JP3783422B2 - Exhaust gas recirculation control device for in-cylinder injection engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust gas recirculation control device for an in-cylinder injection engine, and in particular, in the case where an intake throttle valve is disposed in an intake passage, the intake air when an accelerator pedal depression by a vehicle driver is predicted. It belongs to the technical field of throttle valve control.
[0002]
[Prior art]
Conventionally, as an exhaust gas recirculation control device for this type of in-cylinder injection engine, as disclosed in, for example, Japanese Patent Application Laid-Open No. Sho 63-50544, nitrogen oxide (NOx) in exhaust gas in a turbocharged diesel engine is disclosed. In order to reduce the amount of exhaust gas, an exhaust air recirculation amount is adjusted to control the excess air ratio λ. In this system, an exhaust gas recirculation amount adjustment valve (exhaust gas circulation adjustment device) operated by an actuator is provided in the middle of an exhaust gas recirculation passage communicating the intake and exhaust systems of the engine, and by controlling the opening of this valve, The exhaust gas recirculation amount is adjusted.
[0003]
In general, since the intake negative pressure of the engine becomes low in a low speed operation state such as an idle operation, a sufficient exhaust gas recirculation amount may not be obtained even when the exhaust gas recirculation amount adjustment valve is fully opened. On the other hand, in the exhaust gas recirculation control device disclosed in Japanese Patent Application Laid-Open No. 9-4519, an intake throttle valve is usually provided in an intake passage of a small diesel engine not provided with a throttle valve or the like, and the intake negative valve as described above. In an operating state where the pressure is low, the differential pressure between the intake and exhaust systems is increased by reducing the opening of the intake throttle valve so that a sufficient exhaust gas recirculation amount can be obtained.
[0004]
[Problems to be solved by the invention]
By the way, it is known that a diesel engine is usually operated in a state in which the air-fuel ratio is considerably lean (lean), so that the amount of NOx emission increases. On the other hand, the NOx emission amount can be reduced by increasing the exhaust gas recirculation amount. On the other hand, if the exhaust gas recirculation amount is increased, the amount of oxygen in the intake air decreases, and smoke is likely to be generated. That is, when the air-fuel ratio becomes rich, smoke is likely to occur. Also, in a cylinder injection gasoline engine, if the exhaust gas recirculation amount is increased while the air-fuel ratio is lean, smoke is likely to be generated.
[0005]
Therefore, the present inventor investigated the relationship between the air-fuel ratio and the smoke amount, and as a result, found that the smoke amount rapidly increases when the air-fuel ratio exceeds a certain value and becomes rich. Considering this characteristic, in order to achieve both the NOx reduction and the smoke reduction, the exhaust gas recirculation amount should be controlled by setting the air-fuel ratio on the rich side before the smoke amount starts to increase rapidly as a target. .
[0006]
However, in the conventional exhaust gas recirculation control device, the exhaust gas recirculation amount is adjusted by the exhaust gas recirculation amount adjusting valve provided in the middle of the exhaust gas recirculation passage. If the exhaust gas recirculation amount is controlled, the air-fuel ratio becomes excessively rich at the start of acceleration of the vehicle, causing a problem that the amount of smoke in the exhaust gas rapidly increases. That is, at the start of acceleration of the vehicle, the fuel injection amount is increased in response to the driver depressing the accelerator pedal, and the exhaust gas recirculation amount adjustment valve is operated to the closed side, and the intake air amount is reduced by reducing the exhaust gas recirculation amount. In this case, the air-fuel ratio temporarily deviates from the target to the rich side due to a delay in the operation of the exhaust gas recirculation amount adjustment valve.
[0007]
In particular, when the engine is running at low speed, including during idle operation, the exhaust gas recirculation amount adjustment valve is fully opened to ensure the exhaust gas recirculation amount, and if the accelerator pedal is suddenly depressed in that state, the fully open state Since it takes time until the exhaust gas recirculation amount control valve is fully closed, an increase in the amount of smoke during that time becomes a problem.
[0008]
To solve this problem, when the engine is in a low speed operation state, it is conceivable to suppress the increase in the fuel injection amount corresponding to the accelerator operation for a time corresponding to the operation delay of the exhaust gas recirculation amount adjustment valve. Then, the fuel injection amount immediately after the accelerator pedal is depressed becomes insufficient, and the acceleration performance of the vehicle is impaired.
[0009]
The present invention has been made in view of such various points, and an object of the present invention is to control the exhaust gas recirculation amount so that the air-fuel ratio is set to a predetermined target value in order to reduce both NOx and smoke in the exhaust gas. In the exhaust gas recirculation control system, the exhaust throttle valve control when the driver is expected to depress the accelerator pedal is devised to maintain the acceleration performance of the vehicle corresponding to the accelerator operation while maintaining the exhaust performance. The purpose is to reduce the amount of smoke inside.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, according to the present invention, the intake throttle valve is operated to the closed side in the accelerator return state, for example, when the driver releases the accelerator pedal while the vehicle is running.
[0011]
Specifically, in the first aspect of the invention, as shown in FIG. 1, a fuel injection valve 5 that directly injects fuel into the combustion chamber 4 in the cylinder 2 of the engine 1, and an intake passage to the combustion chamber 4 10, an exhaust throttle valve 14 disposed in the exhaust pipe 10, an exhaust gas recirculation passage 23 that recirculates part of the exhaust gas to the intake passage 10 downstream of the intake throttle valve 14, and an exhaust gas recirculation amount in the exhaust gas recirculation path 23 are adjusted. An exhaust gas recirculation amount adjusting valve 24, a sensor 11 for measuring an intake air amount in the intake passage 10, a fuel injection control means 35a for controlling a fuel injection amount by the fuel injection valve 5 in accordance with an accelerator operation amount, and the intake air Exhaust gas from an in-cylinder injection type engine having exhaust recirculation control means 35b for controlling the opening degree of the exhaust gas recirculation amount adjusting valve 24 so that the air-fuel ratio becomes a predetermined target value based on the air amount and the fuel injection amount. Reflux control device A in front To. Then, an accelerator return state determination unit 35e that determines an accelerator return state in which the accelerator operation amount has decreased by a predetermined value or more, and an intake throttle valve control that operates the intake throttle valve 24 to the closed side when the accelerator return state is determined. From means 35d and when the accelerator return state is determined Respond to accelerator depression during subsequent re-acceleration Gain increase correction means for increasing and correcting the control gain of the exhaust gas recirculation amount control valve by the exhaust gas recirculation control means until a set time elapses In addition, the exhaust gas recirculation control means 35b operates the exhaust gas recirculation amount adjusting valve 24 to the closed side in the acceleration operation state in which the accelerator operation amount greatly changes by a predetermined value or more, and the accelerator return state is determined. The exhaust gas recirculation amount adjustment valve 24 is sometimes operated to be closed. To do.
[0012]
According to this configuration, when the driver releases the accelerator pedal for some reason while the vehicle is traveling, the accelerator return state determination means 35e determines the accelerator return state as the accelerator operation amount decreases. Then, the intake throttle valve 24 is actuated to the closed side by the intake throttle valve control means 35d, and the exhaust gas recirculation control means 35b causes the opening degree of the exhaust gas recirculation amount adjustment valve 24 to correspond to the reduction of the intake air amount. Be made smaller (In other words, the exhaust gas recirculation amount adjustment valve 24 is operated to the closed side) . Accordingly, when the driver once depresses the released accelerator pedal, the fuel injection amount is increased by the fuel injection control means 35a in response to the increase in the accelerator operation amount, and the exhaust gas recirculation control means 35b. The exhaust gas recirculation amount adjustment valve 24 is actuated to the closed side. At this time, since the opening degree of the exhaust gas recirculation amount adjustment valve 24 has already been reduced, the exhaust gas recirculation amount is reduced accordingly and the intake air is reduced. The amount increases rapidly.
[0013]
That is, in the accelerator return state, the accelerator pedal is predicted to be depressed by the driver, and accordingly, the exhaust gas recirculation amount adjusting valve 24 is operated to the closed side in response to this, and then when the accelerator pedal is depressed, Without suppressing the fuel injection amount, the delay in the closing operation of the exhaust gas recirculation amount adjusting valve 24 can be reduced, so that the smoke amount in the exhaust gas can be reduced while maintaining the acceleration performance of the vehicle.
[0014]
In addition, in the situation where the accelerator operation amount by the driver changes suddenly as described above, priority is given to increasing the control response so as not to be delayed by the change, and the set time from when the accelerator return state is determined. Until the time elapses, the control gain of the exhaust gas recirculation control valve by the exhaust gas recirculation control means is increased and corrected. As a result, the responsiveness of the operation of the exhaust gas recirculation amount adjusting valve can be enhanced. Note that if the set time is set to a relatively short time (for example, 1 to 2 seconds), deterioration of control convergence during that time is not a problem.
[0015]
In the second aspect of the invention, the accelerator return state in the first aspect of the invention is accompanied by a shifting operation of the manual transmission during the acceleration operation of the vehicle, and the shifting operation of the manual transmission is completed for a set time. It is assumed that the period until the accelerator is returned is not included.
[0016]
In this way, by reducing the opening degree of the exhaust gas recirculation amount adjustment valve in the accelerator return state accompanying the shift operation, it is possible to reduce the engine slack when the shift operation is finished and the state is shifted to the acceleration operation state. Since the responsiveness of the operation of the exhaust gas recirculation amount adjustment valve is enhanced by the correction correction of the control gain, the above-described slack can be virtually eliminated.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0018]
(overall structure)
FIG. 1 shows an overall configuration of an embodiment of the present invention. Reference numeral 1 denotes an in-line four-cylinder diesel engine having four cylinders 2 (only one is shown). The engine 1 is used in a vehicle equipped with a manual transmission. It is installed. A piston 3 is fitted in each cylinder so as to be able to reciprocate. A combustion chamber 4 is defined in each cylinder 2 by the piston 3. An injector (fuel injection valve) 5 comprising a valve is provided. Each injector 5 is connected to a common rail (pressure accumulating chamber) 6 that stores high-pressure fuel, and is opened and closed at a predetermined injection timing for each cylinder to inject fuel directly into the combustion chamber 4. ing.
[0019]
The common rail 6 is provided with a pressure sensor 6a for detecting the internal fuel pressure (common rail pressure), and connected to a high pressure supply pump 8 driven by a crankshaft 7. Operates so that the fuel pressure in the common rail 6 detected by the pressure sensor 6a is maintained at a predetermined value (for example, 40 MPa during idle operation and 80 MPa or more in other operation states). Furthermore, a crank angle sensor 9 for detecting the rotation angle of the crankshaft 7 is provided at the end of the crankshaft 7. The crank angle sensor 9 is composed of an electromagnetic pickup or the like, and is disposed at a position corresponding to the outer periphery of a plate (not shown) to be detected provided at the end of the crankshaft 7, and protrudes from the outer periphery. A pulse signal is output corresponding to the passage of the protruding portion.
[0020]
Reference numeral 10 denotes an intake passage for supplying intake air (intake) to each cylinder 2 of the engine 1, and a downstream end portion of the intake passage 10 is branched for each cylinder via a surge tank (not shown). An intake port (not shown) is connected to the combustion chamber 4 of each cylinder 2. The surge tank is provided with an intake pressure sensor 10a that can detect the supercharging pressure that is supercharged to each cylinder 2. On the other hand, an upstream end portion of the intake passage 10 is connected to an air cleaner (not shown), and an air flow sensor 11 that measures an intake flow rate in order from the upstream side and a blower 12 that is driven by a turbine 21 (to be described later) to compress intake air. And an intercooler 13 for cooling the intake air compressed by the blower 12 and an intake throttle valve 14 for reducing the passage cross-sectional area. The intake throttle valve 14 is a butterfly valve provided with a notch so that intake air can flow even in a fully closed state. Like the EGR valve 24 described later, the magnitude of the negative pressure acting on the diaphragm 15 is negative. The opening degree of the valve is adjusted by adjusting the electromagnetic valve 16 for control.
[0021]
The air flow sensor 11 is a constant temperature hot film type air flow sensor that can reliably capture the air flow rate even when the flow rate fluctuates. Although not shown, the air flow sensor 11 is arranged in the intake passage 10 so as to be orthogonal to the intake flow direction. And a hot film disposed on the upstream side and the downstream side across the heater, and the intake passage 10 is arranged on the downstream side (the side of each cylinder 2) based on the temperature of both hot films. ) And a backward flow toward the upstream side are detected. Only the air flow rate in the forward direction can be measured based on the measurement value by the air flow sensor 11, and it is possible to avoid an error due to the backflow in the control of the exhaust gas recirculation amount. Instead of the air flow sensor 11, a sensor that detects the intake pipe pressure in the intake passage 10 may be employed.
[0022]
In FIG. 1, reference numeral 20 denotes an exhaust passage for exhausting exhaust gas from the combustion chamber 4 of each cylinder 2. The upstream end of the exhaust passage 20 branches and is connected to the combustion chamber 4 of each cylinder 2 by an exhaust port (not shown). A turbine 21 that is connected and is rotated in sequence by the exhaust gas, and a catalytic converter 22 having a so-called four-way catalyst that purifies HC, CO, NOx, and particulates in the exhaust gas. .
[0023]
The turbocharger 25 composed of the turbine 21 and the blower 12 is for performing sufficient supercharging at the time of acceleration operation or high load operation of the engine 1, and as shown in FIG. A plurality of flaps 21b, 21b,... Are provided in the turbine chamber 21a to be accommodated so as to surround the entire circumference of the turbine 21a, and each of the flaps 21b is rotatable so as to change the nozzle cross-sectional area A of the exhaust passage. VGT (variable geometry turbo). In this VGT, as shown in FIG. 5A, the flaps 21b, 21b,... Are positioned so that their tips face the circumferential direction with respect to the turbine 21, and the nozzle cross-sectional area A is reduced to reduce the so-called A / R. Then, the supercharging efficiency becomes high in the low rotation range of the engine 1 with a small exhaust flow rate, and conversely, the flaps 21b, 21b,... Are directed toward the center of the turbine 21 as shown in FIG. If the nozzle cross-sectional area A is increased and A / R is increased, the supercharging efficiency is lowered in the low rotation range of the engine 1 where the exhaust flow rate is also small.
[0024]
The exhaust passage 20 is branched and connected between the turbine 21 and the catalytic converter 22 at the upstream end of an exhaust gas recirculation passage (hereinafter referred to as an EGR passage) 23 that recirculates a part of the exhaust gas to the intake side. The downstream end of the EGR passage 23 is connected to the downstream side of the intercooler 13 in the intake passage 10, and a negative pressure actuated exhaust gas recirculation amount adjustment valve (hereinafter referred to as an EGR valve) 24 whose opening degree can be adjusted. A part of the exhaust gas in the exhaust passage 20 is recirculated to the intake passage 10 while the flow rate is adjusted by the EGR valve 24.
[0025]
As shown in FIG. 3, the EGR valve 24 has a valve rod 24b fixed to a diaphragm 24a that partitions the valve box, and a valve body 24c that linearly adjusts the opening of the EGR passage 23 at both ends of the valve rod 24b and a lift. A sensor 26 is provided. The valve body 24c is urged in the closing direction (downward in the figure) by a spring 24d, while a negative pressure passage 27 is connected to the negative pressure chamber (the chamber above the diaphragm 24a) of the valve box. The negative pressure passage 27 is connected to a vacuum pump (negative pressure source) 29 via a negative pressure control electromagnetic valve 28. The electromagnetic valve 28 is connected to a negative pressure passage by a control signal (current) from an ECU 35 described later. The EGR valve drive negative pressure in the negative pressure chamber is adjusted by communicating / blocking 27, whereby the opening degree of the EGR passage 23 is linearly adjusted by the valve body 24c.
[0026]
That is, as shown in FIG. 4A, as the current increases, the EGR valve drive negative pressure increases (pressure decreases), and is proportional to the EGR valve drive negative pressure as shown in FIG. 4B. The lift amount of the EGR valve main body 24c changes. However, hysteresis is observed in the change in the lift amount of the EGR valve main body 24c.
[0027]
In addition, a diaphragm 30 is attached to the flaps 21b, 21b,... Of the turbocharger 25 in the same manner as the EGR valve 24, and the negative pressure acting on the diaphragm 30 is adjusted by the electromagnetic valve 31 for negative pressure control. As a result, the operation amount of the flaps 21b, 21b,... Is adjusted.
[0028]
The injectors 5, the high pressure supply pump 8, the intake throttle valve 14, the EGR valve 24, the flaps 21 b, 21 b,... Of the turbocharger 25 are controlled by control signals from a control unit 35 (hereinafter referred to as “ECU”). It is configured to operate. The ECU 35 includes a signal output from the pressure sensor 6a, an output signal from the crank angle sensor 9, an output signal from the air flow sensor 11, an output signal from the lift sensor 26 of the EGR valve 24, and driving of the vehicle. At least an output signal from an accelerator opening sensor 32 that detects an operation amount (accelerator opening) of an accelerator pedal (not shown) by a person is input.
[0029]
(Overall configuration of control system)
An outline of basic processing of engine control in the ECU 35 is shown in a block diagram of FIG. 5. Fuel injection control by the operation of the injector 5 and exhaust gas recirculation control (EGR valve control) by the operation of the EGR valve 24 are performed. In addition to this, the control of the common rail pressure, that is, the fuel injection pressure by the operation of the high pressure supply pump 8, the operation control of the intake throttle valve 14, and the operation control of the flaps 21b, 21b,. (VGT control).
[0030]
1) Overview of exhaust gas recirculation and fuel injection control
In the exhaust gas recirculation and fuel injection control, the basic fuel injection amount is determined based on the accelerator opening, and the EGR rate is adjusted by the operation of the EGR valve 24 to uniformly and accurately control the air-fuel ratio of each cylinder. To do. This EGR rate refers to the ratio of the amount of exhaust gas recirculated (EGR amount) in the total displacement.
[0031]
EGR rate = EGR amount / total displacement
Here, the distribution characteristics of the exhaust gas recirculated from the EGR passage 23 to the intake passage 10 to the respective cylinders are different, and in addition, the air intake characteristics of each cylinder 2 also vary, so the EGR valve in the EGR passage 23 Even if the opening degree of 24 is the same, the EGR rate and intake air amount deviation in each cylinder 2 vary, and the intake air amount is small in a cylinder with a high EGR rate, and the intake air amount is low in a cylinder with a low EGR rate. Become more. Therefore, basically, a target air-fuel ratio common to all cylinders is determined, the intake air amount is detected for each cylinder 2, and the exhaust gas is returned to each cylinder so that the target air-fuel ratio is set according to the intake air amount. Control the flow rate. In other words, the ratio of the EGR amount to the intake air amount of each cylinder 2 is not equalized, but the exhaust gas recirculation amount is controlled for each cylinder with a predetermined air-fuel ratio as a target, so that the air-fuel ratio of each cylinder 2 is made uniform. And it is controlled with high precision.
[0032]
Specifically, the ECU 35 includes a two-dimensional map 36 in which the optimum target torque trqsol determined experimentally in the changes in the accelerator opening degree accel and the engine speed Ne, the engine speed Ne, and the target torque trqsol are recorded. And a three-dimensional map 37 that records the optimum target fuel injection amount Fsol determined experimentally in the change of FAir, and the new air amount (intake air amount and does not include fuel, the same applies hereinafter), and the engine A two-dimensional map 38 in which the optimum target air-fuel ratio A / Fsol determined experimentally for changes in the rotational speed Ne and the target torque trqsol is electronically stored in the memory.
[0033]
The target air-fuel ratio A / Fsol serves as a reference for determining the exhaust gas recirculation amount for achieving both NOx reduction and smoke reduction. That is, as illustrated in FIG. 6 as an example of the relationship between the air-fuel ratio of the diesel engine and the NOx amount in the exhaust gas, the NOx amount tends to increase as the air-fuel ratio increases. When it is lowered, the generation of NOx can be reduced.
[0034]
However, as shown in FIG. 7, according to the relationship between the air-fuel ratio of the same engine and the smoke value in the exhaust, when the air-fuel ratio becomes lower than the air-fuel ratio that has changed to the rich side, the smoke amount suddenly increases. It can be seen that it increases. For this reason, there is a limit to increasing the exhaust gas recirculation amount, and in order to achieve both reduction in the NOx amount in the exhaust gas and suppression of the increase in the smoke amount, the target air-fuel ratio can be reduced to NOx. It can be said that it is necessary to control the exhaust gas recirculation amount to the rich side as much as possible and to a value before the smoke amount starts to increase rapidly, and to set this as a target.
[0035]
2) Exhaust gas recirculation control
Therefore, in the exhaust gas recirculation control in this embodiment, first, the target torque calculation unit 41 uses the accelerator opening degree accel detected by the accelerator opening degree sensor 32 and the engine speed Ne detected by the crank angle sensor 9. The target torque trqsol is determined with reference to the two-dimensional map 36 on the memory. Using this target torque trqsol, the fresh air amount FAir measured by the air flow sensor 11 and the engine speed Ne, the target injection amount calculation unit 42 refers to the three-dimensional map 37 on the memory and the target injection amount Fsol. To decide. On the other hand, using the target torque trqsol and the engine speed Ne, the target air-fuel ratio calculation unit 43 determines a target air-fuel ratio A / Fsol for achieving the compatibility by referring to the two-dimensional map 38 on the memory. .
[0036]
Then, using the target injection amount Fsol and the target air-fuel ratio A / Fsol, the target fresh air amount calculation unit 44 calculates the target fresh air amount FAsol (FAsol = Fsol × A / Fsol). With the target of FAsol, the new air amount control unit 45 performs feedback control of the new air amount FAir. This control is not to directly adjust the fresh air supply amount itself, but to change the fresh air amount by adjusting the exhaust gas recirculation amount. The operation amount EGRsol of the EGR valve 24 is determined, and the EGR valve control is executed based on the target operation amount EGRsol of the EGR valve 24. The target fresh air amount calculation unit 44 and the new air amount control unit 45 correspond to the exhaust gas recirculation means 35b.
[0037]
3) Fuel injection control
Further, the ECU 35 is provided with a two-dimensional map 50 in which the optimum common rail pressure CRPsol determined experimentally for changes in the target torque trqsol and the engine speed Ne is recorded electronically on a memory. Using the target torque trqsol obtained by the target torque calculation unit 41 and the engine speed Ne, the common rail pressure calculation unit 46 calculates the target common rail pressure CRPsol by referring to the map 50 and uses this to calculate the common rail. Control the pressure. Based on the controlled common rail pressure CRP and the target injection amount Fsol determined by the target injection amount calculation unit 42, the excitation time of each injector 5 is determined and controlled. The target injection amount calculation unit 42 corresponds to the fuel injection control means 35a.
[0038]
Four) Inlet throttle valve control
The ECU 35 is provided with a two-dimensional map 51 in which an optimum target intake throttle amount THsol determined experimentally for changes in the target fuel injection amount Fsol and the engine rotational speed Ne is electronically stored in a memory. Then, using the target injection amount Fsol obtained by the target injection amount calculation unit 42 and the engine speed Ne, the target intake throttle amount calculation unit 47 calculates the target intake throttle amount THsol with reference to the map 51. This is used to control the opening of the intake throttle valve 14. The target intake throttle amount calculating unit 47 corresponds to the intake throttle valve control means 35d.
[0039]
Five) VGT control
The ECU 35 is provided with a two-dimensional map 52 in which the optimum target supercharging pressure Boostsol determined experimentally in the change of the target torque trqsol and the engine speed Ne is recorded electronically on a memory. Using the target torque trqsol obtained by the target torque calculator 41 and the engine speed Ne, the target boost pressure calculator 48 calculates the target boost pressure Boostsol with reference to the map 52. Then, using the target supercharging pressure Boostsol and the intake pressure Boost in the intake passage 10 downstream of the intake throttle valve 14 detected by the intake pressure sensor 10a, the supercharging pressure control unit 49 converts the intake pressure Boost into the target supercharging. .. Opening (operation control amount) VGTsol of the flaps 21b, 21b,... Of the turbocharger 25 so that the pressure Boostsol is obtained, and using this, the flaps 21b, 21b,. Control.
[0040]
(Overall flow of exhaust gas recirculation and fuel injection control)
Next, the basic flow of exhaust gas recirculation and fuel injection control by the ECU 35 will be described with reference to FIG. This control is executed in synchronization with the rotation of the engine 1 in accordance with a control program electronically stored in the memory.
[0041]
First, as shown in steps S1 to S3 in the figure, the intake air amount FAir is obtained for each cylinder based on the intake air amount detected by the airflow sensor 11 and the crank angle detected by the crank angle sensor 9. Further, the target fuel injection amount Fsol is obtained based on the engine speed Ne detected by the crank angle sensor 9, the accelerator opening accel detected by the accelerator opening sensor 32, and the intake air amount FAir (steps S4 to S6). ).
[0042]
Based on the accelerator opening degree accel, the engine speed Ne, etc., a transient determination is made as to whether the engine 1 is in a steady operation state of low or medium load or in an acceleration operation state (step S7). A basic target air-fuel ratio is set, a target intake air amount is obtained based on the basic target air-fuel ratio, and EGR valve basic control is performed. Further, this basic control is performed by EGR valve control for each cylinder based on the intake air amount FAir for each cylinder. Correction is performed (steps S8 to S11). On the other hand, during acceleration operation, the target air-fuel ratio during acceleration is set, and EGR valve control and injection amount control during acceleration are performed (steps S12 to S14).
[0043]
(Detection of intake air flow rate for each cylinder and calculation of intake air amount)
An example of the intake air flow rate detected by the air flow sensor 11 is as shown in FIG. The hatched portion in the figure is the intake reverse flow component, and it can be seen that the integrated value obtained by subtracting the reverse flow component, that is, the intake air amount actually sucked into each cylinder 2 slightly fluctuates. .
[0044]
FIG. 10 shows a specific control procedure for calculating the intake air amount for each cylinder using the air flow sensor 11 (steps S1 to S3 in FIG. 8). While integrating the intake air flow rate, the elapsed time is measured, and each time the crank angle reaches 180 degrees, the integral value Q of the intake air flow rate for 180 degrees is calculated as the intake air amount Qi of the cylinder (i). The required time (crank timer time T) is defined as the crank interval Ti of the cylinder (i), and the average value of the obtained intake air amounts Qi of the four cylinders is obtained as the basic intake air amount Qav (steps A1 to A7). . For convenience, the cylinder numbers “0, 1, 2, 3” are assigned to the four cylinders.
[0045]
Further, the intake air amount change rate ΔQi = Qi / Qi-1 and the crank interval change rate ΔTi = Ti with respect to the previous cylinder (i-1) of the intake stroke timing. / Ti-1 is obtained, and a change index [Delta] Qti = [Delta] Qi / [Delta] Ti of the intake air amount in consideration of the intake stroke time is obtained (steps A8 to A10). Here, ΔTi is considered in order to eliminate as much as possible disturbance due to torque fluctuation (angular speed fluctuation of the crankshaft 7), and this process is particularly effective during idling with large torque fluctuation. Based on the change index ΔQti, the intake air amount characteristic ΔQt ′ (i) of each cylinder 2 is obtained by the following equation (step A11).
[0046]
ΔQt ′ (i) = ΔQti × r + ΔQti ′ (1−r)
However, 0 <r ≦ 1
That is, ΔQti ′ is the previous value of the change index ΔQti, and reflects the previous value at a predetermined ratio in the current change index ΔQti. Thereby, the solid difference between cylinders regarding the amount of intake air gradually becomes clear.
[0047]
(Transient judgment)
FIG. 11 shows a specific control procedure for transient determination (steps S4 to S7 in FIG. 8). This transient determination is acceleration determination, and includes determination based on a change in accelerator opening and determination based on a change in fuel injection amount. During the acceleration operation of the engine 1, it is necessary to increase the intake air amount in accordance with the increase in the fuel injection amount. For this purpose, the EGR valve 24 needs to be quickly closed to reduce the exhaust gas recirculation amount. This is transient determination for performing such exhaust gas recirculation reduction control.
[0048]
That is, the fuel injection amount F (= target injection amount Fsol) is read from the three-dimensional map 37 of FIG. 5 using the accelerator opening Acc, the engine speed Ne, and the intake air amount Qav, and the current value of the accelerator opening. The amount of change ΔAcc = Acc−Acc ′ is obtained based on Acc and the previous value Acc ′ (steps B1 to B3). The acceleration determination criterion αcc is read from the two-dimensional map using the fuel injection amount F and the engine speed Ne (step B4).
[0049]
This αcc is for determining acceleration based on the accelerator opening change amount ΔAcc. For example, the higher the engine speed Ne is, the more difficult it is to determine acceleration, while the more the fuel injection amount F is, the more the fuel injection amount F is. Optimum values for changes in the fuel injection amount F and the engine speed Ne are experimentally determined and stored electronically in the memory so that the acceleration becomes smaller and the acceleration is easily determined. Since the exhaust gas recirculation amount is large at the time of low load operation, the fuel recirculation amount reduction control can be promptly shifted to the exhaust gas recirculation amount reduction control when the accelerator opening increase change (fuel injection amount increase change) is large. The larger the injection amount, the smaller the αcc.
[0050]
Then, when the acceleration coefficient α = ΔAcc / αcc is greater than 1, it is determined that the engine 1 is in the acceleration operation state, and the transient time is determined based on the acceleration coefficient α and the separately obtained target air-fuel ratio TA / F. The EGR valve operation amount KTegr is read from the map (steps B5 to B7). That is, when the increase in the accelerator opening is large, the exhaust gas recirculation amount is quickly reduced in order to give priority to the driver's acceleration request over the NOx reduction due to exhaust gas recirculation. For this reason, the EGR valve The map of the operation amount KTegr is created by experimentally obtaining the operation amount so that the opening degree of the EGR valve 24 becomes smaller as the acceleration coefficient α increases, and is electronically stored in the memory.
[0051]
In the acceleration determination based on the accelerator opening, the EGR valve manipulated variable is determined on the basis of the determination, but in the transient determination based on the next fuel injection amount, the actual acceleration request is changed to the fuel injection amount. Based on this, the fuel injection control is performed in accordance with the acceleration request.
[0052]
That is, the rate of change ΔF = F / F ′ is obtained based on the current value F and the previous value F ′ of the fuel injection amount, and the acceleration determination is made from the two-dimensional map using the fuel injection amount F and the engine speed Ne. The reference Fk is read (steps B8 and B9). This Fk is also set in the same manner as the above αcc and is electronically stored in the memory. When the injection amount change coefficient β = ΔF / Fk is greater than 1, control during acceleration is performed, and when it is small, control during steady state is performed (steps B10 and B11).
[0053]
(Control during normal operation)
The constant-time control is shown in FIG. 12. The target torque Ttrq (= Trqsol) is read from the two-dimensional map 36 of FIG. 5 using the engine speed Ne and the accelerator opening Acc, and the Ttrq and Ne are calculated. The target air-fuel ratio TA / F is read from the two-dimensional map 38, and the target intake air amount TQ = TA / F × F is obtained (steps C1 to C3). Then, the intake air amount deviation Qerr = TQ−Qav is obtained, and the basic EGR valve operation amount Tegr is obtained according to the PID control law so that the deviation Qerr becomes zero (steps C4 and C5).
[0054]
That is, for example, a proportional control term in which the control gain (P gain) of the proportional control operation is integrated with the deviation Qerr, and an integral control term in which the control gain (I gain) of the integral control operation is integrated with the integral value of the deviation Qerr; The basic EGR valve operation amount Tegr is determined by adding the differential control term obtained by integrating the differential gain operation control gain (D gain) to the differential value of the deviation Qerr. Here, each of the control gains P, I, and D is obtained by multiplying the basic value by the gain coefficient K. As will be described later, the gain of the gain coefficient K is corrected to decrease or increase, and the control response is obtained. And convergence can be changed.
[0055]
The air-fuel ratio at which the above-mentioned NOx reduction and smoke reduction can be achieved is slightly different depending on the engine speed Ne and the engine torque Ttrq (in other words, the fuel injection amount F). In particular, in the operation region where sufficient turbocharging is performed by the turbocharger 25, the premixing of air and fuel in the combustion chamber is good, and there is less unburned fuel (smoke is reduced). In the supercharging region on the high rotation side and the non-supercharging region on the low rotation side, the former allows the target air-fuel ratio to be set to a richer side, which advantageously works for NOx reduction.
[0056]
Therefore, a condition for steady determination is checked that a predetermined number n cycles of the state where the absolute value of the accelerator opening change amount ΔAcc is smaller than the predetermined threshold value Thacc is continued for a predetermined number n cycles (step C6). This is because the control of this flow is intended to improve emissions during idle operation and subsequent steady operation. In the fuel cut region (F = 0) when the vehicle is decelerated, the opening degree of the EGR valve 24 is set to zero and exhaust gas recirculation is not performed.
[0057]
When the steady operation is confirmed, the EGR valve correction operation amount ΔTegr (i) for each cylinder is obtained from the intake air amount characteristic ΔQt ′ (i) and the EGR correction gain E (i) obtained previously (step). C7). That is,
ΔTegr (i) = ΔQt ′ (i) × E (i) + ΔTegr ′ (i)
However, ΔTegr ′ (i) is the previous value of the EGR valve correction operation amount of the cylinder i.
[0058]
This integration is for emphasizing the value of ΔQt ′ (i) itself, but for causing the EGR valve correction operation amount to reach an appropriate correction amount according to the individual difference between the cylinders.
[0059]
When the EGR valve correction operation amounts for all the four cylinders are obtained, the average value ΔTegr-av of the EGR valve correction operation amounts for the four cylinders is obtained. This average value should originally be zero. However, when the process of step C7 is performed, the average value becomes negative or positive due to various factors, and the basic EGR valve operation amount Tegr is reduced. The original purpose of correcting and controlling the EGR valve operation amount of each cylinder 2 as a reference is lost. Therefore, when the average value is negative, the absolute value is added to ΔTegr (i) of each cylinder 2, and when the positive value is positive, the average value is always zeroed by subtraction. Steps C8 and C9). ΔTegr (i) obtained in this way is added to the basic EGR valve operation amount Tegr to obtain the EGR valve operation amount Tegr (i) of each cylinder 2 (step C10).
[0060]
(Control during acceleration judgment based on acceleration coefficient α)
On the other hand, when acceleration determination is made in step B6 in FIG. 11, the target EGR valve operation amount KTegr at the time of transition obtained in step B7 differs depending on the acceleration coefficient α and the magnitude of TA / F, and the acceleration coefficient α When is large, the opening degree of the EGR valve 24 becomes zero. Therefore, in this case, since the exhaust air recirculation is not performed, the intake air amount of each cylinder 2 increases, so that even if the fuel injection amount increases, the engine output can be increased without increasing the smoke amount. . In addition, in that case, control for giving a preset to the EGR valve 24 is performed so that the subsequent exhaust gas recirculation control can be promptly shifted.
[0061]
In other words, even when the EGR passage 23 is closed during the exhaust gas recirculation control, the EGR valve 24 reduces the force with which the valve body 24c is pressed against the valve seat by the spring 24d so that the pressing force becomes zero. By applying a predetermined EGR valve drive negative pressure (preset negative pressure) to the negative pressure chamber, the pressing force in the closing direction by the spring 24d and the EGR valve drive negative pressure are balanced. As shown in FIG. 4B, the preset negative pressure is an EGR valve drive negative pressure at the time when the EGR valve 24 is controlled in the closing direction and the EGR valve lift amount reaches zero.
[0062]
Specifically, a control flow for applying a preset negative pressure to the EGR valve 24 is shown in FIG. That is, when the EGR valve operation amount Tegr is an operation amount at which the EGR valve lift amount becomes zero, the value EGRVliFt of the lift sensor 26 is read (steps D1 and D2). When this EGRVliFt is larger than the EGR valve lift amount zero EGRV0, EGR valve control is performed until EGRV0 is reached (steps D3 and D4). That is, the EGR valve drive negative pressure is reduced until the preset negative pressure EGRV0 is reached. When the EGR valve operation amount Tegr is an operation amount at which the preset does not become zero due to exhaust gas recirculation, normal EGR valve control is performed (steps D1 → D4).
[0063]
According to such preset control of the EGR valve 24, when the engine 1 shifts from the steady operation state to the acceleration operation state, the exhaust gas recirculation amount is once reduced to zero, and thereafter, the engine 1 shifts to the steady operation state again and the exhaust gas recirculation is performed. Since the preset negative pressure is applied to the EGR valve 24 when the operation is resumed, the EGR valve 24 is opened quickly with almost no response delay as the Tegr increases.
[0064]
(Control at the time of acceleration judgment based on the injection amount change coefficient β)
Further, when the acceleration determination is made in step B11 in FIG. 11, control as shown in each step in FIG. 14 is performed. That is, first, when the acceleration operating state of the engine 1 is determined, the optimum transient target air-fuel ratio KTA / F in these changes is determined using the injection amount change coefficient β, the fuel injection amount F, and the engine speed Ne. The KTA / F is read with reference to the recorded three-dimensional map (step G1). This transient target air-fuel ratio KTA / F is leaner than the steady-state target air-fuel ratio TA / F so that the engine output can be increased quickly while suppressing the generation of smoke by reducing the exhaust gas recirculation amount. Is set to the side. According to the fuel injection amount F, the three-dimensional map is optimized for each change so that the lower the load side, the larger the injection amount change coefficient β, and the lower the engine speed Ne, the leaner the engine becomes. The KTA / F value is experimentally obtained and electronically stored in the memory.
[0065]
A transient target intake air amount TQ is calculated based on the obtained transient target air-fuel ratio KTA / F and the fuel injection amount F (step G2), and based on this TQ, Similarly, the operation amount of the EGR valve is determined, and the intake air amount is increased by the rapid reduction control of the exhaust gas recirculation amount (steps C4 to C6 in FIG. 12, following steps G5 below, and steps D1 to D4 in FIG. 13). .
[0066]
Thus, even when the transient target air-fuel ratio KTA / F is set to be leaner than the steady state, for example, when the driver depresses the accelerator pedal particularly greatly in order to suddenly start the vehicle (accelerator operation amount). When the fuel gas suddenly increases more than a predetermined value), surplus fuel is injected into the combustion chamber 4 of each cylinder 2 and the surplus fuel is discharged almost without being burned, which may cause a significant increase in the amount of smoke. Therefore, in this flow, a certain restriction is imposed on the increase in order to temporarily suppress the increase in fuel. That is, first, the limit air-fuel ratio LimitA / F is read from the map of the fuel injection amount F and the engine speed Ne (step G3). This limit air-fuel ratio LimitA / F is for suppressing the generation of smoke, and the limit smoke amount is larger than the limit smoke amount at the steady state. For example, the smoke amount is about 2 BU, and if this is the case, there is no problem in increasing the output torque of the engine.
[0067]
The relationship between the steady-state target air-fuel ratio TA / F, the transient target air-fuel ratio KTA / F, and the limit air-fuel ratio LimitA / F is as shown in FIG. 15, and is leaner than the steady-state target air-fuel ratio TA / F. The target air-fuel ratio KTA / F at the time of transition is set on the side, and the limit air-fuel ratio LimitA / F is set on the rich side with respect to the target air-fuel ratio TA / F at the steady state. This limit air-fuel ratio LimitA / F can basically be set to the lean side as the fuel injection amount increases, and to the rich side as the engine speed increases, and the fuel injection amount F and the engine speed Ne The optimum value obtained experimentally in the change is electronically recorded on the memory.
[0068]
A fuel injection amount limit value FLimit is calculated based on the obtained limit air-fuel ratio LimitA / F and the current intake air amount Q (i), and the basic injection amount F, the limit value FLimit, and the maximum injection amount Fmax are calculated. The smallest value is set as the target injection amount TF (steps G4 and G5). The basic injection amount F is a fuel injection amount determined by the engine speed Ne and the accelerator opening Acc, and the maximum injection amount Fmax is an upper limit value of the fuel injection amount that does not cause the engine 1 to be destroyed. By setting the fuel injection amount as described above, excessive enrichment of the air-fuel ratio can be suppressed even if the exhaust gas recirculation amount decreases during sudden acceleration of the vehicle, and the smoke amount is significantly increased while satisfying the driver's acceleration request. Increase can be prevented.
[0069]
Each of the steps G3 to G5 corresponds to a fuel increase suppression means that suppresses an increase in the fuel injection amount corresponding to an increase in the accelerator operation amount when the accelerator operation amount increases rapidly by a predetermined value or more.
[0070]
Further, at the time of the acceleration determination by β, the fuel injection timing is gradually advanced according to the increase of the fuel injection amount, and is set at a position considerably retarded from MBT (Minimum advance for Best Torque). Advance ahead of the injection timing. Since the advance of the injection timing causes sufficient premixing of air and fuel, combustion proceeds rapidly and the amount of smoke in the exhaust gas decreases. On the other hand, although the combustion temperature increases, the NOx emission amount increases. However, since NOx generation is originally suppressed by a large amount of exhaust gas recirculation, the NOx emission amount does not increase so much.
[0071]
(Inlet throttle valve control)
The feature of the present invention is that, in addition to the basic control such as the exhaust gas recirculation control as described above, when the driver depresses the accelerator pedal, such as during idling, the EGR valve 24 is prior to the depression. This is because the intake throttle valve 14 is controlled to the closed side so that the opening degree becomes small.
[0072]
The control of the intake throttle valve 14 is executed in synchronization with the rotation of the engine 1 in accordance with a control program electronically stored in a memory, similarly to the exhaust gas recirculation control. That is, as shown in the flowchart of FIG. 16, first, as with the exhaust gas recirculation control, the accelerator opening Acc and the engine speed Ne are detected, and the fuel injection amount F is read (steps H1 to H3).
[0073]
Subsequently, in step H4, it is determined whether or not the accelerator is in a return state. That is, if the accelerator operation amount is decreased by a predetermined value or more and the accelerator opening is YES, the process proceeds to step H5, where the accelerator return determination flag Flag is set to Flag = 1, and in the subsequent step H6, The counter for measuring the elapsed time after the accelerator return state is determined is reset (Tup = 0), and then the process proceeds to Step H9. On the other hand, in step H7, which is determined to be NO in the accelerator return state in step H4, it is determined whether or not the value of the accelerator return determination flag Flag is 1. If Flag = 0 and NO, it will be described later. On the other hand, if Flag = 1 and YES, the process proceeds to Step H8, the process proceeds to Step H8, the counter value is incremented (Tup = Tup + Δt), and the process proceeds to Step H9.
[0074]
In Step H9, it is determined whether or not the counter value Tup is equal to or smaller than a predetermined value Tup1 corresponding to a preset set time. If the counter value Tup is determined to be NO larger than the predetermined value Tup1, step H11 is performed. On the other hand, if the counter value Tup is equal to or less than the predetermined value Tup1 and YES, that is, until the set time elapses after the accelerator return state is determined, the process proceeds to step H10 to control gain of EGR valve control. Is read from the two-dimensional map.
[0075]
In this two-dimensional map, a relatively large value γ1 is set as the gain correction coefficient γ so that the responsiveness of the EGR valve control is enhanced in response to the accelerator return state. As illustrated in FIG. The optimum gain correction coefficient value γ1 corresponding to the intake throttle amount TH and the engine speed Ne is experimentally determined and recorded. The value of γ1 is set to be smaller as the engine speed Ne is higher and the intake throttle amount TH is larger in a range of 0 <γ1 <1. The intake throttle amount TH used in this step is the intake throttle amount TH set in the previous control cycle.
[0076]
On the other hand, in step H11, in which the counter value Tup is determined to be NO larger than the predetermined value Tup1 in step H9, the accelerator return determination flag is cleared (Flag = 0). That is, if the set time elapses after the accelerator return state is determined, NO is determined in step H7 in the next control cycle, and the process proceeds to step H12. In step H12, the two-dimensional map (FIG. 17), the gain correction coefficient γ2 is read from another two-dimensional map. This other two-dimensional map is obtained by setting a normal gain correction coefficient γ2 that is not in the accelerator return state, and γ2 <γ1 in all setting areas of the map.
[0077]
Subsequent to Steps H10, 11 and 12, in Step H13 in the flowchart of FIG. 18, it is determined whether or not the engine 1 is in an idle operation state. That is, if the accelerator is fully closed and the running speed of the vehicle is zero, the process proceeds to step H17 to be described later, while if the engine is not idle, the process proceeds to step H14 to search the two-dimensional intake throttle map. . This intake throttle map corresponds to the map 51 of FIG. 5, but in detail, as shown in FIG. 19, an optimal intake throttle amount TH (= THsol) corresponding to the fuel injection amount F and the engine speed Ne is obtained. It is a digital map determined and recorded experimentally.
[0078]
According to this map, if the engine 1 is in a high speed or high load operation state and the fuel injection amount F or the engine speed Ne is large, the intake throttle amount TH is set to zero and the intake throttle valve 14 is fully opened. Controlled. That is, since the differential pressure between intake and exhaust is high when the engine 1 is operating at high speed, there is a risk that the exhaust gas recirculation amount will increase and the intake air amount will be insufficient. Therefore, the intake air amount with respect to the fuel injection amount may be insufficient. On the other hand, when the intake throttle valve 14 is fully opened and a sufficient amount of intake air is secured, an increase in the amount of smoke due to a shortage of the intake air amount can be prevented. Further, in relatively low load operating conditions other than the above, the intake throttle amount TH is set to be larger as the fuel injection amount F is smaller and as the engine speed Ne is lower. That is, the lower the engine speed Ne, the smaller the differential pressure between the intake and exhaust, and accordingly, by reducing the opening of the intake throttle valve 14 and increasing the differential pressure, A sufficient amount of exhaust gas recirculation can be secured.
[0079]
Subsequent to step H14, in step H15, it is determined whether to throttle the intake based on the value of the accelerator return determination flag Flag and the search result of the intake throttle map. That is, if Flag = 0, or even if Flag = 1, if the engine 1 is in a high load or high speed operation state and NO is not throttled, the process proceeds to step H19 while Flag = 1. If it is YES that throttles the intake air in the operating state other than the above, the process proceeds to step H16, the value set in the intake throttle map is read, and the intake throttle amount TH is set. In Step H14, which is determined as YES in the idling operation state and proceeds to Step H17, the intake throttle amount TH is set so that the intake throttle valve 14 is fully closed corresponding to the idling operation state.
[0080]
In Step H18 following Step H16 or H17, a control signal is output to the electromagnetic valve 16 for negative pressure control based on the intake throttle amount TH set in each of those steps, and the intake throttle valve 14 Execute the opening control. Subsequently, in step H19, a gain coefficient K that determines the value of the control gain in EGR valve control is calculated based on the gain correction coefficient γ read in either step H10 or step H12, and then the process returns.
[0081]
K = K × (1 + γ)
Here, when the gain correction coefficient γ1 corresponding to the accelerator return state is read, the gain coefficient K is increased from the normal operation state by the amount that the value of γ1 is larger than the value of γ2, and the above-described EGR valve The control gain in the control (see FIG. 12), that is, each control gain of P, I, and D increases, and as a result, the operation responsiveness of the EGR valve 24 increases. That is, the accelerator operation amount by the driver changes suddenly from when the accelerator return state is determined until the set time elapses, and the EGR valve 24 is operated so as not to be delayed by the change. It enhances responsiveness. The set time is set to a relatively short time (for example, 1 to 2 seconds) corresponding to a shifting operation of the manual transmission, for example, and deterioration of control convergence during that time is not a problem.
[0082]
In the intake throttle valve control flow shown in FIG. 16 and FIG. 18, step H4 is the accelerator return state determination means 35e for determining the accelerator return state where the accelerator operation amount has decreased by a predetermined value or more, and step H13 is the engine 1 Corresponds to the driving state determination means 35c for determining the low-speed and low-load driving state (in this embodiment, the idle driving state).
[0083]
Further, in step H10, the gain increase correcting means for increasing the control gain of the EGR valve 24 by the exhaust gas recirculation control means 35b until the set time elapses after the accelerator return state is determined, and the accelerator return state Is determined, and when the engine 1 is in a low speed operation state, it corresponds to an accelerator return gain increase correcting means for increasing the control gain of the EGR valve 24. Further, the steps H10 and H12 correspond to a gain reduction correction means for correcting the control gain of the EGR valve 24 to be smaller as the opening of the intake throttle valve 14 is smaller.
[0084]
Next, the operation and effect of the exhaust gas recirculation control apparatus A according to the embodiment will be described first with reference to FIGS. 20 to 22 in the case where the engine 1 shifts from the idle operation state to the acceleration operation state.
[0085]
First, in the idling operation state of the engine 1 in which the accelerator opening is substantially zero as shown in FIG. 10A, the intake throttle valve 14 is substantially controlled by the intake throttle valve control as shown in FIG. Corresponding to the reduction of the intake air amount due to this, the opening degree of the EGR valve 24 is substantially equal to that of the fully opened and fully closed states by the EGR valve control as shown by the solid line in FIG. Controlled to the center half-open state. That is, since the intake air of the engine 1 and the air pressure of the exhaust passages 10 and 20 change according to the opening degree of the intake throttle valve 14 as shown in FIG. 21, respectively, if the intake throttle valve 14 is substantially fully closed, The differential pressure between the intake and exhaust passages is maximized. As a result, as shown in FIG. 22, a sufficient exhaust gas recirculation amount can be ensured even when the EGR valve 24 is in a half-open state. Further, since the fuel injection amount is small in the idle operation state, a sufficient intake air amount is ensured even when the intake throttle valve 14 is fully closed, and no problem occurs.
[0086]
Then, when the accelerator pedal is depressed by the driver in the idling state and the accelerator opening is increased as shown in FIG. 20A (t = t1), fuel injection is performed corresponding to the increase in the accelerator opening. The fuel injection amount is increased by the control, and the intake throttle valve 14 is quickly opened as shown in FIG. 4B, and the EGR valve 24 is closed as shown by the solid line in FIG. Actuated. At that time, since the EGR valve 24 is already in a half-open state, the valve is fully closed in a short time compared to the case of the conventional example in which the EGR valve 24 is in a fully-open state as shown by a dashed line in FIG. Accordingly, the exhaust gas recirculation amount decreases quickly, and the intake air amount increases rapidly as shown in FIG.
[0087]
Therefore, when the engine 1 shifts from the idle operation state to the acceleration operation state at the start of the vehicle, the delay in the closing operation of the EGR valve 24 can be reduced, so that the air-fuel ratio is enriched without suppressing the fuel injection amount. As shown in FIG. 5F, the amount of smoke in the exhaust gas can be reduced while rapidly increasing the engine speed Ne and maintaining good acceleration performance of the vehicle.
[0088]
In particular, in the exhaust gas recirculation control device A of this embodiment, the target air-fuel ratio KTA / F during acceleration operation is set in association with the sudden increase in the amount of smoke in the exhaust gas (see FIG. 15). If the operation delay of the valve 24 cannot be reduced, the amount of smoke will increase rapidly as the air-fuel ratio becomes richer. Therefore, especially in such a case, it is extremely effective to reduce the operation delay of the EGR valve 24 by controlling the intake throttle valve 14 as described above.
[0089]
Note that, as shown in FIG. 20C, the control gain of the EGR valve 24 changes with the opening degree (throttle amount TH) of the intake throttle valve 14 and the engine speed Ne.
[0090]
Secondly, a case where the driver performs a shifting operation of the manual transmission during the acceleration operation of the vehicle will be described with reference to FIG.
[0091]
First, when the driver releases the accelerator pedal in order to change the speed of the manual transmission during the acceleration operation of the vehicle (t = t1), the accelerator opening (accelerator operation amount) is as shown in FIG. Decrease, so that the accelerator return state is determined. Then, as shown in FIG. 8C, the intake throttle valve 24 is operated to the closed side, and in response to the reduction of the intake air amount, the EGR valve 24 of the EGR valve 24 as shown by the solid line in FIG. The opening is reduced.
[0092]
After that, when the driver completes the shifting operation of the manual transmission and once depresses the released accelerator pedal (t = t2), the fuel injection amount is increased corresponding to the increase in the accelerator opening. At the same time, the intake throttle valve 14 is quickly opened as shown in FIG. 4C, and the EGR valve 24 is operated to the closed side as shown by the solid line in FIG. Is done. At this time, since the EGR valve 24 is already operated to the closed side in accordance with the determination of the accelerator return state, and the opening of the valve is reduced, the exhaust gas recirculation amount is reduced in the same manner as in the case of starting the vehicle. The amount of intake air can be increased quickly by reducing the amount quickly.
[0093]
In other words, by operating the EGR valve 24 to the closed side in the accelerator return state during the acceleration operation of the vehicle, when the accelerator pedal is subsequently depressed, the delay in the closing operation of the EGR valve 24 can be reduced. Thus, enrichment of the air-fuel ratio can be suppressed without suppressing the fuel injection amount. Therefore, as indicated by the solid line in FIG. 8 (f), the engine speed Ne at the time of re-acceleration increases rapidly, and does not stagnate as indicated by the dashed line in the same figure, and the amount of smoke in the exhaust gas Can also be reduced.
[0094]
Further, in this embodiment, the opening degree of the intake throttle valve 14 is made smaller as the engine speed Ne is lower. Therefore, the lower the engine speed Ne, the smaller the output torque of the engine 1 is, and the low-speed operation state is likely to be staggered. In this case, the lower the engine speed Ne, the smaller the operation delay of the EGR valve 24 at the time of reacceleration, so that the backlash at the time of reacceleration can be sufficiently suppressed.
[0095]
Furthermore, in this embodiment ,in front As shown in FIG. 23 (b), from the time when the accelerator return state is determined until the reset counter value Tup becomes a predetermined value Tup1 and the set time elapses, the state shown in FIG. Thus, the control gain is corrected to increase. That is, by responding to the accelerator return state accompanying the shift operation by the driver and the accelerator depression at the time of reacceleration accompanying the end of the shift operation, the operation response of the EGR valve 24 is enhanced, so that the EGR valve 24 can be made quicker. Therefore, it is possible to further reduce the shakiness of the engine 1.
[0096]
Further, since the control gain of the EGR control is corrected to increase as the engine speed Ne is lower (see FIGS. 4D and 4F), the execution interval of the EGR control is relatively long when the engine 1 is operating at a low speed. Even if it becomes, the fall of the operation | movement responsiveness of the EGR valve 24 by that can be compensated.
[0097]
Furthermore, the control gain of the EGR control is corrected so as to become smaller as the opening of the intake throttle valve 14 becomes smaller (see FIGS. 2C and 2D). That is, in general, the smaller the opening of the intake throttle valve 14, the greater the differential pressure between intake and exhaust, and the degree of change in the exhaust gas recirculation amount with respect to the change in the opening of the EGR valve 24 increases. However, in this embodiment, the control gain of the EGR control is reduced as the opening of the intake throttle valve 14 is reduced. The deterioration of convergence can be prevented.
[0098]
In addition, this invention is not limited to the said embodiment, Other various embodiment is included. That is, in the embodiment, the exhaust gas recirculation amount is controlled for each cylinder according to the intake air amount detected for each cylinder so that the air-fuel ratio in each cylinder 2 of the engine 1 becomes a common target air-fuel ratio. However, the present invention is not limited to this, and the exhaust gas recirculation amount may be collectively controlled based on the average intake air amount of all the cylinders.
[0099]
Further, in the embodiment, the intake air amount is directly detected based on the output signal from the air flow sensor 11 disposed in the intake passage 10 of the engine 1, but the present invention is not limited to this. A sensor for detecting the intake pipe pressure in the intake passage 10 is adopted, the exhaust gas recirculation amount is obtained based on the output signal from the sensor and the lift sensor of the EGR valve 24, and the intake air amount is detected indirectly from the exhaust gas recirculation amount. You may make it do.
[0100]
【The invention's effect】
As described above, according to the exhaust gas recirculation control apparatus for a direct injection type engine according to the first aspect of the present invention, the intake throttle valve is closed in the accelerator return state while the vehicle is running, and the accelerator is predicted thereafter. Since the exhaust gas recirculation amount adjustment valve is operated to the closed side prior to the depression of the pedal, when the accelerator pedal is subsequently depressed, the operation of closing the exhaust gas recirculation amount adjustment valve is suppressed without suppressing the fuel injection amount. The delay can be reduced, so that the acceleration performance of the vehicle can be maintained satisfactorily and the amount of smoke in the exhaust gas can be reduced while preventing the engine from being slack during shifting.
[0101]
In addition, the control gain of the exhaust gas recirculation amount adjustment valve is increased in such a situation that the accelerator operation amount by the driver changes suddenly, so that the control responsiveness can be improved so as not to be delayed by the change of the accelerator operation amount. Can be increased.
[0102]
According to the second aspect of the present invention, it is possible to virtually eliminate the engine slack caused by the speed change operation by the driver.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram of an engine according to an embodiment of the present invention.
FIG. 2 is an explanatory view showing a part of the turbocharger in a state where the A / R is small (a) or a state where the A / R is large (b).
FIG. 3 is a configuration diagram of an EGR valve and its drive system.
FIG. 4 is a graph showing the relationship between the drive current of the EGR valve and the drive negative pressure (a) or the lift amount (b).
FIG. 5 is an overall configuration diagram of an engine control system.
FIG. 6 is a graph showing the relationship between the air-fuel ratio and the NOx emission amount.
FIG. 7 is a graph showing a relationship between an air-fuel ratio and a smoke value.
FIG. 8 is a diagram showing a basic flow of control.
FIG. 9 is a graph showing temporal changes in the intake air flow rate of the engine.
FIG. 10 is a flowchart of intake air amount calculation.
FIG. 11 is a flowchart of transient determination.
FIG. 12 is a flowchart of EGR valve operation amount calculation.
FIG. 13 is a flowchart of control for giving a preset.
FIG. 14 is a flowchart of fuel injection amount control during transition.
FIG. 15 is a graph showing the relationship between the target air-fuel ratio at a constant time, the target air-fuel ratio at the time of transition, and the limit air-fuel ratio at the time of transition.
FIG. 16 is a flowchart showing a procedure for correcting the control gain of the exhaust gas recirculation control.
FIG. 17 is a map diagram in which gain correction coefficients are set for the intake throttle amount and the engine speed.
FIG. 18 is a flowchart of intake throttle valve control.
FIG. 19 is a map diagram in which an intake throttle amount with respect to a fuel injection amount and an engine speed is set.
FIG. 20 shows the changes in accelerator opening, intake throttle amount, EGR valve control gain, EGR valve opening, intake air amount, and engine speed at the time of transition from the idle operation state to the acceleration operation state. It is a time chart figure.
FIG. 21 is a graph showing the intake passage internal pressure and the exhaust passage internal pressure with respect to changes in the opening of the intake throttle valve.
FIG. 22 is a graph showing the relationship between the opening area of the EGR valve and the exhaust gas recirculation amount.
FIG. 23 is a view corresponding to FIG. 20 with respect to a time when a manual transmission shift operation is performed during acceleration of the vehicle.
[Explanation of symbols]
1 Diesel engine
2-cylinder
4 Combustion chamber
5 Injector (fuel injection valve)
10 Intake passage
11 Air flow sensor
14 Inlet throttle valve
20 Exhaust passage
23 Exhaust gas recirculation passage
24 EGR valve (exhaust gas recirculation control valve)
35a Fuel injection control means
35b Exhaust gas recirculation control means
35c Driving state determination means
35d Inlet throttle valve control means
34e Accelerator return state determination means

Claims (2)

A fuel injection valve that directly injects fuel into a combustion chamber in a cylinder of the engine; an intake throttle valve disposed in an intake passage to the combustion chamber;
An exhaust gas recirculation passage that recirculates part of the exhaust gas to the intake passage downstream of the intake throttle valve; an exhaust gas recirculation amount adjustment valve that adjusts an exhaust gas recirculation amount in the exhaust gas recirculation passage;
A sensor for measuring the amount of intake air in the intake passage;
Fuel injection control means for controlling the fuel injection amount by the fuel injection valve according to the accelerator operation amount;
Exhaust gas from an in-cylinder injection engine having exhaust recirculation control means for controlling the opening degree of the exhaust recirculation amount adjustment valve so that the air-fuel ratio becomes a predetermined target value based on the intake air amount and the fuel injection amount In the reflux control device,
An accelerator return state determination means for determining an accelerator return state in which the accelerator operation amount is equal to or greater than a predetermined value;
An intake throttle valve control means for operating the intake throttle valve to the closed side when the accelerator return state is determined;
A gain that increases and corrects the control gain of the exhaust gas recirculation control valve by the exhaust gas recirculation control means from the time when the accelerator return state is determined until the set time corresponding to the depression of the accelerator during the subsequent reacceleration elapses An increase correction means ,
The exhaust gas recirculation control means operates the exhaust gas recirculation amount adjustment valve to the closed side in an acceleration operation state in which the accelerator operation amount greatly changes by a predetermined value or more, and also adjusts the exhaust gas recirculation amount when the accelerator return state is determined. An exhaust gas recirculation control device for an in-cylinder injection engine, characterized in that the valve is operated to close . In claim 1,
The accelerator return state is associated with the manual transmission shifting operation during vehicle acceleration operation.
The exhaust gas recirculation control device for a direct injection type engine, characterized in that the set time is set to include a period until the shifting operation of the manual transmission is finished and the accelerator is not returned.

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