JPH06117225A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To increase NOx purification efficiency of a lean NOx catalyst by connecting the fuel pressure accumulating pipe which is used commonly in all cylinders to an electronically controlled fuel injection nozzle for injecting fuel into cylinders, and operating (auxiliary injection) the fuel injection nozzle for injection in expansion and exhaust strokes of an engine. CONSTITUTION:A fuel injection nozzle 8 installed facing toward a combustion chamber 5 of each cylinder is connected to a fuel pressure accumulating pipe 11 used commonly with each cylinder through a fuel supply pipe 10, and fuel from a fuel supply pump 14 is supplied to the fuel pressure accumulating pipe 11. Also a lean NOx catalyst 103 which makes purification of NOx in excess oxygen atmosphere is located in an exhaust emission system 102. Then the fuel injection nozzle 8 is provided with a drive device containing a piezoelectric element, and a hydraulic piston is displaced when the piezoelectric element is energized, and fuel in the pressurizing chamber is built up and injected from a nozzle hole. The fuel injection nozzle 8 is controlled by the ECU. Namely, in the expansion and exhaust strokes of an engine, an auxiliary injection following a main injection is made according to the amount of NOx in the exhaust emission system and the operating conditions of the engine.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an internal combustion engine (mainly a diesel engine) in which a catalyst (lean NOx catalyst) for purifying NOx in the presence of hydrocarbons (HC) in oxygen excess exhaust is arranged in the exhaust system. Related to the exhaust purification system of
The present invention relates to an exhaust gas purification device that produces stable HC required for Ox purification by causing a fuel injection valve for in-cylinder injection to perform sub-injection during expansion and an exhaust stroke to enable stable NOx purification.

[0002]

2. Description of the Related Art Japanese Utility Model Laid-Open No. 3-68516 discloses a method for supplying HC to a lean NOx catalyst only when a certain cylinder is in a fuel injection stroke and only when the cylinder is in an exhaust stroke at the same time. It is configured to be jetted when exceeding,
We have proposed an exhaust gas purification device that performs partial oxidation of fuel injected into the cylinder during the exhaust stroke.

[0003]

However, the structure is such that the fuel flow to the cylinder in the exhaust stroke overcomes the biasing force of the spring-biased valve to open the spring. Therefore, the injection timing and amount cannot be finely adjusted with respect to the secondary injection in the exhaust stroke, and NO may occur depending on the operating conditions.
There is a problem that x purification rate and reduction of HC emission vary.

The object of the present invention is to electronically control the sub-injection of fuel into the cylinder in the expansion and exhaust strokes (injection for generating HC), thereby making it possible to finely adjust the timing and amount of the sub-injection. An object of the present invention is to provide an exhaust gas purification device for an internal combustion engine that can cope with various operating conditions, improve the NOx purification rate, and prevent deterioration of HC emissions.

[0005]

An exhaust gas purification apparatus for an internal combustion engine according to the present invention, which achieves the above object, has a lean NOx catalyst provided in an exhaust system of the internal combustion engine and an electronic control for injecting fuel into a cylinder. Type fuel injection valve, fuel accumulator pipe common to all cylinders connected to the fuel injection valve, NOx amount in the exhaust system, and so as to execute in-cylinder injection in the expansion and exhaust stroke of the engine according to the engine operating condition An electronic control unit for controlling the fuel injection valve,
It is composed of

[0006]

In the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, the same fuel injection valve as the main injection is used to execute the secondary injection at one timing of the expansion and exhaust strokes, and the relatively large molecule. The structure HC is decomposed into HC having a relatively small molecular structure by utilizing the heat of combustion gas, and a large amount of active species efficiently generated by partial oxidation of the HC is passed through the lean NOx catalyst to generate active species and NOx. NOx is reduced and purified by the reaction of. In the generation of this HC, the sub injection of fuel into the cylinder is electronically controlled, so that the timing and amount of expansion and injection in the exhaust stroke can be finely adjusted, various operating conditions can be dealt with, and NOx purification can be performed. In addition to improving the rate, HC emission does not have to deteriorate.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of an exhaust gas purifying apparatus for an internal combustion engine of the present invention will be described below with reference to the drawings. The configuration for executing the main injection will be described first, and then the configuration for executing the secondary injection by partially utilizing the main injection executing means will be described.

Referring to FIGS. 1 and 2, 1 is a diesel engine body, 2 is a cylinder block, 3 is a cylinder head, 4 is a piston, 5 is a combustion chamber, 6 is an intake valve, 7 is an exhaust valve, and 8 is combustion. Fuel injection valves 9 arranged in the chamber 5 respectively indicate an intake manifold, and an inlet portion of the intake manifold 9 is connected to the supercharger T. The fuel injection valve 8 is a fuel supply pipe 10.
Is connected to the fuel pressure accumulating pipe 11 common to each cylinder.
The fuel pressure accumulating pipe 11 has a pressure accumulating chamber 12 having a constant volume therein, and the fuel in the pressure accumulating chamber 12 is supplied to the fuel injection valve 8 via the fuel supply pipe 10. On the other hand, the pressure accumulating chamber 12 is provided with a fuel supply pump 14 capable of controlling a discharge pressure via a fuel supply pipe 13.
Is connected to the discharge port of. The suction port of the fuel supply pump 14 is connected to the discharge port of the fuel pump 15.
The suction port of No. 5 is connected to the fuel reservoir tank 16. Further, each fuel injection valve 8 is connected to a fuel reservoir tank 16 via a fuel return conduit 17. The fuel pump 15 is provided to feed the fuel in the fuel reservoir tank 16 into the fuel supply pump 14, and if the fuel can be sucked into the fuel supply pump 14 without the fuel pump 15, It is not necessary to provide the pump 15 in particular. On the other hand, the fuel supply pump 14 is provided for discharging high-pressure fuel, and the high-pressure fuel discharged from the fuel supply pump 14 is accumulated in the pressure accumulating chamber 12.

FIG. 3 shows a side sectional view of the fuel injection valve 8.
Referring to FIG. 3, 20 is a fuel injection valve main body, 21 is a nozzle, 22 is a spacer, 23 is a nozzle holder for fixing the nozzle 21 and the spacer 22 to the fuel injection valve main body 20, 24 is a fuel inlet, and 25 is The nozzle holes formed at the tip of the nozzle 21 are shown respectively. The fuel injection valve body 20 is
In the spacer 22 and the nozzle 23, a control rod 26, a pressure pin 27 and a needle 28 which are arranged in series with each other.
Is slidably inserted. A fuel chamber 29 is formed above the control rod 26, and the fuel chamber 29 has a fuel inlet port 24.
And the pressure accumulating chamber 12 (FIG. 2) via the fuel supply pipe 10. Therefore, the fuel pressure in the pressure accumulating chamber 29 is applied to the fuel chamber 29, and the fuel pressure in the fuel chamber 29 acts on the upper surface of the control rod 26. The needle 28 has a pressure receiving surface 30 having a conical shape, and a needle pressurizing chamber 31 is formed around the pressure receiving surface 30. The needle pressurizing chamber 31 is connected to the fuel chamber 29 via the fuel passage 32 on the one hand, and is connected to the nozzle hole 25 via the annular fuel passage 33 formed around the needle 28 on the other hand. Fuel injection valve body 20
A compression spring 3 that urges the pressure pin 27 downward
4 is inserted, and the needle 28 is pressed downward by this compression spring 34. The control rod 26 has a pressure receiving surface 35 having a conical shape in the middle thereof, and a control rod pressurizing chamber 36 is formed around the pressure receiving surface 35. The pressurizing chamber 36 is communicated with a cylinder 37 formed in the fuel injection valve main body 20, and a hydraulic piston 38 is slidably inserted in the cylinder 37. An O-ring 39 is attached to the hydraulic piston 38.

On the other hand, a drive device 40 for driving the hydraulic piston 38 is attached to the fuel injection valve body 20.
The drive device 40 includes a casing 41 fixed to the fuel injection valve main body 20, and a piezo piezoelectric element 42 inserted between the piston 38 and the casing 40. The piezoelectric element 42 has a laminated structure in which a large number of thin plate piezoelectric elements are laminated. When a voltage is applied to the piezoelectric element 42, the piezoelectric element 42 is distorted in the longitudinal direction due to the electrostrictive effect. That is, it extends in the longitudinal direction. This elongation amount is small, for example, about 50 μm, but the response is extremely good, and the response time from application of voltage to elongation is 8
It is about 0 μsec. When the voltage application is stopped, the piezoelectric element 42 contracts immediately. As shown in FIG. 3, a disc spring 43 is provided between the hydraulic piston 38 and the fuel injection valve body 20.
Is inserted, and the hydraulic force of the disc spring 43 urges the hydraulic piston 38 toward the piezoelectric element 42. As shown in FIG. 4, a fuel passage 44 is formed in the hydraulic piston 38, and a check valve 45 is inserted in the fuel passage 44. Fuel is circulated between the casing 41 and the piezoelectric element 42 by a device (not shown) for cooling the piezoelectric element 42. When the fuel in the control rod pressurizing chamber 36 leaks, the fuel in the casing 41 is replaced by the fuel passage 44.
Further, the pressure is replenished into the control rod pressurizing chamber 36 via the check valve 45.

When the fuel in the control rod pressurizing chamber 36 is not pressurized, the needle 28 has a downward force acting on the upper surface of the control rod 26, a downward force of the compression spring 34, and the needle 28. An upward force acting on the pressure receiving surface 30 is applied. At this time, the diameter of the control rod 26, the spring force of the compression spring 34, and the area of the pressure receiving surface 30 of the needle 28 are set so that the total of the downward force is slightly larger than the upward force. Therefore, a downward force acts on the normal needle 28, and the normal needle 28 moves toward the nozzle hole 25.
Is closed. Next, when a voltage is applied to the piezoelectric element 42, the piezoelectric element 42 expands to move the hydraulic piston 38 to the left, and as a result, the control rod pressurizing chamber 3
The pressure in 6 rises. At this time, since the upward force acts on the pressure receiving surface 35 of the control rod 26, the control rod 26 rises and the needle 28 rises, so that fuel is injected from the nozzle hole 25. The response at this time is about 80 μsec, which is extremely fast, as described above. On the other hand, when the voltage application to the piezoelectric element 42 is stopped, the piezoelectric element 42 contracts, and as a result, the control rod pressurizing chamber 36
Since the fuel pressure in the inside decreases, the control rod 26 and the needle 28 descend and the fuel injection is stopped. The response at this time is about 80 μsec, which is extremely fast.

As described above, the control rod pressurizing chamber 3
The diameter of the control rod 26, the spring force of the compression spring 34, and the pressure of the needle 28 so that the total of the downward force acting on the needle 28 when the fuel in 6 is not pressurized is slightly larger than the upward force. The area of the surface 30 is defined. Therefore, the needle 28 can be raised by applying a small upward force to the pressure receiving surface 35 of the control rod 26. That is, the fuel pressure in the control rod pressurizing chamber 36 to be raised to raise the needle 28 can be small, and the electric power to be applied to the piezoelectric element 42 can be small.

5 and 6 show an example of the fuel supply pump 14 capable of controlling the discharge amount. Referring to FIG. 5, the fuel supply pump 14 includes a fixed shaft 51 fixedly supported by a pump casing 50 and a rotor 52 rotating around the fixed shaft 51.
A stator 54 swingably attached to the pump casing 50 via a pivot pin 53;
And a ring 56 which is rotatably supported in the inside by a bearing 55. The rotor 52 includes a plurality of radial pistons 57 arranged radially, and the radial pistons 57 are provided between each radial piston 57 and the ring 56.
A shoe 58 that rotates together with the shoe 58 is inserted. When the rotor 52 rotates, the radial piston 57 also rotates accordingly. At this time, the shoe 58 slides on the inner peripheral surface of the ring 56, and the ring 56 also rotates due to the frictional force with the shoe 58. A suction port 59 and a discharge port 60 are formed in the fixed shaft 51, and the suction port 59 is connected to the fuel pump 15 (FIG. 1) and the discharge port 60 is connected to the pressure accumulating chamber 12 (FIG. 1). The cylinder chamber 61 of each radial piston 57 communicates with the suction port 59 and the discharge port 60 alternately. Since the radial piston 57 moves radially outward when the cylinder chamber 61 communicates with the suction port 59, fuel is sucked into the cylinder chamber 61 and compressed when the cylinder chamber 61 communicates with the discharge port 60. The fuel is discharged from the cylinder chamber 61 to the discharge port 60. The pressure of the fuel discharged to the discharge port 60 depends on the stroke of the radial piston 57, and the stroke of the radial piston 57 is determined by the position of the stator 54. Therefore, the discharge pressure of the fuel supply pump 14 can be controlled by swinging the stator 54 around the pivot pin 53.

Referring to FIGS. 5 and 6, a control lever 62 slidable in the axial direction of the fixed shaft 51 is arranged at the bottom of the pump casing 50. The control lever 62 has a long groove 63 inclined with respect to the axis of the control lever 62, and an arm 64 formed in the lower portion of the stator 54 is slidably inserted into the long groove 63. Therefore, when the control lever 62 is moved in the axial direction, the stator 54 swings, and thereby the discharge amount of the fuel supply pump 14 is controlled.
The control lever 62 is connected to a drive device 66 via a speed reduction mechanism 65. In this embodiment, the driving device 66 is formed of a step motor, but it is not always necessary to use the step motor, and for example, a linear solenoid or other means can be used as the driving device 66. Drive device 66
This causes the control lever 62 to move in the axial direction, so that the discharge pressure of the fuel supply pump 14 is driven by the drive device 66.
Controlled by.

Referring to FIG. 1, an electronic control unit 70 for controlling the fuel injection valve 8 and the drive device 66 is provided. The electronic control unit 70 is composed of a digital computer, and has a ROM (Read Only Memory) 72 and a RAM which are mutually connected by a bidirectional bus 71.
A (random access memory) 73, a CPU (central processor unit) 74, an input port 75 and an output port 76 are provided.

As shown in FIG. 1, a fuel pressure sensor 8 for detecting the fuel pressure in the pressure accumulating chamber 12 is provided at the end of the fuel pressure accumulating pipe 11.
0 is attached. The fuel pressure sensor 80 generates an output voltage proportional to the fuel pressure in the pressure accumulating chamber 12, and the fuel pressure sensor 80 is connected to the input port 75 via the AD converter 81. On the other hand, in the intake manifold 9, the intake manifold 9
A supercharging pressure sensor 82 for detecting the supercharging pressure inside is attached. The supercharging pressure sensor 82 generates an output voltage proportional to the pressure in the intake manifold 9, and the supercharging pressure sensor 82 has an AD voltage.
It is connected to the input port 75 via the converter 83. A water temperature sensor 84 for detecting the engine cooling water temperature is attached to the engine body 1. The water temperature sensor 84 generates an output voltage proportional to the engine cooling water temperature.
It is connected to the input port 75 via the converter 85. Further, a load sensor 87 that generates an output voltage proportional to the amount of depression of the accelerator pedal 86 is attached to the accelerator pedal 86. The load sensor 87 is connected to the input port 75 via the AD converter 88.

A pair of disks 89, 90 are attached to the engine crankshaft.
A pair of crank angle sensors 9 facing the toothed outer peripheral surface of 90.
1, 92 are arranged. One crank angle sensor 91, for example, generates an output pulse indicating that the first cylinder is at the intake top dead center. Therefore, it is determined which cylinder the fuel injection valve 8 should be operated from based on the output pulse of the crank angle sensor 91. You can decide. The other crank angle sensor 92
Generates an output pulse each time the crankshaft rotates by a certain angle, and therefore the engine speed can be calculated from the output pulse of the crank angle sensor 92. These crank angle sensors 91 and 92 are connected to the input port 75.

On the other hand, the output port 76 is connected to a driving device 66 composed of a step motor via a driving circuit 93,
It is connected to the corresponding piezoelectric element 42 of the fuel injection valve 8 via the drive circuit 94.

FIG. 7 shows a main routine of the main fuel injection, and this main routine is executed by interruption every fixed crank angle. Referring to FIG. 7, first, at step 100, an output signal of the crank angle sensor 92 representing the engine speed N, an output signal of the load sensor 87 representing the accelerator pedal depression amount L, and a supercharging pressure representing the supercharging pressure B. The output signal of the pressure sensor 82, the output signal of the water temperature sensor 84 representing the engine cooling water temperature T, and the output signal of the fuel pressure sensor 80 representing the fuel pressure P in the accumulator 12 are C
The engine speed N is calculated from the output signal of the crank angle sensor 92, which is sequentially input into the PU 74. The engine speed N, the accelerator pedal depression amount L, the boost pressure B, the water temperature T, and the fuel pressure P are stored in the RAM 73. Next, in step 200, the injection amount τ is calculated, in step 300 the injection timing is calculated, and in step 40
At 0, the fuel pressure P is controlled. The calculation of the injection quantity τ in step 200 is shown in FIG.
The calculation of the injection timing at is shown in FIG.
The control of the fuel pressure P at 0 is shown in FIG.

FIG. 8 shows a flow chart for calculating the fuel injection amount τ. Referring to FIG. 8, first, at step 201, the basic fuel injection amount τ ₀ is calculated from the accelerator pedal depression amount, that is, the load L. Figure 11
(A) shows the relationship between the basic fuel injection amount τ ₀ and the load L, and this relationship is stored in the ROM 72 in advance.
Next, at step 202, from the supercharging pressure P to the supercharging correction coefficient K
₁ is calculated. As shown in FIG. 11B, the supercharging correction coefficient K ₁ increases as the supercharging pressure P increases. Figure 1
The relationship shown in 1 (b) is stored in the ROM 72 in advance. Next, at step 203, the injection amount τ = K ₁ · τ ₀ is calculated. Next, at step 204, the maximum injection amount MAX is calculated from the water temperature T. As shown in FIG. 11C, the maximum injection amount MAX becomes smaller as the water temperature T becomes higher in order to prevent the generation of white smoke. Next, at step 205, it is judged if the injection amount τ is larger than the maximum injection amount MAX. If τ> MAX, the routine proceeds to step 206, where τ = MAX. Therefore, the maximum injection amount MAX is the water temperature T
Will be limited by.

FIG. 9 is a flow chart for calculating the fuel injection period.
-Show chart. Referring to FIG. 9, first of all,
At 301, injection starts from engine speed N and load L
Time τ_aIs calculated. Injection as shown in FIG.
Start time τ₁₁, ... τ_mnBetween engine speed N and load L
Is stored in the ROM 72 in advance in the form of a map.
From the map of injection start timing τ_aIs calculated. Then
In step 302, a water temperature correction coefficient K is calculated from the water temperature T.₂Is calculated
Be done. Water temperature correction coefficient K₂Is water as shown in FIG.
As the temperature T increases, it decreases and the relationship shown in FIG.
Are stored in the ROM 72 in advance. Then step
In 303, the supercharging pressure P to the supercharging correction coefficient K ₃Is calculated
It Supercharging pressure correction coefficient K₃As shown in Fig. 11 (e).
It increases as the supply pressure P increases, and the function shown in FIG.
The member is stored in the ROM 72 in advance. Then step
In step 304, the injection start timing calculated in step 301
τ_aCorrection coefficient K₂, K₃Is added and the actual injection starts
Time τ_aIs required. Actual injection start timing τ_aIs
K₂, K₃Becomes larger as is increased. I.e.
Be done. Next, at step 305, the routine shown in FIG. 8 is executed.
Injection amount τ calculated in advance and the actual injection start timing τ_a
To injection completion timing τ_bIs calculated. Thus obtained
Injection start timing τ_aAnd injection completion timing τ_bIs step 3
In 06, it is output to the output port 76 and these τ_a,
τ_bAccordingly, the injection control of each fuel injection valve 8 is performed.

FIG. 10 shows a flowchart for controlling the fuel pressure P. Referring to FIG. 10, first, at step 401, the reference fuel pressure P ₀ is calculated from the engine speed N and the load L. As shown in FIG. 11 (g), the relationship between the reference fuel pressure P ₁₁ ... P _mn and the engine speed N and the load L is stored in advance in the ROM 72 in the form of a map, and the reference fuel pressure P ₀ is calculated from this map. Is calculated. Next, at step 402, a water temperature correction coefficient K ₄ is calculated from the water temperature T. The water temperature correction coefficient K ₄ increases as the water temperature T increases as shown in FIG. 11 (i), and the relationship shown in FIG. 11 (i) is stored in the ROM 72 in advance. Next, at step 403, the boost pressure correction coefficient K ₅ is calculated from the boost pressure P. The supercharging pressure correction coefficient K ₅ increases as the supercharging pressure P increases, as shown in FIG.
The relationship shown in (h) is stored in the ROM 72 in advance. Next, at step 404, the reference fuel pressure P ₀ obtained at step 401 is multiplied by the correction factors K ₄ and K ₅ to obtain a target reference fuel pressure P ₀ , that is, the target fuel pressure P ₀ .
₀ is required. The target fuel pressure P ₀ increases as the water temperature T increases, and increases as the supercharging pressure P increases.

Next, at step 405, the target fuel pressure P ₀
It is determined whether or not the absolute value of the difference between the current fuel pressure P and the current fuel pressure P is smaller than ΔP. When | P ₀ −P | ≧ ΔP, the routine proceeds to step 406, where it is judged if P> P ₀ .
When P> P _0, the process proceeds to step 407 and the driving device 6
6, that is, the constant step number A is subtracted from the step position ST of the step motor 66. As a result, the control lever 62 (FIGS. 5 and 6) of the fuel supply pump 14 is moved in the direction of decreasing the discharge pressure of the fuel supply pump 14, so that the fuel pressure in the pressure accumulating chamber 12 immediately decreases. On the other hand, P ≦
When P _0, the process proceeds to step 408 and the step motor 6
The constant step number A is added to the step position ST of 6. As a result, the control lever 62 of the fuel supply pump 14 is moved in a direction to increase the discharge amount of the fuel supply pump 14, so that the fuel pressure in the pressure accumulating chamber 12 immediately rises.
On the other hand, if it is determined in step 405 that | P ₀ −P | <ΔP, the processing routine is completed, and at this time, the step motor 66 is held stationary. In this way, the fuel pressure P in the pressure accumulating chamber 12 is maintained at the target fuel pressure P ₀ .

Next, a structure for purifying the exhaust gas by the secondary injection will be described. As shown in FIG. 1, an exhaust manifold 101 and an exhaust pipe 102 are sequentially connected to the in-cylinder injection internal combustion engine 1. The lean NOx catalyst 10 is provided in the exhaust pipe 102.
3 is arranged, and an HC sensor 104 for detecting the HC concentration is provided upstream thereof. The HC sensor 104 outputs a voltage signal according to the HC concentration in the exhaust gas. The output of the HC sensor 104 is input to the input port 75 of the electronic control unit 70 via the AD converter 105. The ROM 72 of the electronic control unit 70 stores a program for sub-injection control in FIG. 13 and a map for sub-injection control in FIG. 14, which is read out by the CPU 74 to execute the control.

The lean NOx catalyst 103 has a lean air-fuel ratio.
Exhaust (the stoichiometric exhaust is neutral and oxygen richer than that)
Nitrogen oxides in the presence of hydrocarbons (HC)
Defined as a catalyst that reduces or decomposes (NOx)
It Such a lean NOx catalyst 103 has
, A catalyst in which a transition metal such as Cu is ion-exchanged and supported,
A catalyst in which a precious metal is supported on zeolite or alumina, etc.
Is included. The lean NOx catalyst 103 reduces NOx
In order to achieve this, HC is required as a reducing agent. Moreover, HC
Has a relatively small molecular size (the number of C is 8 or less)
The NOx purification rate is high. Diesel fuel has more C than that
As it contains a large amount of large molecular size HC,
In the form of, it will be supplied immediately upstream of the lean NOx catalyst 103.
Injects into the cylinder of the cylinder in the expansion and exhaust strokes (intake
If the fuel is injected in the compression stroke, it will burn and become power.
Small) due to thermal decomposition by high temperature exhaust gas
It is supplied to the lean NOx catalyst 103 as molecular HC.
Thus, the H supplied to the lean NOx catalyst 103
C partially oxidizes partially to generate active species, and this activity
The species reacts with NOx to reduce NOx and N₂, H ₂O, C
O₂To generate.

When injecting fuel into the cylinders of the cylinders in the expansion and exhaust strokes, if the injection amount is too small, HC in the exhaust gas
When the injection amount is too large, the amount of HC is more than consumed for the reduction of NOx, and excess HC is discharged, resulting in deterioration of HC emission. , Causes a reduction in fuel consumption. Further, the generated NOx amount changes according to the engine operating state (engine speed N, accelerator depression amount or load L), and the NO
The amount of HC required to reduce x also changes (Fig. 14
(See (a)), it is necessary to execute the optimum amount of sub-injection (see FIG. 14 (b)) according to the engine operating state (N, L). This is controlled by the control routine of FIG. 13, and the map group used for the calculation is the map of FIG. The map of FIG. 14 is a map in which the characteristics have been obtained in advance at the experimental stage and is stored in the ROM 72.

The routine shown in FIG. 13 is executed by the electronic control unit 7
It is stored in the ROM 72 of 0 and is called by the CPU 74 to execute the operation, and is interrupted at regular intervals. Step 101
Then, the CPU 74 reads the engine speed N calculated from the output signal of the crank angle sensor 92, the engine load L calculated from the depression amount of the accelerator pedal 86, and the current HC concentration calculated from the output signal of the HC sensor 104. Put in. Next, at step 102, it is known from the output pulse of the crank angle sensor 91, for example, when the first cylinder has reached the top dead center, and from the output signal of the crank angle sensor 92, for example, 1
The current crank angle can be calculated by knowing how many times the cylinder is rotated from the top dead center position, and if the stroke of the first cylinder is known, the strokes of the other cylinders can be known. Is in the expansion or exhaust stroke, and therefore, the cylinder number (the number of the cylinder in either the expansion or exhaust stroke) for which the secondary injection is to be executed can be determined.

Next, at step 103, using the map of FIG. 14A from the present engine speed N and load L,
The target HC concentration HC ₁ is determined. The engine operating state is almost determined from N and L, and the amount of NOx produced in that state is determined and the HC amount or HC concentration for purifying it is also determined, but that is the target HC concentration HC ₁ , and is made into a map beforehand. Store in ROM. HC ₁ is shown in FIG.
As shown in (a), HC ₁ also becomes large when N large and L large. When the target HC concentration HC ₁ is determined, the required sub injection amount Q for obtaining the HC ₁ amount is also determined. FIG. 14B is a map of this. Proceeding from step 103 to step 104, using the map in FIG.
To decide. As shown in FIG. 14B, when N and L are large, Q is also large.

The fuel injection amount Q in the sub-injection is
Of the fuel injection valve under the engine operating conditions (N, L)
Period T_mAnd the fuel pressure P. Therefore, the figure
14 (c), depending on the engine speed N and the load L
When the fuel pressure P is determined by the injection, as shown in FIG.
Firing period T_mIs also determined. Rotation, as shown in FIG.
As the speed N and the load L are larger, the fuel pressure P is larger.
As shown in Fig. 4 (d), when a certain sub injection amount Q is given,
The larger the combined fuel pressure P, the injection period T_mIs small. did
Therefore, the sub injection amount Q is determined in step 104 of FIG.
Then, the process proceeds to step 105, and as shown in FIGS.
Injection period T of the secondary injection using the map _mTo decide.

Next, in step 106, the injection start timing τ _s is determined based on the injection period T _m calculated in step 105. The fuel injected in the sub-injection is as shown in FIG.
As shown in Fig. 4, the entire amount of the fuel must be injected into the cylinder during the expansion and exhaust strokes of the engine, and before the overlap opening timing when both the intake valve and the exhaust valve open near the end of the exhaust stroke. The secondary injection must be finished. This is because if sub-injection is executed at the valve opening overlap timing of the intake and exhaust valves, the fuel is combined with the fuel injected in the next main injection and burned, causing an overrun. This is because it must be prevented. In this way, if the end timing of the sub-injection is determined under the condition that the intake / exhaust valve opening valve overlap timing is not set, the timing advanced by T _m is the sub-injection start timing τ _s . Based on the injection period T _m of the sub-injection obtained in step 105,
The sub injection start timing τ _s under the operating conditions N and L is shown in FIG.
It is mapped as shown in 4 (e). Step 10
In 6, the sub injection start timing τ _s is determined using the map of FIG. 14 (e). By performing the sub-injection in accordance with the sub-injection amount Q, the injection period T _m , and the injection start timing τ _s obtained above, the sub-injection can be performed with high accuracy corresponding to the operating conditions that change from moment to moment. Therefore, highly accurate and highly responsive NOx purification control can be executed.

The control routine of FIG. 13 is a feedback control portion (step 107-1) for correcting the condition of the secondary injection so that the lean NOx catalyst 103 works at a high NOx purification rate.
14). Steps 107-114 are HC
The HC concentration detected by the sensor 104 is the target HC concentration HC ₁
If it is larger, the fuel injection amount Q of the secondary injection is decreased by a predetermined amount ΔQ, and if the HC concentration is the target HC concentration HC ₁ or less, it is increased by ΔQ, and ΔQ is increased. At this time, if the fuel injection end timing is in the intake and exhaust valve opening overlap timing, the fuel injection start timing τ _s of the sub-injection is advanced by ΔT _m .

In this feedback control, first, in steps 107 and 108, the HC concentration sensor 104
The current HC concentration in the exhaust gas, which was calculated in
It is determined whether or not the concentration is HC ₁ . actually,
Since HC is rarely exactly equal to HC ₁ , H
It is determined whether C is within HC ₁ ± α (a range in which an allowable range of α is provided above and below HC ₁ ).
Of these, step 107 determines whether HC is HC ₁ + α or less, and step 108 determines whether HC is HC ₁ −α or more. If HC is within the range of HC ₁ ± α, the HC concentration is controlled to the required HC concentration HC ₁ and there is no need to correct the auxiliary injection amount Q, and therefore the cycle ends.

If it is determined in step 107 that the current HC concentration exceeds the target HC concentration HC ₁ + α, the process proceeds to steps 109 and 110 because the fuel injection amount Q of the sub injection has been reduced. In step 109, HC
The injection amount excess ΔQ corresponding to the ratio of excess concentration (HC-HC ₁ ) to HC ₁ is obtained, and in step 110, this excess ΔQ is subtracted from the current injection amount Q to obtain a new injection amount. Let's call it Q. Therefore, the sub-injection with a smaller injection amount by ΔQ is executed. When Q is decreased, the fuel injection end timing does not enter the intake / exhaust valve open valve overlap timing, so there is no need to accelerate the fuel injection start timing, and the cycle is ended as it is.

If it is determined in step 108 that the current HC concentration is lower than the target HC concentration HC _1- α, step 11 is executed in order to increase the fuel injection amount Q of the secondary injection.
Proceed to 1, 112. In step 110, the injection amount under-reservation ΔQ corresponding to the ratio of the HC concentration under-representation (HC ₁ −HC) to HC ₁ is obtained, and in step 112, this under-relief ΔQ is increased to the current injection amount Q. To set a new injection amount Q. Therefore, the sub-injection with a larger injection amount by ΔQ is executed.

If the fuel injection amount Q is increased, then ΔQ
Fuel injection period increment ΔT for injecting fuel_mBecause there is
Fuel injection end timing (τ_s+ T_m+ △ T_m) Is an intake and exhaust valve
Valve opening overlap start time T₀Sometimes later
It may be. To determine this, step 11
3, the fuel injection end timing (τ_S+ T_m+ △ T_m) Is T ₀
It is judged whether it is earlier, and if it is earlier, the secondary injection sucks, the exhaust valve
Since there is no entry into the valve opening overlap period,
The cycle ends as it is. However, in step 113
Charge injection end timing (τ_s+ T_m+ △ T_m) Is T₀Slower
And the sub-injection period is the intake and exhaust valve opening overlap period.
It will be tedious, so to prevent it, step 1
14, the fuel injection start timing τ of the secondary injection_sΔT_mIs
And then complete the cycle. by this,
Even when the sub injection amount Q is increased by ΔQ, the sub injection is sucked and exhausted.
It does not take time for the valve opening overlap time to
Does not occur.

Next, the operation will be described. In the embodiment of the present invention, the fuel injection valve 8 that executes the main injection is used, and the ROM 72 of the electronic control unit 70 is additionally stored with the control routine for controlling the sub injection, and the lean NOx provided in the exhaust system is stored. The NOx purification control by the catalyst 103 can be executed with high accuracy. This control is a highly accurate control and a high response control which are similar to those of the main injection control, and moreover, step 1
07-The feedback control of step 114 is carried out. More specifically, in steps 101-106, the sub injection amount Q, the injection period T _m , and the injection start timing τ _s are determined using the map obtained by the preliminary experiment, and the determined parameters are Based on this, the secondary injection is executed.
Then, in steps 107-114, it is determined whether or not the amount of HC is a sufficient amount of HC required for NOx purification,
If not, the sub injection amount Q is corrected. in this case,
When Q is increased, it is determined whether the fuel injection of the secondary injection is performed before the intake / exhaust valve opening overlap period start timing, and if not, the injection start timing τ.
_s is advanced by the required amount.

[0037]

According to the present invention, the in-cylinder injection of the sub-injection is electronically controlled, so that the period, amount, and start timing of the sub-injection in the expansion and exhaust strokes can be finely adjusted to meet various operating conditions. Therefore, the NOx purification rate of the lean NOx catalyst can be improved, and the deterioration of HC emission can be prevented.

[Brief description of drawings]

FIG. 1 is a system diagram of an exhaust gas purification device for an internal combustion engine according to an embodiment of the present invention.

FIG. 2 is a partial cross-sectional view of the internal combustion engine of FIG.

FIG. 3 is a cross-sectional view of the fuel injection valve in FIG.

FIG. 4 is an enlarged sectional view of the hydraulic piston in FIG.

5 is a cross-sectional view of the fuel supply pump of FIG.

6 is a plan view of the control lever of FIG. 5 and its drive mechanism.

FIG. 7 is a flowchart of a main routine of main injection.

FIG. 8 is a flowchart for executing calculation of an injection amount of main injection.

FIG. 9 is a flowchart for executing the calculation of the injection period of the main injection.

FIG. 10 is a flowchart for executing control of fuel pressure of main injection.

11 (a) to (i) are various characteristic diagrams used for calculating a correction coefficient in the main injection.

FIG. 12 is a timing diagram showing the relationship between the timing of the secondary injection and the engine stroke.

FIG. 13 is a flowchart of a control routine for sub injection.

14 (a) to 14 (e) are maps used to control the secondary injection.

[Explanation of symbols]

 8 Fuel injection valve 70 Electronic control unit 102 Exhaust passage 103 Lean NOx catalyst 104 HC sensor

Claims (1)

[Claims] 1. A lean N provided in an exhaust system of an internal combustion engine.
An Ox catalyst, an electronically controlled fuel injection valve for injecting fuel into the cylinder, a fuel pressure accumulator pipe common to all cylinders connected to the fuel injection valve, an NOx amount in the exhaust system, and an engine expansion depending on the engine operating condition ,
An electronic control unit for controlling the fuel injection valve so as to execute in-cylinder injection in an exhaust stroke, and an exhaust gas purification apparatus for an internal combustion engine.