JP2022136516A - engine - Google Patents

Abstract

To provide an engine capable of suppressing occurrence of abnormal combustion while enhancing fuel consumption performance.SOLUTION: In an engine including an engine body 1 having a cylinder 2, and a turbosupercharger 59, a geometric compression ratio of each of the cylinders 2 is set to be 11 or more, an open timing of an intake valve 8 is set to be a crank angle of 270 degrees or more, and in a high load region, the intake valve 8 is opened before an exhaust top dead center and is closed after an intake bottom dead center, and an exhaust valve 9 is closed after the exhaust top dead center, and a rate of the crank angle from a valve open start timing of the intake valve 8 to a valve close timing of the exhaust valve 9 with respect to the crank angle from the valve open start timing of the intake valve 8 to the exhaust top dead center is 1.77 or more and 3.7 or less.SELECTED DRAWING: Figure 1

Description

The present invention provides an engine body in which cylinders are provided with an intake port, an exhaust port, an intake valve and an exhaust valve, an intake passage and an exhaust passage connected to the engine body, and a turbine and intake passage provided in the exhaust passage. It relates to an engine with a turbocharger including a compressor provided.

2. Description of the Related Art In an engine mounted on an automobile or the like, a supercharger is provided to supercharge intake air in order to improve output performance. For example, Patent Literature 1 discloses an engine having a mechanical supercharger that is driven by an engine body.

JP 2019-39393 A

In addition, increasing the geometric compression ratio of the cylinder is conceivable in order to improve fuel efficiency. From this, it is considered that if a supercharger is provided in an engine having a cylinder with a relatively high geometric compression ratio, it is possible to increase the output and improve the fuel consumption performance. However, if this configuration is simply adopted, there is a problem that abnormal combustion is likely to occur.

Specifically, when the engine load is high and the temperature in the cylinder is high, the high-temperature, high-pressure air-fuel mixture containing the intake air supercharged by the supercharger is excessively compressed in the cylinder, causing premature ignition and Knocking may occur.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an engine capable of suppressing the occurrence of abnormal combustion while improving fuel efficiency.

In order to solve the above problems, the engine of the present invention comprises an engine body in which a cylinder is provided with an intake port, an exhaust port, an intake valve and an exhaust valve, and an intake passage and an exhaust passage connected to the engine body. , an engine comprising a turbocharger including a turbine provided in the exhaust passage and a compressor provided in the intake passage, wherein the geometric compression ratio of the cylinder is set to 11 or more, The valve opening period of the intake valve is set to 270 degrees crank angle or more, and in a high load region where the engine load is equal to or greater than a predetermined reference load, the intake valve opens before exhaust top dead center and intake bottom dead center. The exhaust valve closes after exhaust top dead center, and the crank angle from the opening start timing of the intake valve to the closing timing of the exhaust valve is set as a valve overlap period, and the intake valve The ratio of the valve overlap period to the intake valve opening advance amount is 1.77 or more and 3.7 when the crank angle from the valve opening start timing to the exhaust top dead center is the intake valve opening advance amount. It is characterized in that the intake valve and the exhaust valve are opened and closed as follows.

According to the present invention, the geometric compression ratio of the cylinder is set to a high value of 11 or more, and the engine is provided with a turbocharger, so that the output of the engine can be increased and the fuel efficiency can be improved. . Moreover, the opening period of the intake valve is set to a long period of 270 degrees crank angle or more, and the intake valve and the exhaust valve are opened and closed as described above in the high load range, thereby suppressing the occurrence of abnormal combustion. .

Specifically, the intake valve is configured to close after the intake bottom dead center in the high load region. Therefore, the effective compression ratio of the cylinder can be lowered to keep the temperature and pressure of the air-fuel mixture low near the compression top dead center. Therefore, it is possible to suppress pre-ignition (premature ignition) in which the air-fuel mixture in the cylinder self-ignites before the assumed timing.

Further, in a high load region, the intake valve is opened before exhaust top dead center and the exhaust valve is closed after exhaust top dead center. In other words, a valve overlap is realized in which the intake valve and the exhaust valve are both opened for a predetermined period across the exhaust top dead center. Therefore, it is possible to improve the scavenging performance of the cylinder and reduce the amount of high-temperature burned gas remaining in the cylinder. Therefore, after the mixture starts to burn, it is possible to prevent the mixture from being locally overheated and overpressured in the cylinder, and it is possible to suppress the occurrence of knocking. Moreover, the opening period of the intake valve is set to a long period of 270 degrees crank angle or more. Therefore, the intake valve can be opened sufficiently early before exhaust top dead center and closed sufficiently late after intake bottom dead center. is sufficiently ensured, the effective compression ratio can be reliably reduced, and both pre-ignition and knocking, that is, the occurrence of abnormal combustion can be suppressed.

Furthermore, based on the research by the inventors of the present application, if the ratio of the valve overlap period to the intake valve opening advance amount is set to 1.77 or more and 3.7 or less, the occurrence of knocking can be suppressed and the fuel consumption performance can be improved. I know it can go higher. On the other hand, in the present invention, the intake valve and the exhaust valve are configured to open and close so that the ratio is 1.77 or more and 3.7 or less. Therefore, it is possible to reliably suppress abnormal combustion and improve fuel efficiency performance.

Here, if the ratio of the valve overlap period to the intake valve opening advance amount is set in the range of 1.9 or more and 2.8 or less in the range of 1.77 to 3.7, the fuel consumption performance is improved. I know it will definitely get higher.

Therefore, in the above configuration, preferably, in the high load region, the intake valve and the The exhaust valve opens and closes (claim 2).

Further, in the above configuration, preferably, the engine body has a plurality of cylinders and a plurality of exhaust ports corresponding to each of the cylinders, and the exhaust passage is provided for one or more of the cylinders having discontinuous exhaust strokes. The turbine has a plurality of independent exhaust passages each communicating with an exhaust port, the turbine includes a turbine body having a plurality of blades that rotate with the energy of the exhaust, and a turbine housing that houses the turbine body, The inner space of the turbine housing is partitioned into a plurality of intake passages formed along the outer periphery of the turbine body and aligned in the rotational axis direction of the turbine body in a portion from the upstream end to the turbine body, The plurality of independent exhaust passages are connected to different intake passages (Claim 3).

According to this configuration, exhaust interference between independent exhaust passages, that is, between cylinders having continuous exhaust strokes can be suppressed. Therefore, the scavenging performance of each cylinder can be further enhanced, and the occurrence of knocking can be suppressed more reliably.

According to the engine of the present invention, it is possible to suppress the occurrence of abnormal combustion while enhancing fuel efficiency.

1 is a schematic configuration diagram showing an engine according to an embodiment of the present invention; FIG. It is a schematic sectional drawing of a cylinder head. 3 is a block diagram showing a control system of the engine; FIG. 1 is a schematic cross-sectional view of a turbine; FIG. FIG. 5 is a cross-sectional view taken along line VV of FIG. 4; It is a map showing the operating range of the engine. FIG. 4 is a diagram schematically showing valve lifts of an intake valve and an exhaust valve; 4 is a graph showing the relationship between the ratio of valve overlap to the intake valve and the fuel consumption rate.

A preferred embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

(1) Entire Configuration of Engine FIG. 1 is a schematic configuration diagram of an engine E according to an embodiment of the present invention. Note that FIG. 1 is a schematic diagram for explaining the configuration of the engine E, and the length of each passage and the arrangement of each device are different from the actual ones. FIG. 2 is a schematic cross-sectional view of the cylinder head 3, which will be described later. The engine E includes a four-stroke engine body 1, an intake passage 50 through which air (intake air) introduced into the engine body 1 flows, and an exhaust passage 60 through which exhaust gas discharged from the engine body 1 flows. there is The engine E is a multi-cylinder engine in which a plurality of cylinders 2 are formed in an engine body 1. In this embodiment, as shown in FIG. 2, the engine body 1 is an in-line six-cylinder engine having six cylinders 2 arranged in a row. The engine E is mounted on the vehicle as, for example, a driving source of the vehicle.

The engine E is a supercharged engine having a turbocharger 59 . The turbocharger 59 has a turbine 61 provided in the exhaust passage 60 and a turbine 61 provided in the intake passage 50 . The turbine 61 is rotationally driven by the exhaust gas to rotationally drive the compressor 52 . When the compressor 52 is rotationally driven, it supercharges the intake air in the intake passage 50 . As described above, FIG. 1 is a schematic diagram, and the turbocharger 59 is arranged at a position close to one side surface of the engine body 1 .

The engine body 1 has a cylinder block 13 in which a cylinder 2 is formed, a cylinder head 3 covering the cylinder block 13, and a piston 4 inserted into the cylinder 2 so as to be reciprocally slidable. The piston 4 is connected to the crankshaft 15 via a connecting rod, and the crankshaft 15 rotates around its central axis in accordance with the reciprocating motion of the piston 4 . A combustion chamber 5 is formed above the piston 4 .

The geometric compression ratio ε of the cylinder 2a, that is, the volume V1 of the combustion chamber 5 when the piston 4 is at the bottom dead center (the position farthest away from the cylinder head 3), the piston 4 is at the top dead center (when the piston 4 is A ratio (ε=V0/V1) of the volume V0 of the combustion chamber 5 when the combustion chamber 5 is at the closest position to the cylinder head 3 is set to 11 or more. In this embodiment, the geometric compression ratio ε of the cylinder 2 is set to 12.

An injector 11 for injecting fuel into the combustion chamber 5 is attached to the cylinder block 13 . A spark plug 10 is attached to the cylinder head 3 for igniting the air-fuel mixture (air-fuel mixture) in the combustion chamber 5 by spark discharge. The cylinder head 3 includes an intake port 6 for introducing air into the combustion chamber 5 of each cylinder 2, an intake valve 8 opening and closing the intake port 6, and exhaust gas generated in the combustion chamber 5 of each cylinder 2. An exhaust port 7 for derivation and an exhaust valve 9 for opening and closing the exhaust port 7 are provided.

A valve mechanism 18 that drives the intake valve 8 incorporates an intake S-VT 18a capable of changing the opening/closing timing of the intake valve 8. As shown in FIG. Similarly, the valve mechanism 19 for the exhaust valve 9 incorporates an exhaust S-VT 19a capable of changing the opening/closing timing of the exhaust valve 9. As shown in FIG. The intake S-VT 18a (exhaust S-VT 19a) is a so-called phase-type variable mechanism that simultaneously and simultaneously changes the opening timing IVO (EVO) and the closing timing IVC (EVC) of the intake valve 8 (exhaust valve 9). Change only the amount. That is, the valve opening start timing IVO (EVO) and the valve closing timing IVC (EVC) of the intake valve 8 (exhaust valve 9) are changed while the valve opening period is maintained constant. In this embodiment, the open period of the intake valve 8 is maintained at 270°CA (crank angle), and the open period of the exhaust valve 9 is maintained at 250°CA.

The intake passage 50 is provided with an air cleaner 51, a compressor 52, an intercooler 53, a throttle valve 54, and a surge tank 55 in this order from the upstream side. Chilled air is introduced at . The throttle valve 54 is a valve that can open and close the intake passage 50 , and the amount of intake air flowing through the intake passage 50 can be adjusted according to the opening degree of the throttle valve 54 .

The exhaust passage 60 is provided with a turbine 61 and a catalytic converter 63 containing a catalyst such as a three-way catalyst in this order from the upstream side. The detailed structure of the turbine 61 and the exhaust gas flow path from each cylinder 2 to the turbine 61 will be described later.

A bypass passage 65 for bypassing the turbine 61 is provided in the exhaust passage 60 . A downstream end of the bypass passage 65 is connected to a portion of the downstream exhaust passage 68 between the turbine 61 and the catalytic converter 63 . The upstream end of the bypass passage 65 branches into two passages, each of which is connected to two independent exhaust passages 64a and 64b, which will be described later. A waste gate valve 66 for opening and closing the bypass passage 65 is provided. In the example of FIG. 1, each branch passage is opened and closed simultaneously by one wastegate valve 66 .

The engine E is provided with an EGR device 70 that recirculates part of the exhaust gas to the intake air. The EGR device 70 has an EGR passage 71 through which exhaust gas flows, an EGR cooler 72 that cools the EGR gas that flows through the EGR passage 71 , and an EGR valve 73 that opens and closes the EGR passage 71 . In this embodiment, as shown in FIG. 2, an in-head EGR passage 71a forming an upstream end portion of the EGR passage 71 is formed in the cylinder head 3 . The in-head EGR passage 71a communicates with a second in-head exhaust passage 17b, which is formed in the cylinder head 3 to be described later and through which the exhaust gas flows. A part of the exhaust gas flowing through the passage 17b is recirculated to the intake passage 50 as EGR gas.

The engine E is provided with various sensors. Specifically, the cylinder block 13 is provided with a crank angle sensor SN1 for detecting the rotation angle of the crankshaft 15, that is, the engine speed. An airflow sensor SN2 is provided in the intake passage 50 between the air cleaner 51 and the compressor 52 to detect the flow rate of the intake air introduced into each cylinder 2 through this portion. In addition, in a portion of the intake passage 50 between the intercooler 53 and the throttle valve 54 and downstream of the compressor 52, a boost pressure sensor for detecting the pressure of the intake air passing through this portion, that is, the boost pressure, is provided. A pressure sensor SN3 is provided.

(Turbine 61 and Exhaust Gas Flow Path)
Next, the structure of the turbine 61 and the exhaust gas flow path from each cylinder 2 to the turbine 61 will be described. FIG. 4 is a schematic cross-sectional view of turbine 61 in a plane orthogonal to the centerline of rotation of turbine 61 . 5 is a schematic cross-sectional view taken along line VV of FIG. 4. FIG.

As shown in FIG. 1, in this embodiment, the upstream portion of the exhaust passage 60 is branched into two passages, and the exhaust passage 60 includes a first independent exhaust passage 64a and a second independent exhaust passage 64a that constitute the upstream portion. and an independent exhaust passage 64b. Exhaust gas discharged from cylinders 2 whose exhaust strokes are discontinuous is introduced into each independent exhaust passage 64a. In this embodiment, the exhaust ports 7 of the cylinders 2 whose exhaust strokes are discontinuous are gathered in the cylinder head 3, and independent exhaust passages 64a and 64b are connected to the respective gathering portions.

Specifically, the cylinder head 3 is formed with a first in-head exhaust passage 17 a and a second in-head exhaust passage 17 b extending along the direction in which the cylinders 2 are arranged. The six cylinders 2 are designated as a first cylinder 2a, a second cylinder 2b, a third cylinder 2c, a fourth cylinder 2d, a fifth cylinder 2e, and a sixth cylinder 2f in order from one side of the arrangement direction. The first in-head exhaust passage 17a communicates with the exhaust ports 7 of the three cylinders 2 located on one side in the direction in which the cylinders 2 are arranged, that is, the first cylinder 2a, the second cylinder 2b, and the third cylinder 2c. The exhaust ports 7 of these cylinders 2a, 2b and 2c are gathered at a first in-head exhaust passage 17a. On the other hand, the second in-head exhaust passage 17b communicates with the exhaust ports 7 of the three cylinders 2 located on the other side in the arrangement direction of the cylinders 2, that is, the fourth cylinder 2d, the fifth cylinder 2e, and the sixth cylinder 2f. The exhaust ports 7 of these cylinders 2d, 2e, and 2f meet at a second in-head exhaust passage 17b. The first in-head exhaust passage 17 a and the second in-head exhaust passage 17 b are individually opened to one side surface of the engine body 1 . The first in-head exhaust passage 17a is connected to and communicates with the opening of the first in-head exhaust passage 17a, and the second in-head exhaust passage 17b communicates with the opening of the second in-head exhaust passage 17b. connected to and in communication with the portion;

The order of ignition of the six cylinders 2, that is, the order of combustion of the air-fuel mixture in the cylinders 2 is as follows: first cylinder 2a→fifth cylinder 2e→third cylinder 2c→sixth cylinder 2f→second cylinder 2b→fourth cylinder 2d. , and the exhaust stroke is also performed continuously in this order. As a result, the exhaust strokes of the first cylinder 2a, the second cylinder 2b, and the third cylinder 2c communicating with the first in-head exhaust passage 17a are not continuous, and the exhaust strokes of the first independent exhaust passage 64a are not continuous. Exhaust gas discharged from cylinder 2 is introduced. Similarly, the exhaust strokes of the fourth cylinder 2d, the fifth cylinder 2e, and the sixth cylinder 2f are not continuous, and the exhaust gas discharged from the cylinders 2 whose exhaust strokes are not continuous is introduced into the second independent exhaust passage 64b. will be

The turbine 61 is a twin-scroll turbine, and the first independent exhaust passage 64a and the second independent exhaust passage 64b are connected to the turbine 61 independently of each other.

Specifically, the turbine 61 is a so-called radial turbine, and has a plurality of blades 101 on its outer periphery. and a turbine housing 103 that houses the The turbine housing 103 includes an intake portion 104 for introducing exhaust gas inside, and a turbine scroll portion 105 extending from the downstream end of the intake portion 104 along the outer periphery of the turbine body 102 to surround the turbine body 102 over its entire circumference. , and a lead-out portion 106 for leading the exhaust gas after being expanded in the turbine body 102 to the downstream side. A tongue portion 107 is provided at the downstream end of the turbine scroll portion 105 so as to protrude toward the turbine main body 102 and partition the suction portion 104 from the downstream portion of the turbine scroll portion 105 . The turbine scroll portion 105 has a spiral shape, and the flow passage area of the turbine scroll portion 105 decreases toward the tongue portion 107 toward the downstream side.

A bulkhead extending along the outer circumference of the turbine housing 103 is located substantially in the center of the turbine 61 (turbine main body 102) in the rotation axis direction inside the portion of the turbine housing 103 including the intake portion 104 and the turbine scroll portion 105. 110 is provided. The partition wall 110 creates an inner space of a portion of the turbine housing 103 that consists of the intake portion 104 and the turbine scroll portion 105, that is, a portion of the turbine housing 103 from the upstream end in the flow direction of the exhaust gas to the turbine main body 102. It is divided into two intake passages 108108 that are aligned in the rotation axis direction of the turbine 61 (turbine main body 102 ) and extend along the outer circumference of the turbine main body 102 . That is, the inner space is provided with a first intake passage 108a provided on one side of the turbine 61 in the rotation axis direction and a second intake passage 108b provided on the other side. The intake passages 108a and 108b are formed so as to be independent of each other over substantially the entire circumference of the turbine body 102 in the circumferential direction.

The first independent exhaust passage 64a and the second independent exhaust passage 64b are connected to these two intake passages 108a and 108b, respectively. That is, the first independent exhaust passage 64a is connected to the first intake passage 108a, and the second independent exhaust passage 64b is connected to the second intake passage 108b.

With this configuration, in this embodiment, between two cylinders 2 whose exhaust strokes are continuous, the exhaust gas discharged from each cylinder 2 flows through passages independent of each other until it reaches the turbine main body 102. A single downstream exhaust passage 68 that forms a downstream portion of the exhaust passage 60 is connected to the lead-out portion 106 of the turbine 61. After passing through the turbine body 102 , the exhaust gases are all introduced into the common downstream passage portion 56 .

(control system)
FIG. 3 is a block diagram showing the control system of the engine E. As shown in FIG. Each actuator of engine E is controlled by PCM100. A PCM 100 shown in this figure is a microprocessor for overall control of the engine and the like, and is composed of a well-known CPU, ROM, RAM and the like.

Detection signals from various sensors are input to the PCM 100 . For example, the PCM 100 is electrically connected to the crank angle sensor SN1, the airflow sensor SN2, and the supercharging pressure sensor SN3, and information detected by these sensors is sequentially input to the PCM 100. Further, the vehicle equipped with the engine E is provided with an accelerator opening sensor SN4 for detecting the opening of the accelerator pedal operated by the driver who drives the vehicle. Information is also input to PCM 100 sequentially.

The PCM 100 controls each part of the engine E while executing various determinations and calculations based on the input information from each sensor. Specifically, the PCM 100 is electrically connected to the spark plug 10, the injector 11, the throttle valve 54, a wastegate valve 66 (to be described later), the intake S-VT 18a, the exhaust S-VT 19a, the EGR valve 73, and the like. Control signals are output to each of these devices based on the results of calculations and the like.

The PCM 100 controls the spark plug 10 so that the air-fuel mixture is ignited at the ignition timing set for each operating condition, and controls the injector 11 so that the fuel set for each operating condition is injected into the cylinder 2. The throttle valve 54 is controlled so that the amount of intake air set for each operating condition is introduced into the cylinder 2 . In addition, the PCM 100 controls the opening of the wastegate valve 66 so that the boost pressure becomes the value set for each operating condition, and the EGR rate in cylinder 2 becomes the value set for each operating condition. , the EGR valve 73 is controlled. In addition, the PCM 100 controls the intake S-VT 18a and the exhaust S-VT 19a so that the intake valve 8 and the exhaust valve 9 are opened and closed at times set for each operating condition.

(Opening/closing timing of intake valve and exhaust valve in low-speed high-load region)
FIG. 6 is a map showing the operating range of the engine, with the engine speed on the horizontal axis and the engine load on the vertical axis. In the following, the intake valve 8 in a low-speed high-load region A1 in which the engine speed is equal to or lower than a predetermined reference speed N1 in the region A1 shown in FIG. Control of the exhaust valve 9 (control of the intake S-VT 18a and the exhaust S-VT 19a) will be described. The reference rotational speed N1 is set at approximately 1500 rpm, and the reference load T1 is set near the maximum value of the engine load, that is, near full load.

FIG. 7 is a diagram schematically showing the valve lift in the low speed high load region A1. As shown in FIG. 7, in the low-speed high-load region A1, the PCM 100 realizes a valve overlap in which the intake valve 8 and the exhaust valve 9 are both opened for a predetermined period across the exhaust top dead center (TDC). , the intake S-VT 18a and the exhaust S-VT 19a are controlled. That is, the PCM 100 controls the intake S-VT 18a so that the opening timing IVO of the intake valve 8 is on the advanced side of the exhaust top dead center (TDC), and the closing timing EVC of the exhaust valve 9 is The exhaust S-VT 19a is controlled so that the timing is retarded from the exhaust top dead center (TDC).

Further, as shown in FIG. 7, in the low-speed high-load region A1, the PCM 100 is arranged so that the intake valve 8 closes at a timing later than intake bottom dead center (BDC), that is, the closing timing IVC of the intake valve 8 is The intake S-VT 18a is controlled so that the timing is retarded from the intake bottom dead center (BDC).

Here, if the valve opening period of the intake valve 8 is shorter than 180° CA, the valve opening start timing IVO of the intake valve 8 is set to a timing on the advance side of exhaust top dead center (TDC) and the intake valve 8 The valve closing timing IVC cannot be retarded from the intake bottom dead center (BDC). On the other hand, as described above, in the present embodiment, the opening period of the intake valve 8 is set to a period sufficiently longer than 270°CA and 180°CA. Therefore, as described above, the opening timing IVO of the intake valve 8 is set on the advanced side of the exhaust top dead center (TDC), and the closing timing IVC of the intake valve 8 is set on the intake bottom dead center (BDC). can also be set to the timing on the retarded side.

As described above, in the low-speed, high-load region A1, performing valve overlap and setting the closing timing IVC of the intake valve 8 to the retarded timing relative to the intake bottom dead center (BDC) is abnormal. This is to prevent combustion from occurring.

Specifically, in this embodiment, the geometric compression ratio ε of the cylinder 2 is set to 12 and the turbocharger 59 is provided, so that the pressure in the cylinder 2 tends to increase during compression. Therefore, in a region such as the low-speed high-load region A1 where the engine load is high and a large amount of intake air is introduced into the cylinder 2 and the temperature and pressure inside the cylinder 2 before compression are high, the spark plug 10 ignites the air-fuel mixture. Pre-ignition, in which the air-fuel mixture self-ignites at a timing earlier than the ignition timing used, is likely to occur. On the other hand, if the closing timing IVC of the intake valve 8 is retarded from the bottom dead center (BDC) of the intake valve 8 as described above, the effective compression ratio of the cylinder 2 is reduced. It is possible to avoid the internal pressure from becoming excessively high and prevent the occurrence of pre-ignition.

Further, in an engine with a turbocharger, knocking tends to occur in a region where the engine speed is low and the engine load is high. It is known that a high temperature and high pressure field is generated, and the mixture self-ignites without waiting for flame propagation, resulting in a rapid pressure rise. On the other hand, if the valve overlap is performed, the scavenging performance of the cylinder 2 is enhanced, so the amount of high-temperature burned gas remaining in the cylinder 2 is reduced, and the temperature in the cylinder 2 is kept low. Generation of local high-temperature and high-pressure fields as described above is suppressed. Therefore, if the valve overlap is performed, the occurrence of knocking is suppressed.

Here, as described above, if valve overlap is performed, the effect of suppressing knocking can be obtained. However, the inventors of the present application have found that depending on how the valves are overlapped, a sufficient effect of suppressing knocking cannot be obtained, and that the ignition timing must be retarded in order to reliably avoid the occurrence of knocking. was found to be worsening. As a result of intensive research on this, it was found that the crank angle advance of the opening timing IVO of the intake valve 8 with respect to the exhaust top dead center (TDC) was found to be sufficient to avoid deterioration of fuel efficiency and to sufficiently suppress knocking. The optimum ratio of the overlap period CA_OL, which is the crank angle period from the opening timing IVO of the intake valve 8 to the closing timing EVC of the exhaust valve 9, to the intake valve opening advance amount CA_IVO, which is an angular amount. It turns out that there is a range. Hereinafter, the ratio of the overlap period CA_OL to the intake valve opening advance amount CA_IVO is referred to as the intake valve overlap ratio R (R=CA_OL/CA_IVO).

Specifically, as a result of various experiments, the relationship between the intake valve overlap ratio R and the fuel consumption rate (consumed fuel weight with respect to engine output) is shown in the graph of FIG. The graph in FIG. 8 shows the results of experiments with a turbocharged engine having a geometric compression ratio ε of cylinder 2 of 11 or more, and the results of experiments when the engine was operated in the low-speed high-load region A1. be. Further, the fuel consumption rate in the graph shown in FIG. 8 is the fuel consumption rate when the ignition timing is most advanced and the combustion center of gravity timing is most advanced within the range in which knocking does not occur, and is the range in which knocking does not occur. is the minimum achievable fuel consumption rate at

From the graph of FIG. 8, the fuel consumption rate reaches the minimum value Xm when the intake valve overlap ratio R is around 2.15. It can be seen that the larger the value, the higher the fuel consumption rate. In addition, the fuel consumption rate becomes 1% or less of the minimum value Xm, that is, the combustion rate becomes less than the value X10 obtained by multiplying the minimum value Xm by 1.01 when the intake valve overlap It can be seen that the ratio R is 1.77 or more and 3.7 or less. In addition, the reason why the fuel consumption rate is 0.5% or less of the minimum value Xm, that is, the reason why the combustion rate is less than the value X5 obtained by multiplying the minimum value Xm by 1.005 is that the intake valve It can be seen that the overlap ratio R is 1.9 or more and 2.8 or less.

For example, when the closing timing EVC of the exhaust valve 9 is ATDC 27° CA (27° crank angle after exhaust top dead center), if the intake valve opening advance amount CA_IVO is set to 10 or more and 35 or less, If the valve opening start timing IVO is set to BTDC 10° CA or more and 35° CA or less (10° crank angle or more before exhaust top dead center and 35° crank angle or less before exhaust top dead center), the valve overlap ratio R for the intake valve is 1.77 or more and 3.7 or less, and the fuel consumption rate becomes 1% or less of the minimum value Xm. Further, when the closing timing EVC of the exhaust valve 9 is 27° CA ATDC, the intake valve opening advance angle CA_IVO is 15 or more and 30 or less, that is, the opening timing IVO of the intake valve 8 is BTDC 15° CA or more and 30° CA or less. (15 degrees crank angle or more before exhaust top dead center and 30 degrees crank angle or less before exhaust top dead center), the valve overlap ratio R with respect to the intake valve is 1.9 or more and 2.8 or less, and the fuel consumption rate is is 0.5% or less of its minimum value Xm.

Based on the above knowledge, in the present embodiment, in order to suppress the fuel consumption rate to 1% or less of the minimum value Xm, the PCM 100 has a valve overlap ratio R of 1.9 or more and The intake S-VT 18a and the exhaust S-VT 19a are controlled so that it becomes 2.8 or less. Specifically, the opening timing IVO of the intake valve 8 and the closing timing EVC of the exhaust valve 9 are set in advance so that the valve overlap ratio R for the intake valve is 1.9 or more and 2.8 or less. It is stored in the PCM 100, and the PCM 100 controls the intake S-VT 18a and the exhaust S-VT 19a so that these timings are realized in the low speed high load region A1. As described above, the opening timing IVO of the intake valve 8 and the closing timing EVC of the exhaust valve 9 in the low-speed, high-load region A1 are set so that the closing timing IVC of the intake valve 8 is lower than intake bottom dead center (BDC) is set to be on the retarded side, and the closing timing EVC of the exhaust valve 9 is set to be on the retarded side of exhaust top dead center (TDC). For example, at an operating point where the engine speed is 1500 rpm and the engine load is full load and which is included in the low speed high load region A1, the closing timing EVC of the exhaust valve 9 is ATDC 27° CA (after exhaust top dead center). The opening timing IVO and the closing timing IVC of the intake valve 8 are set to BTDC 27° CA (exhaust top dead center 27° crank angle) and ABDC 63°CA (intake 63° after bottom dead center), respectively. degree crank angle).

(action, etc.)
As described above, the geometric compression ratio ε of each cylinder 2 is set to 12 in the engine E according to the above embodiment. Moreover, the engine E is provided with a turbocharger 59 to supercharge the intake air. Therefore, it is possible to increase the output of the engine E and improve the fuel efficiency. However, in an engine having a high geometric compression ratio ε and a turbocharger 59, pre-ignition and knocking are likely to occur in the low-speed high-load region A1 where the engine speed is low and the engine load is high. .

In contrast, in the above-described embodiment, the closing timing IVC of the intake valve 8 is retarded relative to the intake bottom dead center (BDC) in the low-speed high-load region A1 to reduce the effective compression ratio of the cylinder 2. It is possible to suppress the occurrence of pre-ignition. Further, as described above, since the valve opening period of the intake valve 8 is set to a long period of 270° CA, the closing timing IVC of the intake valve 8 is retarded from the intake bottom dead center (BDC). It is configured so that valve overlap can be achieved in a timely manner, and is configured so that valve overlap is performed in the low speed and high load region A1, so that knocking can occur in the low speed and high load region A1. can be suppressed. Furthermore, as described above, in the low-speed high-load region A1, the intake valve overlap ratio R (the ratio of the overlap period CA_OL to the intake valve opening advance amount CA_IVO) is 1.9 or more and 2.8 or less. The value is set within a range in which the fuel consumption rate can be kept within 0.5% of the minimum value while avoiding knocking. Therefore, according to the above-described embodiment, the occurrence of abnormal combustion such as pre-ignition and knocking can be suppressed while improving the fuel efficiency performance.

In the above-described embodiment, the portion of the exhaust passage 60 between the engine body 1 and the turbine 61 is composed of the two independent exhaust passages 64a and 64b. , the exhaust ports 7 of the first cylinder 2a, the second cylinder 2b and the third cylinder 2c whose exhaust strokes are discontinuous, and the second independent exhaust passage 64b communicates with the exhaust ports 7 of the first cylinder 2a, the second cylinder 2b and the third cylinder 2c whose exhaust strokes are discontinuous. It is configured to communicate with each exhaust port 7 of the second cylinder 2b and the third cylinder 2c. Therefore, exhaust interference occurs, specifically, the exhaust gas discharged from a predetermined cylinder 2 enters the cylinder 2 in which the exhaust stroke is performed one before this cylinder 2, and the predetermined cylinder It is possible to prevent the exhaust gas discharged from the cylinder 2 from interfering with the discharge of the exhaust gas from the cylinder 2 in which the exhaust stroke is performed after the cylinder 2 by one. Therefore, the residual amount of burnt gas in the cylinder 2 can be kept small, and pre-ignition can be suppressed more reliably.

In particular, in the above embodiment, the inner space of the portion of the turbine housing 103 from its upstream end to the turbine main body 102 is divided into two intake passages 108 (108a, 108b) aligned in the rotation axis direction of the turbine main body 102, In addition, the intake passages 108 (108a, 108b) are configured to be independent of each other over the entire circumference of the turbine main body 102 in the circumferential direction. A first independent exhaust passage 64a and a second independent exhaust passage 64b are individually connected to each intake passage 108 (108a, 108b). Therefore, exhaust interference can be reliably suppressed, and pre-ignition can be suppressed more reliably.

Specifically, as described above, the flow area of the turbine scroll portion 105 surrounding the turbine main body 102 decreases toward the tongue portion 107 toward the downstream side. Therefore, the flow velocity of the exhaust gas introduced into the turbine scroll portion 105 is increased toward the tongue portion 107, that is, the downstream end of the passage surrounding the turbine body 102, and the exhaust gas is discharged downstream with respect to the turbine body 102 at a high velocity. will be Accordingly, as described above, the two intake passages 108 (108a, 108b) are independent over the entire circumference of the turbine body 102, so that the exhaust gas in each intake passage 108 (108a, 108b) is discharged into the turbine body 102. , can be derived at high speed downstream. Therefore, the exhaust gas that has passed through one intake passage 108a (108b) and one independent exhaust passage 64a (64b) connected thereto flows into the other intake passage 108b (108a) and the other independent exhaust passage connected thereto. Intrusion into the passage 64b (64a), that is, the occurrence of exhaust interference can be reliably suppressed.

(Modification)
In the above embodiment, the intake valve overlap ratio R is set to 1.9 or more and 2.8 or less in the low speed high load region A1. If R is set within the range of 1.77 or more and 3.7 or less, the fuel consumption rate can be made 1% or less of the minimum value Xm. Therefore, the intake valve 8 and the exhaust valve 9 may be opened and closed so that the valve overlap ratio R with respect to the intake valve is 1.77 or more and 3.7 or less in the low speed high load region A1.

Further, in the above-described embodiment, in the high load region A where the engine load is equal to or higher than the predetermined reference load T1, the intake valve 8 is positioned at the bottom dead center (BDC ), the intake valve 8 and the exhaust valve 9 are both opened for a predetermined period across the exhaust top dead center (TDC), and the valve overlap ratio R to the intake valve is 1.9 or more and 2.9. Although the case of setting it to 8 or less has been described, this configuration may be adopted in the entire high load region A, that is, in the entire region where the engine load is equal to or greater than the reference load T1 regardless of the engine speed. Further, even when this configuration is adopted only in the low speed high load region A1, the specific value of the reference speed N1 that defines the low speed high load region A1 is not limited to the above.

Further, in the above-described embodiment, a case has been described in which the in-head exhaust passages 17a and 17b are formed in the cylinder head 3, and the exhaust ports 7 of the cylinders 2 whose exhaust strokes are not continuous are joined in the cylinder head 3. The exhaust port 7 may be merged outside the cylinder head 3 and the engine body 1 .

In the above embodiment, the geometric compression ratio ε of each cylinder 2 is 12. However, as described above, the geometric compression ratio ε of each cylinder 2 may be 11 or more. The value is not limited to twelve. That is, it is known that pre-ignition and knocking are likely to occur when the geometric compression ratio ε of the cylinder 2 is 11 or more in an engine with a turbocharger, and the geometric compression ratio ε of the cylinder 2 is 11 or more. The above effect can be obtained in the engine of Note that the upper limit of the geometric compression ratio ε of the cylinder 2 is preferably 20 from the viewpoint of practicality. That is, the geometric compression ratio ε of the cylinder 2 is preferably 11 or more and 20 or less.

Further, in the above embodiment, the case where the valve opening period of the intake valve 8 is 270° CA has been described, but the valve opening period of the intake valve 8 may be 270° CA or longer. That is, if the opening period of the intake valve 8 is 270°CA or more, in a turbocharged engine in which the geometric compression ratio ε of the cylinder 2 is 11 or more, the effective compression of each cylinder 2 is as described above. Pre-ignition and knocking can be avoided by lowering the ratio and securing the overlap period of the intake valve 8 and the exhaust valve 9 . From the viewpoint of practicality such as avoiding interference between the intake valve 8 and the piston, the upper limit of the opening period of the intake valve 8 is preferably 290°CA. That is, the open period of the intake valve 8 is preferably 270° CA or more and 290° CA or less.

Further, in the above embodiment, the case where the number of cylinders 2 formed in the engine body 1 is six has been described, but the number of cylinders of the engine is not limited to this. Also, the number of independent exhaust passages is not limited to two, and two or more independent exhaust passages may be provided according to the number of cylinders. Further, the number of intake passages 108 provided in the turbine 61 is not limited to two, and the number of intake passages 108 corresponding to the number of independent exhaust passages may be provided. Also, each independent exhaust passage may communicate with the exhaust port of a cylinder whose exhaust strokes are discontinuous. For example, a predetermined independent exhaust passage may be configured to communicate only with the exhaust port of one cylinder.

1 engine body 2 cylinder 3 cylinder head 8 intake valve 19 exhaust port 59 turbocharger (supercharger)
60 exhaust passage 61 turbine 64a first independent exhaust passage (independent exhaust passage)
64b Second independent exhaust passage (independent exhaust passage)
101 Blade 102 Turbine Main Body 103 Turbine Housing 104 Turbine Scroll Part 108 Intake Passage ε Geometric Compression Ratio E Engine

Claims (3)

An engine body in which a cylinder is provided with an intake port, an exhaust port, an intake valve and an exhaust valve; an intake passage and an exhaust passage connected to the engine body; a turbine provided in the exhaust passage and a turbine provided in the intake passage; an engine comprising a turbocharger including a compressor fitted with
The geometric compression ratio of the cylinder is set to 11 or more,
The opening period of the intake valve is set to 270 degrees crank angle or more,
In a high load region where the engine load is equal to or higher than a predetermined reference load, the intake valve opens before exhaust top dead center and closes after intake bottom dead center, and the exhaust valve closes after exhaust top dead center. A crank angle from the intake valve opening start timing to the exhaust valve closing timing is defined as a valve overlap period, and a crank angle from the intake valve opening start timing to the exhaust top dead center is defined as the intake valve opening advance. The intake valve and the exhaust valve are opened and closed so that the ratio of the valve overlap period to the intake valve opening advance amount is 1.77 or more and 3.7 or less when expressed as an angular amount. engine. 2. The engine of claim 1, wherein
In the high load region, the intake valve and the exhaust valve are opened and closed such that a ratio of the valve overlap period to the intake valve opening advance amount is 1.9 or more and 2.8 or less. engine. 3. The engine according to claim 1 or 2,
The engine body has a plurality of cylinders and a plurality of exhaust ports corresponding to each of the cylinders,
The exhaust passage has a plurality of independent exhaust passages respectively communicating with exhaust ports of one or more of the cylinders having discontinuous exhaust strokes,
The turbine includes a turbine body having a plurality of blades that rotate with the energy of exhaust gas, and a turbine housing that houses the turbine body,
The inner space of the turbine housing is divided into a plurality of intake passages formed along the outer periphery of the turbine body along the rotation axis direction of the turbine body in the portion from the upstream end to the turbine body. ,
An engine according to claim 1, wherein the plurality of independent exhaust passages are connected to different intake passages.

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