculation control valve set based on the engine speed and the intake pipe internal pressure is less than the first threshold value The recirculation control valve is closed, and when it is greater than or equal to the first threshold, the recirculation control valve is opened so as to reach the target opening, and after becoming greater than or equal to the first threshold and smaller than the first threshold An exhaust gas recirculation control method for an internal combustion engine that closes the recirculation control valve when the recirculation control valve is less than the second threshold, the valve timing when the recirculation control valve opens, The greater the difference from the valve timing, The first and second threshold values are set so that the difference between the first threshold value and the second threshold value becomes large, and the actual timing for starting the exhaust gas recirculation by the exhaust gas recirculation mechanism is exhausted. It is characterized in that it is set after switching to valve timing for exhaust gas recirculation by the gas recirculation mechanism.

  In such a configuration, the difference between the first threshold value and the second threshold value is set larger as the difference in valve timing by the variable valve timing mechanism between when the recirculation control valve is open and when it is closed is larger. Thus, mode hunting during exhaust gas recirculation control by the exhaust gas recirculation mechanism can be suppressed.

  The present invention is configured as described above, and mode hunting at the time of switching from exhaust gas recirculation control by a variable valve timing mechanism to exhaust gas recirculation control by an exhaust gas recirculation mechanism can be suppressed, Fuel consumption can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS Structure explanatory drawing which shows schematic structure of embodiment of this invention. The flowchart which shows the outline of the control procedure of the embodiment. The flowchart which shows the outline of the control procedure of the embodiment. The flowchart which shows the outline of the control procedure of the embodiment. Explanatory drawing of an effect | action of a prior art example.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

An engine 100 schematically showing the configuration of one cylinder in FIG. 1 is mounted on, for example, an automobile. The engine 100 includes an intake system 1, a cylinder 2, and an exhaust system 5. The intake system 1 is provided with a throttle valve 11 that opens and closes in response to an accelerator pedal (not shown), and an intake manifold 12 that integrally has a surge tank 13 is attached downstream of the throttle valve 11. A spark plug 8 is attached to the ceiling portion of the combustion chamber 23 formed in the upper part of the cylinder 2. A fuel injection valve 3 is attached to an intake port side end of the intake manifold 12. The fuel injection valve 3 is controlled by an electronic control device 4 described later. Further, an EGR mechanism 6 is connected between the surge tank 13 and the exhaust system 5 including the O ₂ sensor 51, the three-way catalyst 52, and the exhaust manifold 53.

  The EGR mechanism 6 includes an EGR pipe 61 connected at one end so as to communicate with the surge tank 13, and a flow rate of exhaust gas that is provided in the EGR pipe 61 and passes through the EGR pipe 61, that is, an EGR amount And an EGR control valve 62 for controlling the motor. The other end of the EGR pipe 61 is connected to the exhaust manifold 53 so as to communicate with the exhaust system 5 upstream of the three-way catalyst 52 provided in the exhaust system 5. When the EGR control valve 62 is controlled, that is, opened, the EGR device 6 passes the EGR pipe 61 at a flow rate corresponding to the opening degree of the EGR control valve 62 and is located downstream of the throttle valve 11. It is made to recirculate in the surge tank 13. The amount of EGR to be refluxed depends on the opening degree of the EGR control valve 62, and the opening degree of the EGR control valve 62 is controlled by the electronic control unit 4.

  The engine 100 has a variable valve timing mechanism for changing the opening / closing timing (hereinafter referred to as valve timing) of the intake valve 21 to a target valve timing set based on the intake pipe internal pressure and the engine speed. 9 is provided. The variable valve timing mechanism 9 uses a so-called oscillating cylinder mechanism, and includes a rotor fixed to the intake camshaft 91, a housing fitted outside the rotor, and an electromagnetic for rotating the housing relative to the rotor. An oil control valve 92 which is a four-way switching control valve, a pair of gears 94 and 95 which are attached to the housing and fixed to the exhaust camshaft 93 so as to mesh with each other, and attached to the end of the intake camshaft 91 A crank sensor 96 that outputs a crank angle signal and a cylinder discrimination signal, and a timing sensor 97 that is attached to the end of the exhaust cam shaft 93 and outputs an exhaust cam signal each time it rotates 240 ° CA (crank angle); It is the structure provided with.

  In such a configuration, the opening / closing timing of the intake valve 21, that is, the valve timing, is changed by the variable valve timing mechanism 9 operated by the opening / closing timing signal p output from the electronic control device 4. That is, when the variable valve timing mechanism 9 receives the opening / closing timing signal p, the oil control valve 92 controls the direction and amount of hydraulic fluid flowing into and out of the housing. As a result, the relative angle of the housing with respect to the rotor changes, and a desired rotational phase difference is generated between the intake camshaft 91 and the exhaust camshaft 93 to variably control the valve timing. That is, the valve timing of the intake valve 21 and the valve timing of the exhaust valve 24 are changed by changing the valve timing of the intake valve 21 while the exhaust valve 24 is always opened and closed with respect to the rotation of the crankshaft. The relative phase difference can be freely changed within a predetermined angle range. Then, by opening the intake valve 24 earlier, so-called internal EGR control is performed in which exhaust gas is blown back to the intake port and mixed with intake air.

  The electronic control unit 4 is mainly configured by a microcomputer system including a central processing unit 41, a storage unit 42, an input interface 43, and an output interface 44. The central processing unit 41 controls the operation of the engine 100 by executing various programs described below stored in the storage device 42. Information necessary for operation control of the engine 100 is input to the central processing unit 41 via the input interface 43, and the central processing unit 41 includes the fuel control valve 3, the exhaust gas recirculation control valve 62, and the oil control valve 92. A control signal is output via the output interface 44.

Specifically, the input interface 43 includes an intake pressure signal a output from the intake pressure sensor 71 for detecting the pressure in the surge tank 13 as the intake pipe internal pressure, and a rotation speed sensor for detecting the engine speed. 72, a rotation speed signal b output from the vehicle 72, a vehicle speed signal c output from the vehicle speed sensor 73 for detecting the vehicle speed, an IDL signal d output from the idle switch 74 for detecting the open / closed state of the throttle valve 11, and the engine A water temperature signal f output from the water temperature sensor 76 for detecting the cooling water temperature of 100, a voltage signal h output from the O ₂ sensor 51, and the like are input. On the other hand, from the output interface 44, the ignition signal m for the spark plug 8, the fuel injection signal n for the fuel control valve 3, the valve opening / closing signal o for the exhaust gas recirculation control valve 62, the variable valve timing mechanism 9 An opening / closing timing signal p or the like is output to the oil control valve 92.

  In such a configuration, the electronic control unit 4 sets the intake pressure signal a output from the intake pressure sensor 71 and the rotation speed signal b output from the rotation speed sensor 72 as main information according to the driving state. The fuel injection amount is calculated using the coefficient to determine the fuel injection time corresponding to the fuel injection amount, that is, the energization time for the fuel injection valve 3, and the fuel injection valve 3 is controlled by the determined energization time, Fuel is injected into the intake system 1. Such fuel injection control itself may apply what is known in this field.

  Further, the electronic control unit 4 closes the EGR control valve 62 when the target opening of the EGR control valve 62 set based on the engine speed and the intake pipe internal pressure is less than the first threshold, When the EGR control valve 62 is opened to reach the target opening when the first threshold is exceeded, and when the EGR control valve 62 becomes less than the second threshold, which is smaller than the first threshold after becoming the first threshold or more. Is for closing the EGR control valve 62, and the greater the difference between the valve timing when the EGR control valve 62 is opened and the valve timing when the EGR control valve 62 is closed, the larger the first threshold value and the second threshold value are. The first and second threshold values are set so as to increase the difference between the first and second thresholds, the actual timing for starting the exhaust gas recirculation by the EGR mechanism 6, the valve timing for the exhaust gas recirculation by the EGR mechanism 6 Valve timing EGR control program set to be after switching to the are stored in the electronic control unit 4. A schematic procedure of the EGR control program is shown in FIGS.

  FIG. 2 is a routine for setting the target opening of the EGR control valve 62, and is repeatedly executed at predetermined time intervals while the engine 100 is in operation. First, in step S1, the intake pipe internal pressure is detected based on the intake pressure signal a, and the engine rotational speed is detected based on the rotational speed signal b. The intake pipe internal pressure and the engine speed are the same as those detected when calculating the fuel injection amount.

  In step S2, a map is searched based on the detected intake pipe internal pressure and engine speed, and a target opening degree of the EGR control valve 62 is set. In the map, the target opening is set according to typical intake pipe internal pressure and engine speed. For other intake pipe internal pressure and engine speed, interpolation calculation is performed to set the target opening. To do.

  Next, a control procedure for switching the valve timing of the intake valve 21 in the variable valve timing mechanism 9 from that for internal EGR control to that for external EGR control will be described with reference to FIG. Note that initial values are set for the first threshold and the second threshold lower than the first threshold, and when switching from internal EGR control to external EGR control described below, the valve timing at that time is set. It is updated based on this. The initial value of the first threshold is set to a value that can be estimated that mode hunting due to hysteresis does not occur when switching the EGR control. On the other hand, when the opening degree of the EGR control valve 62 is further reduced, the initial value of the second threshold is set to a value that is more effective for internal EGR control, that is, advantageous in terms of fuel consumption. In making these settings, the initial value of the second threshold is determined first.

  First, in step S11, it is determined whether or not the target opening is equal to or greater than the first threshold when the internal valve EGR control is performed by the variable valve timing mechanism 9 while the EGR mechanism 6 is not operated. . If it is determined that the target opening is equal to or greater than the first threshold, the valve timing is switched to that for executing external EGR control in step S12. Specifically, the valve timing is retarded by a set retard amount, thereby reducing the amount of burned gas remaining in the cylinder 2 corresponding to the EGR amount in the internal EGR control.

  In step S13, the EGR control valve 62 is opened until the target opening is reached at the timing after the valve timing is switched from that for internal EGR control to that for external EGR control in step S12.

  In step S14, while the EGR control valve 62 is being controlled, it is determined whether or not the target opening has become less than the second threshold because the intake pipe pressure has decreased as the valve timing is switched. If it is determined that the target opening is less than the second threshold, the valve timing is switched to that for internal EGR control in step S15. In step S16, the EGR control valve 62 is closed to stop the external EGR control.

  Next, the procedure for setting the first threshold value and the second threshold value will be described with reference to FIG.

  The first and second threshold values are set based on the valve timing in each case when the EGR control valve 62 is opened and closed. First, in step S21, the valve timing when the EGR control valve 62 is opened is detected. In this embodiment, the valve timing is set to a constant value. Therefore, while the EGR control valve 62 is being controlled, that is, while the external EGR control is being performed, the valve timing of the intake valve 21 is a fixed valve timing without being changed.

  In step S22, the valve timing when the EGR control valve 62 is closed is detected. That is, the valve timing is detected based on the intake pipe internal pressure and the engine speed when the operating state changes and the target opening of the EGR control valve 62 becomes less than the second threshold.

  In step S23, the difference in valve timing detected in steps S21 and S22 is calculated.

  In step S24, a first threshold value and a second threshold value are set based on the calculated magnitude of the difference. In the case of this embodiment, the first threshold value and the second threshold value are set so that the difference between the first threshold value and the second threshold value increases as the difference increases.

  In such a configuration, when the variable valve timing mechanism 9 is operating and the EGR control valve 62 is not operating, that is, not open, the valve timing of the intake valve 21 is controlled by the variable valve timing mechanism 9. Thus, the internal EGR control is performed. In this case, the burned gas having a temperature higher than that of the EGR gas in the external EGR control remains in the cylinder 2, so that the combustion temperature does not decrease in the low rotation range, and good combustion can be obtained, thereby suppressing the reduction in fuel consumption. Can do.

  Thus, even while the variable valve timing mechanism 9 is in operation, the target opening of the EGR control valve 62 is continuously set by executing steps S1 and S2 at a predetermined cycle. In parallel with the setting of the calculated target opening, the relationship between the set target opening and the first and second threshold values is monitored, and when the target opening becomes equal to or greater than the first threshold, the valve timing Is switched to one for external EGR control (steps S11 and S12), and the opening of the EGR control valve 62 is opened so as to reach the target opening (step S13). The EGR control is switched to the external EGR control by the mechanism 6.

Thereafter, the EGR control valve 62 is opened to reach the target opening until the target opening set by the execution of steps S1 and S2 is less than the second threshold (“Yes” in step S14). continue. When the target opening becomes less than the second threshold due to a change in the operating state, the valve timing is switched to that for internal EGR control, and the EGR control valve 62 is closed (step S15 and step S16).
As described above, when switching the EGR control, the difference in valve timing when the EGR control valve 62 is opened and closed is calculated, and the difference between the first threshold value and the second threshold value changes based on the magnitude of the difference. The first and second threshold values are set (steps S21 to S24). That is, since the valve timing for closing the EGR control valve 62 changes according to the operating state of the engine 100, the required hysteresis amount based on the first and second threshold values can also be changed according to the operating state. For this reason, it is possible to suppress the occurrence of mode hunting when switching from the internal EGR control to the external EGR control regardless of the operating state.

  The present invention is not limited to the above embodiment.

  In the above-described embodiment, the valve timing when the EGR control valve 62 is opened is a constant value, but may be set according to the operating state. Thus, the difference between the first threshold value and the second threshold value can be further increased by adjusting the opening valve timing of the EGR control valve 62 to the operating state.

  In the above-described embodiment, the difference between the valve timing when the EGR control valve 62 is opened and the valve timing when the EGR control valve 62 is closed is calculated by detecting each valve timing. Since the timing and the EGR control valve 62 are a function of the engine speed and the intake pipe internal pressure, the engine speed and the intake pipe from when the EGR control valve 62 is opened to when the EGR control valve 62 is closed are detected without detecting each valve timing. It may be calculated directly from the amount of change in pressure.

  In addition, the specific configuration of each part is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention.

  An application example of the present invention is an engine mounted on a vehicle such as an automobile.

DESCRIPTION OF SYMBOLS 4 ... Electronic control device 6 ... EGR mechanism 9 ... Variable valve timing mechanism 21 ... Intake valve 24 ... Exhaust valve 62 ... EGR control valve 71 ... Intake pressure sensor 72 ... Speed sensor

Claims (1)

The internal combustion engine includes a variable valve timing mechanism that controls the valve timing of at least one of the exhaust valve and the intake valve, and an exhaust gas recirculation mechanism that has a recirculation control valve that controls the recirculation amount of the exhaust gas. When the target opening of the recirculation control valve set based on the engine speed and the intake pipe internal pressure is less than the first threshold, the recirculation control valve is closed and Opens the recirculation control valve so that it reaches the target opening, and when it becomes less than the second threshold that is smaller than the first threshold after the first threshold is exceeded, the recirculation control valve is An internal combustion engine exhaust gas recirculation control method comprising:
As the difference between the valve timing when the recirculation control valve is opened and the valve timing when the recirculation control valve is closed is larger, the difference between the first threshold value and the second threshold value is larger. Set the threshold of
Exhaust gas from an internal combustion engine that sets the actual timing for starting the exhaust gas recirculation by the exhaust gas recirculation mechanism to be after the valve timing is switched to the valve timing for exhaust gas recirculation by the exhaust gas recirculation mechanism Gas recirculation control method.

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