KR20160147467A - Diesel engine - Google Patents

Abstract

The present invention relates to a diesel engine to recirculate exhaust gas. According to the present invention, the diesel engine comprises: a cylinder block including at least two cylinders; an exhaust manifold extending from each exhaust port of the at least two cylinders; and an exhaust valve to open the exhaust port to exhaust exhaust gas in the cylinder, wherein the exhaust valve is configured to perform a first opening and closing which opens and closes the exhaust port once during an exhaust stroke, and then performing a second opening and closing which opens and closes the exhaust post at least once more when a pressure of the exhaust valve is greater than that of a pressure inside the cylinder where the exhaust valve is included.

Description

DIESEL ENGINE {DIESEL ENGINE}

The present invention relates to a diesel engine, and more particularly, to a diesel engine that recirculates exhaust gas.

In general, industrial vehicles and construction machines use diesel engines with higher output torque and higher fuel efficiency than gasoline engines. Particulate matter (PM) and nitrogen oxides (NOx) such as soot, soluble organic fraction (SOF) and the like contained in the exhaust gas discharged from the diesel engine as the usage of the diesel engine increases. ) Are increasing. This is pointed out as the main cause of air pollution, and the regulation of emission of these substances is increasing. Diesel particulate filters (DPF) and Selective Catalytic Reduction (SCR) have been studied to reduce harmful substances emitted from diesel engines. However, system operation cost and fuel efficiency improvement In terms of efficiency, it is a nitrogen oxide (NOx) reduction technique utilizing exhaust gas recirculation (recirculation). The exhaust gas recirculation technique is effective in suppressing the generation of nitrogen oxides in the combustion stage of the engine.

1 is an example of an engine system having an exhaust gas recirculation system. 1, an engine system having an exhaust gas recirculation system includes a cylinder block 1, an intake line 2, an exhaust line 3, a recirculation flow path 4, a recirculation valve 5, a recirculation flow rate sensor 6, and a recirculation cooler 7. The intake line 2 is connected to the combustion chamber of the cylinder block 1 and the combustion air can be supplied to the combustion chamber of the cylinder block 1 through the intake line 2. [ When the cylinder block 1 includes a plurality of cylinders, the intake line 2 can be connected to the cylinder block 1 through the intake manifold. The exhaust line 3 is connected to the combustion chamber of the cylinder block 1, and the exhaust gas is discharged from the combustion chamber through the exhaust line 3. When the cylinder block 1 includes a plurality of cylinders, the exhaust line 3 can be connected to the cylinder block 1 through an exhaust manifold. The recirculation flow path 4 branches from the exhaust line 3 and joins to the intake line 2. [ A part of the exhaust gas discharged from the cylinder block 1 is recirculated to the intake line 2 again through the recirculation flow path 4. [ The exhaust gas recirculated through the recirculation flow path 4 is mixed with the incoming air from the outside through the intake line 2 and supplied to the combustion chamber of the cylinder block 1. [ A recirculation valve (5) is provided on the recirculation flow path (4) to regulate the flow rate of the recirculated exhaust gas. The recirculation cooler 7 is installed in the recirculation flow path 4 to lower the temperature of the exhaust gas passing through the recirculation flow path 4. The recirculation flow rate sensor 6 measures the flow rate of the exhaust gas recirculated through the recirculation flow path 4. The exhaust gas recirculation system reduces the generation of nitrogen oxides (NOx) by reducing the combustion temperature by recirculating a part of the exhaust gas discharged from the combustion chamber to the combustion chamber.

However, in order to provide the exhaust gas recirculation system, the recirculation flow path 4, the recirculation valve 5, the recirculation flow rate sensor 6, the recirculation cooler 7, and the like must be additionally installed in the existing engine. As a result, the layout of the engine becomes complicated, and the exhaust gas recirculation system itself can not be installed due to a narrow engine room. Also, there is a problem that manufacturing and maintenance costs increase due to the addition of parts.

KR 10-2012-0059928 A

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems of the prior art, and to provide a diesel engine capable of realizing exhaust gas recirculation without additionally providing a separate member for exhaust gas recirculation such as a recirculation passage and a recirculation valve do.

In order to solve the above problems, the present invention provides a cylinder block including at least two cylinders; An exhaust manifold extending from the exhaust ports of the at least two cylinders, respectively; And an exhaust valve for opening the exhaust port to exhaust exhaust gas inside the cylinder, wherein, during one cycle of the engine, after the exhaust valve is first opened and closed to open and close the exhaust port once during an exhaust stroke, Closing the exhaust port at least once when the pressure of the exhaust manifold is greater than the pressure inside the cylinder to which the exhaust valve belongs.

The exhaust valve can open the exhaust port to the maximum when the pressure difference between the exhaust manifold and the cylinder to which the exhaust valve belongs is greatest.

The secondary opening and closing can be performed so that the exhaust valve has a maximum lift amount when the crank angle is 430 to 450 degrees or when the crank angle is 550 to 570 degrees.

According to the embodiment of the present invention, the exhaust gas flows back into the combustion chamber by the second opening and closing of the exhaust port once again after the exhaust valve is first opened and closed for one cycle of the engine, There is an effect that the exhaust gas recirculation can be realized without having to provide parts.

According to an embodiment of the present invention, when the pressure difference between the exhaust manifold and the inside of the cylinder during the second opening and closing operation is greatest, the lift amount is maximized, thereby achieving a sufficient exhaust gas recirculation.

1 is an example of an engine system having an exhaust gas recirculation system.
2 is a diagram showing the overall configuration of a diesel engine according to an embodiment of the present invention.
3 is a graph showing the relationship between the valve lift during the first opening and closing of the exhaust valve and the valve lift during the second opening and closing of the exhaust valve during one cycle of the diesel engine according to the embodiment of the present invention and the pressure change in the exhaust manifold, FIG.
4 is a graph showing the EGR rate and the performance reduction rate for the plurality of secondary opening and closing cases shown in FIG.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the drawings, the same reference numerals are used to designate the same or similar components throughout the drawings. In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

2 is a diagram showing the overall configuration of a diesel engine according to an embodiment of the present invention. 2, a diesel engine according to an embodiment of the present invention includes a cylinder block 10, an intake line 20, an intake manifold 22, an intake port 24, an intake valve 26, The intake valve 30, the exhaust manifold 32, the exhaust port 34, the exhaust valve 36, the piston 16, the connecting rod 18, and the crankshaft 40.

At least two cylinders (12) are provided in the cylinder block (10). The plurality of cylinders 12 can be arranged in a specific pattern. The diesel engine according to an embodiment of the present invention may be an engine of various types such as an I-type and V-type engine. A piston (16) is slidably inserted into each cylinder (12), and a combustion chamber (14) is formed inside the cylinder (12). At least one intake port (24) and at least one exhaust port (34) are formed in the combustion chamber (14) of each cylinder (12). Air or a mixed gas of air and fuel can be introduced into the combustion chamber 14 through the intake port 24 and the exhaust gas can be exhausted from the combustion chamber 14 through the exhaust port 34. [

The intake line 20 is connected to the intake ports 24 of each cylinder 12 and the intake manifold 22 is formed between the intake line 20 and the plurality of intake ports 24. [ An exhaust line 30 is connected to the exhaust ports 34 of each cylinder and an exhaust manifold 32 is formed between the exhaust line 30 and the plurality of exhaust ports 34. The intake manifold 22 may be branched from the intake line 20 to extend to the intake port 24 of each cylinder and the exhaust manifold 32 may extend from the exhaust ports 34 of each cylinder, (30). ≪ / RTI > The air supplied through the intake line 20 or a mixed gas of air and fuel flows through the intake line 20 and is distributed from the intake manifold 22 to the combustion chamber 14 of each cylinder 12 . The exhaust gas discharged from the combustion chamber 14 of each cylinder 12 may be joined to the exhaust line 30 through the exhaust manifold 32. [ The intake valve 26 and the exhaust valve 36 open and close the intake port 24 and the exhaust port 34, respectively. When the intake port 24 and the exhaust port 34 are opened, air and exhaust gas can be sucked and discharged into the combustion chamber 14, and when the intake port 24 and the exhaust port 34 are closed, Can not enter or exit the combustion chamber (14).

The diesel engine according to an embodiment of the present invention may be an engine in which one cycle consists of four strokes of suction, compression, explosion, and exhaust. The piston 16 of each cylinder 12 moves up and down in the cylinder 12 by the explosive force generated in the explosion stroke and is connected to the piston 16 and the connecting rod 18 by the up and down movement of the piston 16. [ The crankshaft 40 is rotated. At this time, the explosion timings of the cylinders 12 may be different from each other.

3 is a graph showing the relationship between the valve lift during the first opening and closing of the exhaust valve and the valve lift during the second opening and closing of the exhaust valve during one cycle of the diesel engine according to the embodiment of the present invention and the pressure change in the exhaust manifold, FIG. 3, the pressure of the exhaust manifold 32 is not maintained constant but is periodically increased or decreased by the exhaust stroke of each cylinder 12, which is referred to as an exhaust pulsation phenomenon. In FIG. 3, it can be seen that the exhaust pulsation occurs six times in the exhaust manifold 32 while the crankshaft 40 rotates by 720 degrees and one cycle proceeds. This is because the diesel engine according to an embodiment of the present invention is a six-cylinder engine having six cylinders. Generally, in the exhaust manifold 32, Lt; / RTI > For example, in a four-cylinder engine, exhaust pulsation generally occurs four times during one cycle. However, this may vary depending on the ignition sequence of each cylinder, the arrangement of the cylinders, and the exhaust valve lift timing.

The exhaust valve 36 opens and closes the exhaust port 34 at least twice during one cycle of the engine. The opening and closing of the exhaust port 34 during the exhaust stroke is defined as a primary opening and closing of the exhaust valve 36. The exhaust valve 36 opens and closes the exhaust port 34 again after the primary opening and closing for one cycle of the engine The operation is defined as secondary opening and closing.

The primary opening and closing is performed at the time of the exhaust stroke, and the normal exhaust of the exhaust gas generated by the combustion by the primary opening and closing is performed. In other words, the exhaust port 34 is opened and closed by the primary opening and closing of the exhaust valve 36 during the exhaust stroke. When the exhaust gas generated by the combustion while the exhaust port 34 is opened is exhausted to the exhaust port 34 .

The secondary opening and closing can be performed between the start of the intake stroke and the end of the compression stroke after completion of the primary opening and closing of the cylinder 12. The pressure of the exhaust manifold 32 is lower than the pressure of the cylinder 12 to which the specific exhaust valve 36 belongs And the exhaust valve 36 is configured to open and close the exhaust port 34 when it is large. As described above, in the engine in which the plurality of cylinders 12 are provided and the exhaust gas is exhausted through the exhaust manifold 32, even if the exhaust valve 36 of one of the cylinders is closed, the exhaust gas discharged from the other cylinder So that exhaust pulsation occurs in the exhaust manifold (32). Since the exhaust manifold 32 is connected to the exhaust port 34 of each cylinder 12, the pressure change of the exhaust manifold 32 acts on the exhaust port 34 of each cylinder 12 as it is. A part of the exhaust gas discharged from the combustion chamber 14 to the exhaust manifold 32 by the second opening and closing performed when the pressure of the exhaust manifold 32 is larger than the pressure of the cylinder 12 is again supplied to the combustion chamber 14 ). That is, when the exhaust valve 36 opens the exhaust port 34 at the time of the second opening / closing, the pressure from the exhaust manifold 32, which has a large pressure due to the pressure difference between the exhaust manifold 32 and the cylinder 12, The exhaust gas flows back into the small cylinder 12 again. Such secondary opening and closing is performed at least once during one cycle, and may be performed twice or more depending on the characteristics of the engine.

On the other hand, the lift amount of the exhaust valve 36 at the time of the second opening and closing is generally smaller than the lift amount of the exhaust valve 36 at the time of the first opening and closing. At this time, the lift amount means the degree to which the exhaust valve 36 moves upward or downward to open the exhaust port 34. [ Therefore, the amount of the exhaust gas re-flowing into the combustion chamber 14 during the second opening and closing may be insufficient. In this case, the exhaust gas recirculation rate (EGR rate) can be increased by increasing the lift amount or by increasing the number of secondary open / close operations.

Further, in order to cause a sufficient amount of exhaust gas recirculation, it is desirable that the lift amount is maximized when the pressure difference within the cylinder 12 to which the exhaust manifold 32 and the exhaust valve 36 belong is greatest. In other words, it is preferable that the exhaust valve 36 opens the exhaust port 34 to the maximum when the pressure difference between the exhaust manifold 32 and the cylinder 12 to which the exhaust valve 36 belongs is the largest.

4 is a graph showing the EGR rate and the performance reduction rate for the plurality of secondary opening and closing cases shown in FIG. FIG. 4 shows the EGR rate and the performance reduction rate when the secondary opening and closing is performed separately at different crank angles. As shown in Figs. 3 and 4, even when the plurality of secondary open / close cases are all performed when the pressure of the exhaust manifold 32 is larger than the pressure inside the cylinder 12 to which the exhaust valve 36 belongs, When the difference in pressure between the manifold 32 and the cylinder 12 is greatest, it can be seen that the EGR rate is large and the performance reduction rate is low in the case of No. 3 and No. 15 where the valve lift amount is largest.

The timing at which the pressure difference between the exhaust manifold 32 and the cylinder 12 is greatest may vary depending on the characteristics of the engine. For example, in the case of a six-cylinder engine, the phase difference of the exhaust pulsation occurs depending on the primary open / close timing of the exhaust valve 36, the volume of the exhaust manifold 32, and the length of the runner. Generally, To 450 degrees or when the crank angle is in the range of 550 to 570 degrees, a large EGR rate can be obtained and the performance reduction rate can be lowered.

As described above, according to the present invention, the exhaust gas flows back into the combustion chamber by the second opening and closing of the exhaust port 34 once after the exhaust valve 36 is opened and closed once during one cycle of the engine, The exhaust gas recirculation can be realized without having to include the recirculation flow path and the related parts, thereby reducing the generation of NOx.

It will be apparent to those skilled in the art that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims. . Therefore, the embodiments disclosed in the present invention are not intended to limit the scope of the present invention but to limit the scope of the technical idea of the present invention. The scope of protection of the present invention should be construed according to the following claims, and all technical ideas within the scope of equivalents should be construed as falling within the scope of the present invention.

10: cylinder block 12: cylinder
14: combustion chamber 16: piston
18: connecting rod 20: intake line
22: intake manifold 24: intake port
26: intake valve 30: exhaust line
32: exhaust manifold 34: exhaust port
36: exhaust valve 40: crankshaft

Claims (3)

A cylinder block including at least two cylinders;
An exhaust manifold extending from the exhaust ports of the at least two cylinders, respectively; And
And an exhaust valve for opening the exhaust port to exhaust exhaust gas inside the cylinder,
The exhaust valve according to claim 1, wherein, during one cycle of the engine, when the pressure of the exhaust manifold is greater than a pressure inside the cylinder to which the exhaust valve belongs, the exhaust valve A diesel engine for performing a second opening and closing operation for opening and closing at least one time. The method according to claim 1,
Wherein the exhaust valve opens the exhaust port to the maximum when the pressure difference between the exhaust manifold and the cylinder to which the exhaust valve belongs is greatest. The method according to claim 1,
Wherein the secondary opening and closing is performed so that the exhaust valve has a maximum lift amount when the crank angle is 430 to 450 degrees or when the crank angle is 550 to 570 degrees.

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