JP3153283B2 - Engine with mechanical supercharger - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine with a mechanical supercharger.

[0002]

BACKGROUND ART recent engine, HC is harmful components in the exhaust gas, CO, in order to purify the NO _X, the three-way catalyst is disposed (Japanese Patent 1-163411 discloses referenced exhaust system ). This three-way catalyst has the characteristic of exhibiting the highest purification ability when the air-fuel ratio (A / F) is the stoichiometric air-fuel ratio (λ = 1).

In recent years, many engines have been equipped with an electronic fuel injection valve as a fuel supply means, and the fuel injection valve is controlled by a control unit (Japanese Patent Application Publication No. Hei. 36772). This type of engine has an advantage that the air-fuel ratio of the air-fuel mixture to be drawn into the engine can be freely adjusted. Incidentally, in the conventional air-fuel ratio control, it is customary that the control is performed such that the air-fuel ratio becomes richer than the stoichiometric air-fuel ratio, for example, A / F = 13 in the low rotation speed and high load region.

Further, as a supercharger mounted on a so-called supercharged engine, a turbocharger driven by exhaust gas of an engine and a mechanical supercharger mechanically driven by an output shaft of the engine (Japanese Patent Application Laid-Open (See Japanese Patent Application Laid-Open No. 63-167027). .

[0005]

However, in an engine having a mechanical supercharger, there is an inherent problem of a blow-by phenomenon of intake air. That is, unlike the turbocharger, in the mechanical supercharger, since the exhaust pressure is not increased by the presence of the mechanical supercharger, the opening period of the intake valve and the opening period of the exhaust valve are not increased. During the overlap period in which the supercharged air overlaps with the above, a phenomenon that the supercharged intake air blows through to the exhaust system as it is is likely to occur. In particular, the problem of blow-by becomes a problem in a low-speed and high-load operation range which is a supercharging region, and the problem of blow-by of the intake greatly affects purification of exhaust gas (HC component).

That is, as described above, in the air-fuel ratio control of the engine, the engine is generally operated under an air-fuel ratio (rich air-fuel ratio) smaller than the stoichiometric air-fuel ratio in a high load region. Therefore, there is a problem that HC, which is an unburned component in the exhaust gas, is difficult to be purified by the three-way catalyst. In order to cope with this problem, in a conventional engine with a mechanical supercharger, secondary air is injected into the upstream side of the three-way catalyst to promote the purification of HC (Japanese Patent Application Laid-open No. Sho 61). -250352). SUMMARY OF THE INVENTION It is an object of the present invention to provide an engine with a mechanical supercharger which eliminates the problem of HC during low rotation and high load operation without using secondary air.

[0007]

In order to achieve the above-mentioned object, the present invention adopts the following construction.

In an engine with a mechanical supercharger having a mechanical supercharger linked to an output shaft of the engine and driven by the output of the engine, an engine for purifying exhaust gas provided in an exhaust system of the engine is provided. A three-way catalyst, operating state detecting means for detecting an operating state of the engine, and a mixture which is taken in by the engine when the operating state of the engine is in a low speed and a high load state by receiving a signal from the operating state detecting means. Air-fuel ratio control means for performing feedback control so that the air-fuel ratio of air becomes a stoichiometric air-fuel ratio, and a valve overlap period change for changing an overlap period in which the opening period of the intake valve and the opening period of the exhaust valve overlap. Means for receiving the signal from the operating state detecting means, the overrun period when the operating state of the engine is in a low rotation state and a high load state, and the over period in a low rotation state and a low load state. Valve overlap control means for controlling the overlap change means so that the overlap period is increased even when the operation state of the engine is in a steady operation state. The supercharger is set to perform supercharging when the operating state of the engine in which the overlap period is increased is low rotation and high load.

[0009]

The feedback control of the air-fuel ratio of the air-fuel mixture to the stoichiometric air-fuel ratio eliminates the lack of oxygen in the HC purification reaction in the three-way catalyst. That is,
If the air-fuel ratio is the stoichiometric air-fuel ratio, there is no excess or deficiency of oxygen in the HC purification reaction in the three-way catalyst.

[0010] Further, since the valve scavenging in the cylinder is promoted by the expansion of the valve overlap period in the low-rotation and high-load operation state in which the supercharging is performed, the temperature in the cylinder is reduced. Can be suppressed.
Of course, by supercharging, it is possible to secure high output at low rotation and high load,

[0011]

Embodiments of the present invention will be described below with reference to the accompanying drawings. In FIGS. 1 and 2, reference numeral 1 denotes an engine, and
It is a so-called V-type six-cylinder engine having left and right bank portions 2L, 2R forming a V-shape with each other, and three cylinders 4 arranged in series for each of the left and right bank portions 2L, 2R. . In the following, members constituting left and right bank portions 2L, 2R or members related to each bank portion 2L, 2R correspond to the left bank portion 2L or the right bank portion 2R, and have reference characters "L", While “R” is added and illustrated, in the description of these members, the addition of reference numerals “L” and “R” is omitted unless it is particularly necessary.

The engine 1 will be described in detail. The engine 1 has a cylinder block 3, and each cylinder 4 has a combustion chamber 8 formed by a piston 6 inserted into a cylinder 5 and a cylinder head 7. . In the cylinder head 7, first and second two intake ports 9, 10 and first and second two exhaust ports 11, 12, both of which open to the combustion chamber 8, are formed. As shown in FIG. 2, the first and second intake ports 9 and 10
A first intake valve 13 and a second intake valve 14 are provided, respectively, and a first exhaust valve 15 and a second exhaust valve 16 are provided at the first and second exhaust ports 11 and 12, respectively. Have been.

That is, the engine 1 is a four-valve engine in which each cylinder 4 includes two intake valves 13 and 14 and two exhaust valves 15 and 16, and each of the valves 13 to 1
The valve system 17 for opening and closing the valve 6 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 used for the intake valves 13 and 14, the second camshaft 19 is used for the exhaust valves 15 and 16, and these first and second camshafts 18 and 19 have A cam pulley 20 (see FIG. 2, the exhaust valve cam pulley is not shown) is provided at the shaft end.
As is known, the re-bar 20 is linked to an engine output shaft (crankshaft) 23 via a timing belt 22, and the intake valves 13, 14 or the exhaust valves 15, 1
6 is opened and closed at a predetermined timing in synchronization with the rotation of the engine output shaft 23.

The first camshaft 18 is provided with a variable valve timing mechanism 24 (variable valve timing for intake valve) for changing the phase of the first camshaft 18 with respect to the cam pulley 20 for intake valve. The second camshaft 19 is provided with a variable valve timing mechanism (variable valve timing mechanism for exhaust valve, not shown) for changing the phase of the second camshaft 19 with respect to the cam pulley for exhaust valve. . 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
It is arranged facing the center of.

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, the intake system 40 of the engine 1 will be described in detail with reference to FIG. Intake system 40
Is a common intake pipe 41 sequentially connected from the upstream side to the downstream side, and the left and right surge tanks 34L, 34R,
The common intake pipe 41 is provided with the air cleaner 4 in order from the upstream side to the downstream side.
2, an air flow meter 43, a throttle valve 44, the screw-type supercharger 32, and the intercooler 33 are provided. The common intake pipe 41 has a first bypass passage 45 for bypassing the throttle valve 44 and a second bypass passage 46 for bypassing the screw supercharger 32 and the intercooler 33. Have been.

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).

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

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

The engine 1 has first and second two external EGR passages 65 and 66, and a first external EGR passage 6
5 and the second external EGR passage 66, the first
The passage diameter of the external EGR passage 65 is reduced, and the second external
The passage diameter of the GR passage 66 is made large, and as described later, the first external EGR passage 65 is used in a low load region,
On the other hand, the second external EGR passage 66 is used in a high load area.

The first external EGR passage 65 has one end connected to the exhaust manifold 61L or 61R and the other end connected to the first intake port 9. And
The first external EGR passage 65 is provided with a first EGR valve 67 and a collecting chamber 68 in order from the one end side to the other end side, and the collecting chamber 68 is connected to the common intake pipe via a bypass air pipe 69. The bypass air pipe 69 is connected to the bypass air-conditioning control valve 7.
0 is interposed. On the other hand, the second external EGR passage 6
6 is connected at one end to a common exhaust pipe 62 downstream of the catalytic converter 63 and at the other end to a common intake pipe 41 upstream of the supercharger 32 (downstream of the throttle valve 44). It is connected to the. Then, the second external EGR
In the passage 66, from the one end side to the other end side,
Carbon trap 71, EGR cooler 72, second EGR
A valve 73 is provided.

Engine Specifications Specific specifications of the engine 1 are as follows. (1) Engine type: V6, DOHC4 valve (2) Bank angle between left bank and right bank: 90 degrees (3) Total displacement: 1496 cc (4) Cylinder bore diameter: 63 mm diameter (5) Piston stroke: 80 mm (6) Compression ratio (ε): 10 (7) Valve clamping angle between intake and exhaust valves: 30 degrees (8) Turbocharger: screw type (pressure ratio (2.5) (9) Intercooler outlet temperature: 60 ° C (10) Fuel used: Regular gasoline (octane number = 9)
1)

That is, in the engine 1, the bore diameter of the cylinder 5 is small, and the piston stroke is a long stroke larger than the bore. The compression ratio is set to a high compression ratio, and the supercharging pressure is set to a high supercharging pressure.

The engine 1 is provided with a control unit U shown in FIG. 4, and the control unit U is constituted by, for example, a microcomputer and, as is well known, C
A PU, a ROM, a RAM, and the like are provided. 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 is a throttle valve 4
4 is to detect the opening degree (engine load). The sensor 81 detects the engine speed. The sensor 82 detects the rotation speed of the supercharger 32. On the other hand, a control signal is output from the control unit U to the injectors 56, 57 and the like.

The contents of various controls performed by the control unit U will be described below. Control of the Shutter Valve 54 The shutter valve 54 has, for example, an engine speed of 3.000.
It is closed in the low rotation range and open in the high rotation range across rpm. That is, in the low rotation region where the intake air amount is small, the second independent intake passage 53 is closed and the first independent intake passage 5 is closed.
Inspiration is performed using only two. On the other hand, in the high rotation region where the intake air amount is large, the first and second independent intake passages 5 are provided.
Intake is performed using both 2 and 53.

Valve Timing Control Based on the map shown in FIG.
To III, the following valve timing is set. Region I (low load, low rotation region) The opening timing of the exhaust valves 15, 16 is before bottom dead center (BBD
C) The angle is set to 70 degrees (crank angle, the same applies hereinafter), and the closing timing is set to 10 degrees after the top dead center (ATDC). On the other hand, when the opening timing of the intake valves 13 and 14 is before the top dead center (B
TDC) is set to 10 degrees, and the closing timing is after the bottom dead center (A
BDC) is set to 100 degrees. Region II (the engine speed is 3,000 rpm or less) The opening timing of the exhaust valves 15, 16 is before the bottom dead center (BBD
C) The angle is set to 70 degrees (crank angle, the same applies hereinafter), and the closing timing is set to 10 degrees after the top dead center (ATDC). On the other hand, when the opening timing of the intake valves 13 and 14 is before the top dead center (B
TDC) is set to 40 degrees, and the closing timing is after the bottom dead center (A
(BDC) 70 degrees. Region III (the engine speed is higher than 3,000 rpm) The opening timing of the exhaust valves 15 and 16 is before the bottom dead center (BBD
C) 40 degrees (crank angle, the same applies hereinafter), and the closing timing is 40 degrees after top dead center (ATDC). On the other hand, when the opening timing of the intake valves 13 and 14 is before the top dead center (B
TDC) is set to 40 degrees, and the closing timing is after the bottom dead center (A
(BDC) 70 degrees.

That is, the intake valves 13 and 14 are set so as to close slowly in all regions, and in particular, in the region I, the intake valves 13 and 14 are extremely closed slowly. Also, exhaust valve 1
In the so-called overlap in which both the valves 5 and 16 and the intake valves 13 and 14 are open, the overlap amount is small in the region I, the overlap amount is large in the region II, and the overlap amount is large in the region II. In III, the overlap amount is maximized. The above is summarized as follows.

Region I (Low Load, Low Rotation Region) The overlap amount is “small”, and the intake late closes extremely. Region II (engine speed is 3,000 rpm or less) Overlap amount is "large", intake late closing. Region III (engine speed higher than 3,000 rpm) Overlap amount is "maximum", intake late closing.

EGR Control Based on the map shown in FIG. 9, the following EGR control is performed on the three regions I, IV, and V (control of the first and second EGR valves 67 and 73). Region I (Low Load, Low Rotation Region) Both the first and second EGR valves 67 and 73 are fully closed. Region IV (1/2 load or less) The second EGR valve 73 is closed, and the first EGR valve 67 adjusts the EGR rate. That is, the first
Using the external EGR passage 65, the exhaust gas is recirculated (EG
R) is performed. Region V (supercharging region larger than 1/2 load and including full load) The first EGR valve 67 is closed, and the EGR rate is adjusted by the second EGR valve 73. That is, EG
Exhaust gas recirculation (EGR) is performed using the second external EGR passage 66 having the R cooler 72. The EGR rate in region III is constant or increases as the load increases.

If the above EGR control and the valve timing control are combined, FIG. 1 combining FIG. 5 and FIG.
As shown in FIG. 0, regions I and VI to IX are divided into five regions, but regions I, VI and VI in which combustion stability, fuel consumption or occurrence of knocking are problematic.
I will be described in detail below, and in these regions, the engine 1 is in the following control state.

Region I (Extremely Light Load Region, That is, Low Load and Low Rotation Region) In this region I where combustion tends to be unstable,
Since the GR is prohibited and the overlap amount is set to "small" as described above, the residual gas remaining in the combustion chamber 8 becomes small, and the combustion stability can be ensured. Further, in this region I where the opening of the throttle valve 44 is small, the intake valves 13 and 14 are extremely lately closed as described above, so that the pumping loss in this region I can be reduced.

Region VI (Light Load Region, That is, Low Rotation, Low Load Region) In this region VI where the engine speed is 3,000 rpm or less and 負荷 load or less, the combustion is relatively stable, and the overlap amount is small. In this case, the internal EGR is performed in addition to the EGR from the first external EGR passage 65. That is, by setting the overlap amount to “large”, the internal EGR in which a large amount of residual gas remains in the combustion chamber 8 is performed. The internal EGR is at a high temperature, and the upstream end of the first external EGR passage 65 is connected to the exhaust manifold 61 so that the exhaust gas discharged from the engine 1 is cooled before the exhaust gas is cooled by the exhaust system 60.
Since the gas is recirculated to the engine 1 through the external EGR passage 65, the temperature of the EGR gas from the first external EGR passage 65 is also relatively high. In addition, since the intake valves 13 and 14 are closed late, the pumping loss in the region VI can be reduced by the intake late closing and the high temperature EGR gas.

Region VII (Low-Rotation, High-Load (Including Full-Load) Region) This region VII in which the engine speed is 3,000 rpm or less and larger than 1/2 load is also a supercharging region. Therefore, in this region VII, the scavenging in the combustion chamber 8 is promoted by setting the overlap amount to “large”,
An increase in the in-cylinder temperature (the temperature in the cylinder 4) due to the internal EGR is suppressed. In addition, the intake valves 13 and 14 are closed late, and the effective stroke of the piston 6 during the compression stroke is shortened, so that the rise in the in-cylinder temperature accompanying the compression of the intake air is reduced. Further, in this region VII, E
Since the cooled EGR gas is recirculated (cold EGR) using the second external EGR passage 66 provided with the GR cooler 72, the rise of the in-cylinder temperature is also suppressed by the cold EGR. Will be.

Since the upstream end of the second external EGR passage 66 is connected to the downstream of the exhaust system 60, the exhaust system 6
The exhaust gas cooled in the second external EGR passage 66
Will be introduced. Since the downstream end of the second external EGR passage 66 is connected to the upstream side of the intercooler 33, the second external EGR passage 66 is returned to the intake system 40 through the second external EGR passage 66. EGR gas is inter-
It is cooled again by the cooler 33. From the above, the temperature of the external EGR using the second external EGR passage 66 is thoroughly reduced. As described above, in this region VII, the in-cylinder temperature is lowered by scavenging, the intake valves 13 and 14 are slowly closed, and the cold EGR is performed, so that knocking is suppressed in the region VII and NO in exhaust gas is reduced. It is designed to reduce _X.

Air-fuel ratio (A / F) control In the engine 1, feedback control of a conventionally known air-fuel ratio is performed in all regions. In the feedback control of the air-fuel ratio, the target air-fuel ratio in the region VI (light load region, that is, low rotation speed, low load region) shown in FIG. Also has a large air-fuel ratio A / F = 20
A lean air-fuel ratio in the vicinity is set.
In II (low rotation, high load (including full load) region), the stoichiometric air-fuel ratio (λ = 1) is set as the target air-fuel ratio.

In the engine 1, since the shutter valve 54 is located far from the second intake port 10, the following effects are obtained in scavenging. That is, in a region VII (supercharging region) shown in FIG. 10, the shutter valve 54 is in a closed state. However, the shutter valve 54 does not completely close the second independent intake passage 53, but allows some leakage. Therefore, in the region VII, when the supercharged fresh air is accumulated in the second independent intake passage 54 and the second intake port 10 and the second intake valve 10 is opened, the second independent intake passage is opened. The compressed fresh air in the passage 54 and the second intake port 10 enters the combustion chamber 8, and the fresh air causes the second fresh air.
Burned gas around the intake port 10 can be actively scavenged.

While the embodiment of the present invention has been described above, the present invention includes the following modifications. (1) In the above embodiment, the supercharging is performed with a pressure ratio = 2.5, but a smaller pressure ratio may be used. When the pressure ratio is small,
The need to perform the above-described late closing of intake air is reduced, and the need for cold EGR is also reduced.

(2) In the above-described embodiment, an extremely large compression ratio of "compression ratio = 10" is set in spite of the supercharged engine. It may be a compression ratio. Also in this case, the necessity of performing the above-described late closing of intake air is reduced and the necessity of cold EGR is also reduced.

(3) In the air-fuel ratio control in the region VII (the supercharging region shown in FIG. 10), the target air-fuel ratio may be set to an air-fuel ratio (lean air-fuel ratio) larger than the stoichiometric air-fuel ratio.

[0042]

According to the present invention, the problem of purifying HC due to blow-by of intake air in a supercharging region, which is a problem specific to an engine having a mechanical supercharging, can be solved without introducing secondary air. Can be. In addition, while suppressing knocking,
Sufficient high output can be secured by supercharging.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of an engine according to an embodiment.

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

FIG. 3 is an expanded view showing an intake system and an exhaust system of the engine according to the embodiment.

FIG. 4 is an overall system diagram of various controls of the engine according to the embodiment.

FIG. 5 is a control map of a shutter valve arranged in an intake passage.

FIG. 6 is an explanatory diagram of the operation of variable valve timing (region I).

FIG. 7 is an explanatory diagram of an operation of variable valve timing (region I).
I).

FIG. 8 is an explanatory diagram of an operation of variable valve timing (region II).
I).

FIG. 9 is a control map for EGR.

FIG. 10 is a control map in which shutter valve control and EGR control are combined.

[Explanation of symbols]

 Reference Signs List 1 engine 23 crankshaft (engine output shaft) 24 variable valve timing means 25 spark plug 32 mechanical supercharger 56 upstream injector 57 downstream injector 80 throttle opening sensor 81 engine speed sensor U control unit VII supercharging area (Low rotation, high load area)

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) F02D 41/02 305 F02D 41/02 301 F02D 13/02

Claims (1)

(57) [Claims] 1. An engine equipped with a mechanical supercharger having a mechanical supercharger linked to an output shaft of the engine and driven by the output of the engine, wherein an exhaust gas purification system provided in an exhaust system of the engine is provided. Three-way catalyst, operating state detecting means for detecting the operating state of the engine, and receiving the signal from the operating state detecting means, the engine is inhaled when the operating state of the engine is in a low rotation and high load state. the air-fuel ratio of the air-fuel mixture so that becomes the stoichiometric air-fuel ratio Fi
The air-fuel ratio control means for performing feedback control, and an automatic valve in which the opening period of the intake valve and the opening period of the exhaust valve overlap.
Valve overlap changing means for changing the overlap period; and receiving a signal from the operating state detecting means, wherein the engine is in the low rotation and high load state when the engine is in the low rotation and high load state. And a valve overlap control means for controlling the overlap changing means so as to have a large overlap period even when the operation state of the engine is in a steady operation state. And wherein the supercharger is set to perform supercharging when the operating state of the engine for which the overlap period is increased is low rotation and high load. Engine with charge.