JP2004176620A - Overhead valve type multiple cylinder engine capable of two-cycle operation - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide technique for enlarging a range of operation conditions in which self-ignition combustion is possible in an overhead valve type engine capable of conducting two-cycle operation. <P>SOLUTION: A plurality of exhaust passages 16a-16c from combustion chambers 1-3 in each cylinder to a turbine chamber 52a are isolated from each other, and they have roughly similar length. To enter the turbine chamber 52a, constitution of entrance from an outer circumferential surface of the turbine chamber 52a and constitution of entrance from the bottom surface side are possible. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an overhead valve type multi-cylinder engine capable of two-cycle operation.
[0002]
[Prior art]
A gasoline engine normally performs four-cycle operation, but a gasoline engine capable of performing two-cycle operation using a supercharger has also been proposed (for example, Patent Document 1).
[0003]
[Patent Document 1] JP-A-7-91267 [Patent Document 2] JP-A-2001-304014 [Patent Document 3] JP-A-2000-213342 [Patent Document 4] JP-A 7-17275 [Patent] Document 5: Japanese Patent Application Laid-Open No. 8-177503 [Patent Document 6] Japanese Utility Model Publication No. 4-1309
The engine described in Patent Document 1 is an overhead valve type engine in which both an air supply valve and an exhaust valve are provided in a cylinder head. In an overhead valve type engine capable of two-cycle operation, exhaust is discharged from a combustion chamber by fresh air by a so-called scavenging action.
[0005]
In recent years, it has been studied to employ a combustion method in which an air-fuel mixture is self-ignited (also referred to as a “premixed self-ignition combustion method”) in an overhead valve type two-cycle engine. In this self-ignition combustion system, for example, gasoline is premixed with air supply and self-ignition is performed by compression. The use of such self-ignition combustion has the advantages of improving fuel economy and reducing the emission of air pollutants (particularly NOx).
[0006]
[Problems to be solved by the invention]
However, in a multi-cylinder two-cycle engine, the scavenging effect tends to be slightly different for each cylinder due to the influence of pressure pulsation in the exhaust pipe of each cylinder. For example, some cylinders have too much exhaust gas (called "internal EGR") remaining in the combustion chamber, so that fresh air is reduced to a rich mixture, while other cylinders have too little residual exhaust gas. In some cases, the fresh air increases and the mixture becomes lean. When the required load (torque) of the engine is small, the amount of fuel injection is small, and therefore, in a cylinder having a leaner air-fuel mixture, a decrease in torque or misfire may occur. On the other hand, when the required load of the engine is large, there is a possibility that knocking may occur or combustion noise may increase in a cylinder with a richer air-fuel mixture. Therefore, when the composition of the air-fuel mixture of each cylinder differs due to the influence of the pressure pulsation in the exhaust pipe of each cylinder, there is a problem that the range of operating conditions under which auto-ignition combustion can be performed is narrowed.
[0007]
SUMMARY OF THE INVENTION The present invention has been made to solve the above-described conventional problems, and in an overhead valve type engine capable of two-cycle operation, the range of operating conditions in which self-ignition combustion can be performed can be expanded as compared with the related art. It aims to provide technology.
[0008]
[Means for Solving the Problems and Their Functions and Effects]
In order to achieve at least a part of the above object, an engine of the present invention is a multi-cylinder engine capable of performing two-cycle self-ignition operation,
A supercharger having a turbine chamber that houses a turbine driven by exhaust gas,
A plurality of exhaust paths from the combustion chambers of the plurality of cylinders to the turbine chamber are independent of each other and have substantially equal lengths.
[0009]
According to this configuration, since the plurality of exhaust paths are separated by the turbine blade, it is possible to prevent the pressures of the respective exhaust paths from interfering with each other. In other words, it is possible to prevent the pressure pulsation in one exhaust path from propagating to another exhaust path. Therefore, it is possible to prevent a difference in the composition of the air-fuel mixture between the cylinders due to the influence of the pressure pulsation in the exhaust pipe of each cylinder, and to obtain an air-fuel mixture having substantially the same composition. As a result, it is possible to extend the range of operating conditions under which self-ignition combustion can be performed, as compared with the related art.
[0010]
In addition, it is preferable that the inlets of the plurality of exhaust paths to the turbine chamber are evenly arranged.
[0011]
According to this configuration, the efficiency of the supercharger can be improved. As a result, a sufficient supercharging effect can be obtained even when the engine speed and load are low, so that the range of operating conditions under which self-ignition combustion can be performed can be further expanded.
[0012]
Further, it is preferable that the pipes in the vicinity of the inlets to the turbine chamber of the plurality of exhaust paths are configured so as to enter the turbine chamber obliquely while proceeding substantially spirally around the central axis of the turbine.
[0013]
According to this configuration, it is possible to further shorten the exhaust path.
[0014]
Further, it is preferable that three exhaust paths of the combustion chambers of the three cylinders that explode at equal intervals are connected to the same turbine chamber.
[0015]
If three exhaust paths for each of the three cylinders are connected to one turbine chamber, the efficiency of the supercharger is improved, so that the range of operating conditions in which self-ignition combustion can be performed can be further expanded. .
[0016]
Note that the present invention can be realized in various aspects, for example, in aspects of an engine, an exhaust device of the engine, a control method of the engine and the exhaust device, and the like.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
A. First embodiment:
Next, embodiments of the present invention will be described based on examples. FIG. 1 is an explanatory diagram conceptually showing the configuration of a gasoline engine 100 as a first embodiment of the present invention. FIG. 1 shows the structure of the combustion chamber when a cross section is taken at the center of the combustion chamber of the gasoline engine 100.
[0018]
The combustion chamber of the gasoline engine 100 includes a hollow cylindrical cylinder 142 provided in a cylinder block 140, a piston 144 sliding up and down in the cylinder 142, and a cylinder head 130 provided above the cylinder block 140. Is formed by Note that a cylindrical body composed of both the cylinder block 140 and the cylinder head 130 is called a "cylinder" in a broad sense.
[0019]
The cylinder head 130 has an air supply valve 132 that opens and closes an opening of an air supply port through which intake air flows, an exhaust valve 134 that opens and closes an opening of an exhaust port through which exhaust gas flows out, a spark plug 136, A fuel injection valve 14 for injecting fuel spray into the room is provided. The supply valve 132 and the exhaust valve 134 are driven by electric actuators 162 and 164, respectively. The electric actuators 162 and 164 can open and close the respective supply valves 132 and exhaust valves 134 at an arbitrary timing. Note that the air supply valve 132 and the exhaust valve 134 may be driven by a hydraulic actuator or a cam mechanism instead of the electric actuator.
[0020]
An air supply passage 12 for guiding intake air is connected to the air supply port, and an exhaust passage 16 through which exhaust gas passes is connected to the exhaust port. Downstream of the exhaust passage 16, a catalyst 26 for purifying air pollutants contained in exhaust gas and a turbine 52 of a supercharger 50 are provided. The exhaust gas passing through the exhaust passage 16 rotates the turbine 52 and is then released to the atmosphere. Further, the compressor 54 of the supercharger 50 is provided in the air supply passage 12. The compressor 54 is connected to the turbine 52 via a shaft 56. When the turbine 52 rotates by the exhaust gas, the compressor 54 also rotates. As a result, the compressor 54 pressurizes the air sucked from the air cleaner 20 and then sends the air toward the air supply port.
[0021]
Note that the engine 100 of the present embodiment has three cylinders, and the length of the exhaust pipe 16 (the length from the exhaust port to the supercharger 50) of each cylinder is set to be equal to each other. . This will be described later.
[0022]
When pressurized by the compressor 54, the air temperature rises, so that an intercooler 62 is provided downstream of the compressor 54 to cool the intake air. Further, a surge tank 60 and a throttle valve 22 are provided in the air supply passage 12. The surge tank 60 has a function of alleviating a pressure wave generated when the combustion chamber sucks air, and the throttle valve 22 is set to an appropriate opening by the electric actuator 24 to adjust the amount of intake air. It has the function to do.
[0023]
The piston 144 is connected to a crankshaft 148 via a connecting rod 146, and the crankshaft 148 is provided with a crank angle sensor 32 for detecting a crank angle.
[0024]
The operation of the gasoline engine 100 is controlled by an engine control unit (hereinafter, ECU) 30. The ECU 30 detects the engine rotation speed Ne and the accelerator opening θac, and controls the opening of the throttle valve 22, the ignition timing of the spark plug 136, and the control of the fuel injection valve 14 based on these. The engine rotation speed Ne is detected by a crank angle sensor 32, and the accelerator opening θac is detected by an accelerator opening sensor 34 built in an accelerator pedal.
[0025]
FIG. 2 is a map showing an operation mode of the engine 100 of the first embodiment. As shown in this map, the engine 100 of the first embodiment can switch between two-cycle operation and four-cycle operation and execute it. The horizontal axis in FIG. 2 is the engine speed, and the vertical axis is the load (torque). When the engine speed is low, a two-cycle operation is executed, and when the engine speed is high, a four-cycle operation is executed. The two-cycle operation region is divided into a spark ignition region under low load and high load, and a self-ignition region under medium load. The self-ignition region is an operation region in which combustion is caused by self-ignition without performing spark ignition. It should be noted that self-ignition combustion can be performed even during four-cycle operation.
[0026]
The reason why the two-cycle operation and the four-cycle operation are properly used in this way is as follows. In general, in the two-cycle operation, an explosion occurs once for each rotation of the crankshaft, so that under the same fuel injection amount, a torque approximately twice that of the four-cycle operation can be obtained. Therefore, when the same torque is output, the two-cycle operation requires less fuel injection per operation than the four-cycle operation, and operation can be performed under leaner conditions (conditions with a larger excess air ratio). It is. By operating the gasoline engine under leaner conditions, fuel efficiency can be improved and the concentration of pollutants in exhaust gas can be reduced. Furthermore, it is known that the effect of improving fuel efficiency and reducing the concentration of pollutants in exhaust gas is further enhanced by performing self-ignition operation. However, in the two-cycle operation, so-called scavenging (operation of pushing out exhaust gas by air supply) is performed, but scavenging may not be performed sufficiently at high rotation speed. Thus, under high-rotation operating conditions, four-cycle operation is more suitable.
[0027]
FIG. 3 is an explanatory diagram showing a state of self-ignition combustion in two-cycle operation. 3 (a) to 3 (c) show the expansion / exhaust / first-stage scavenging stroke (downward stroke) of the two-cycle operation, and FIGS. 3 (d) to (f) show the second-stage scavenging / intake / compression. The stroke (upstroke) is shown. FIG. 4 schematically shows the open / close periods of the air supply valve (IN valve) and the exhaust valve (EX valve) during the two-cycle operation.
[0028]
FIG. 3A shows a state in which the air-fuel mixture in the combustion chamber has started combustion by self-ignition. When the air-fuel mixture burns, high-pressure combustion gas is generated in the combustion chamber and pushes down the piston 144. When the piston 144 descends to a certain extent, the exhaust valve 134 is opened at an appropriate timing (FIG. 3B). In the example of FIG. 4, the exhaust valve 134 is opened at a timing of about 70 ° before the bottom dead center (BDC) of the piston.
[0029]
When the air supply valve 132 is opened at a timing when a certain amount of combustion gas flows out of the exhaust valve, air flows in from the air supply port accordingly (FIG. 3C). Since the air in the air supply passage 12 is pressurized to a predetermined pressure by the supercharger 50, the fresh gas flowing from the air supply valve 132 can scavenge the combustion gas in the combustion chamber. In the example of FIG. 4, the air supply valve 132 is opened at a timing of about 60 ° before the bottom dead center (BDC) of the piston.
[0030]
When the piston 144 is near the bottom dead center during the scavenging period, the fuel injection valve 14 injects fuel spray into the combustion chamber (FIGS. 3D and 4). Since the exhaust valve 134 is closed shortly after the bottom dead center, if the fuel spray is injected near the bottom dead center, the injected fuel spray is not discharged from the exhaust valve 134, and the fuel and fresh air are discharged. Can be sufficiently mixed.
[0031]
After the fuel is injected and the exhaust valve 134 is closed at a predetermined timing, the air pressurized from the air supply valve 132 flows into the combustion chamber as shown in FIG. In the example of FIG. 4, the timing of closing the exhaust valve 134 is set to about 50 ° after the bottom dead center of the piston. The fuel spray injected during the scavenging period is dispersed in the combustion chamber by the flow of the intake air, and mixes with the intake air.
[0032]
After the air supply valve 132 is closed, the air-fuel mixture in the combustion chamber is compressed as the piston 144 rises. While the air supply valve 132 is open, the air-fuel mixture in the combustion chamber cannot be compressed even if the piston rises. Therefore, in the two-cycle operation, the substantial compression ratio of the air-fuel mixture is determined by the timing at which the air supply valve 132 is closed. In the example of FIG. 4, the timing of closing the air supply valve 132 is set to about 60 ° after the bottom dead center of the piston.
[0033]
When the piston 144 is moved up after closing the air supply valve 132, the air-fuel mixture is compressed in the combustion chamber as shown in FIG. 3F, and self-ignites near the top dead center of the piston 144. As a result, the formed air-fuel mixture in the combustion chamber can be quickly burned.
[0034]
As described above, in the two-cycle self-ignition operation, since the lean air-fuel mixture having a large excess air ratio is compressed and self-ignited, the fuel consumption can be reduced, and the emission of air pollutants can be significantly reduced. . It should be noted that when the load is high, the fuel injection amount increases and the excess air ratio decreases, so that knocking tends to occur during compression. Therefore, when the load is high, it is preferable to set the compression ratio slightly lower and burn the air-fuel mixture by igniting with an ignition plug. On the other hand, when the load is extremely low, the self-ignition may be unstable because the fuel injection amount is small. Therefore, even when the load is extremely low, the air-fuel mixture may be burned by igniting with an ignition plug.
[0035]
FIG. 5A is a perspective view showing the exhaust pipe of the first embodiment. This engine is a three-cylinder engine, and a cylinder head 130 is provided with three combustion chambers # 1 to # 3. The valve timing is set so that the three combustion chambers # 1 to # 3 perform combustion (ie, explosion) at equal intervals.
[0036]
The exhaust pipes 16a to 16c of the three combustion chambers # 1 to # 3 are independently connected to a substantially hollow cylindrical turbine chamber 52a (also referred to as a "turbine housing"). The turbine room 52a is a storage room for storing the turbine 52 (FIG. 1) of the turbocharger 50. In FIG. 5, a compressor chamber for housing the compressor 54 (FIG. 1) is omitted.
[0037]
As shown in FIG. 5B, the turbine chamber 52a has three inlet pipes 201 to 203 provided at equal intervals along the outer periphery thereof. These inlet pipes 201 to 203 are arranged on a plane perpendicular to the central axis 53 of the turbine 52 (FIG. 1) so that exhaust gas is introduced from the outer peripheral surface of the turbine chamber 52 a to the outer periphery of the turbine 52. It is configured. In this embodiment, the inlet pipes 201 to 203 are evenly arranged at intervals of 120 degrees.
[0038]
Note that the inlet pipes 201 to 203 constitute a part of the exhaust pipes 16a to 16c. In other words, the exhaust pipes 16a to 16c mean a path from the attachment portion 130a of the exhaust pipes 16a to 16c to the cylinder head 130 to the substantially hollow cylindrical turbine chamber 52a.
[0039]
In this embodiment, the lengths of the exhaust pipes 16a to 16c of the three combustion chambers # 1 to # 3 are set to be equal to each other. Normally, the length of the exhaust port of each combustion chamber in the cylinder head 130 is the same. In this case, if the lengths of the three exhaust pipes 16a to 16c are set equal to each other, the lengths of the exhaust paths from the three combustion chambers to the turbine chamber 52a can be equalized. If the lengths of the exhaust ports of the respective combustion chambers in the cylinder head 130 are different, the length of the exhaust pipes 16a to 16c is adjusted to adjust the length of the exhaust pipes from the three combustion chambers to the turbine chamber 52a. The lengths of the exhaust paths can be made equal to each other.
[0040]
As described above, in the first embodiment, the exhaust paths of the three combustion chambers # 1 to # 3 are configured as independent paths from the combustion chamber to the turbine chamber 52a. They are equally set and are connected to the outer periphery of the turbine chamber 52a at equal intervals of 120 degrees. As a result, the exhaust gas from each of the combustion chambers # 1 to # 3 flows into the turbine chamber 52a under the same conditions, so that the pressure pulsations in the exhaust pipes 16a to 16c of each of the combustion chambers # 1 to # 3 become substantially the same. . In particular, in the present embodiment, the blades (turbine blades) of the turbine 52 (FIG. 1) function as barriers for preventing the propagation of pressure fluctuations in the exhaust pipes 16a to 16c. As a result, the amount of air flowing into each combustion chamber and the amount of residual exhaust gas become substantially the same, and a mixture having substantially the same composition can be obtained in each combustion chamber. That is, it is possible to prevent a specific combustion chamber from becoming excessively rich or excessively lean from other combustion chambers.
[0041]
As described in the related art, in general, when the required load (torque) of the engine is small, the fuel injection amount is small. Therefore, in a combustion chamber in which the air-fuel mixture is leaner, there is a problem that a torque reduction or misfire occurs. I can do it. Further, when the required load of the engine is large, there may occur a problem that knocking occurs in a cylinder in which the air-fuel mixture is richer and combustion noise increases. However, in this embodiment, since the composition of the air-fuel mixture becomes substantially the same in each combustion chamber, any of such problems can be avoided. Such an effect is maintained even when the operating conditions (the number of rotations and the load) change. Therefore, according to the engine of the present embodiment, it is possible to widen the range of operating conditions (FIG. 2) in which self-ignition combustion is possible.
[0042]
Further, in this embodiment, since the turbine blade functions as a barrier for preventing the propagation of the pressure fluctuation in each of the exhaust pipes 16a to 16c, the mutual interference of the pressure in each of the exhaust pipes 16a to 16c is extremely reduced, and the supercharging is performed. The output (efficiency) of the vessel 50 is improved. If the efficiency of the supercharger 50 is improved, a sufficient supercharging effect can be obtained even when the engine speed and load are low, so that the range in which self-ignition combustion can be performed can be expanded.
[0043]
B. Second embodiment:
FIG. 6 is a perspective view showing an exhaust pipe of the second embodiment. The second embodiment differs from the first embodiment only in the way of connecting the exhaust pipe and the turbine chamber 52a, and the other points are the same as the first embodiment.
[0044]
In the second embodiment, three exhaust pipes 160a to 160c are assembled at one flange 210, where they are connected to three inlet pipes 211 to 213. The three inlet pipes 211 to 213 are configured to introduce exhaust gas into the turbine chamber 52a from the axial direction of the turbine 52 (FIG. 1). More specifically, the three inlet pipes 211 to 213 are configured to obliquely enter the turbine chamber 52a while proceeding substantially spirally around the central axis of the turbine 52. Here, “substantially spiral” means that the traveling direction has both a component parallel to the central axis of the turbine 52 and a direction around the central axis of the turbine 52. ing. On the other hand, in the first embodiment shown in FIG. 5, directions in which the inlet pipes 201 to 203 enter the turbine chamber 52 a include directions around the central axis of the turbine 52, but are parallel to the central axis of the turbine 52. It differs from the second embodiment in that it does not include any directions. In FIG. 6, a path 220 of the exhaust gas discharged from the turbine chamber 52a is drawn by a broken line for convenience of illustration.
[0045]
In the second embodiment, as in the first embodiment described above, since the inflow air amount and the residual exhaust gas amount in each combustion chamber are substantially the same, a mixture having substantially the same composition can be obtained in each combustion chamber. effective.
[0046]
Further, the configuration of the second embodiment has an advantage that the length of the exhaust pipe can be made shorter than that of the first embodiment. This is because the inlet pipes 201 to 203 are not arranged on the outer peripheral surface of the turbine chamber 52a, but are arranged on one bottom surface of the substantially cylindrical turbine chamber 52a. .
[0047]
As described above, in the second embodiment, the exhaust paths of the three combustion chambers # 1 to # 3 are configured so that the exhaust gas is introduced into the turbine chamber 52a from the axial direction of the turbine 52. Can be shortened. That is, even with a short exhaust pipe length, it is possible to make the exhaust path from the combustion chamber of each cylinder to the turbine chamber 52a equal.
[0048]
In the second embodiment, since the exhaust path can be shortened, there is an effect that the efficiency of the supercharger 50 is improved and the transient response of the engine is also improved. Therefore, a sufficient supercharging effect can be obtained even under an operating condition where the engine speed and load are low, and as a result, the range in which self-ignition can be performed can be expanded. Further, since the exhaust path is short, the number of parts can be reduced, and the assemblability and productivity of the engine can be improved. Further, since the whole engine is compact, there is an advantage that a so-called heat integrator (one that covers around the exhaust pipe and shields heat) can be reduced in size, and the overall weight can be reduced.
[0049]
C. Modification:
The present invention is not limited to the above-described examples and embodiments, but can be implemented in various modes without departing from the gist of the invention, and for example, the following modifications are possible.
[0050]
C1. Modification 1
In the above embodiment, the lengths of the exhaust paths of the three combustion chambers # 1 to # 3 are set equal to each other, but the lengths of the respective exhaust paths (more precisely, the lengths from the combustion chamber to the turbine chamber) are slightly different. And they may be almost equal to each other. In the present specification, "the lengths of the exhaust paths are equal to each other" means that the difference in length is within about 5%.
[0051]
C2. Modified example 2:
In the above embodiment, a three-cylinder engine has been described, but the present invention is generally applicable to a multi-cylinder engine. However, it is preferable that the number of cylinders is an integral multiple of three. In this case, it is preferable that exhaust pipes from three cylinders are connected to the turbine chamber of one supercharger. For example, in the case of a six-cylinder engine, it is preferable to use a twin turbocharger provided with two turbine chambers.
[0052]
C3. Modification 3:
In the above embodiment, an engine capable of switching between two-cycle operation and four-cycle operation has been described. However, the present invention is also applicable to an engine that performs only two-cycle operation.
[Brief description of the drawings]
FIG. 1 is an explanatory view conceptually showing a configuration of a gasoline engine 100 as a first embodiment of the present invention.
FIG. 2 is a map showing an operation mode of the engine 100 according to the first embodiment.
FIG. 3 is an explanatory diagram showing a state of two-cycle operation.
FIG. 4 is an explanatory diagram schematically showing an open / close period of a supply valve and an exhaust valve during two-cycle operation.
FIG. 5 is a perspective view showing an exhaust pipe of the first embodiment.
FIG. 6 is a perspective view showing an exhaust pipe according to a second embodiment.
[Explanation of symbols]
12 ... air supply passage 14 ... fuel injection valve 16, 16a-16c ... exhaust pipe (exhaust passage)
20 ... air cleaner 22 ... throttle valve 24 ... electric actuator 26 ... catalyst 30 ... ECU
32 crank angle sensor 34 accelerator opening sensor 50 turbocharger 52 turbine 52a turbine chamber 53 central shaft 54 compressor 56 shaft 60 surge tank 62 intercooler 100 gasoline engine 130 cylinder head 130a ... exhaust pipe attachment part 132 ... air supply valve 134 ... exhaust valve 136 ... spark plug 140 ... cylinder block 142 ... cylinder 144 ... piston 146 ... connecting rod 148 ... crankshafts 160a to 160c ... exhaust pipes 162, 164 ... electric actuator 201 -203 ... inlet pipe 210 ... flanges 211 to 213 ... inlet pipe 220 ... exhaust path

Claims (4)

A multi-cylinder engine capable of two-cycle self-ignition operation,
A supercharger having a turbine chamber that houses a turbine driven by exhaust gas,
An engine, wherein a plurality of exhaust paths from combustion chambers of a plurality of cylinders to the turbine chamber are independent of each other and have substantially equal lengths. The engine according to claim 1, wherein
An engine, wherein inlets of the plurality of exhaust paths to the turbine chamber are arranged evenly. 3. The engine according to claim 2, wherein
An engine configured such that pipes near inlets of the plurality of exhaust paths to the turbine chamber enter the turbine chamber obliquely while traveling in a substantially spiral manner around a central axis of the turbine. 3. The engine according to claim 2, wherein
An engine, wherein three exhaust paths of combustion chambers of three cylinders that explode at equal intervals are connected to the same turbine chamber.

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