JP3285908B2 - Engine with turbocharger - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a supercharged engine having a supercharger in an intake system.

[0002]

2. Description of the Related Art A supercharged engine in which the engine output is increased by supercharging has a problem that the heat load inside the engine is large.
As disclosed in JP-A-327, the air-fuel ratio of the air-fuel mixture taken by the engine is made leaner than the stoichiometric air-fuel ratio in a supercharging region where the supercharger exhibits its supercharging ability.
There is known an engine in which the internal temperature of the engine (the temperature of a valve bridge or the like) is reduced while improving the fuel consumption rate.

[0003]

However, as is apparent from FIG. 6, the effect of improving the fuel consumption rate with the lean air-fuel ratio is, for example, according to FIG. 6, A / F = 15.
Saturation occurs in the vicinity, and even if the air-fuel ratio is further reduced, no significant improvement in the fuel consumption rate can be obtained. In addition, FIG.
This is data under the same load (when the same engine-generated torque is obtained).

According to the above fact, even if the air-fuel ratio in the supercharging region is made leaner than A / F = 15, the effect associated with the leaning of the air-fuel ratio is mainly due to the decrease in the engine internal temperature. It will be limited to.

Accordingly, an object of the present invention is to provide a higher effect of lowering the internal temperature of the engine than the leaning of the air-fuel ratio without impairing the effect of improving the fuel consumption rate accompanying the leaning of the air-fuel ratio. It is an object of the present invention to provide a supercharged engine.

[0006]

Means for Solving the Problems In order to achieve the above technical object, the present invention has the following constitution. That is,

On the premise of a supercharged engine having a supercharger in an intake system, an EGR means for recirculating exhaust gas of the engine to an intake system via an external conduit, and an operation state detection for detecting an operation state of the engine Means for receiving a signal from the operating state detecting means, and when the operating state of the engine is in a supercharging region in which the supercharging capability of the turbocharger is exhibited, the air-fuel ratio of the air-fuel mixture to be taken in by the engine increases the fuel consumption. Air-fuel ratio control means for controlling the air-fuel ratio so as to attain a lean air-fuel ratio at which the rate improving effect is saturated; and a supercharging capability of the supercharger when an operation state of the engine is received from a signal from the operation state detection means. EGR means for recirculating the exhaust gas of the engine to the intake system via an external EGR conduit when the engine is in the supercharging region. The said Together is performed air-fuel ratio control as to the lean air-fuel ratio by the ratio control means, said E
The exhaust gas is recirculated to the intake system via the external EGR conduit by the GR means.

[0008]

According to FIG. 6, the supercharging pressure is increased from 600 mmHg to 700 mm.
mmHg to increase the air / fuel ratio from A / F = 15.1 to A / F =
When the air-fuel ratio is reduced to 16.2, the effect of improving the fuel consumption rate due to the lean air-fuel ratio is small, and the effect of reducing the temperature inside the engine (valve bridge) is about 3.5 ° C. . On the other hand, similarly, boost pressure is increased from 600 mmHg to 700 mmHg.
When the EGR rate is increased from 5.5% to 13%, the effect of reducing the temperature inside the engine (valve bridge) is about 7 ° C., which is about 2 ° C. more than the case where the air-fuel ratio is made lean.
The effect is doubled. Incidentally, the effect of reducing the exhaust gas temperature by leaning the air-fuel ratio is about 30 ° C., while the effect of reducing the exhaust gas temperature by EGR is about 40 ° C. According to FIG. 7, the EGR is more than the leaning of the air-fuel ratio.
It is understood that the large NO _X reduction effect in the exhaust gas. Here, in the figure, the solid line A indicates NO _X when the EGR gas is recirculated. On the other hand, the broken line B indicates EGR
Shows the NO _X when no reflux gas. Solid line A and broken line B indicate NO _X under the same load, and solid line A
Is an air-fuel ratio Li - is representative of the NO _X when the refluxing weight of EGR gas equivalent to the excess air required for the down.

Therefore, according to the configuration of the present invention,
Air-fuel ratio of Li - down of only it is possible to reduce the large engine internal temperature than to lower the engine internal temperature, also it is possible to greatly reduce the NO _X in the exhaust gas. In other words, if the same effect of lowering the internal temperature of the engine is obtained, the amount of the EGR gas is smaller than the amount of air required to make the air-fuel ratio lean. A supercharger having a smaller capacity is sufficient as compared with the capacity of the supercharger required when the internal temperature of the engine is lowered only by leaning.

[0010]

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 is provided with a variable valve timing mechanism 24 (variable valve timing mechanism 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 area below a crank chamber 27 for housing 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 mechanically driven by the rotational force of a crankshaft 23 is provided in a central bank space 31 sandwiched between the left and right bank portions 2L and 2R. 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.

In the first bypass passage 45, an ISC valve 47 is interposed.
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 schematically shown 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 has first and second two
Two external EGR passages (both are composed of external piping)
65, 66 are provided, and when the first external EGR passage 65 is compared with the second external EGR passage 66, the first external EGR passage 65 is provided.
The passage diameter of the GR passage 65 is made small, and the passage diameter of the second external EGR passage 66 is made large.
The external EGR passage 65 is used in a low load region, while the second
The 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 above engine 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)

The engine body 1 has 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 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 and 57, the first and second EGR valves 67 and 73, and the like.

The details of the EGR control and the air-fuel ratio control performed by the control unit U will be described below. EGR Control and Air-Fuel Ratio Control Based on the map shown in FIG.
The following EGR control (control of the first and second EGR valves 67 and 73) and air-fuel ratio control (control of the amount of fuel supplied by the injectors 56 and 57) are performed on .about.IV. still,
Since the details of the air-fuel ratio control are the same as those in the related art, only the target air-fuel ratio in each of the regions I to IV is shown, and the description of the specific air-fuel ratio control is omitted.

Region I (Very Low Load, Very Low Rotation Region: Nearly Idle Region) Both the first and second EGR valves 67 and 73 are fully closed. The target air-fuel ratio is set to the stoichiometric air-fuel ratio (λ = 1).

Region II (Low Load, Low Rotation Region) Exhaust gas recirculation (EG
R) is performed, while the second EGR valve 73 is fully closed. The target air-fuel ratio is a stoichiometric air-fuel ratio (λ = 1).

Region III (All Regions of Medium Load and High Speed) In this region III, the EGR control by the second EGR valve 73 is performed on the higher load side than the line C shown in FIG. On the other hand, at the lower load side than the line D shown in FIG.
The EGR control by the EGR valve 67 is performed, and the first EGR valve 67 and the second EGR valve 73 are located in a region sandwiched between the line C and the line D (a region shown by oblique lines in the drawing).
And EGR control is performed in combination.

That is, in the region III, on the relatively low load side, the first EGR valve 67 is used to recirculate the relatively high temperature EGR gas. On the other hand, on the relatively high load side, the second
The EGR valve 73 is used to cool the low-temperature EGR gas (
EGR) is returned. The target air-fuel ratio is leaner than the stoichiometric air-fuel ratio, for example, A / F = 1.
6 is assumed.

That is, in this region III, on the relatively low load side, the first external EGR passage 65
The upstream end is connected to the exhaust manifold 61, and the exhaust gas discharged from the engine body 1 is returned to the engine body 1 through the first external EGR passage 65 before being cooled in the exhaust system 60. The EGR gas from the first external EGR passage 65 has a relatively high temperature, and it is possible to reduce the pumping loss in the area II by using the EGR gas.

In this region III, on the relatively high load side, the use of the second EGR valve 73 and the use of the second external EGR passage 66 having the EGR cooler 72 as described above are used. The recirculation of cold EGR gas (cold EGR) is performed. Further, since the upstream end of the second external EGR passage 66 is connected to the downstream of the exhaust system 60, the exhaust gas cooled in the exhaust system 60 is introduced into the second external EGR passage 66, 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
EGR after being returned to the intake system 40 through the R passage 66
The gas will be cooled again by the intercooler 33.

Therefore, on the relatively high load side in the region III, the cold EGR suppresses an increase in the engine internal temperature (valve bridge temperature) caused by setting the target air-fuel ratio to A / F = 16. become. Matako - increase in the exhaust gas temperature by field EGR is suppressed, so that further NO _X in the exhaust gas is reduced. This is effective in increasing the reliability of the engine in relation to the high compression ratio and high supercharging in the engine.

Region IV (High Load and Low Rotation Region) 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 target air-fuel ratio is set to A / F = about 13 from the viewpoint of emphasizing the output.

Therefore, in this region V, the internal temperature (valve bridge temperature) of the engine body 1 which is set to a high supercharging and a high compression ratio is lowered by supplying the cold EGR as described above, or It becomes possible to lower the exhaust gas temperature. Further, it becomes possible to reduce NO _X in the exhaust gas.

Although the embodiment of the present invention has been described above, the present invention is not limited to this embodiment. For example, the second external EGR passage may be constituted by a long tube.
Exhaust gas (EGR gas) while passing through this long external conduit
Heat is largely dissipated (a large air cooling effect is obtained).

[0036]

As is apparent from the above description, according to the present invention, while the effect of improving the fuel consumption rate is ensured, especially in the high-speed and high-load region of the engine where the heat load is a major problem, Leaning the fuel ratio alone can lower the internal temperature of the engine more than reducing the internal temperature of the engine, and can increase the effect of reducing NOx in exhaust gas. Therefore, if the same effect of lowering the internal temperature of the engine can be obtained, the supercharger having a smaller capacity than the supercharger required when lowering the internal temperature of the engine only by leaning the air-fuel ratio. Can be fitted, which can further improve the fuel consumption rate.

[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 map for EGR control and air-fuel ratio control.

FIG. 6 is a graph showing a relationship between an air-fuel ratio and an EGR rate with a valve bridge temperature and the like.

FIG. 7: NO in exhaust gas with respect to air-fuel ratio and EGR rate
₉ is a graph showing an _X reduction effect.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 engine body 4 cylinder 5 cylinder 6 piston 8 combustion chamber 23 engine output shaft 25 spark plug 32 mechanical supercharger 56, 57 injector (fuel injection valve) 65 first external EGR passage (for low load) 66 second external EGR Passageway (for high load) 67 EGR control valve for low load 73 EGR control valve for high load 80 Edge load sensor 81 Engine speed sensor U Control unit

Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI F02D 23/00 F02D 23/00 EJ 41/04 305 41/04 305D F02M 25/07 550 F02M 25/07 550C 580 580B 580E (72) Invention Person Kenji Kashiyama 3-1, Fuchi-cho, Fuchu-cho, Aki-gun, Hiroshima Prefecture Inside Mazda Co., Ltd. (72) Inventor Junzo Sasaki 3-1, Shin-chi, Fuchu-cho, Aki County, Hiroshima Prefecture Mazda Co., Ltd. JP-A-4-17755 (JP, A) JP-A-3-117648 (JP, A) JP-A-3-23327 (JP, A) JP-A-56-124664 (JP, A) JP-A-4-17743 (JP, A) JP-A-61-138844 (JP, A) JP-B-62-40538 (JP, B1) (58) Fields investigated (Int. Cl. ⁷ , DB name) F02D 13/00-27/02 F02D 41/00-41/40 F02D 43/00-45/00 F02M 25/07

Claims (4)

(57) [Claims] 1. An engine with a supercharger having a supercharger in an intake system, an EGR means for recirculating exhaust gas of the engine to an intake system via an external conduit, and an operation state detection for detecting an operation state of the engine. Means for receiving a signal from the operating state detecting means, and when the operating state of the engine is in a supercharging region in which the supercharging capability of the turbocharger is exhibited , the air-fuel ratio of the air-fuel mixture sucked by the engine increases the fuel consumption. Air-fuel ratio control means for controlling the air-fuel ratio so as to attain a lean air-fuel ratio at which the rate improving effect is saturated; and a supercharging capability of the supercharger when an operation state of the engine is received from the signal from the operation state detection means. when in the supercharging region exerts, comprising an EGR means for recirculating exhaust gas from the engine to the intake system through the external EGR conduit, the high rotation and Komake engine to be the supercharging region
Also in the load area, the air-fuel ratio control means
When the air-fuel ratio control is performed to obtain the lean air-fuel ratio
In addition, the exhaust gas is supplied to the external EGR by the EGR means.
An engine with a supercharger , which is returned to an intake system via a conduit . 2. The air-fuel ratio according to claim 1, wherein the lean air-fuel ratio at which the fuel efficiency improving effect is saturated is substantially A / F.
= 15-16, the engine with a supercharger. 3. The engine according to claim 1, further comprising an intercooler in an intake system of the engine, wherein a downstream end of the external EGR conduit is connected to an upstream side of the intercooler. Engine with charge. 4. The engine with a supercharger according to claim 1 , wherein an EGR cooler is interposed in the external EGR conduit.