JP2012036798A - Engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an engine which reduces unburned fuel by setting valve timing, and thereby can improve exhaust emission and fuel economy.SOLUTION: The engine 50A includes: four valves provided at one cylinder and composed of first and second intake valve 54A, 54B and first and second exhaust valve 55A, 55B; and VVT 56, 57 which can set independently valve timing of at least the first and second exhaust valve 55A. 55B out of four valves. The VVT 56, 57 causes phase difference to be generated in valve opening time of the first and second exhaust valve 55A, 55B. In the engine 50A, the first exhaust valve 55A is opened first as one of the exhaust valves out of the first and second exhaust valve 55A, 55B.

Description

  The present invention relates to an engine, and more particularly to an engine capable of setting valve timings of intake valves and exhaust valves.

  In an engine, the valve timing of an intake valve or an exhaust valve may be changed. For example, Patent Document 1 discloses an internal combustion engine in which an intake valve is closed slowly. Patent Document 2 discloses a valve operating device that changes valve timings of first and second engine valves that are the same type of engine valve provided for one combustion chamber.

  In Patent Document 3, two large-diameter and small-diameter intake valves and two exhaust valves that open and close independently in one combustion chamber are provided, and the large-diameter intake valve and the small-diameter exhaust valve face each other. An internal combustion engine arranged in this manner is disclosed. In this internal combustion engine, the valve timing is set so that the large-diameter intake valve opens later than the small-diameter intake valve and the large-diameter exhaust valve closes earlier than the small-diameter exhaust valve. In addition, Patent Document 4 discloses a valve operating control apparatus for an internal combustion engine that closes a first intake valve earlier than a second intake valve.

Japanese Patent Laid-Open No. 10-184370 JP 2009-144521 A JP-A 61-58920 JP 2007-303386 A

  In the internal combustion engine disclosed in Patent Document 1, the pumping loss is reduced by closing the intake valve late. However, when the intake valve is closed late, the compression period is shortened. When the compression period is shortened, the temperature rise in the cylinder is reduced, resulting in insufficient fuel vaporization promotion, and fuel adhesion to the cylinder wall surface may increase. Further, as a result of combustion and exhaust in a state where the air-fuel mixture is not sufficiently formed, deterioration in exhaust emission and fuel consumption due to increase in unburned loss may be caused.

  Note that the internal combustion engine disclosed in Patent Document 3 is a technique for reducing blow-through of the air-fuel mixture during valve overlap. For this reason, the internal combustion engine disclosed in Patent Document 3 does not specifically disclose the setting of the valve timing in view of the above problems. Also, Patent Document 2 does not specifically disclose the setting of the valve timing between the exhaust valves.

  In view of the above problems, an object of the present invention is to provide an engine capable of reducing unburned fuel by setting valve timing and improving exhaust emission and fuel consumption.

  The present invention relates to four valves provided per cylinder consisting of first and second intake valves, first and second exhaust valves, and at least the first and second of the four valves. A valve operating device capable of setting valve timings of the exhaust valves independently of each other, wherein the valve operating device generates a phase difference between the opening timings of the first and second exhaust valves. .

  Further, according to the present invention, the valve operating device further causes a phase difference between the opening timings of the first and second intake valves, and of the four valves, the first intake valve and the second intake valve Preferably, the valve overlaps with the exhaust valve, and the first intake valve and the second exhaust valve are arranged diagonally.

  Further, according to the present invention, the valve device opens the first exhaust valve earlier than the second exhaust valve, and a valve diameter of the second exhaust valve is larger than a valve diameter of the first exhaust valve. It is preferable that the configuration is set larger.

  According to the present invention, unburnt fuel can be reduced by setting the valve timing, and exhaust emission and fuel consumption can be improved.

1 is a schematic configuration diagram of an engine according to Embodiment 1. FIG. It is a figure which shows valve arrangement | positioning of the engine of Example 1. FIG. It is a figure which shows the engine valve timing of Example 1. FIG. It is a figure which shows the discharge characteristic of general unburned HC. It is a figure which shows a mode that unburned HC is discharged | emitted. It is a figure which shows the engine valve timing of Example 2. FIG. It is a figure which shows valve arrangement | positioning of the engine of Example 3. FIG.

  Embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic configuration diagram of the engine 50A. FIG. 2 is a view showing a valve arrangement of the engine 50A. 1 and 2 show a main part of the engine 50A per cylinder. The engine 50A includes a cylinder block 51, a cylinder head 52, a piston 53, first and second intake valves 54A and 54B, first and second exhaust valves 55A and 55B, and an intake side VVT (InVVT) 56. And an exhaust side VVT (ExVVT) 57.

  A cylinder 51 a is formed in the cylinder block 51. A piston 53 is accommodated in the cylinder 51a. A cylinder head 52 is fixed to the upper surface of the cylinder block 51. The combustion chamber 58 is formed as a space surrounded by the cylinder block 51, the cylinder head 52 and the cylinder 53. The cylinder head 52 is formed with first and second intake ports 52aA and 52aB that guide intake air to the combustion chamber 58. Further, first and second exhaust ports 52bA and 52bB for exhausting gas from the combustion chamber 58 are formed.

  The cylinder head 52 is provided with first and second intake valves 54A and 54B that open and close the intake ports 52aA and 52aB, and first and second exhaust valves 55A and 55B that open and close the exhaust ports 52bA and 52bB. ing. The first intake valve 54A and the second exhaust valve 55B are arranged diagonally. Similarly, the second intake valve 54B and the first exhaust valve 55A are arranged diagonally. The engine 50A is a four-valve engine in which four valves including intake valves 54A and 54B and exhaust valves 55A and 55B are provided per cylinder.

  The cylinder head 52 is provided with an intake side VVT 56 and an exhaust side VVT 57. The intake side VVT 56 makes the valve timings of the intake valves 54A and 54B variable, and the exhaust side VVT 57 makes the valve timings of the exhaust valves 55A and 55B variable. The intake side VVT 56 applies what can set the valve timings of the intake valves 54A and 54B independently of each other, and the exhaust side VVT 57 applies what can set the valve timings of the exhaust valves 55A and 55B independently of each other. . As the VVTs 56 and 57, for example, the valve gear disclosed in Patent Document 2 described above can be applied.

  VVTs 56 and 57 correspond to valve gears that can set the valve timings of at least the exhaust valves 55A and 55B independently of each other among the four valves provided per cylinder. For example, the valve operating device can be realized as a configuration having each of the electromagnetic driving devices when the driving of the intake valves 54A and 54B and the exhaust valves 55A and 55B (or at least the exhaust valves 55A and 55B) is electromagnetically driven.

  The VVTs 56 and 57 are electrically connected to the ECU 1 as control targets. The VVTs 56 and 57 are driven under the control of the ECU 1 that is an electronic control unit. The valve timing can be set via the ECU 1 that controls the VVTs 56 and 57. In this embodiment, the valve timings are set so that the VVTs 56 and 57 cause a phase difference in the opening timings of the exhaust valves 55A and 55B. Specifically, the valve timing is set as follows.

  FIG. 3 is a diagram showing valve timing of the engine 50A. The vertical axis represents the valve lift, and the horizontal axis represents the crank angle. The engine 50A is a four-cycle engine, and in the crank angle shown in FIG. 3, the process in which the piston 53 descends from 0 ° to 180 ° corresponding to the combustion stroke, and the angle from 180 ° to 360 ° corresponds to the exhaust stroke. The process in which the piston 53 rises is the process from 360 ° to 540 ° corresponding to the intake stroke, the process in which the piston 53 descends, and the process from 540 ° to 720 ° is the process in which the piston 53 rises corresponding to the compression stroke. .

  The valve timings of the intake valves 54A and 54B are both set to open at a timing before the top dead center and to be closed at a timing after the bottom dead center. The valve timing of the first exhaust valve 55A is set so that it opens at a timing before the bottom dead center and closes at a timing before the top dead center. The valve timing of the first exhaust valve 55A is set so that no valve overlap occurs between the intake valves 54A and 54B.

  The second exhaust valve 55B is set to open at the bottom dead center and to close at a timing later than the top dead center. The valve timing of the second exhaust valve 55B is set so that valve overlap occurs between the intake valves 54A and 54B. The valve timing of the first exhaust valve 55A is set so that the valve opening timing and the valve closing timing are integrally advanced with respect to the valve timing of the second exhaust valve 55B. Then, by providing an integral phase difference between the opening timing and closing timing of the exhaust valves 55A and 55B, a phase difference is provided in the opening timing of the exhaust valves 55A and 55B. The phase difference is 40 °, for example.

  Next, the function and effect of the engine 50A will be described. FIG. 4 is a diagram showing a general unburned HC emission characteristic. The vertical axis represents HC emissions, and the horizontal axis represents the crank angle. FIG. 5 is a diagram schematically showing how unburned HC is discharged. Among these, FIG. 5A shows the state of unburned HC discharge at the time of blowdown, and FIG. 5B shows the state of unburned HC discharge when the piston 53 is raised. FIG. 5 shows an engine 50X that is substantially the same as the engine 50A except that the valve timings of the exhaust valves 55A and 55B are matched as a general engine.

  In general, the unburned HC discharged at the time of exhaust includes unburned HC mainly discharged from around the cylinder head 52 at the time of blowdown (see A part of FIG. 4 and FIG. 5A), and scraped when the piston 53 is raised. The unburned HC around the wall surface of the cylinder 51a (refer to the portion B in FIG. 4 and FIG. 5B) accounts for a large proportion of the whole. The reason is as follows.

  That is, the cylinder pressure increases at the start of exhaust. For this reason, blowdown occurs due to a large pressure difference between the inside and outside of the cylinder at the initial stage of exhaust, and the flow rate of exhaust increases. For this reason, at the time of blowdown, a large amount of unburned HC is taken into the exhaust and discharged. On the other hand, the flow rate of the exhaust gas decreases rapidly thereafter, but then increases again as the piston 53 rises. For this reason, even when the piston 53 is raised, a large amount of unburned HC is taken into the exhaust and discharged. Therefore, reducing these unburned HC is important for improving exhaust emission and fuel consumption.

  On the other hand, the engine 50A has a phase difference between the opening timings of the exhaust valves 55A and 55B. For this reason, in the engine 50A, one of the exhaust valves 55A and 55B (here, the first exhaust valve 55A) is opened first. As a result, when exhaust starts to be performed at a high flow rate, a gas flow is generated in the cylinder so as to be pulled by the exhaust. As a result, an exhaust swirl airflow is generated in the cylinder. Thereafter, the other exhaust valve (here, the second exhaust valve 55B) is opened. At this time, the pressure difference between the inside and outside of the cylinder is small. For this reason, even if the other exhaust valve is opened, the influence on the in-cylinder gas flow is reduced. As a result, the exhaust swirl airflow is maintained during the exhaust stroke.

  The exhaust swirling airflow thus formed takes in unburned HC adhering to the wall surface of the cylinder 51a and carries it toward the center of the cylinder 51a. And by this, by making unburned HC react, unburned HC discharged especially when piston 53 raises can be reduced. Further, the loss of unburned HC can be reduced by reducing the unburned HC, and as a result, fuel consumption can be improved. Thus, the engine 50A can reduce the unburned fuel by setting the valve timing, and can improve the exhaust emission and the fuel consumption.

  In the engine 50B, the VVTs 56 and 57 further cause a phase difference between the opening timings of the intake valves 54A and 54B, and among the four valves, between the first intake valve 54A and the second exhaust valve 55B. It is substantially the same as the engine 50A except that the valve timing is set so as to cause valve overlap. For this reason, the illustration of the engine 50B is omitted.

  FIG. 6 is a diagram showing valve timing of the engine 50B. Compared to the case of the engine 50A, the engine 50B causes a phase difference in the valve opening timing of the intake valves 54A and 54B by integrally delaying the valve timing of the second intake valve 54B. The valve timing of the second intake valve 54B is set so that it opens at a timing after the top dead center and closes at a timing after the bottom dead center (center of the compression stroke). In this regard, the opening timing of the second intake valve 54B is set to a timing later than the closing timings of the exhaust valves 55A and 55B. For this reason, valve overlap does not occur between the second intake valve 54B and the exhaust valves 55A and 55B.

  The opening timing of the first intake valve 54A is set in accordance with the closing timing of the first exhaust valve 55A. For this reason, valve overlap does not occur between the first intake valve 54A and the first exhaust valve 55A. The opening timing of the first intake valve 54A is set to a timing before the closing timing of the second exhaust valve 55B. For this reason, valve overlap occurs between the first intake valve 54A and the second exhaust valve 55B.

  In the engine 50B, based on such settings, the VVTs 56 and 57 cause a valve overlap between the first intake valve 54A and the second exhaust valve 55B arranged diagonally among the four valves. Let In the relationship between the first intake valve 54A and the second exhaust valve 55B, the closing timing of the first exhaust valve 55A can be set to a timing before the opening timing of the first intake valve 54A. The opening timing of the second intake valve 54B can be set to a timing after the closing timing of the second exhaust valve 55B.

  Next, the function and effect of the engine 50B will be described. The engine 50B generates a valve overlap between the first intake valve 54A and the second exhaust valve 55B among the four valves. At this time, the engine 50B inhales intake air with the first intake valve 54A opened among the intake valves 54A and 54B. As a result, the engine 50B can generate an intake swirl airflow in the cylinder while suppressing direct exhaust of the intake air.

  The intake swirl airflow is generated from the stage before exhaust ends. For this reason, the intake swirling air flow promotes the formation of the air-fuel mixture for the next combustion while taking in the unburned HC remaining in the cylinder. Therefore, the engine 50B can further promote combustion compared with the engine 50A, and as a result, exhaust emission and fuel consumption can be further improved. In addition, when inhaling the air-fuel mixture, the engine 50B can also be prevented from being directly exhausted so that the intake air as the air-fuel mixture blows through. Even in this case, not only the effect of suppressing the blow-through but also the exhaust emission and the fuel consumption can be further improved by promoting the combustion.

  The opening timing of the first intake valve 54A can be set within a timing range after the closing timing of the first exhaust valve 55A and before the closing timing of the second exhaust valve 55B. . On the other hand, by setting the opening timing of the first intake valve 54A in accordance with the closing timing of the first exhaust valve 55A, the valve overlap period can be secured longer toward the exhaust stroke side. And thereby, the above-mentioned effect can be produced suitably.

  FIG. 7 is a view showing a valve arrangement of the engine 50C. The engine 50C includes exhaust valves 55A ′ and 55B ′ instead of the exhaust valves 55A and 55B, and accordingly, a cylinder head 52 ′ in which exhaust ports 52bA ′ and 52bB ′ are formed instead of the cylinder head 52. The engine 50A is substantially the same as the engine 50A. Similar changes can be applied to the engine 50B, for example.

  As shown in FIG. 7, the valve diameter of the second exhaust valve 55B ′ is set larger than the valve diameter of the first exhaust valve 55A ′. The exhaust ports 52bA ′ and 52bB ′ are formed according to the valve diameters of the exhaust valves 55A ′ and 55B ′. In the engine 50C, the VVTs 56 and 57 open the first exhaust valve 55A ′ earlier than the second exhaust valve 55B ′, so that the exhaust valve having the smaller valve diameter among the exhaust valves 55A ′ and 55B ′. Is opened earlier than the exhaust valve with the larger valve diameter.

  Next, the function and effect of the engine 50C will be described. In the engine 50C, the first exhaust valve 55A ′ having a small valve diameter is opened earlier than the second exhaust valve 55B ′. For this reason, the engine 50C can increase the flow velocity of the exhaust at the time of blowdown. As a result, the engine 50C can enhance the exhaust swirl airflow as compared with the engine 50A, and as a result, the exhaust emission and the fuel consumption can be further improved.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims. It can be changed.
For example, in the above-described embodiment, the case where the valve opening timing and the valve closing timing are set integrally as the valve timing has been described. However, the present invention is not limited to this, and the valve opening timing and the valve closing timing may be set individually in setting the valve timing.
An engine will not be specifically limited if it is an engine which can implement this invention. For example, a diesel engine other than a gasoline engine may be used. In addition to an engine of a type that injects fuel outside the cylinder and sucks an air-fuel mixture, an in-cylinder fuel direct injection engine may be used.

ECU 1
Engine 50A, 50B, 50C, 50X
Cylinder block 51
Cylinder head 52, 52 '
Piston 53
First intake valve 54A
Second intake valve 54B
First exhaust valve 55A, 55A '
Second exhaust valve 55B, 55B ′
Intake side VVT 56
Exhaust side VVT 57
Combustion chamber 58

Claims (3)

Four valves provided per cylinder consisting of first and second intake valves and first and second exhaust valves;
A valve operating device capable of setting valve timings of at least the first and second exhaust valves independently of each other among the four valves;
An engine in which the valve gear causes a phase difference between the opening timings of the first and second exhaust valves. The engine according to claim 1,
The valve operating device further causes a phase difference between the opening timings of the first and second intake valves, and of the four valves, the first intake valve and the second exhaust valve Causing valve overlap between
An engine in which the first intake valve and the second exhaust valve are arranged diagonally. The engine according to claim 1 or 2,
The valve gear opens the first exhaust valve earlier than the second exhaust valve;
An engine in which a valve diameter of the second exhaust valve is set larger than a valve diameter of the first exhaust valve.

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