JP3119925B2 - Engine control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for an engine, and more specifically, to a valve control system for an intake valve and an exhaust valve.
In engines of-overlap variable, and in particular those to reduce NO _X in the exhaust gas.

[0002]

2. Description of the Related Art Japanese Unexamined Patent Publication No. 2-119621 discloses a technique in which a valve overlap in which an intake valve and an exhaust valve are both opened is variable.

[0003] Also, Japanese Patent Publication No. 2-36772 discloses that
The air-fuel ratio is made leaner than the stoichiometric air-fuel ratio.
A combo engine is disclosed.

[0004]

By the way, when the valve overlap between the intake valve and the exhaust valve is reduced in a low load region, the amount of burned gas flowing back into the intake pipe through the intake port is small. Therefore, there is an advantage that the combustion state is stabilized.

On the other hand, when the valve overlap is increased in the high load range, the amount of burned gas flowing back into the intake pipe through the intake port becomes large, and the burned gas flowing backward becomes large in the next intake stroke. Since the gas is introduced into the cylinder, the N
There is an advantage that it is possible to reduce the O _X. In addition, since hot burned gas is introduced into the cylinder, that is, burned gas having a large volume relative to its weight is introduced into the cylinder, there is an advantage that so-called pumping loss can be reduced.

However, in the high load area,
Barubuo - when the load is increased in-overlap same state, decreases the ratio of burned gas flowing back to the intake pipe as the load increases (residual gas ratio) is, Therefore NO _X reduction effect in the exhaust gas is reduced There is a problem.

Accordingly, an object of the present invention is to set a small valve overlap in a low load region and to set a large valve overlap in a high load region to secure combustion stability in a low load region and to achieve a high load. Given the engine so as to achieve both reduction of the NO _X and pumping loss in the region, to provide a control apparatus for an engine which is adapted to maintain the NO _X reduction effect at a high level in the high load region .

[0008]

In order to achieve the technical object, according to the present invention, in the high load region where a large valve overlap is set, an increase in load (a decrease in the ratio of the residual gas). The following configuration is adopted, paying attention to the fact that the margin of combustion stability increases with the above. That is,

In an engine provided with an overlap variable means for varying a valve overlap in which both an intake valve and an exhaust valve are opened, a load detecting means for detecting a load of the engine, and And when the load of the engine is in the low load range, the valve overlap is set to a small value, and when it is in the high load range, the valve overlap is set to a large value. In the high load region, the air-fuel ratio (A / F) when the load of the engine is smaller than the predetermined load is set to a rich air-fuel ratio smaller than A / F = 16, The air-fuel ratio at this time is set to a lean air-fuel ratio larger than A / F = 16, and the lean air-fuel ratio between the rich air-fuel ratio and the lean air-fuel ratio at the predetermined load is determined. To change the ratio stretch, yet at the predetermined load or more regions gradually re of the air-fuel ratio in accordance with the increase of the load - a configuration equipped with a air-fuel ratio control means for increasing a down degree.

[0010]

[Action] As is known, the air-fuel ratio larger Li than A / F = 16 - when set down air-Li of the air-fuel ratio - can be reduced NO _X in the exhaust gas by the emissions of It is. Therefore, in the high load region, a large Barubuo - this list and sets the down air - NO _X reduction effect based on-overlap is greater re than A / F = 16 to air-fuel ratio when it becomes smaller than a predetermined level - Li of down air - by increasing with a down degree to increased load, it is possible to improve the NO _X reduction effect in the exhaust gas. In addition, it is possible to reduce fuel consumption by making the air-fuel ratio lean.

[0011]

Embodiments of the present invention will be described below with reference to the accompanying drawings. In mechanical diagram 1, 2 of the engine 1 is an engine body, the engine body 1 has a bank portion 2L, 2R of the right and left forming a V-type with each other, the bank portion 2L of the left and right, each 2R, 3 each
This is a so-called V-type six-cylinder engine in which two cylinders 4 are arranged in series. Below, the left and right bank units 2L, 2L
R, or members related to each of the banks 2L, 2R, include the left bank 2L or the right bank 2R.
Corresponding to the reference numerals, "L" and "R" are added to the reference numerals, and in the description of these members, the addition of the reference numerals "L" and "R" is used unless otherwise necessary. Omitted.

The engine body 1 will be described in detail. The engine body 1 has a cylinder block 3,
In each of the cylinders 4, a piston 6 and a cylinder head 7 fitted into a cylinder 5 form a pen-tower combustion chamber 8, respectively. The cylinder head 7 is provided with a combustion chamber 8 together.
First and second two intake ports 9, 10 opening to
First and second two exhaust ports 11 and 12 are formed (see FIG. 2), and the first and second intake ports 9 and 10 are respectively provided as shown in FIG. A first intake valve 13 and a second intake valve 14 are provided, and the first and second exhaust ports 11,
The 12 has a first exhaust valve 15 and a second exhaust valve 16 respectively.

That is, the engine body 1 is a four-valve engine in which each cylinder 4 is provided with two intake valves 13 and 14 and two exhaust valves 15 and 16.
The valve system 17 for opening and closing the valves 16 to 16 is a so-called double overhead cam (DOHC) type in which two camshafts 18 and 19 are accommodated in the cylinder head 7. That is, the first camshaft 18 is connected to the intake valve 13,
14, the second camshaft 19 is provided with the exhaust valve 15,
16, the first and second camshafts 18,
19, a cam pulley 20 (see FIG. 2, the exhaust valve cam pulley is not shown) is provided at the shaft end thereof.
Through the intake valve 13, 14 or the exhaust valve 1.
5 and 16 are opened and closed at a predetermined timing in synchronization with the rotation of the engine output shaft 23.

The first camshaft 18 has an intake valve 1
A variable valve timing mechanism 24 (variable valve timing mechanism for intake valve) for changing the cam face for 3 (14) is provided, while the second cam shaft 19 has a cam face for exhaust valve 15 (16). A variable valve timing mechanism (variable valve timing mechanism for exhaust valve, not shown) for changing the valve timing is provided. The variable valve timing mechanism for the exhaust valve has the same configuration as the variable valve timing mechanism for the intake valve 24. Since such a variable valve timing mechanism 24 is conventionally known, detailed description thereof will be omitted. An ignition plug 25 is mounted on the cylinder head 7, and the ignition plug 25 is arranged facing the center of the combustion chamber 8.

The piston 6 is connected to the crankshaft 23 via a connecting rod 26. An oil storage chamber 28 for storing engine oil is provided in an oil pan 29 below the crank chamber 27 for accommodating the crankshaft 23.
Is formed by Reference numeral 30 shown in FIG. 2 is an oil strainer.

In a central bank space 31 sandwiched between the left and right bank portions 2L and 2R, as shown in FIG. Installed and this supercharger 32
The interlacer 33 is arranged above the. On the other hand,
A surge tank 34 extending in the longitudinal direction of the crankshaft 23 is disposed above each of the banks 2L and 2R. The surge tank 34 and the intake ports 9 and 10 are connected to each cylinder 4 Each is connected via an independent intake pipe 35. The upstream ends of the intake ports 9 and 10 in the left and right banks 2L and 2R respectively correspond to the bank central space 31.
The independent intake pipe 35 is,
The surge tank 34 has a shape which once extends in the lateral direction toward the bank center space 31 and then curves downward.

Hereinafter, an intake system 40 of the engine body 1 will be described.
Will be described in detail with reference to FIG. The intake system 40 includes a common intake pipe 41 which is sequentially connected from the upstream side to the downstream side, and the left and right surge tanks 34L, 34.
R, the independent intake pipe 35, and the common intake pipe 4
1 is an air cleaner in order from the upstream side to the downstream side.
A screw 42, an air flow meter 43, a throttle valve 44, the screw-type supercharger 32, and the intercooler 33. The common intake pipe 41 has a first bypass passage 45 that bypasses the throttle valve 44,
A second bypass passage 46 is provided to bypass the screw supercharger 32 and the intercooler 33.

An ISC valve 47 is interposed in the first bypass passage 45 and, as is known, the ISC valve 4
7, the idle speed is adjusted. In the second bypass passage 46, a relief valve 49 driven by a diaphragm type actuator 48 is interposed, and when the supercharging pressure becomes a predetermined value or more, the relief valve 49 is opened (second valve). (The bypass passage 46 is opened.) On the other hand, the left and right surge tanks 34L and 34R are communicated with each other by a communication pipe 50, and a valve 51 for a variable intake control is interposed in the communication pipe 50 in the middle thereof, for example, for engine rotation. The valve 51 is opened and closed according to the number, so as to obtain a dynamic effect of intake air over a wide area, as is known.

The independent intake pipe 35 has a partition wall 35a for partially partitioning its internal space into two parts on the left and right sides.
5a form a first independent intake passage 52 and a second independent intake passage 53, and the first independent intake passage 52
The second independent intake passage 53 is connected to the intake port 9 and the second independent intake passage 53 is connected to the second intake port 10. The second independent intake passage 53 is configured to be opened and closed by a shutter valve 54 disposed at an upstream end of the second independent intake passage 53. Each shutter valve 54L disposed in the left bank 2L has a common shaft for the left bank. Each shutter valve 54R connected to the right bank 2R is connected to a common shaft 55R for the right bank, and these common shafts 55L and 55R are respectively provided with an actuator (shown in FIG. (Omitted), and each of the shutter valves 54L, 54R has an engine speed of about 3,000.
It is closed at low rpm and opened at high rpm with the rpm in between.

The fuel supply system of the engine body 1 includes an upstream injector 56 and a downstream injector 57. The upstream injector 56 is disposed immediately upstream of the supercharger 32. 57 is provided in the independent intake pipe 35, and more specifically, the downstream injector 57 includes a first intake port 9 and a second intake port.
It is arranged facing the front 10. Note that reference numeral 58 shown in FIG. 3 is an assist air passage, and 59 is a check valve.

As shown schematically in FIG. 3, the exhaust system 60 of the engine body 1 sequentially moves from the upstream side to the downstream side.
Exhaust manifold 61L for left and right banks 2L, 2R,
61R and a common exhaust pipe 62, a catalyst converter 63 for purifying exhaust gas is interposed in the middle of the common exhaust pipe 62, and a downstream end of the common exhaust pipe 62 A silencer (not shown) is provided as is known.

The engine body 1 is provided with an external EGR passage 66 constituted by an external EGR conduit. One end of the external EGR passage 66 is connected to the catalyst converter.
The other end is connected to a common intake pipe 41 downstream of the turbocharger 32 (downstream of the throttle valve 44). And
The carbon trap 71 and the EGR cooler 7 are sequentially arranged in the external EGR passage 66 from the one end side to the other end side.
2. An EGR valve 73 is provided.

The engine main body 1 includes a control unit U shown in FIG. 4, and the control unit U is constituted by, for example, a microcomputer, and includes a CPU, a ROM, a RAM, and the like, as is known. I have. Signals from the sensors 43, 80 to 82, and the like are input to the control unit U. The air flow meter 43 detects the amount of intake air. The sensor 80 detects the engine load based on the intake negative pressure. The sensor 81 detects the engine speed. The sensor 82 detects an accelerator opening. On the other hand,
From the control unit U, the injector 5
6, 57, control signals are output to the EGR valve 73, the variable valve timing mechanism 24 of the intake and exhaust valves, the actuator 84 for driving the throttle valve 44, and the like.

Hereinafter, various controls performed by the control unit U will be described. First, EGR control, valve timing control, and air-fuel ratio control are performed based on a control map shown in FIG. That is, the control is divided into a low-speed low-load region I, a partial load region II, and a high-load region III, and the following control is performed in each of these regions I, II, and III.

In the EGR control regions I and II, the EGR valve 73 is fully closed,
External EGR is prohibited. On the other hand, in the high load region III, E
The GR valve 73 is opened, and the cooled EGR gas (cold EGR) is recirculated using the external EGR passage 66 including the EGR cooler 72. Thus, lowering the engine internal temperature, it is possible to reduce the NO _X in the exhaust gas.

The valve timing control will be described with reference to the low-rotation low-load region I and the partial load region II. The valve timing of the intake valve 13 (14) and the exhaust valve 15 (16) is changed so that the intake valve 13 ( The valve overlap (O / L) between the valve 14) and the exhaust valve 15 (16) is set to the following value.

(1) Low-speed low-load region I In this region I, the intake valve 13 (14) is set at 10d before the top dead center.
EG and the exhaust valve 15 (16) is 10d after top dead center.
The valve is closed at eg. That is, the valve overlap O /
L is set to 20 deg in crank angle.

(2) Partial load region II In this region II, the intake valve 13 (14) is set at 25d before top dead center.
EG and the exhaust valve 15 (16) is 25d after top dead center
The valve is closed at eg. That is, the valve overlap O /
L is set to 50 deg in crank angle.

By changing the valve overlap O / L, the residual gas in the cylinder is reduced under the small valve overlap in the low rotation and low load region I, and the combustion stability can be ensured. . On the other hand, in the partial load region II, a large amount of residual gas due to a large valve overlap (internal E
GR) makes it possible to reduce NO _x and pumping loss.

[0030] By way limited to the air-fuel ratio control part load region II, as shown in FIG. 6 which represents the characteristics of a rotational speed N _1, in the region II, when in the predetermined load L ₂ smaller load condition empty ratio is set to the stoichiometric air-fuel ratio (lambda = 1), in the predetermined load L _2, a / F = 21 is set, when in the heavy load state than the predetermined load L ₂ are in response to an increase in load gradual The lean degree is increased.

By the above-described air-fuel ratio control, as shown by the solid line in FIG. 6, it is possible to secure a good NOx reduction effect in the partial load region II, and to realize a good fuel efficiency in terms of fuel efficiency. it can. Here, the rich air-fuel ratio (the stoichiometric air-fuel ratio of λ = 1) with the predetermined load L2 as a boundary
The change of the air-fuel ratio between the air-fuel ratio and the lean air-fuel ratio (A / F = 21) is performed not at once but at once. That is, in general, in the air-fuel ratio between the stoichiometric air-fuel ratio and A / F = 16, the NOx emission is gradually increased as the air-fuel ratio becomes lean, and the air-fuel ratio becomes larger in the region where the air-fuel ratio is larger than 16. Since the NOx emission amount gradually decreases as the fuel ratio becomes lean, it is possible to surely change the air-fuel ratio to a region where NOx is reduced by increasing the air-fuel ratio by changing the air-fuel ratio at a stretch ( (It is possible to pass through the air-fuel ratio region where the amount of NOx emission is large.) In addition, the predetermined load L2
The lean air-fuel ratio (A / F = 2)
As is clear from FIG. 6, 1) indicates NOx at a rich air-fuel ratio (theoretical air-fuel ratio) set in the load range of L1 to L2.
The emission amount is set so as to be smaller than the emission amount. The dashed line in FIG. 6 shows the characteristics when the engine is operated under the stoichiometric air-fuel ratio in a load state equal to or higher than the predetermined load L2.

Second Embodiment (FIGS. 7 and 8) In this embodiment , as shown in FIG. 7, the control map includes an extremely low rotation extremely low load region V and a low rotation low load region V
I, a partial load region VII, and a high load region VIII.

In the regions V, VI, and VII other than the EGR control high load region VIII, the EGR valve 73 is fully closed and the external EGR is prohibited, while the EGR valve 7 is in the high load region VIII.
3 is opened to perform a cold EGR.

The valve overlap O / L is set to the following value in the other areas V, VI, VII except the valve load control high load area VIII. (1) Extremely Low Rotation Extremely Low Load Region V In this region V, the intake valve 13 (14) has a top dead center of 5 deg.
, And the exhaust valve 15 (16) is closed at 5 deg after top dead center. That is, the valve overlap O / L is set to 10 deg in crank angle.

(2) Low-speed low-load region In this region VI, the intake valve 13 (14) is 5d before the top dead center.
EG and the exhaust valve 15 (16) is 30d after top dead center
The valve is opened at eg. That is, the valve overlap O /
L is set to 35 deg in crank angle.

(3) Partial load area VII In the area VII, the intake valve 13 (14)
deg, and the exhaust valve 15 (16) is 30
The valve is closed at deg. That is, the valve overlap O
/ L is set to 60 deg in crank angle.

By changing the valve overlap O / L as described above, combustion stability can be secured under a small valve overlap in the extremely low rotation and extremely low load region V. Further, it is possible to reduce the reduction and pumping loss of the NO _X by the large amount of internal EGR by low rotation low load regions VI and part load region VII in large valve overlap.

When the air heat ratio control is limited to the low-speed low-load region VI and the partial load region VII, as shown in FIG. 8 showing the characteristics at the rotation speed N ₂ , the predetermined load in the low-speed low-load region VI Check heat ratio stoichiometric air heat ratio when L ₃ is in the lower load condition (lambda =
Is set to 1), in the above-mentioned predetermined load L ₃ A / F =
21 is set, when in the heavy load state than the predetermined load L ₃ gradually leanness in response to an increase in the load, including the part-load region VII is increased.

By the above air-heat ratio control, as shown by the solid line in FIG. 8, it is possible to secure a favorable NOx reduction effect in the low rotation load region VI and the partial load region VII. At the same time, it is possible to realize a good heat cost ratio in terms of heat cost. Also in the second embodiment, the rich air-fuel ratio (stoichiometric air-fuel ratio) and the lean air-fuel ratio (A / F = 2
The change of the air-fuel ratio between 1) is performed at once, not gradually. Further, the lean air-fuel ratio (A / F = 21) that is changed at a stretch from the predetermined load L3 is a rich air-fuel ratio that is set in a load region smaller than the predetermined load L3 in the load region VI, as is clear from FIG. N at air-fuel ratio (stoichiometric air-fuel ratio)
The emission amount is set to be smaller than the Ox emission amount. The broken line in FIG. 8 indicates the predetermined load L3.
In the above-mentioned load state, the characteristics when operating under the theoretical air-heat ratio are shown.

The embodiments of the present invention have been described above.
The present invention includes, but is not limited to, the following modifications. (1) The air heat ratio at the above-mentioned predetermined loads L ₂ and L ₃ is A / F
It is only necessary to be leaner than = 16. (2) The supercharger 32 may be a turbocharger driven by exhaust energy. (3) The present invention can be applied to a naturally aspirated engine having no supercharger 32.

[0041]

As is apparent from the above description, according to the present invention, the valve overlap is made variable, and the combustion stability in the low load region, the NOx reduction and the pumping loss reduction in the high load region are reduced. In the engine designed to achieve both, the effect of reducing NOx in a high load region can be maintained at a high level, and the fuel consumption can be reduced. In particular, in the high-load region, the air-fuel ratio is changed at a stroke between the rich air-fuel ratio and the lean air-fuel ratio at a predetermined load, and the air-fuel ratio is passed through the air-fuel ratio region in which the amount of NOx emission increases. By increasing the lean degree of the air-fuel ratio with an increase in the load in the load region, the above-described NOx reduction effect can be maintained at a high level.

[Brief description of the drawings]

FIG. 1 is a front view of an engine with a supercharger according to an embodiment in a partially sectional view.

FIG. 2 is a sectional view taken along the line II-II shown in FIG.

FIG. 3 is a development view of the engine shown in FIG. 1;

FIG. 4 is an overall system diagram of a control system according to the embodiment.

FIG. 5 is a control map used in the first embodiment.

FIG. 6 is a diagram showing the contents and operation of air-heat ratio control of the first embodiment.

FIG. 7 is a control map used in the second embodiment.

FIG. 8 is a diagram showing the contents and operation of air-heat ratio control according to a second embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Engine main body 13 1st intake valve 14 2nd intake valve 15 1st exhaust valve 16 2nd exhaust valve 24 Variable valve timing mechanism 43 Air flow meter 56 Upstream injector 57 Downstream injector 80 Load detection sensor U Control unit O / L valve overlap L ₂ given load L ₃ predetermined load

────────────────────────────────────────────────── ⁷ Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI F02D 41/04 305 F02D 41/04 305D (56) References JP-A-3-199633 (JP, A) JP-A-60-93137 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) F02D 13/00-28/00 F02D 29/00-29/06 F02D 41/00-41/40 F02D 43/00- 45/00 F02P 5/145-5/155

Claims (7)

(57) [Claims] 1. An engine provided with an overlap variable means for varying a valve overlap in which both an intake valve and an exhaust valve are opened, and load detection means for detecting a load of the engine; Means for receiving a signal from the control means and setting the valve overlap to be small when the engine load is in a low load range, and setting the valve overlap to be large when the engine load is in a high load range; Receiving a signal from the control means when the load of the engine is smaller than a predetermined load in the high load region.
Air-fuel ratio (A / F) with rich air smaller than A / F = 16
And the air-fuel ratio when the load is equal to or greater than the predetermined load is A / F.
= 16 and the lean air-fuel ratio is set to
The difference between the rich air-fuel ratio and the lean air-fuel ratio at a predetermined load
Once to change the air-fuel ratio between, yet gradually re of the air-fuel ratio in accordance with the increase of the load Oite the predetermined load or more regions - and a, and the air-fuel ratio control means for increasing a down degree An engine control device, characterized in that: 2. The engine control device according to claim 1, wherein the engine is a supercharged engine. 3. The engine control device according to claim 1, wherein the engine is a naturally-aspirated engine. 4. The air-fuel ratio control unit according to claim 1 , wherein the air-fuel ratio control unit sets the air-fuel ratio to a stoichiometric air-fuel ratio in the high load region when an engine load is smaller than the predetermined load. Engine control device. 5. The overlap control means according to claim 1, wherein both the intake valve and the exhaust valve are provided.
An engine control device as set forth in claim 1, wherein the valve overlap in the open state is set to about 20 deg in crank angle in the low load range, and set to about 50 deg in crank angle in the high load range. . 6. The overlap control means according to claim 1, wherein both the intake valve and the exhaust valve are provided.
As the valve overlap of the open state, the about 5 to crank angle in the low load region is set to 10 DE g, to set <br/> constant about 35De g crank angle in the high load region, the Characteristic engine control device. 7. The method according to claim 1, When the engine load is high, the predetermined load
The value of the lean air-fuel ratio when changed at a stretch,
N smaller than the NOx emission amount at the rich air-fuel ratio
Ox emission amount is set.
Engine control device.