JPH05215002A - Control device for engine - Google Patents

Abstract

PURPOSE:To keep high level NOx reduction effect in a high load area of an engine which is provided with a means for varying a valve overlapping time of an intake valve and an exhaust valve. CONSTITUTION:A valve overlapping time where an intake valve and an exhaust valve are closed at the same time is set small in a low speed low load area, for securing stability in combustion. On the other hand, a large valve overlapping time is provided in a partial load area II, so that NOx and pumping loss are reduced by means of a large amount of inner EGR. When a load in the partial load area is smaller than a specified load L2, a theoretical air-fuel ratio is set. When the load is equal to the specified load L2, an equation for showing NOx reduction effect, for instance, A/F=21, is set. When the load exceeds the specified load L2, a lean degree is gradually increased according to increase of the load. Accordingly, when the load is not less than the specified load L2, NOx is reduced through a leaned condition of an air-fuel ratio.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine control device, and more specifically, to a valve opening and closing valve for an intake valve and an exhaust valve.
The present invention relates to an engine having a variable burlap, in particular, an engine that reduces NO _{X in} exhaust gas.

[0002]

2. Description of the Related Art Japanese Unexamined Patent Publication (Kokai) No. 2-119621 discloses a technique for varying a valve overlap in which both an intake valve and an exhaust valve are open.

Further, Japanese Patent Publication No. 2-36772 discloses that
A so-called lean that makes the air-fuel ratio leaner than the theoretical air-fuel ratio
A ban engine is disclosed.

[0004]

By the way, when the valve overlap of the intake valve and the exhaust valve is made small in the low load region, the amount of burnt 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 region, the amount of burnt gas that flows back into the intake pipe through the intake port becomes large, and the burned gas that has flowed back in the next intake stroke. Since it is introduced into the cylinder, the amount of N in the exhaust gas is the same as when a large amount of EGR was performed.
There is an advantage that O _X can be reduced. In addition, since hot burned gas is introduced into the cylinder, that is, burned gas having a large volume relative to the weight is introduced into the cylinder, there is an advantage that so-called pumping loss can be reduced.

However, in the above high load region,
When the load increases under the same valve overlap condition, as the load increases, the ratio of burnt gas that flows back into the intake pipe (residual gas ratio) decreases, and therefore the NO _X reduction effect in the exhaust gas decreases. There is a problem.

Therefore, an object of the present invention is to set a small valve overlap in the low load region and set a large valve overlap in the high load region to secure combustion stability in the low load region and to increase the high load. It is an object of the present invention to provide an engine control device that maintains a high level of NO _X reduction effect in a high load region on the premise of an engine designed to achieve both NO _X and pumping loss reduction in the region. ..

[0008]

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

A load detecting means for detecting the load of the engine and a signal from the load detecting means are provided, and when the engine load is in the low load region, the small valve overlap is set, and when it is in the high load region, the large valve overlap is set. An overlap control means for setting the valve overlap,
In response to the signal from the load detection means, the air-fuel ratio (A / F) is set to a lean air-fuel ratio larger than A / F = 16 when the engine load becomes equal to or higher than a predetermined load in the high load region. Air-fuel ratio control means for setting and gradually increasing the lean degree of the air-fuel ratio in accordance with the increase of the load in the region above the predetermined load.

[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 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 By increasing the lean degree of the lean air-fuel ratio as the load increases, it is possible to improve the NO _X reduction effect in the exhaust gas. In addition, fuel efficiency can be reduced by leaning the air-fuel ratio.

[0011]

Embodiments of the present invention will be described below with reference to the accompanying drawings. Mechanical Configuration of Engine In FIGS. 1 and 2, reference numeral 1 denotes an engine main body, and the engine main body 1 has left and right bank portions 2L and 2R that form a V shape with each other. 3 each
It is a so-called V-type 6-cylinder engine in which two cylinders 4 are arranged in series. Below, the left and right bank sections 2L, 2
The left bank portion 2L or the right bank portion 2R is included in the members constituting R or the members associated with the respective bank portions 2L and 2R.
Corresponding to the above, the reference numerals "L" and "R" are added and illustrated, while the reference numerals "L" and "R" are added in the description of these members unless particularly necessary. Omit it.

The engine body 1 will be described in detail. The engine body 1 has a cylinder block 3.
In each cylinder 4, a piston 6 fitted in a cylinder 5 and a cylinder head 7 form a Pentorf-type combustion chamber 8. The cylinder head 7 has a combustion chamber 8
First and second intake ports 9 and 10 which are opened to
Two first and second exhaust ports 11 and 12 are formed (see FIG. 2), and the first and second intake ports 9 and 10 are respectively, 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,
A first exhaust valve 15 and a second exhaust valve 16 are provided at 12, respectively.

That is, the engine body 1 is a four-valve engine in which each cylinder 4 has two intake valves 13 and 14 and two exhaust valves 15 and 16.
The valve operating system 17 for opening and closing ~ 16 is a so-called double over head cam (DOHC) type in which two cam shafts 18 and 19 are housed in the cylinder head 7. That is, the first camshaft 18 is the intake valve 13,
The second camshaft 19 is for the exhaust valve 15,
16 for the first and second camshafts 18,
A cam pulley 20 (see FIG. 2, the exhaust valve cam pulley is not shown) is provided on the shaft end of the cam 19, and these cam pulleys 20 are provided with a timing belt 22 as is known.
Is connected to the engine output shaft (crankshaft) 23 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 intake valve 1 is attached to the first camshaft 18.
3 (14) is provided with a valve timing variable mechanism 24 (intake valve valve timing variable mechanism) for changing the cam face, while the second camshaft 19 is provided with a cam face for the exhaust valve 15 (16). A valve timing varying mechanism (exhaust valve valve timing varying mechanism, not shown) for changing the valve timing is provided. This exhaust valve variable valve timing mechanism has the same configuration as the intake valve variable valve timing mechanism 24. Since such a valve timing variable mechanism 24 has been conventionally known, detailed description thereof will be omitted. An ignition plug 25 is attached to 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, and an oil storage chamber 28 for storing engine oil is provided in an oil pan 29 below the crank chamber 27 for storing the crankshaft 23.
Is formed by. Reference numeral 30 shown in FIG. 2 is an oil strainer.

As shown in FIG. 1, a screw type supercharger 32, which is mechanically driven by the rotational force of the crankshaft 23, is provided in the central bank space 31 sandwiched between the left and right bank portions 2L and 2R. Installed and also this supercharger 32
An intercooler 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 respectively. Each of them is connected via an independent intake pipe 35. The upstream ends of the intake ports 9 and 10 in the left and right bank portions 2L and 2R respectively correspond to the bank central space 31.
The independent intake pipe 35 is
The serge tank 34 temporarily extends laterally toward the bank central space 31 and then curves downward.

The intake system 40 of the engine body 1 will be described below.
Will be described in detail with reference to FIG. The intake system 40 includes a common intake pipe 41 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 has an air cleaner in order from the upstream side to the downstream side.
An air 42, an air flow meter 43, a throttle valve 44, the screw type supercharger 32, and the intercooler 33 are arranged. Further, in the common intake pipe 41, a first bypass passage 45 that bypasses the throttle valve 44,
A second bypass passage 46 that bypasses the screw type supercharger 32 and the intercooler 33 is provided.

An ISC valve 47 is provided in the first bypass passage 45, and as is known, the ISC valve 4 is provided.
The idle speed is adjusted by 7. A relief valve 49 driven by a diaphragm type actuator 48 is provided in the second bypass passage 46, and the relief valve 49 is opened when the supercharging pressure exceeds a predetermined value (second The bypass passage 46 is opened) and is relieved. On the other hand, the left and right serge 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, for example, to rotate the engine. The valves 51 are opened / closed in accordance with the number, and as is known, the dynamic effect of intake is obtained over a wide area.

The independent intake pipe 35 has a partition wall 35a for partitioning the internal space thereof into two right and left parts.
The first independent intake passage 52 and the second independent intake passage 53 are formed by 5a, and the first independent intake passage 52 is formed into 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 arranged at the upstream end thereof, and each shutter valve 54L arranged in the left bank portion 2L is a common shaft for the left bank. Each shutter valve 54R connected to 55L and arranged in the right bank portion 2R is connected to a common shaft 55R for the right bank, and these common shafts 55L and 55R respectively have actuators (shown in the figure) at their shaft ends. (Omitted) are combined, and the shutter valves 54L and 54R are set to have an engine speed of about 3,000
It is designed to be closed in the low rpm range and open in the high rpm range across the rpm.

The fuel supply system of the engine body 1 comprises an upstream injector 56 and a downstream injector 57. The upstream injector 56 is arranged immediately upstream of the supercharger 32, while the downstream injector 56 is provided. 57 is disposed in the independent intake pipe 35, and more specifically, the downstream side injector 57 includes the first intake port 9 and the second intake port 57.
It is arranged so as to face the vehicle. Reference numeral 58 shown in FIG. 3 is an assist air passage, and 59 is a check valve.

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

An external EGR passage 66 constituted by an external EGR conduit is attached to the engine body 1. One end of the external EGR passage 66 is the catalyst converter.
Is connected to the common exhaust pipe 62 on the downstream side of the engine 63, and the other end is connected to the common intake pipe 41 on the upstream side of the supercharger 32 (downstream of the throttle valve 44). And
In the external EGR passage 66, in order from the one end side to the other end side, the carbon trap 71 and the EGR cooler 7 are sequentially arranged.
2, EGR valve 73 is provided.

The engine body 1 is provided with a control unit U shown in FIG. 4, and the control unit U is composed of, for example, a micro computer, and is provided with a CPU, a ROM, a RAM, etc. as is known. There is. Signals from the sensors 43, 80 to 82, etc. 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 the accelerator opening. On the other hand,
From the control unit U, the injector 5
6, 57, the EGR valve 73, the variable valve timing mechanism 24 for the intake valve and the exhaust valve, the actuator 84 for driving the throttle valve 44, and the like.

Various controls performed by the control unit U will be described below. First, the EGR control, the valve timing control, and the air-fuel ratio control are performed based on the control map shown in FIG. That is, it is divided into a low rotation and 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 area III, E
The GR valve 73 is opened and the cooled EGR gas (cold EGR) is recirculated using the external EGR passage 66 provided with the EGR cooler 72. Thus, lowering the engine internal temperature, it is possible to reduce the NO _X in the exhaust gas.

Valve Timing Control Explaining only in the low rotation and low load region I and the partial load region II, the valve timings of the intake valve 13 (14) and the exhaust valve 15 (16) are changed so that the intake valve 13 ( The valve overlap (O / L) between 14) and the exhaust valve 15 (16) is set to the following value.

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

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

By changing the valve overlap O / L as described above, 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 secured. .. On the other hand, in the partial load area II, a large amount of residual gas (internal E
By GR), it is possible to reduce and reduction of pumping loss of NO _X.

The explanation will be limited to the air-fuel ratio control partial load region II. As shown in FIG. 6 showing the characteristic at the rotational speed N ₁ , when the load condition is smaller than the predetermined load L ₂ in the region II, the air-fuel ratio control partial load region II becomes 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 air-fuel ratio control, as shown by the solid line in FIG. 6, it becomes possible to secure a good NO _X reducing effect in the partial load region II, and at the same time, to realize a good fuel consumption rate. You can The broken line in FIG. 6 represents the characteristics when the engine is operated under the stoichiometric air-fuel ratio under a load of a predetermined load L ₂ or more.

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

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

Valve Timing Control In the areas V, VI and VII other than the high load area VIII, the valve overlap O / L is set to the following value. (1) Very low rotation extremely low load region V In the region V, the intake valve 13 (14) has a top dead center of 5 deg.
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 rotation and low load region In the region VI, the intake valve 13 (14) is 5d before top dead center.
The exhaust valve 15 (16) is opened 30 seconds after the top dead center.
The valve is opened by eg. That is, valve overlap O /
L is a crank angle set to 35 deg.

(3) Partial load area VII In the area VII, the intake valve 13 (14) is set to 30 before top dead center.
The exhaust valve 15 (16) is opened 30 degrees after top dead center.
The valve is closed at deg. That is, valve overlap O
/ L is a crank angle set to 60 deg.

By changing the valve overlap O / L as described above, combustion stability can be ensured under a small valve overlap in the extremely low rotation and extremely low load region V. Further, in the low rotation and low load region VI and the partial load region VII, NO _X and pumping loss can be reduced by a large amount of internal EGR due to a large valve overlap.

The air-heat ratio control will be limited to the low rotation low load region VI and the partial load region VII. As shown in FIG. 8 showing the characteristic at the rotation speed N ₂ , a predetermined load is obtained in the low rotation low load region VI. When the load is smaller than L ₃ , the air-heat ratio is the theoretical air-heat ratio (λ =
Is set to 1), in the above-mentioned predetermined load L ₃ A / F =
When 21 is set and the load is larger than the predetermined load L _{3, the} lean degree is gradually increased in accordance with the increase of the load including the partial load region VII.

By the above air-heat ratio control, as shown by the solid line in FIG. 8, it becomes possible to secure a good NO _X reducing 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 rate in heat cost. The broken line in FIG. 8 represents the characteristics when operating under the theoretical air-heat ratio in the load state of the predetermined load L ₃ or more.

The embodiments of the present invention have been described above.
The present invention is not limited to this and includes the following modifications. (1) The air-heat ratio at the predetermined loads L ₂ and L ₃ is A / F
It should be leaner than = 16. (2) The supercharger 32 may be a turbocharger driven by exhaust energy. (3) It can also be applied to a naturally aspirated engine that does not have the supercharger 32.

[0041]

As is apparent from the above description, according to the present invention, the valve overlap is made variable, the combustion stability in the low load region and the NO _x reduction and pumping loss reduction in the high load region are achieved. in engines to achieve both, not only can maintain the NO _X reduction effect in the high load range at a high level, it is possible to lower fuel consumption.

[Brief description of drawings]

FIG. 1 is a front view showing a partial cross-section of an engine with a supercharger according to an embodiment.

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

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

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

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

FIG. 6 is a diagram showing the content 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 of air-heat ratio control and its action in the second embodiment.

[Explanation of symbols]

1 Engine 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 predetermined load L ₃ predetermined load

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display area F02D 43/00 301 E 7536-3G

Claims (7)

[Claims] 1. An engine equipped with an overlap variable means for changing a valve overlap in which both an intake valve and an exhaust valve are open, and a load detecting means for detecting a load of the engine, and the load detecting means. An overlap control means for receiving a signal from the means and setting a small valve overlap when the engine load is in a low load area and setting a large valve overlap when the engine load is in a high load area; In response to the signal from the means, the air-fuel ratio (A / F) is set to a lean air-fuel ratio larger than A / F = 16 when the engine load exceeds a predetermined load in the high load region. An air-fuel ratio control means for gradually increasing the lean degree of the air-fuel ratio in accordance with an increase in the load in the region of the predetermined load or more. Engine control unit. 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 A / F according to claim 1, wherein the air-fuel ratio control means, when the load of the engine is smaller than the predetermined load in the high load region.
A rich air-fuel ratio smaller than 16 is set. 5. The air-fuel ratio control means according to claim 4, wherein the air-fuel ratio is set to the stoichiometric air-fuel ratio when the engine load is smaller than the predetermined load in the high load region. Control device for the engine. 6. The valve overlap control means according to claim 1, wherein the valve overlap is set to about 20 deg in a crank angle in the low load region, and the valve overlap is set to about 50 deg in a crank angle in the high load region. An engine control device, characterized in that it sets a burlap. 7. The overlap control means according to claim 1, wherein the valve overlap is set to about 5 to 10 deg in the crank angle in the low load region, and is set to about 35 d in the crank angle in the high load region.
An engine control device, characterized in that the valve overlap of an egg is set.